App 2.40.4: the recorder's listening works on Android 9

listenToProperties looked only for registerCallback (Android 10); the
car's car library has registerListener/unregisterListener. Take either,
unsubscribe property by property, and say why when it fails.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhzAVaUyqcw5PkGjz4mWW6

AGENTS.md

@@ -20,7 +20,8 @@ MG4 head unit (Android 9, AAOS, MT2712)
   server and to ABRP, and updates itself.
 - **server/** — Go 1.27 API at `https://car.k8s.stinnesbeck.com`: stores telemetry, consumption
   and charging in InfluxDB, pairs cars by QR code, carries settings typed on a phone, relays
-  app releases from the private forge. It does **not** talk to ABRP. See `server/README.md`.
+  app releases from the private forge, and serves the roads for the Grid's map from
+  OpenStreetMap vector tiles (OpenFreeMap), fetched per tile on demand and cached on a volume. It does **not** talk to ABRP. See `server/README.md`.
 - **k8s/** — plain Kubernetes manifests (InfluxDB, server, Grafana with three provisioned
   dashboards, Traefik routes). See `k8s/README.md`.
 - **EVHardware/** — vendored shared vehicle layer (PolyForm Noncommercial, see `LICENSE.md`).
@@ -75,12 +76,12 @@ Repository: `ssh://git@git.stinnesbeck.com:2222/nils/mg4.git` (remote `origin`),
 
 | Tab | Contents |
 |---|---|
-| Overview | value tiles (battery, range, range/usage/energy since start, 5-min averages of range, usage, power, speed), vehicle info (odometer, lease allowance and the odometer against it), tyre pressures; read every 0.2 s on a background thread. Styles (Settings → Overview style): Tiles, Gauges (`GaugeView` needles), Cockpit (`RingView` rings, `TraceView` power trace), Retro (`RetroView`, seven-segment VFD), Futuristic (`FlowView`, animated energy flow), Sci-fi (`SciFiView`, starship console), Cartoon (`CartoonView`), MG (`OctagonView`, octagonal dials after the classic MG dashboards), and on `ClusterCanvasView`: Minimal, Terminal, Nixie tubes, Chronograph, Grid (`GridView`, neon lines over a moving grid floor, power as a light-cycle trail from `ClusterValues.powerTrail`), Time circuits (`TimeCircuitsView`, the time machine's LED rows with `Segments14` letters and a flux capacitor), Quest (`QuestView`, a fantasy game interface), Visor (`VisorView`, a helmet display with a motion tracker of the power trail), Empire (`EmpireView`, a strategy game with an isometric world and ages by odometer, `EmpireAge`); the drawn styles share `ClusterValues`. A style shown in its own palette (Sci-fi, Cartoon, Nixie, Time circuits, Quest, Empire; Retro, Terminal, Grid and Visor with "Original") gives the whole app its colours (`StylePalette`, `res/values/style_palettes.xml`) instead of the accent colour. A button in the navigation's header hides the navigation for a full-width Overview (`PREF_OVERVIEW_FULLSCREEN`); a swipe in from the left edge (`EdgeSwipe`) brings it back; without the app's own full screen the car's sidebar takes that edge, so a tab at the left edge (`edge_tab`) is tapped or swiped instead. Pages change only by the navigation (the pager's own swiping is off) |
+| Overview | value tiles (battery, range, range/usage/energy since start, 5-min averages of range, usage, power, speed), vehicle info (odometer, lease allowance and the odometer against it), tyre pressures; read every 0.2 s on a background thread. Styles (Settings → Overview style): Tiles, Gauges (`GaugeView` needles), Cockpit (`RingView` rings, `TraceView` power trace), Retro (`RetroView`, seven-segment VFD), Futuristic (`FlowView`, animated energy flow), Sci-fi (`SciFiView`, starship console), Cartoon (`CartoonView`), MG (`OctagonView`, octagonal dials after the classic MG dashboards), and on `ClusterCanvasView`: Minimal, Terminal, Nixie tubes, Chronograph, Grid (`GridView`, neon lines over a moving grid floor, power as a light-cycle trail from `ClusterValues.powerTrail`), Grid with map (the same `GridView` over the roads round the car, top-down: GPS while it is shown, tiles from the server's `/v1/map/roads` through `MapRoads`, cached in `files/map`; `RoadTile`, `MapGeometry`; the map is `MapLayerView`, a hardware layer drawn once and moved and turned by the GPU every display frame), Time circuits (`TimeCircuitsView`, the time machine's LED rows with `Segments14` letters and a flux capacitor), Quest (`QuestView`, a fantasy game interface), Visor (`VisorView`, a helmet display with a motion tracker of the power trail), Empire (`EmpireView`, a strategy game with an isometric world and ages by odometer, `EmpireAge`); the drawn styles share `ClusterValues`. A style shown in its own palette (Sci-fi, Cartoon, Nixie, Time circuits, Quest, Empire; Retro, Terminal, Grid and Visor with "Original") gives the whole app its colours (`StylePalette`, `res/values/style_palettes.xml`) instead of the accent colour. A button in the navigation's header hides the navigation for a full-width Overview (`PREF_OVERVIEW_FULLSCREEN`); a swipe in from the left edge (`EdgeSwipe`) brings it back; without the app's own full screen the car's sidebar takes that edge, so a tab at the left edge (`edge_tab`) is tapped or swiped instead. Pages change only by the navigation (the pager's own swiping is off) |
 | Consumption / Charging | period totals, daily log, charging sessions and curve |
 | Live data | on/off, ABRP API key and user token, upload frequency |
 | Server | URL, pairing by QR, ingest token, installation ID (read-only), config import |
-| Settings | drive mode (Eco, Normal, Sport, Snow, Custom; the lit one is what the car reports; changes only in P at a standstill, `DriveModeWrite`; "Set at start" sets the last confirmed choice again when the service starts with the head unit), full screen, voice key, Overview style with the accent colour beside it (offered only for styles drawn in it, `OverviewStyle.usesAccent`; Retro, Terminal, Grid and Visor add "Original" for their own palette, `hasOriginal`), tyre unit, battery and charging price (one card on wide screens), version, update check, install from USB, About |
-| Logs | signal recorder (`SignalRecorder`/`SignalRecording`: every property and vendor getter via `VendorSurfaceProbe.capture`, again and again for 3 minutes, plus steering-wheel key broadcasts; lists what changed, rarest first; saved to the app and a USB stick; how to find where the car publishes something), update log (every install step, with the platform's words), upload log |
+| Settings | drive mode (Eco, Normal, Sport, Snow, Custom; the lit one is what the car reports; changes only in P at a standstill, `DriveModeWrite`; "Set at start" sets the last confirmed choice again when the service starts with the head unit), full screen, voice key, Overview style with the accent colour beside it (offered only for styles drawn in it, `OverviewStyle.usesAccent`; Retro, Terminal, Grid (and Grid with map, sharing Grid's choice) and Visor add "Original" for their own palette, `hasOriginal`), tyre unit, battery and charging price (one card on wide screens), version, update check, install from USB, About |
+| Logs | signal recorder (`SignalRecorder`/`SignalRecording`: every property and vendor getter via `VendorSurfaceProbe.capture`, again and again for 3 minutes, plus change events of the driver-assistance block it subscribes to, `EVHardware.listenToProperties` with `AssistBlock`, and steering-wheel key broadcasts; lists what changed, rarest first; saved to the app and a USB stick; how to find where the car publishes something), update log (every install step, with the platform's words), upload log |
 
 Key classes (`app/src/main/java/com/evsuite/abrp/`): `AbrpUploadService` (foreground service,
 15 s tick), `TelemetryUploader` (+ `TelemetryQueue`, persisted), `TelemetryPayload` (server

EVHardware/lib/src/main/java/com/evsuite/hardware/AssistBlock.kt

@@ -0,0 +1,24 @@
+package com.evsuite.hardware
+
+/**
+ * The block of vendor properties the head unit's driver-assistance manager
+ * (`CarAdvancedAssistedDrivingManager`, its `AAD_*` ids) lives in: global vendor properties
+ * `0x21x0A1xx`, of any value type — `0x2140A101` (int) to `0x2160A15B` (float, `AAD_EPTCCTRGTSPD`,
+ * by its name the cruise control's target speed) and the rest of the same block. Used to choose
+ * what the signal recorder listens to; nothing here is ever written. Pure, unit-tested.
+ */
+object AssistBlock {
+
+    private const val GROUP_MASK = 0xF0000000.toInt()
+    private const val GROUP_VENDOR = 0x20000000
+    private const val AREA_MASK = 0x0F000000
+    private const val AREA_GLOBAL = 0x01000000
+    private const val BLOCK_MASK = 0x0000FF00
+    private const val BLOCK = 0x0000A100
+
+    /** Whether [propertyId] is a global vendor property in the assistance block. */
+    fun contains(propertyId: Int): Boolean =
+        propertyId and GROUP_MASK == GROUP_VENDOR &&
+            propertyId and AREA_MASK == AREA_GLOBAL &&
+            propertyId and BLOCK_MASK == BLOCK
+}

EVHardware/lib/src/main/java/com/evsuite/hardware/EVHardware.kt

@@ -320,6 +320,144 @@ object EVHardware {
         ignitionCallbacks.remove(callback)
     }
 
+    // -------------------------------------------------------------------------
+    // Listening to properties (the app's signal recorder) — read only
+    // -------------------------------------------------------------------------
+
+    /** Why the last [listenToProperties] returned null, in a few words; null after a success. */
+    @Volatile var listenProblem: String? = null
+        private set
+
+    /** A subscription made by [listenToProperties]; [close] ends it. */
+    class PropertyListening internal constructor(
+        /** Properties subscribed to, and those the car service refused. */
+        val subscribed: Int,
+        val refused: Int,
+        private val stop: () -> Unit,
+    ) : AutoCloseable {
+        override fun close() = stop()
+    }
+
+    /**
+     * Subscribes to every CarPropertyManager property whose id [admit] accepts, the way the
+     * head unit's own managers do (`CarAdvancedAssistedDrivingManager` registers each of its
+     * `AAD_*` ids for change events and never polls them), and hands each change event to
+     * [onEvent] as (property id, area, value as text) on the car service's thread. A vendor HAL
+     * may fill a property from the car network only while someone listens, so a poll alone can
+     * read its default. ON_CHANGE properties are asked for every change, CONTINUOUS ones for
+     * 1 Hz within their limits. Read only: nothing is set. Null when there is no
+     * CarPropertyManager or no way to subscribe, with the reason in [listenProblem];
+     * [PropertyListening.close] unsubscribes.
+     *
+     * Android 9's car library (the MG4's) names the calls `registerListener(CarPropertyEventListener,
+     * int, float)` and `unregisterListener`; Android 10 renamed them `registerCallback` and
+     * `unregisterCallback`. Both are looked for. Unsubscribing goes property by property: the
+     * one-argument `unregisterListener` of Android 9 removes entries from the list it walks and so
+     * leaves every other property subscribed.
+     */
+    fun listenToProperties(admit: (Int) -> Boolean, onEvent: (Int, Int, String) -> Unit): PropertyListening? {
+        listenProblem = null
+        val cpm = sCarPropertyManager ?: run {
+            listenProblem = "no car service"
+            return null
+        }
+        return try {
+            val methods = cpm.javaClass.methods
+            val register = methods.firstOrNull {
+                (it.name == "registerListener" || it.name == "registerCallback") && it.parameterCount == 3 &&
+                    it.parameterTypes[1] == Int::class.javaPrimitiveType &&
+                    it.parameterTypes[2] == Float::class.javaPrimitiveType
+            } ?: run {
+                listenProblem = "no way to subscribe"
+                return null
+            }
+            val callbackType = register.parameterTypes[0]
+            val unregister = methods.firstOrNull {
+                it.name == register.name.replaceFirst("register", "unregister") && it.parameterCount == 2 &&
+                    it.parameterTypes[0] == callbackType && it.parameterTypes[1] == Int::class.javaPrimitiveType
+            }
+            val unregisterAll = methods.firstOrNull {
+                it.name == register.name.replaceFirst("register", "unregister") && it.parameterCount == 1 &&
+                    it.parameterTypes[0] == callbackType
+            }
+            if (!callbackType.isInterface) {
+                listenProblem = "unexpected listener type ${callbackType.simpleName}"
+                return null
+            }
+            val proxy = Proxy.newProxyInstance(callbackType.classLoader, arrayOf(callbackType)) { self, method, args ->
+                when (method.name) {
+                    "onChangeEvent" -> {
+                        val cpv = args?.getOrNull(0)
+                        if (cpv != null) {
+                            try {
+                                val type = cpv.javaClass
+                                val id = type.getMethod("getPropertyId").invoke(cpv) as Int
+                                val area = type.getMethod("getAreaId").invoke(cpv) as Int
+                                onEvent(id, area, com.evsuite.hardware.probe.VendorSurfaceRules.render(
+                                    type.getMethod("getValue").invoke(cpv)))
+                            } catch (e: Exception) {
+                                AppLogger.d(TAG, "listen: event unreadable: ${e.readFailureReason()}")
+                            }
+                        }
+                        null
+                    }
+                    "onErrorEvent" -> {
+                        val id = args?.getOrNull(0) as? Int
+                        val area = args?.getOrNull(1) as? Int
+                        if (id != null) onEvent(id, area ?: AREA_GLOBAL, "error event")
+                        null
+                    }
+                    "equals" -> self === args?.getOrNull(0)
+                    "hashCode" -> System.identityHashCode(self)
+                    "toString" -> "PropertyListening"
+                    else -> null
+                }
+            }
+            val configs = cpm.javaClass.getMethod("getPropertyList").invoke(cpm) as? List<*> ?: return null
+            val subscribedIds = ArrayList<Int>()
+            var refused = 0
+            for (config in configs) {
+                if (config == null) continue
+                val type = config.javaClass
+                val id = runCatching { type.getMethod("getPropertyId").invoke(config) as Int }.getOrNull() ?: continue
+                if (!admit(id)) continue
+                val continuous = runCatching { type.getMethod("getChangeMode").invoke(config) as Int }.getOrNull() == 2
+                val rate = if (!continuous) 0f else {
+                    val min = runCatching { type.getMethod("getMinSampleRate").invoke(config) as Float }.getOrNull() ?: 0f
+                    val max = runCatching { type.getMethod("getMaxSampleRate").invoke(config) as Float }.getOrNull() ?: 1f
+                    1f.coerceIn(min, maxOf(min, max))
+                }
+                try {
+                    if (register.invoke(cpm, proxy, id, rate) == false) refused++ else subscribedIds.add(id)
+                } catch (e: Exception) {
+                    refused++
+                    AppLogger.d(TAG, "listen: 0x%08X refused: %s".format(id, e.readFailureReason()))
+                }
+            }
+            AppLogger.i(TAG, "listening to ${subscribedIds.size} properties ($refused refused) via ${register.name}")
+            PropertyListening(subscribedIds.size, refused) {
+                for (id in subscribedIds) {
+                    try {
+                        if (unregister != null) unregister.invoke(cpm, proxy, id)
+                    } catch (e: Exception) {
+                        AppLogger.d(TAG, "listen: unsubscribe 0x%08X failed: %s".format(id, e.readFailureReason()))
+                    }
+                }
+                if (unregister == null) {
+                    try {
+                        unregisterAll?.invoke(cpm, proxy)
+                    } catch (e: Exception) {
+                        AppLogger.d(TAG, "listen: unsubscribe failed: ${e.readFailureReason()}")
+                    }
+                }
+            }
+        } catch (e: Exception) {
+            listenProblem = e.readFailureReason()
+            AppLogger.w(TAG, "listenToProperties: ${e.readFailureReason()}")
+            null
+        }
+    }
+
     /** Unregisters the CarPropertyManager proxy (call from Service.onDestroy). */
     fun unregisterIgnitionPropertyCallback() {
         val cpm = sCarPropertyManager ?: return

EVHardware/lib/src/test/java/com/evsuite/hardware/AssistBlockTest.kt

@@ -0,0 +1,29 @@
+package com.evsuite.hardware
+
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class AssistBlockTest {
+
+    @Test
+    fun `the assistance manager's properties are in the block`() {
+        // First and last int, the target speed and the object distance (floats).
+        for (id in intArrayOf(0x2140A101, 0x2140A171, 0x2160A15B, 0x2160A12C, 0x2160A114)) {
+            assertTrue("0x%08X".format(id), AssistBlock.contains(id))
+        }
+    }
+
+    @Test
+    fun `other properties are not`() {
+        for (id in intArrayOf(
+            0x2140A0FF, // the block before
+            0x2140A201, // the block after
+            0x11400400, // a standard (system) property
+            0x2340A101, // not global
+            0x0140A101, // no group
+        )) {
+            assertFalse("0x%08X".format(id), AssistBlock.contains(id))
+        }
+    }
+}

EVHardware/lib/src/test/java/com/evsuite/hardware/PropertyListeningTest.kt

@@ -0,0 +1,105 @@
+package com.evsuite.hardware
+
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotNull
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class PropertyListeningTest {
+
+    class Config(val propertyId: Int, val changeMode: Int, val minSampleRate: Float, val maxSampleRate: Float)
+    class Value(val propertyId: Int, val areaId: Int, val value: Any)
+
+    /** Shaped like Android 9's CarPropertyManager, the car's: registerListener, and an
+     *  unregisterListener(listener) that skips every other property as the car's does. */
+    class Android9Manager(private val configs: List<Config>) {
+        interface CarPropertyEventListener {
+            fun onChangeEvent(value: Any?)
+            fun onErrorEvent(propertyId: Int, areaId: Int)
+        }
+
+        val active = LinkedHashMap<Int, MutableList<CarPropertyEventListener>>()
+        val rates = HashMap<Int, Float>()
+
+        fun getPropertyList(): List<Config> = configs
+
+        fun registerListener(listener: CarPropertyEventListener, propertyId: Int, rate: Float): Boolean {
+            active.getOrPut(propertyId) { ArrayList() }.add(listener)
+            rates[propertyId] = rate
+            return true
+        }
+
+        fun unregisterListener(listener: CarPropertyEventListener) {
+            val ids = active.keys.toMutableList()
+            var i = 0
+            while (i < ids.size) {
+                unregisterListener(listener, ids[i])
+                if (active[ids[i]] == null) ids.removeAt(i) // as SparseArray.remove under keyAt(i)
+                i++
+            }
+        }
+
+        fun unregisterListener(listener: CarPropertyEventListener, propertyId: Int) {
+            val list = active[propertyId] ?: return
+            list.remove(listener)
+            if (list.isEmpty()) active.remove(propertyId)
+        }
+
+        fun fire(propertyId: Int, value: Any) {
+            active[propertyId]?.toList()?.forEach { it.onChangeEvent(Value(propertyId, 0x01000000, value)) }
+        }
+    }
+
+    class NoListeners {
+        fun getPropertyList(): List<Config> = emptyList()
+    }
+
+    private val field = EVHardware::class.java.getDeclaredField("sCarPropertyManager").apply { isAccessible = true }
+
+    @After
+    fun reset() = field.set(null, null)
+
+    @Test
+    fun `subscribes through Android 9's registerListener and unsubscribes every property`() {
+        val manager = Android9Manager(listOf(
+            Config(0x2160A15B, 1, 0f, 0f),     // in the block, on change
+            Config(0x2140A15A, 1, 0f, 0f),
+            Config(0x2160A1A3, 2, 0f, 10f),    // continuous
+            Config(0x2140A101, 1, 0f, 0f),
+            Config(0x11400400, 1, 0f, 0f),     // outside the block
+        ))
+        field.set(null, manager)
+        val heard = ArrayList<String>()
+
+        val listening = EVHardware.listenToProperties(AssistBlock::contains) { id, area, value ->
+            heard += "%08X/%d=%s".format(id, area, value)
+        }
+
+        assertNotNull(EVHardware.listenProblem, listening)
+        assertEquals(4, listening!!.subscribed)
+        assertEquals(0, listening.refused)
+        assertEquals(setOf(0x2160A15B, 0x2140A15A, 0x2160A1A3, 0x2140A101), manager.active.keys)
+        assertEquals(0f, manager.rates[0x2160A15B])
+        assertEquals(1f, manager.rates[0x2160A1A3])
+
+        manager.fire(0x2160A15B, 90f)
+        assertEquals(1, heard.size)
+        assertTrue(heard[0], heard[0].startsWith("2160A15B/16777216="))
+
+        listening.close()
+        assertTrue(manager.active.toString(), manager.active.isEmpty())
+    }
+
+    @Test
+    fun `says why when there is no way to subscribe`() {
+        field.set(null, NoListeners())
+        assertNull(EVHardware.listenToProperties(AssistBlock::contains) { _, _, _ -> })
+        assertEquals("no way to subscribe", EVHardware.listenProblem)
+
+        field.set(null, null)
+        assertNull(EVHardware.listenToProperties(AssistBlock::contains) { _, _, _ -> })
+        assertEquals("no car service", EVHardware.listenProblem)
+    }
+}

LICENSE.md

@@ -18,6 +18,14 @@ Nils' MG4 is a fork of a chain of forks, all MIT:
 MIT requires the copyright notice to travel with any copy or substantial portion of the
 software. `LICENSE` names all of them; keep every line.
 
+## Map data
+
+The roads of the "Grid with map" style are © OpenStreetMap contributors, under the
+[Open Database Licence](https://opendatacommons.org/licenses/odbl/), in vector tiles
+© OpenMapTiles served by [OpenFreeMap](https://openfreemap.org). The style shows
+"OpenFreeMap © OpenMapTiles · © OpenStreetMap contributors" whenever it draws them. The server
+fetches the tiles (`server/maps.go`).
+
 ## The EVHardware library
 
 `EVHardware/` (the shared vehicle layer from EVSuite) is source-available under the
@@ -31,8 +39,9 @@ top. Those are Fatih's reads the car needs and upstream does not have — the ve
 ids `0x21401553`–`56`, the vendor mileage `0x21401566` for the odometer, the charging status
 from `0x2140F409`, SoC, range, power, pack voltage and current on SWI69 as on SWI68, and SWI69
 speed already in km/h — plus translated comments and, from this fork, the gear's raw code
-(`EVHardware.getGearRaw`, `EnergySnapshot.gearRaw`) and a drive mode write without the binder
-fallback (`writeDriveModeProperty`). To take upstream again, merge three ways with
+(`EVHardware.getGearRaw`, `EnergySnapshot.gearRaw`), a drive mode write without the binder
+fallback (`writeDriveModeProperty`), and read-only listening to properties for the signal
+recorder (`listenToProperties`, `AssistBlock`). To take upstream again, merge three ways with
 `e4e1158` as the base.
 
 The car app links EVHardware into its APK, so the **built app** may only be used and passed on

OTA.md

@@ -110,3 +110,10 @@ That screen needs a `file://` URI on the car build: a read grant on our FileProv
 when it comes from the system user (`not exported from UID 1000`), and the installer reports the
 unreadable file as "There was a problem parsing the package". On the emulator the session still
 installs silently.
+
+The refusal does not always come at once: the platform may also answer a moment later, through
+the session's result (`OtaInstallResultReceiver`). Since 2.40.1 that answer opens the installer
+screen too, as does a confirmation the platform asks for but cannot show; only **Cancel** on that
+screen ends the update there. And if the session says nothing at all for 20 s, the app abandons
+it and opens the installer screen. Before 2.40.1 a late refusal ended in a short message only:
+the update downloaded and then nothing seemed to happen.

README.md

@@ -39,8 +39,8 @@ APIs.
 
 ## Screenshots
 
-**Overview styles:** the Overview comes in seventeen looks, from an 80s fluorescent display to a
-starship console, a watch face, a neon grid, a time machine, a fantasy game, a helmet display and a strategy game. [THEMES.md](THEMES.md) shows each one, with and without the
+**Overview styles:** the Overview comes in eighteen looks, from an 80s fluorescent display to a
+starship console, a watch face, a neon grid (also over a map of the roads round the car), a time machine, a fantasy game, a helmet display and a strategy game. [THEMES.md](THEMES.md) shows each one, with and without the
 navigation, and what inspired it.
 
 <p align="center">
@@ -81,20 +81,21 @@ car ──live telemetry───▶ car.k8s.stinnesbeck.com (Go)
 ```
 
 The car sends live data to ABRP itself, with the ABRP credentials set on the Live data tab, so
-ABRP and the server do not depend on each other. The server only stores. The car authenticates
+ABRP and the server do not depend on each other. The server stores, relays the app's updates
+from the forge and serves the roads for the Grid's map (OpenStreetMap, through OpenFreeMap). The car authenticates
 with the server using a token of its own, obtained by pairing with a phone (below).
 
 ## The app
 
 | Tab | What it shows |
 |---|---|
-| **Overview** | Battery, range, power and speed; range, usage and energy since start; 5-minute averages of range, usage, power and speed; vehicle info (odometer, lease allowance, climate setpoint) and tyre pressures. Read five times a second. Looks to choose from in Settings → Overview style: Tiles, Gauges, Cockpit, Retro, Futuristic, Sci-fi, Cartoon, MG, Minimal, Terminal, Nixie tubes, Chronograph, Grid, Time circuits, Quest, Visor and Empire ([THEMES.md](THEMES.md) shows them all). A style with its own colours (Sci-fi, Cartoon, Nixie tubes, Time circuits, Quest, Empire, and Retro, Terminal, Grid and Visor with "Original") colours the whole app to match, e.g. turquoise for Retro. The small button next to the MG4 logo in the navigation hides the navigation for a full-width Overview; swipe in from the left edge (a faint handle marks it) to bring it back; with Settings → Full screen off, the car's own sidebar sits at that edge, so tap the small tab at the left edge (›) instead. Pages change only by the navigation, not by swiping sideways |
+| **Overview** | Battery, range, power and speed; range, usage and energy since start; 5-minute averages of range, usage, power and speed; vehicle info (odometer, lease allowance, climate setpoint) and tyre pressures. Read five times a second. Looks to choose from in Settings → Overview style: Tiles, Gauges, Cockpit, Retro, Futuristic, Sci-fi, Cartoon, MG, Minimal, Terminal, Nixie tubes, Chronograph, Grid, Grid with map, Time circuits, Quest, Visor and Empire ([THEMES.md](THEMES.md) shows them all). A style with its own colours (Sci-fi, Cartoon, Nixie tubes, Time circuits, Quest, Empire, and Retro, Terminal, Grid and Visor with "Original") colours the whole app to match, e.g. turquoise for Retro. Grid with map lays the roads round the car on the Grid's floor: the app asks the car's server for the map tile it is in (not its position), the server fetches only that tile from OpenFreeMap's OpenStreetMap vector tiles and keeps it, and the GPS runs for it only while that style is on screen. The small button next to the MG4 logo in the navigation hides the navigation for a full-width Overview; swipe in from the left edge (a faint handle marks it) to bring it back; with Settings → Full screen off, the car's own sidebar sits at that edge, so tap the small tab at the left edge (›) instead. Pages change only by the navigation, not by swiping sideways |
 | **Consumption** | Lifetime, last 7 and 30 days, Trip A and B (distance, energy, average consumption and speed, SOC change), and a daily log of the last four months |
 | **Charging** | The current session (SOC, voltage, current, power, energy into the battery and from the grid, time, cost) and its SOC/power curve |
 | **Live data** | Live data on/off, ABRP credentials for sending directly from the car, upload frequency |
 | **Server** | Server URL, pairing by QR code, ingest token, installation ID, config import |
 | **Settings** | Full screen, voice key, Overview style and accent colour, tyre pressure unit; drive mode (Eco, Normal, Sport, Snow, Custom: changes only in P at a standstill; the highlighted one is what the car reports; with "Set at start" the last confirmed choice is set again when the car starts, while it is still in P); battery (manual SoH, usable capacity) and charging price; entry on the phone; version, update check, install from USB stick, About |
-| **Logs** | Signal recorder (records every value the head unit offers for 3 minutes and lists what changed, to find where the car publishes something; saved to a USB stick too), update log (every install step), upload log |
+| **Logs** | Signal recorder (records every value the head unit offers for 3 minutes, listens to the driver-assistance values for every change they report, and lists what changed, to find where the car publishes something; saved to a USB stick too), update log (every install step), upload log |
 
 - **Opening the app:** the MG4 launcher does not list third-party apps. **Double-press the
   voice key** on the steering wheel and the app comes to the front (switch on the Settings

SPECS.md

@@ -39,7 +39,7 @@ car ──live telemetry───▶ car.k8s.stinnesbeck.com (Go)
 
 ### Status
 
-Current: app 2.35.3 (installed on the car over the air), server 2.6.2 (pinned by digest in
+Current: app 2.38.0 (installed on the car over the air, 2026-10-26), server 2.6.2 (pinned by digest in
 `k8s/server.yaml`; applied and running since 2026-10-25).
 
 - [x] On the car: QR pairing, values on the Overview, voice-key double press, full screen
@@ -78,7 +78,9 @@ tyre pressures, GPS (lat, lon, elevation, heading) and the is_* flags. It does *
   (`AAD_EPTCCTRGTSPD` `0x2160A15B` 0.0, `AAD_ACC_OBJ_*` 0.0 / -128.0, modes 0). A signal recording
   of all 1,194 values while the set speed was 101, 90 and 80 km/h shows none of those numbers
   (also tried as m/s, mph and ×2/×10/×16/×64) outside the actual speed, and the ACC buttons send
-  no key broadcast. Most likely only the instrument cluster has it.
+  no key broadcast. Most likely only the instrument cluster has it. Not yet tried: listening
+  (subscribing) instead of polling, as the head unit's own manager does — the recorder does it
+  since 2.40.3; a drive with ACC will tell.
 
 ## To do
 
@@ -138,6 +140,133 @@ tyre pressures, GPS (lat, lon, elevation, heading) and the is_* flags. It does *
   confirmed car facts, app structure, UI conventions, build/test/ship, documents. It replaces
   upstream's EVABRPUploader text. The test emulator is now in the flake: `nix run .#car-emulator`
   (Android 9 AOSP at 1920×720, 160 dpi; the car build installs as the system user — checked).
+- 2026-10-27 — App 2.40.4: **the recorder's listening works on Android 9**. Both recordings
+  from the car (08:49 and 08:52, 2.40.3) said "listening to the assistance properties: not
+  possible": `listenToProperties` looked only for `registerCallback`, Android 10's name; the car's
+  car library (Android 9) has `registerListener(CarPropertyEventListener, int, float)` and
+  `unregisterListener`, as the app's `CarPropertyAdapter` already knew. It now takes either, and
+  unsubscribes property by property (Android 9's one-argument `unregisterListener` removes
+  entries from the list it walks and would leave every other property subscribed). A failure now
+  says why (`EVHardware.listenProblem`: no car service, no way to subscribe, or the exception).
+  Tested with a stand-in manager of Android 9's shape (`PropertyListeningTest`). Correction to
+  2.40.3: the ignition listener it was compared with also looks only for `registerCallback`, so
+  it most likely never subscribes on the car either (it reads the state once at start); left as
+  it is. What the polled part of the two recordings shows of the block: `0x2160A15B` (by name
+  the target speed) 0.0 throughout; `0x2140A15A` between 3 and 7 every few captures;
+  `0x2160A1A3`/`0x2160A1A4` counting up by 0.1; speeds 8–33 km/h. Not tried on the car.
+- 2026-10-27 — App 2.40.3 published (`car-2.40.3`; also carries 2.40.1 and 2.40.2).
+- 2026-10-27 — App 2.40.3: **the signal recorder listens** (owner: "is there really nothing we
+  can do about the readout of the cruise control set point"). The 2.32.0 recording only polled.
+  The head unit's `CarAdvancedAssistedDrivingManager` never polls its 108 `AAD_*` properties: it
+  registers a listener for each (`registerListener(…, 0.0f)`, on change), and a vendor HAL may
+  fill a value from the car network only while someone listens — which would read as the
+  defaults we saw. EVHardware gains `listenToProperties` (read only: the CarPropertyManager's
+  `registerCallback` per admitted property, rate 0 for ON_CHANGE, 1 Hz within limits for
+  CONTINUOUS, one proxy, `unregisterCallback` on close) and `AssistBlock` (global vendor
+  properties `0x21x0A1xx`, which holds all 108 `AAD_*` ids; tested). The recorder subscribes to
+  that block for its 3 minutes; `SignalRecording.event` counts every event and puts value changes
+  on the timeline; the file and the Logs tab list the properties heard, those with changing
+  values first ("heard …"). Emulator (no car service): the recorder notes that listening is not
+  possible, records, saves the new section; no crash. The subscription itself is the same
+  reflection as the ignition listener that works on the car, but untried on the car.
+- 2026-10-27 — App 2.40.2: **the map moves on the GPU** (owner: "is the map screen gpu
+  accelerated? it looks a bit slow on update"). It was hardware-rendered, but every frame (20 a
+  second) recomputed every road point on the main thread, rebuilt all paths, and drew the big
+  roads three times for the glow; and the car jumped with each GPS fix (1 Hz). Now the map is
+  its own view under the Grid (`MapLayerView`, `LAYER_TYPE_HARDWARE`): drawn once into a GPU
+  texture round an anchor and only redrawn when tiles come or go or the car is ~280 layout units
+  (≈230 m) from the anchor; each display frame (`postOnAnimation`, only while that style is on
+  screen and the map shows) sets its translation, pivot and rotation, which the GPU composites.
+  The car glides towards each fix (eased, snaps beyond 200 m), the heading eases; GridView over
+  the map no longer animates itself (only the readings redraw it), the "far roads fainter" sort
+  is a fixed dark gradient towards the top. Layer size on the car about 2500 px square (~25 MB).
+  Measured on the emulator: with SwiftShader (software GPU) old and new both ~57 ms a frame, and
+  with the host's Intel GPU (`-gpu host`) both run at the display rate (~18 ms) — the emulator
+  is too fast to show the car's slowness, so the gain on the head unit is reasoned, not
+  measured. Not tried on the car.
+- 2026-10-27 — App 2.40.1: **an update that downloaded but never reached the installer** (owner:
+  "sometimes … downloads the update but then doesn't start the installer"). The car refuses the
+  installer session ("Not allowed to install non-system apps on internal storage"); only a
+  refusal thrown at once led to the installer screen. A refusal that came back through the
+  session's result was a toast and nothing else. Now any answer but success, the confirmation and
+  the driver's own cancel opens the installer screen with the verified APK (path and session id
+  ride on the result intent; `goAsync` for the copy), a confirmation that cannot be shown does
+  too, and a session silent for 20 s is abandoned for it. Emulator, with a throwaway build whose
+  session bytes were damaged (refused later, status 4 `INSTALL_PARSE_FAILED_NOT_APK`) and which
+  read the update from Downloads: the installer screen opened by itself, Install, now 2.40.1; the
+  update log shows every step. The 20 s watch is untested (no way to make a session stay silent).
+  Not tried on the car. OTA.md updated.
+- 2026-10-27 — App 2.40.0 published (`car-2.40.0`).
+- 2026-10-27 — App 2.40.0: **Grid with map straight from above, full height** (owner: 2.39.2
+  "does not look right"; wanted the map over the whole height and fully top-down). The map is
+  the whole background in map mode: orthographic, heading up, 1.2 layout units per metre (about
+  400 m ahead, 125 m behind, 450 m to each side on the car's screen), the car 150 units above
+  the bottom edge; ground grid every 50 m fixed to the ground; roads from 250 m ahead fainter;
+  the camera, the sky and the floor are gone there. The speed moves to a panel under the gears
+  (120 units), and the battery wall, the clock, the gears and the disc get dark panels. The
+  plain Grid is unchanged. Emulator with the Berlin tiles, both layouts. Not tried on the car.
+- 2026-10-27 — App 2.39.2 published (`car-2.39.2`).
+- 2026-10-27 — App 2.39.2: **Grid with map seen from higher up** (owner: the map looked like a
+  fish-eye; wanted it more top-down). The map has its own pinhole camera now: 45° down, 300 m
+  up, the car on its axis just above the read-outs, the top of the floor about 420 m ahead
+  (scale there ~60 % of the car's, before ~1/20 at 900 m); the floor starts at half height in
+  map mode and the speed is 170 instead of 210 units; the floor's grid becomes a ground grid
+  (a line every 50 m, fixed to the ground, turning with the roads); roads from 250 m ahead
+  fainter; the power disc gets a dark backing over the map. Emulator with the Berlin tiles,
+  both layouts. Not tried on the car.
+- 2026-10-26 — Server 2.8.0 image pushed and pinned in `k8s/server.yaml` by digest
+  `sha256:8b8d94e0562833d196162866b7fdc6910d5dd219f6eb84572d4d5c91b74f7ff1` (checked with skopeo);
+  app 2.39.1 published (`car-2.39.1`). Not applied yet: the owner applies it.
+- 2026-10-26 — App 2.39.1 and server 2.8.0: **the map's roads come from OpenFreeMap, on
+  demand.** In the car, server 2.7.0 logged `overpass answered 502`, `overpass could not be
+  reached`, and the owner saw 429s: the public Overpass limits per IP, and a tile takes it ~40 s
+  while the car gives up after 8 s (`ServerHttp.TIMEOUT_MS`) — the server then cancelled the
+  query, threw the work away, and the car's retries added to the load. Owner's choice: fetch
+  only the tiles the car asks for (a self-hosted Overpass would need a whole region imported).
+  Server: the zoom-14 OpenStreetMap vector tile (OpenMapTiles schema) from the TileJSON at
+  `MAP_TILES_URL` (default OpenFreeMap, free, no key, no limits; its template re-read every 6 h,
+  https only), decoded by our own minimal protobuf/MVT reader (`mvt.go`, the `transportation`
+  layer; classes motorway/trunk, primary/secondary, tertiary, minor), simplified as before. A
+  fetch runs to its end without the car (requests wait ≤ 6 s, then 503 with `Retry-After: 10`),
+  at most two at once, one per tile; tiles kept 30 days in `MAP_CACHE_DIR` (a 1 Gi volume
+  `mg4-server-maps`, pod `fsGroup` 65532) and the last 300 in memory; `OVERPASS_URL` is gone.
+  Tests with an encoded vector tile and a fake tile host (classes, split lines, scaled extent,
+  malformed tiles, gzip from the host, fetched once and kept across a restart, a slow fetch
+  finished for the next try, failures not cached and no tile in the log, http template refused,
+  config). Real: the 9 Berlin tiles in 0.7 s (9–15 KB each). App 2.39.1: "OpenFreeMap ©
+  OpenMapTiles · © OpenStreetMap contributors" on the map, a tile the server did not have yet is
+  asked for again after 15 s (was a minute). Emulator with those tiles: same roads as before.
+  Not tried: the deployed server and the car.
+- 2026-10-26 — Server 2.7.0 image pushed (`git.stinnesbeck.com/nils/mg4-server:2.7.0`, Go 1.27.3,
+  govulncheck clean) and pinned in `k8s/server.yaml` by digest
+  `sha256:e5da9452a9dbdfabe3340766cc51f18bb1418b2588ab534714550470abe1ce29` (checked with skopeo);
+  manifests valid (kubeconform). Not applied yet: the owner applies it.
+- 2026-10-26 — App 2.39.0 and server 2.7.0: **Grid with map**, a new Overview style — the Grid
+  over the roads round the car from OpenStreetMap (owner's choice of design: roads through the
+  car's own server, drawn as the floor). Server: `POST /v1/map/roads` `{z:14, x, y}` (the tile,
+  not the position, and in the body so it stays out of access logs) fetches the tile's drivable
+  roads from Overpass (`OVERPASS_URL`, default the public instance, `off` disables; https only;
+  one request at a time, ≥ 1 s apart, identifying User-Agent), turns them into tile-local points
+  in 4 classes simplified with Douglas–Peucker (~1.5 m), caches them in memory (30 days, 3000
+  tiles; failures not cached), gzips when accepted, answers 503 when Overpass fails and never logs
+  the tile. Tests with a fake Overpass (classes, split at missing points, simplification, cache,
+  gzip, validation, 503 without caching, no tile in the log, config). App: `MapRoads` keeps the
+  3×3 tiles round the car (files/map, 30 days, 400 tiles; one at a time on a background thread;
+  a failed tile waits a minute), `RoadTile` parses them failing closed, `MapGeometry` does the
+  web-mercator arithmetic (both tested). GPS only while that style is shown and the app is in
+  front; the bearing from the GPS, or worked out from positions 8 m apart when it gives none.
+  `GridView` with a map draws the roads in the floor's perspective, heading up, 40 m floor steps,
+  up to 900 m ahead, far roads fainter, the car as a chevron, its position run on with the speed
+  between fixes, 20 fps while moving; the trail gives way to the map; "© OpenStreetMap
+  contributors" shown; otherwise the plain floor saying why (waiting for GPS, set up the server,
+  loading, not available). `OVERPASS_URL` in `k8s/server.yaml`; LICENSE.md notes the ODbL. Tested:
+  server unit tests; one real fetch of 3×3 tiles in central Berlin through the server code
+  (20–30 KB each; Overpass answered 502 a few times and the retry got them); on the emulator those
+  tiles from the app's cache with emulator GPS, north up and turning with a simulated drive, both
+  layouts, no GPS, no server; no crash. Not tried: the app fetching tiles from the deployed
+  server (not deployed yet) and anything on the car.
+- 2026-10-26 — App 2.38.0 published (`car-2.38.0`) and installed on the car through the in-app
+  updater, from 2.35.3 (so Grid, Time circuits, Quest, Visor and Empire are on the car).
 - 2026-10-26 — App 2.38.0: Overview styles **Visor** (after Halo's helmet display, `VisorView`)
   and **Empire** (after Age of Empires' interface, `EmpireView`). Visor: shield bar = battery (24
   segments, red and blinking "BATTERY LOW" below 20 %), ammunition counter = range (number and

THEMES.md

@@ -1,6 +1,6 @@
 # Overview styles
 
-The Overview can look seventeen ways: pick one under **Settings → Overview style**. Every style shows
+The Overview can look eighteen ways: pick one under **Settings → Overview style**. Every style shows
 the same readings (battery, range, power, speed, gear, usage, trip, climate, odometer, time) and
 shows "—" for anything the car did not answer, never a made-up zero.
 
@@ -10,7 +10,7 @@ emulator at the car's resolution with **sample values** (87 km/h in D, 76 %, 18.
 emulator has no car; on the car the values are live.
 
 **Colours.** Most styles are drawn in the accent colour you pick from the MG4 paints (Settings →
-Accent colour; shown here in Dynamic Red). Retro, Terminal, Grid and Visor can also show their original
+Accent colour; shown here in Dynamic Red). Retro, Terminal, Grid (with or without the map) and Visor can also show their original
 colours, and Sci-fi, Cartoon, Nixie tubes, Time circuits, Quest and Empire always do; while one of those is shown, the whole app
 (navigation, buttons, switches) takes on its colours too.
 
@@ -29,6 +29,7 @@ colours, and Sci-fi, Cartoon, Nixie tubes, Time circuits, Quest and Empire alway
 | [Nixie tubes](#nixie-tubes) | glowing glass tubes | own |
 | [Chronograph](#chronograph) | a watch face | accent |
 | [Grid](#grid) | neon lines on a glowing grid floor | original or accent |
+| [Grid with map](#grid-with-map) | the Grid, with the real roads round the car on its floor | original or accent |
 | [Time circuits](#time-circuits) | a time machine's LED displays | own |
 | [Quest](#quest) | a fantasy game's interface | own |
 | [Visor](#visor) | a soldier's helmet display | original or accent |
@@ -162,6 +163,22 @@ films' other side.
 ![Grid with the navigation](screenshots/themes/grid-panel.png)
 ![Grid, full screen](screenshots/themes/grid.png)
 
+## Grid with map
+
+The Grid over a map: the roads round the car from OpenStreetMap (through OpenFreeMap) fill the
+whole screen as light lanes, straight from above and turned with the direction you drive, about
+400 m ahead and 450 m to each side: motorways glow brightest, then main roads, then the smaller
+streets, the far ones fainter, over a ground grid every 50 m that turns and slides with them.
+The speed, the battery wall, the power disc and the clock stand on dark panels over the map. The car is the chevron on the
+floor, and between GPS fixes it runs on with the speed. The roads come through the car's own
+server, which fetches only the map tiles you drive through and keeps them (see the README); the car also keeps
+the last few hundred tiles itself. Without GPS, the server or the roads, the floor says so and
+stays the plain grid. The light-cycle trail makes way for the map here; power stays on the disc.
+Shown with sample values over real roads in central Berlin.
+
+![Grid with map, with the navigation](screenshots/themes/grid-map-panel.png)
+![Grid with map, full screen](screenshots/themes/grid-map.png)
+
 ## Time circuits
 
 After the time machine in Back to the Future: three rows of LED read-outs in a metal panel,

app/build.gradle

@@ -34,8 +34,8 @@ android {
         applicationId "com.stinnesbeck.nilsmg4"
         minSdk 27
         targetSdk 36
-        versionCode 141
-        versionName "2.38.0"
+        versionCode 149
+        versionName "2.40.4"
 
         // Nothing about the server ships in the APK: its URL and ingest token are entered in
         // the app's Server tab (ServerConfig), and the database is only reachable by the server.

app/src/main/java/com/evsuite/abrp/GridView.java

@@ -22,6 +22,17 @@ import android.os.SystemClock;
  * row of read-outs along the bottom. Unread values show "—", light nothing and leave gaps in
  * the trail; the floor stands still when the speed is unread.
  *
+ * With a map ("Grid with map", {@link MapRoads}): the roads round the car from OpenStreetMap lie
+ * under everything, heading up, the bigger ones glowing brighter, with the car as a light
+ * marker low on the screen; between GPS fixes the car's position runs on
+ * with the speed. The map is then the whole background, straight from above (about
+ * 400 m ahead, 450 m to each side), over a ground grid (a line every 50 m) that turns and slides
+ * with the roads, fading into the dark towards the top. It is its own view under this one
+ * ({@link MapLayerView}): drawn once into a hardware layer and moved and turned by the GPU each
+ * display frame, the car gliding between fixes; the speed, the battery wall, the disc and the clock stand on dark panels over
+ * it, and the trail makes way for the map. Without a fix, a server or the roads, the plain floor with a line
+ * saying why.
+ *
  * Two palettes: the original cyan, or the chosen accent colour ({@link #setAccentPalette}). A
  * low battery is orange in the original (the films' other side) and white in the accent one,
  * so it never looks like the accent itself. The floor and the disc animate (about 30 frames a
@@ -44,6 +55,12 @@ final class GridView extends ClusterCanvasView {
     private final Typeface thin = Typeface.create("sans-serif-thin", Typeface.NORMAL);
     private final Typeface label = Typeface.create("sans-serif-condensed", Typeface.BOLD);
     private final int accent, accentLight;
+    /** Null for the plain Grid. */
+    private final MapRoads map;
+    /** The map under this view (a hardware layer, moved by the GPU); null for the plain Grid. */
+    private final MapLayerView mapLayer;
+    private final Paint fade = new Paint();
+    private int fadeFor = -1;
 
     private int main, light, dim, alert;
     /** The floor's position within one tile (0..1) and the disc's inner ring angle. */
@@ -52,7 +69,13 @@ final class GridView extends ClusterCanvasView {
     private int skyFor = -1;
 
     GridView(Context context) {
+        this(context, null);
+    }
+
+    GridView(Context context, MapRoads map) {
         super(context);
+        this.map = map;
+        mapLayer = map == null ? null : new MapLayerView(context, map);
         accent = AccentColor.resolve(context, R.attr.evAccent);
         accentLight = AccentColor.resolve(context, R.attr.evAccentLight);
         line.setStyle(Paint.Style.STROKE);
@@ -68,9 +91,24 @@ final class GridView extends ClusterCanvasView {
         dim = AccentColor.withAlpha(main, 0x40);
         alert = useAccent ? 0xFFFFFFFF : 0xFFFF8A1F;
         skyFor = -1;
+        if (mapLayer != null) mapLayer.setColours(main, light);
         invalidate();
     }
 
+    /** The map layer, for the pane to put under this view; null for the plain Grid. */
+    MapLayerView mapLayer() {
+        return mapLayer;
+    }
+
+    @Override
+    void setValues(ClusterValues values) {
+        super.setValues(values);
+        if (mapLayer != null) {
+            mapLayer.setSpeed(v.speedKmh);
+            mapLayer.kick();
+        }
+    }
+
     @Override
     protected void onDraw(Canvas c) {
         super.onDraw(c);
@@ -78,21 +116,32 @@ final class GridView extends ClusterCanvasView {
         if (w <= 0 || h <= 0) return;
         float u = Math.min(h / 640f, w / 1100f);
         advance();
-        c.drawColor(0xFF000000);
-
+        // With a map, the map layer underneath is the whole background (this view stays clear
+        // there), and the rest stands on dark panels over it.
+        boolean mapShown = mapLayer != null && mapLayer.isShowing();
         float horizon = h * 0.55f;
-        drawSky(c, w, horizon);
-        drawFloor(c, w, h, horizon, u);
+        if (mapShown) {
+            drawCar(c, w, h, u);
+        } else {
+            c.drawColor(0xFF000000);
+            drawSky(c, w, horizon);
+            drawFloor(c, w, h, horizon, u);
+        }
+        if (map != null && !mapShown) drawMapState(c, w, h, horizon, u);
+        if (mapShown) drawPanels(c, w, horizon, u);
         drawGears(c, w, u);
         drawClock(c, w, u);
-        drawSpeed(c, w, horizon, u);
+        if (mapShown) drawMapSpeed(c, w, u);
+        else drawSpeed(c, w, horizon, u);
         drawWall(c, horizon, u);
-        drawDisc(c, w, u);
-        drawTrail(c, w, h, u);
+        drawDisc(c, w, mapShown, u);
+        if (!mapShown) drawTrail(c, w, h, u);
         drawReadouts(c, w, h, u);
+        if (mapShown) drawAttribution(c, w, h, u);
 
         boolean moving = v.speedKmh != null && v.speedKmh > 0.5f;
-        keepAnimating(moving, 33);
+        // Over the map only the readings change; the map layer moves itself.
+        keepAnimating(moving && !mapShown, 33);
     }
 
     /** Moves the floor by the distance driven since the last frame, and turns the disc. */
@@ -138,6 +187,75 @@ final class GridView extends ClusterCanvasView {
         glowLine(c, 0, horizon, w, horizon, main, 1.5f * u);
     }
 
+    // ---------- Map ----------
+
+    /** Over the map: the far roads fading into the dark towards the top, and the car. */
+    private void drawCar(Canvas c, float w, float h, float u) {
+        float carSx = w / 2f, carSy = h - MapLayerView.CAR_FROM_BOTTOM * u;
+        if (fadeFor != (int) (carSy + h)) {
+            fade.setShader(new LinearGradient(0, 0, 0, carSy, 0xB0000000, 0x00000000, Shader.TileMode.CLAMP));
+            fadeFor = (int) (carSy + h);
+        }
+        c.drawRect(0, 0, w, carSy, fade);
+        // A light-cycle chevron pointing ahead.
+        path.reset();
+        path.moveTo(carSx, carSy - 18f * u);
+        path.lineTo(carSx + 12f * u, carSy + 11f * u);
+        path.lineTo(carSx, carSy + 5f * u);
+        path.lineTo(carSx - 12f * u, carSy + 11f * u);
+        path.close();
+        fill.setColor(light);
+        c.drawPath(path, fill);
+        glow(c, path, light, 1.5f * u);
+    }
+
+    /** Dark panels under the battery wall and the clock, so the map does not run through them. */
+    private void drawPanels(Canvas c, float w, float horizon, float u) {
+        chamfer(16f * u, 78f * u, 360f * u, horizon + 86f * u, 14f * u);
+        fill.setColor(0xC8000000);
+        c.drawPath(path, fill);
+        chamfer(w - 210f * u, 12f * u, w - 12f * u, 82f * u, 10f * u);
+        c.drawPath(path, fill);
+        // Behind the gears as well.
+        chamfer(w / 2f - 150f * u, 12f * u, w / 2f + 150f * u, 72f * u, 10f * u);
+        c.drawPath(path, fill);
+    }
+
+    /** The speed over the map: smaller, on a panel under the gears. */
+    private void drawMapSpeed(Canvas c, float w, float u) {
+        chamfer(w / 2f - 130f * u, 80f * u, w / 2f + 130f * u, 232f * u, 14f * u);
+        fill.setColor(0xC8000000);
+        c.drawPath(path, fill);
+        line.setColor(dim);
+        line.setStrokeWidth(1.5f * u);
+        c.drawPath(path, line);
+        text.setTypeface(thin);
+        text.setTextSize(120f * u);
+        text.setTextAlign(Paint.Align.CENTER);
+        glowText(c, fmt(v.speedKmh, "%.0f", "—"), w / 2f, 194f * u, light, u);
+        caption(c, "KM/H", w / 2f, 220f * u, u, Paint.Align.CENTER);
+    }
+
+    /** Why the map is not there, on the floor. */
+    private void drawMapState(Canvas c, float w, float h, float horizon, float u) {
+        MapRoads.State state = map.state();
+        String why = state == MapRoads.State.NO_SERVER ? "MAP · SET UP THE SERVER FIRST"
+                : state == MapRoads.State.WAITING_FOR_GPS ? "MAP · WAITING FOR GPS"
+                : state == MapRoads.State.UNAVAILABLE ? "MAP · NOT AVAILABLE, TRYING AGAIN"
+                : "MAP · LOADING";
+        caption(c, why, w / 2f, horizon + (h - horizon) * 0.2f, u, Paint.Align.CENTER);
+    }
+
+    /** The tiles' and the data's licences ask for their names wherever the map is shown. */
+    private void drawAttribution(Canvas c, float w, float h, float u) {
+        text.setTypeface(label);
+        text.setTextSize(12f * u);
+        text.setTextAlign(Paint.Align.RIGHT);
+        text.setStyle(Paint.Style.FILL);
+        text.setColor(dim);
+        c.drawText("OpenFreeMap © OpenMapTiles · © OpenStreetMap contributors", w - 26f * u, h - 80f * u, text);
+    }
+
     // ---------- Top ----------
 
     private void drawGears(Canvas c, float w, float u) {
@@ -225,8 +343,13 @@ final class GridView extends ClusterCanvasView {
     // ---------- Power disc ----------
 
     /** Zero at the top, −50 kW a quarter turn anticlockwise, 150 kW three quarters clockwise. */
-    private void drawDisc(Canvas c, float w, float u) {
+    private void drawDisc(Canvas c, float w, boolean overMap, float u) {
         float cx = w - 170f * u, cy = 238f * u, outer = 132f * u, ring = 22f * u;
+        if (overMap) {
+            // The map runs under the disc: a dark backing keeps it readable.
+            fill.setColor(0xD0000000);
+            c.drawCircle(cx, cy, outer + 16f * u, fill);
+        }
         line.setColor(dim);
         line.setStrokeWidth(1.5f * u);
         c.drawCircle(cx, cy, outer + 10f * u, line);

app/src/main/java/com/evsuite/abrp/MainActivity.java

@@ -70,6 +70,11 @@ public class MainActivity extends AppCompatActivity {
     private TerminalView terminalView;
     private GridView gridView;
     private VisorView visorView;
+    /** "Grid with map": the same style over the roads round the car (MapRoads, fed by GPS here). */
+    private GridView gridMapView;
+    private MapRoads mapRoads;
+    private android.location.LocationListener mapListener;
+    private boolean inFront;
     /** The pane of each Overview style, by its {@link OverviewStyle} ordinal. */
     private View[] stylePanes;
     private View consumptionPane;
@@ -345,12 +350,16 @@ public class MainActivity extends AppCompatActivity {
                 mgPane = drawnPane(octagonView);
         terminalView = new TerminalView(this);
         gridView = new GridView(this);
+        mapRoads = new MapRoads(this);
+        gridMapView = new GridView(this, mapRoads);
         visorView = new VisorView(this);
         java.util.Collections.addAll(canvasStyles, new MinimalView(this), terminalView,
-                new NixieView(this), new ChronographView(this), gridView, new TimeCircuitsView(this),
+                new NixieView(this), new ChronographView(this), gridView, gridMapView, new TimeCircuitsView(this),
                 new QuestView(this), visorView, new EmpireView(this));
         View[] canvasPanes = new View[canvasStyles.size()];
         for (int i = 0; i < canvasPanes.length; i++) canvasPanes[i] = drawnPane(canvasStyles.get(i));
+        // Grid with map: its map layer goes under it, in the same pane.
+        ((android.widget.FrameLayout) canvasPanes[canvasStyles.indexOf(gridMapView)]).addView(gridMapView.mapLayer(), 0);
         View[] fixedPanes = { vehiclePane, gaugesPane, cockpitPane, retroPane,
                 futuristicPane, sciFiPane, cartoonPane, mgPane };
         // By OverviewStyle ordinal: the fixed styles, then the canvas styles in their order.
@@ -487,6 +496,8 @@ public class MainActivity extends AppCompatActivity {
         // Poll state and log only while the screen is up; onPause cancels it.
         uiHandler.post(uiRefresh);
         uiHandler.post(overviewRefresh);
+        inFront = true;
+        updateMapLocation();
     }
 
     @Override
@@ -534,6 +545,8 @@ public class MainActivity extends AppCompatActivity {
         // Stop polling off-screen: this activity has no reason to spend cycles then.
         uiHandler.removeCallbacks(uiRefresh);
         uiHandler.removeCallbacks(overviewRefresh);
+        inFront = false;
+        updateMapLocation();
     }
 
     @Override
@@ -1725,9 +1738,56 @@ public class MainActivity extends AppCompatActivity {
         retroView.setAccentPalette(!originalColours(OverviewStyle.RETRO));
         terminalView.setAccentPalette(!originalColours(OverviewStyle.TERMINAL));
         gridView.setAccentPalette(!originalColours(OverviewStyle.GRID));
+        gridMapView.setAccentPalette(!originalColours(OverviewStyle.GRID_MAP));
         visorView.setAccentPalette(!originalColours(OverviewStyle.VISOR));
         // The accent choices depend on the style ("Original colours" for Retro and Terminal).
         if (settingsPane != null) bindAccentColor();
+        updateMapLocation();
+    }
+
+    /**
+     * GPS for the Grid's map, only while "Grid with map" is the style and the app is in front;
+     * every fix goes to {@link MapRoads}. Without the location permission there is no map (the
+     * floor says it waits for GPS), never a crash.
+     */
+    private void updateMapLocation() {
+        android.location.LocationManager lm =
+                (android.location.LocationManager) getSystemService(LOCATION_SERVICE);
+        if (lm == null || mapRoads == null) return;
+        boolean wanted = inFront && overviewStyle() == OverviewStyle.GRID_MAP;
+        if (!wanted) {
+            if (mapListener != null) {
+                try {
+                    lm.removeUpdates(mapListener);
+                } catch (RuntimeException ignored) {
+                    // already gone
+                }
+                mapListener = null;
+            }
+            return;
+        }
+        if (mapListener != null) return;
+        if (checkSelfPermission(android.Manifest.permission.ACCESS_FINE_LOCATION)
+                != android.content.pm.PackageManager.PERMISSION_GRANTED) {
+            return;
+        }
+        android.location.LocationListener listener = new android.location.LocationListener() {
+            @Override public void onLocationChanged(android.location.Location location) { mapRoads.onFix(location); }
+            @Override public void onStatusChanged(String provider, int status, android.os.Bundle extras) { }
+            @Override public void onProviderEnabled(String provider) { }
+            @Override public void onProviderDisabled(String provider) { }
+        };
+        try {
+            lm.requestLocationUpdates(android.location.LocationManager.GPS_PROVIDER, 1000L, 0f, listener);
+            mapListener = listener;
+            android.location.Location last = lm.getLastKnownLocation(android.location.LocationManager.GPS_PROVIDER);
+            if (last != null && android.os.SystemClock.elapsedRealtimeNanos() - last.getElapsedRealtimeNanos()
+                    < MapRoads.FIX_FRESH_MS * 1_000_000L) {
+                mapRoads.onFix(last);
+            }
+        } catch (RuntimeException e) {
+            android.util.Log.w("MainActivity", "No GPS for the map: " + e.getClass().getSimpleName());
+        }
     }
 
     /**
@@ -1757,6 +1817,7 @@ public class MainActivity extends AppCompatActivity {
                 getString(R.string.overview_style_minimal), getString(R.string.overview_style_terminal),
                 getString(R.string.overview_style_nixie),
                 getString(R.string.overview_style_chronograph), getString(R.string.overview_style_grid),
+                getString(R.string.overview_style_grid_map),
                 getString(R.string.overview_style_time_circuits), getString(R.string.overview_style_quest),
                 getString(R.string.overview_style_visor), getString(R.string.overview_style_empire) };
     }

app/src/main/java/com/evsuite/abrp/MapGeometry.java

@@ -0,0 +1,63 @@
+package com.evsuite.abrp;
+
+/**
+ * Web-mercator arithmetic for the Grid's map: which tile the car is in, positions in the
+ * server's tile units (4096 across a zoom-14 tile) and metres per unit. Pure Java, unit-tested.
+ */
+final class MapGeometry {
+
+    static final int ZOOM = 14;
+    static final int EXTENT = 4096;
+    /** Tile units across the world at {@link #ZOOM}. */
+    static final double WORLD = (double) (1 << ZOOM) * EXTENT;
+    private static final double EQUATOR_M = 40_075_016.686;
+
+    private MapGeometry() {}
+
+    /** The position east, in tile units from the date line. */
+    static double worldX(double lon) {
+        return (lon + 180d) / 360d * WORLD;
+    }
+
+    /** The position south, in tile units from the top of the map. */
+    static double worldY(double lat) {
+        double r = Math.toRadians(lat);
+        return (1d - Math.log(Math.tan(r) + 1d / Math.cos(r)) / Math.PI) / 2d * WORLD;
+    }
+
+    static int tileX(double lon) {
+        return clampTile((int) Math.floor(worldX(lon) / EXTENT));
+    }
+
+    static int tileY(double lat) {
+        return clampTile((int) Math.floor(worldY(lat) / EXTENT));
+    }
+
+    private static int clampTile(int t) {
+        return Math.max(0, Math.min((1 << ZOOM) - 1, t));
+    }
+
+    /** Metres per tile unit on the ground at this latitude. */
+    static double metresPerUnit(double lat) {
+        return EQUATOR_M * Math.cos(Math.toRadians(lat)) / WORLD;
+    }
+
+    /** One number for a tile, for maps and file names. */
+    static long key(int x, int y) {
+        return ((long) x << 20) | y;
+    }
+
+    static int keyX(long key) {
+        return (int) (key >> 20);
+    }
+
+    static int keyY(long key) {
+        return (int) (key & 0xFFFFF);
+    }
+
+    /** Whether the position is one a map can show (web mercator stops short of the poles). */
+    static boolean usable(double lat, double lon) {
+        return Double.isFinite(lat) && Double.isFinite(lon) && Math.abs(lat) < 85d && Math.abs(lon) <= 180d
+                && !(lat == 0d && lon == 0d);
+    }
+}

app/src/main/java/com/evsuite/abrp/MapLayerView.java

@@ -0,0 +1,223 @@
+package com.evsuite.abrp;
+
+import android.content.Context;
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.graphics.Path;
+import android.os.SystemClock;
+import android.view.View;
+
+/**
+ * The map under "Grid with map": the roads round the car and a ground grid, straight from
+ * above, heading up — drawn once into a hardware layer (a GPU texture) and then only moved and
+ * turned, by the view's own translation and rotation, once per display frame. Nothing is
+ * redrawn while driving until new tiles arrive or the car nears the layer's edge; then it is
+ * drawn again round the car. {@link GridView} draws everything else on top.
+ *
+ * The layer is a square about twice the distance from the car to the farthest screen corner,
+ * plus a margin, so it covers the screen at any angle; the car sits {@link #CAR_FROM_BOTTOM}
+ * layout units above the bottom edge.
+ */
+final class MapLayerView extends View {
+
+    /** Pixels (layout units) per metre, the car's height above the bottom edge, grid spacing. */
+    static final float MAP_SCALE = 1.2f, CAR_FROM_BOTTOM = 150f;
+    private static final float GRID_M = 50f;
+    /** How far the car may move from the layer's centre before it is drawn again, in layout units. */
+    private static final float MARGIN = 280f;
+
+    private final MapRoads map;
+    private final Paint line = new Paint(Paint.ANTI_ALIAS_FLAG);
+    private final Path[] roads = new Path[RoadTile.CLASSES];
+    private final Path grid = new Path();
+    private int main = 0xFF18E6FF, light = 0xFFC8FCFF;
+
+    /** The layer's centre (world tile units) and what it was drawn from. */
+    private double anchorX = Double.NaN, anchorY;
+    private int drawnVersion = -1;
+    private float drawnScale;
+    /** The car as shown, eased towards where it is (world tile units), and the heading. */
+    private double shownX = Double.NaN, shownY;
+    private float heading = Float.NaN;
+    private boolean showing, ticking;
+    /** The car's speed, from the readings; NaN when unread. */
+    private float speedMps = Float.NaN;
+
+    MapLayerView(Context context, MapRoads map) {
+        super(context);
+        this.map = map;
+        for (int i = 0; i < roads.length; i++) roads[i] = new Path();
+        line.setStyle(Paint.Style.STROKE);
+        line.setStrokeJoin(Paint.Join.ROUND);
+        line.setStrokeCap(Paint.Cap.ROUND);
+        setLayerType(LAYER_TYPE_HARDWARE, null);
+        setVisibility(INVISIBLE);
+        setWillNotDraw(false);
+    }
+
+    void setColours(int main, int light) {
+        this.main = main;
+        this.light = light;
+        invalidate();
+    }
+
+    /** Whether the map is there to be seen (a fix and roads). */
+    boolean isShowing() {
+        return showing;
+    }
+
+    /** Layout units, as GridView uses them, for this size. */
+    private float unit() {
+        View parent = (View) getParent();
+        int w = parent == null ? getWidth() : parent.getWidth() - parent.getPaddingLeft() - parent.getPaddingRight();
+        int h = parent == null ? getHeight() : parent.getHeight() - parent.getPaddingTop() - parent.getPaddingBottom();
+        return Math.min(h / 640f, w / 1100f);
+    }
+
+    @Override
+    protected void onMeasure(int widthSpec, int heightSpec) {
+        int w = MeasureSpec.getSize(widthSpec), h = MeasureSpec.getSize(heightSpec);
+        float u = Math.min(h / 640f, w / 1100f);
+        int side = (int) (2 * (Math.hypot(w / 2f, h - CAR_FROM_BOTTOM * u) + MARGIN * u));
+        setMeasuredDimension(Math.max(side, 1), Math.max(side, 1));
+    }
+
+    /** The car's speed in km/h, or null when unread; GridView passes it with every reading. */
+    void setSpeed(Float kmh) {
+        speedMps = kmh == null ? Float.NaN : kmh / 3.6f;
+    }
+
+    /** Starts the frame loop if it is not running; GridView calls it with every reading. */
+    void kick() {
+        if (!ticking && isAttachedToWindow()) {
+            ticking = true;
+            postOnAnimation(this::tick);
+        }
+    }
+
+    /** One display frame: where the car is, which way, and the layer moved there. */
+    private void tick() {
+        View pane = (View) getParent();
+        if (pane == null || !pane.isShown()) {
+            ticking = false;
+            return;
+        }
+        MapRoads.Fix fix = map.fix();
+        boolean ready = fix != null && !map.tiles().isEmpty() && getWidth() > 0;
+        if (ready != showing) {
+            showing = ready;
+            setVisibility(ready ? VISIBLE : INVISIBLE);
+        }
+        if (!ready) {
+            ticking = false;
+            return;
+        }
+        float target = Float.isNaN(fix.bearing) ? (Float.isNaN(heading) ? 0f : heading) : fix.bearing;
+        if (Float.isNaN(heading)) heading = target;
+        else heading = (heading + (((target - heading) % 360f + 540f) % 360f - 180f) * 0.12f + 360f) % 360f;
+
+        // Between fixes the car runs on with the speed (at most 2.5 s), and what is shown glides
+        // there rather than jumping with each fix.
+        double mpu = MapGeometry.metresPerUnit(fix.lat);
+        float ran = Float.isNaN(fix.bearing) || Float.isNaN(speedMps) ? 0f
+                : speedMps * Math.min(2.5f, (SystemClock.elapsedRealtime() - fix.elapsedMs) / 1000f);
+        double run = Math.toRadians(Float.isNaN(fix.bearing) ? 0f : fix.bearing);
+        double carX = MapGeometry.worldX(fix.lon) + ran * Math.sin(run) / mpu;
+        double carY = MapGeometry.worldY(fix.lat) - ran * Math.cos(run) / mpu;
+        if (Double.isNaN(shownX) || Math.hypot(carX - shownX, carY - shownY) * mpu > 200) {
+            shownX = carX;
+            shownY = carY;
+        } else {
+            shownX += (carX - shownX) * 0.15;
+            shownY += (carY - shownY) * 0.15;
+        }
+
+        float u = unit(), px = MAP_SCALE * u;
+        if (drawnVersion != map.version() || Double.isNaN(anchorX) || drawnScale != px
+                || Math.hypot(shownX - anchorX, shownY - anchorY) * mpu * px > MARGIN * u) {
+            build(shownX, shownY, mpu);
+            drawnScale = px;
+            invalidate(); // the only redraw of the layer
+        }
+
+        // The car's spot in the layer goes to its spot on screen, turned round it.
+        float half = getWidth() / 2f;
+        float inX = half + (float) ((shownX - anchorX) * mpu) * px;
+        float inY = half + (float) ((shownY - anchorY) * mpu) * px;
+        float carSx = pane.getPaddingLeft() + (pane.getWidth() - pane.getPaddingLeft() - pane.getPaddingRight()) / 2f;
+        float carSy = pane.getHeight() - pane.getPaddingBottom() - CAR_FROM_BOTTOM * u;
+        setPivotX(inX);
+        setPivotY(inY);
+        setRotation(-heading);
+        setTranslationX(carSx - getLeft() - inX);
+        setTranslationY(carSy - getTop() - inY);
+        postOnAnimation(this::tick);
+    }
+
+    /** The roads and the grid in metres east and south of an anchor at the car. */
+    private void build(double atX, double atY, double mpu) {
+        anchorX = atX;
+        anchorY = atY;
+        drawnVersion = map.version();
+        float m = (float) mpu;
+        for (Path p : roads) p.reset();
+        float u = unit();
+        double reach = getWidth() / 2f / (MAP_SCALE * u);
+        double range = reach / mpu;
+        for (RoadTile tile : map.tiles()) {
+            double ox = (double) tile.x * MapGeometry.EXTENT - atX, oy = (double) tile.y * MapGeometry.EXTENT - atY;
+            if (ox > range || oy > range || ox + MapGeometry.EXTENT < -range || oy + MapGeometry.EXTENT < -range) {
+                continue;
+            }
+            float fx = (float) ox, fy = (float) oy;
+            for (int i = 0; i < tile.points.length; i++) {
+                int[] b = tile.bounds[i];
+                if (fx + b[2] < -range || fx + b[0] > range || fy + b[3] < -range || fy + b[1] > range) continue;
+                Path p = roads[tile.classes[i]];
+                int[] pts = tile.points[i];
+                p.moveTo((fx + pts[0]) * m, (fy + pts[1]) * m);
+                for (int k = 2; k < pts.length; k += 2) p.lineTo((fx + pts[k]) * m, (fy + pts[k + 1]) * m);
+            }
+        }
+        // Grid lines on whole multiples of GRID_M east and north, so they stay put on the ground.
+        grid.reset();
+        float r = (float) reach;
+        float offE = (float) ((atX * mpu) % GRID_M), offS = (float) ((atY * mpu) % GRID_M);
+        int lines = (int) (r / GRID_M) + 1;
+        for (int k = -lines; k <= lines; k++) {
+            float x = k * GRID_M - offE, y = k * GRID_M - offS;
+            grid.moveTo(x, -r);
+            grid.lineTo(x, r);
+            grid.moveTo(-r, y);
+            grid.lineTo(r, y);
+        }
+    }
+
+    @Override
+    protected void onDraw(Canvas c) {
+        if (Double.isNaN(anchorX) || drawnScale <= 0f) return;
+        float u = unit(), px = drawnScale;
+        c.save();
+        c.translate(getWidth() / 2f, getHeight() / 2f);
+        c.scale(px, px);
+        stroke(c, grid, AccentColor.withAlpha(main, 0x26), 1f * u / px);
+        stroke(c, roads[3], AccentColor.withAlpha(main, 0xA0), 1.6f * u / px);
+        stroke(c, roads[2], AccentColor.withAlpha(main, 0xD8), 2.2f * u / px);
+        glow(c, roads[1], main, 2.6f * u / px);
+        glow(c, roads[0], light, 3.4f * u / px);
+        c.restore();
+    }
+
+    private void stroke(Canvas c, Path p, int colour, float width) {
+        line.setColor(colour);
+        line.setStrokeWidth(width);
+        c.drawPath(p, line);
+    }
+
+    /** As GridView's glow: two wide faint strokes under a sharp one. */
+    private void glow(Canvas c, Path p, int colour, float width) {
+        stroke(c, p, AccentColor.withAlpha(colour, 0x18), width * 6f);
+        stroke(c, p, AccentColor.withAlpha(colour, 0x40), width * 3f);
+        stroke(c, p, colour, width);
+    }
+}

app/src/main/java/com/evsuite/abrp/MapRoads.java

@@ -0,0 +1,210 @@
+package com.evsuite.abrp;
+
+import android.content.Context;
+import android.location.Location;
+import android.os.SystemClock;
+import android.util.Log;
+
+import org.json.JSONObject;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/**
+ * The roads around the car for the Grid's map, and where the car is: the activity hands in
+ * GPS fixes ({@link #onFix}) while "Grid with map" is shown; this keeps the 3×3 tiles round
+ * the car loaded from the app's own cache (files/map, 30 days, at most {@value #DISK_TILES}
+ * tiles) or from the car's server ({@code POST /v1/map/roads}, server/maps.go), one at a time
+ * on a background thread, and drops tiles from memory once the car is two tiles away. The car
+ * asks only its own server, naming a tile rather than its position. Without a configured
+ * server, a fix or the roads, the Grid shows its plain floor ({@link #state}).
+ */
+final class MapRoads {
+
+    /** Why the map shows nothing (or {@link #SHOWING}). */
+    enum State { NO_SERVER, WAITING_FOR_GPS, LOADING, UNAVAILABLE, SHOWING }
+
+    /** One GPS fix: where, which way (degrees from north, NaN before the car has moved), when. */
+    static final class Fix {
+        final double lat, lon;
+        final float bearing;
+        final long elapsedMs;
+
+        Fix(double lat, double lon, float bearing, long elapsedMs) {
+            this.lat = lat;
+            this.lon = lon;
+            this.bearing = bearing;
+            this.elapsedMs = elapsedMs;
+        }
+    }
+
+    private static final String TAG = "MapRoads";
+    private static final int DISK_TILES = 400;
+    private static final long DISK_AGE_MS = 30L * 24 * 60 * 60 * 1000;
+    /** A tile the server did not have yet (it goes on fetching) is asked for again after this. */
+    private static final long RETRY_MS = 15_000L;
+    /** A fix older than this is not drawn from. */
+    static final long FIX_FRESH_MS = 15_000L;
+
+    private final Context context;
+    private final File dir;
+    private final Map<Long, RoadTile> tiles = new ConcurrentHashMap<>();
+    private final Map<Long, Long> failedAt = new ConcurrentHashMap<>();
+    private final Map<Long, Boolean> queued = new ConcurrentHashMap<>();
+    private final ExecutorService worker = Executors.newSingleThreadExecutor(r -> {
+        Thread t = new Thread(r, "map-roads");
+        t.setPriority(Thread.MIN_PRIORITY);
+        return t;
+    });
+    private volatile Fix fix;
+    /** Goes up whenever a tile arrives or is dropped, so a view knows to rebuild its shapes. */
+    private volatile int version;
+    /** The last bearing while moving; GPS has none at a standstill. */
+    private volatile float bearing = Float.NaN;
+    private volatile boolean serverMissing;
+    /** Where the bearing was last worked out from, for a GPS that gives none. */
+    private Location anchor;
+
+    MapRoads(Context context) {
+        this.context = context.getApplicationContext();
+        dir = new File(this.context.getFilesDir(), "map");
+    }
+
+    /** A GPS fix. Main thread; the loading happens on the worker. */
+    void onFix(Location location) {
+        if (location == null || !MapGeometry.usable(location.getLatitude(), location.getLongitude())) return;
+        if (location.hasBearing() && location.hasSpeed() && location.getSpeed() > 1.5f) {
+            bearing = location.getBearing();
+            anchor = location;
+        } else if (anchor == null || location.getElapsedRealtimeNanos() - anchor.getElapsedRealtimeNanos() > 10_000_000_000L) {
+            anchor = location;
+        } else if (anchor.distanceTo(location) >= 8f) {
+            // No bearing from the GPS: the way from the last place 8 m or more behind.
+            bearing = (anchor.bearingTo(location) + 360f) % 360f;
+            anchor = location;
+        }
+        Fix f = new Fix(location.getLatitude(), location.getLongitude(), bearing, SystemClock.elapsedRealtime());
+        fix = f;
+        want(MapGeometry.tileX(f.lon), MapGeometry.tileY(f.lat));
+    }
+
+    /** The latest fix, or null when there is none or it is stale. */
+    Fix fix() {
+        Fix f = fix;
+        return f == null || SystemClock.elapsedRealtime() - f.elapsedMs > FIX_FRESH_MS ? null : f;
+    }
+
+    int version() {
+        return version;
+    }
+
+    Collection<RoadTile> tiles() {
+        return tiles.values();
+    }
+
+    State state() {
+        if (serverMissing) return State.NO_SERVER;
+        Fix f = fix();
+        if (f == null) return State.WAITING_FOR_GPS;
+        long here = MapGeometry.key(MapGeometry.tileX(f.lon), MapGeometry.tileY(f.lat));
+        if (tiles.containsKey(here)) return State.SHOWING;
+        return failedAt.containsKey(here) ? State.UNAVAILABLE : State.LOADING;
+    }
+
+    /** Queues the 3×3 tiles round (cx, cy), the car's own first, and forgets far ones. */
+    private void want(int cx, int cy) {
+        for (Long key : tiles.keySet()) {
+            if (Math.abs(MapGeometry.keyX(key) - cx) > 2 || Math.abs(MapGeometry.keyY(key) - cy) > 2) {
+                tiles.remove(key);
+                version++;
+            }
+        }
+        int[][] order = { {0, 0}, {0, -1}, {1, 0}, {0, 1}, {-1, 0}, {1, -1}, {1, 1}, {-1, 1}, {-1, -1} };
+        long now = SystemClock.elapsedRealtime();
+        for (int[] d : order) {
+            int x = cx + d[0], y = cy + d[1];
+            if (x < 0 || y < 0 || x >= (1 << MapGeometry.ZOOM) || y >= (1 << MapGeometry.ZOOM)) continue;
+            long key = MapGeometry.key(x, y);
+            if (tiles.containsKey(key) || queued.containsKey(key)) continue;
+            Long failed = failedAt.get(key);
+            if (failed != null && now - failed < RETRY_MS) continue;
+            queued.put(key, Boolean.TRUE);
+            worker.execute(() -> {
+                try {
+                    load(key, x, y);
+                } finally {
+                    queued.remove(key);
+                }
+            });
+        }
+    }
+
+    /** From the cache when fresh enough, else from the server; a stale copy beats nothing. */
+    private void load(long key, int x, int y) {
+        File file = new File(dir, MapGeometry.ZOOM + "_" + x + "_" + y + ".json");
+        RoadTile cached = null;
+        try {
+            if (file.isFile()) {
+                cached = RoadTile.parse(new String(Files.readAllBytes(file.toPath()), StandardCharsets.UTF_8), x, y);
+                if (cached == null) file.delete();
+            }
+        } catch (Exception e) {
+            Log.w(TAG, "Cached map tile unreadable: " + e.getClass().getSimpleName());
+        }
+        if (cached != null) {
+            tiles.put(key, cached);
+            version++;
+            if (System.currentTimeMillis() - file.lastModified() < DISK_AGE_MS) return;
+        }
+        ServerConfig config = ServerConfig.get(context);
+        if (!config.isConfigured()) {
+            serverMissing = true;
+            return;
+        }
+        serverMissing = false;
+        try {
+            JSONObject body = new JSONObject().put("z", MapGeometry.ZOOM).put("x", x).put("y", y);
+            ServerHttp.Response r = ServerHttp.request("POST", config.url + "/v1/map/roads", config.token, body);
+            RoadTile tile = r.status == 200 ? RoadTile.parse(r.body, x, y) : null;
+            if (tile == null) {
+                // The tile stays out of the log: it says where the car is.
+                Log.w(TAG, "Map tile not loaded: HTTP " + r.status);
+                if (cached == null) failedAt.put(key, SystemClock.elapsedRealtime());
+                return;
+            }
+            failedAt.remove(key);
+            tiles.put(key, tile);
+            version++;
+            save(file, r.body);
+        } catch (Exception e) {
+            Log.w(TAG, "Map tile not loaded: " + e.getClass().getSimpleName());
+            if (cached == null) failedAt.put(key, SystemClock.elapsedRealtime());
+        }
+    }
+
+    private void save(File file, String body) {
+        try {
+            if (!dir.isDirectory() && !dir.mkdirs()) return;
+            File tmp = new File(dir, file.getName() + ".tmp");
+            try (FileOutputStream out = new FileOutputStream(tmp)) {
+                out.write(body.getBytes(StandardCharsets.UTF_8));
+            }
+            if (!tmp.renameTo(file)) tmp.delete();
+            File[] all = dir.listFiles((d, name) -> name.endsWith(".json"));
+            if (all != null && all.length > DISK_TILES) {
+                Arrays.sort(all, (a, b) -> Long.compare(a.lastModified(), b.lastModified()));
+                for (int i = 0; i < all.length - DISK_TILES; i++) all[i].delete();
+            }
+        } catch (Exception e) {
+            Log.w(TAG, "Map tile not cached: " + e.getClass().getSimpleName());
+        }
+    }
+}

app/src/main/java/com/evsuite/abrp/OverviewStyle.java

@@ -27,6 +27,7 @@ enum OverviewStyle {
     NIXIE(false, false),
     CHRONOGRAPH(true, false),
     GRID(true, true),
+    GRID_MAP(true, true),
     TIME_CIRCUITS(false, false),
     QUEST(false, false),
     VISOR(true, true),
@@ -53,7 +54,8 @@ enum OverviewStyle {
 
     /** Where the choice between the original palette and the accent colour is kept. */
     String originalKey() {
-        return "original_colours_" + name();
+        // Grid with map is the Grid over a map: one choice for both.
+        return "original_colours_" + (this == GRID_MAP ? GRID : this).name();
     }
 
     /**

app/src/main/java/com/evsuite/abrp/RoadTile.java

@@ -0,0 +1,76 @@
+package com.evsuite.abrp;
+
+import org.json.JSONArray;
+import org.json.JSONObject;
+
+/**
+ * The roads of one map tile as the server sends them (server/maps.go): per road its class
+ * (0 motorway and trunk, 1 primary and secondary, 2 tertiary and unclassified, 3 residential)
+ * and its points in tile units, plus each road's bounding box for skipping far ones quickly.
+ * {@link #parse} fails closed: anything unexpected is no tile at all. Pure Java, unit-tested.
+ */
+final class RoadTile {
+
+    static final int CLASSES = 4;
+    /** Points may lie a little beyond the tile (a road is kept to its first point outside). */
+    private static final int SLACK = MapGeometry.EXTENT;
+    private static final int MAX_ROADS = 20_000;
+
+    final int x, y;
+    final int[] classes;
+    /** Per road: x0, y0, x1, y1, … in tile units. */
+    final int[][] points;
+    /** Per road: minX, minY, maxX, maxY. */
+    final int[][] bounds;
+
+    private RoadTile(int x, int y, int[] classes, int[][] points, int[][] bounds) {
+        this.x = x;
+        this.y = y;
+        this.classes = classes;
+        this.points = points;
+        this.bounds = bounds;
+    }
+
+    /** The tile in {@code json}, which must be the one asked for; null when it is not usable. */
+    static RoadTile parse(String json, int expectX, int expectY) {
+        try {
+            JSONObject o = new JSONObject(json);
+            if (o.getInt("z") != MapGeometry.ZOOM || o.getInt("x") != expectX || o.getInt("y") != expectY
+                    || o.getInt("extent") != MapGeometry.EXTENT) {
+                return null;
+            }
+            JSONArray ways = o.getJSONArray("ways");
+            if (ways.length() > MAX_ROADS) return null;
+            int n = ways.length();
+            int[] classes = new int[n];
+            int[][] points = new int[n][];
+            int[][] bounds = new int[n][];
+            for (int i = 0; i < n; i++) {
+                JSONObject way = ways.getJSONObject(i);
+                int c = way.getInt("c");
+                JSONArray p = way.getJSONArray("p");
+                if (c < 0 || c >= CLASSES || p.length() < 4 || p.length() % 2 != 0) return null;
+                int[] pts = new int[p.length()];
+                int minX = Integer.MAX_VALUE, minY = Integer.MAX_VALUE, maxX = Integer.MIN_VALUE, maxY = Integer.MIN_VALUE;
+                for (int k = 0; k < pts.length; k++) {
+                    int value = p.getInt(k);
+                    if (value < -SLACK || value > MapGeometry.EXTENT + SLACK) return null;
+                    pts[k] = value;
+                    if (k % 2 == 0) {
+                        minX = Math.min(minX, value);
+                        maxX = Math.max(maxX, value);
+                    } else {
+                        minY = Math.min(minY, value);
+                        maxY = Math.max(maxY, value);
+                    }
+                }
+                classes[i] = c;
+                points[i] = pts;
+                bounds[i] = new int[] { minX, minY, maxX, maxY };
+            }
+            return new RoadTile(expectX, expectY, classes, points, bounds);
+        } catch (Exception e) {
+            return null;
+        }
+    }
+}

app/src/main/java/com/evsuite/abrp/SignalRecorder.java

@@ -7,6 +7,8 @@ import android.content.IntentFilter;
 import android.os.Bundle;
 import android.os.Environment;
 
+import com.evsuite.hardware.AssistBlock;
+import com.evsuite.hardware.EVHardware;
 import com.evsuite.hardware.probe.VendorSurfaceProbe;
 
 import java.io.File;
@@ -26,7 +28,11 @@ import java.util.Map;
  * The signal recorder on the Logs tab: for {@link #DURATION_MS} it reads every value the
  * head unit offers (`VendorSurfaceProbe.capture`: every CarPropertyManager property and every
  * value getter of the vendor objects, read only) again and again, and every steering-wheel key
- * the head unit reports, into a {@link SignalRecording}. The driver notes the times they do
+ * the head unit reports, into a {@link SignalRecording}. It also listens, as the head unit's own
+ * driver-assistance manager does, to the properties of the assistance block
+ * ({@link AssistBlock}): subscribed for change events the whole time, because a value that is
+ * only filled while someone listens reads as its default when polled (2.40.3, still the
+ * cruise control). The driver notes the times they do
  * what is to be found; the values that change then are the leads. (Built to find the adaptive
  * cruise control, 2.32.0: on SWI68 the head unit gets none of it, see SPECS.md.)
  *
@@ -85,6 +91,22 @@ final class SignalRecorder {
         } catch (RuntimeException ignored) {
             // No key reports: the properties are recorded all the same.
         }
+        EVHardware.PropertyListening listening = null;
+        try {
+            listening = EVHardware.INSTANCE.listenToProperties(AssistBlock.INSTANCE::contains,
+                    (id, area, value) -> {
+                        rec.event(System.currentTimeMillis(),
+                                String.format(Locale.US, "CPM 0x%08X/%d", id, area), value);
+                        return kotlin.Unit.INSTANCE;
+                    });
+        } catch (Throwable t) {
+            rec.note(System.currentTimeMillis(), "listening failed: " + t.getClass().getSimpleName());
+        }
+        rec.note(System.currentTimeMillis(), listening == null
+                ? "listening to the assistance properties: not possible ("
+                        + EVHardware.INSTANCE.getListenProblem() + ")"
+                : "listening to " + listening.getSubscribed() + " assistance properties ("
+                        + listening.getRefused() + " refused)");
         try {
             long end = startedMs + DURATION_MS;
             while (running && System.currentTimeMillis() < end) {
@@ -99,6 +121,13 @@ final class SignalRecorder {
         } catch (Throwable t) {
             rec.note(System.currentTimeMillis(), "recorder stopped: " + t.getClass().getSimpleName());
         } finally {
+            if (listening != null) {
+                try {
+                    listening.close();
+                } catch (Throwable ignored) {
+                    // the car service is gone
+                }
+            }
             if (keysRegistered) {
                 try {
                     app.unregisterReceiver(keys);
@@ -130,7 +159,10 @@ final class SignalRecorder {
         text.add("Steering-wheel keys and notes:");
         text.addAll(rec.notes());
         text.add("");
-        text.add("Changed values, the rarest first:");
+        text.add("Assistance properties heard (" + rec.events() + " change events), changing ones first:");
+        text.addAll(rec.heard());
+        text.add("");
+        text.add("Changed values (polled), the rarest first:");
         text.addAll(rec.summary());
         text.add("");
         text.add("Everything, in order:");
@@ -168,14 +200,17 @@ final class SignalRecorder {
         long elapsed = (running ? System.currentTimeMillis() : startedMs + DURATION_MS) - startedMs;
         if (running) {
             out.add(context.getString(R.string.signal_recorder_running, elapsed / 60_000, (elapsed / 1000) % 60,
-                    recording.captures()));
+                    recording.captures(), recording.events()));
         } else {
             out.add(context.getString(R.string.signal_recorder_done, SignalRecording.time(startedMs),
-                    recording.captures(), result == null ? "…" : result));
+                    recording.captures(), recording.events(), result == null ? "…" : result));
         }
         // Steering-wheel keys and the like first: few, and each one a lead.
         List<String> notes = recording.notes();
         out.addAll(notes.subList(Math.max(0, notes.size() - 10), notes.size()));
+        // Then what the listening heard, changing properties first.
+        List<String> heard = recording.heard();
+        for (String line : heard.subList(0, Math.min(12, heard.size()))) out.add("heard " + line);
         out.addAll(recording.summary());
         return out;
     }

app/src/main/java/com/evsuite/abrp/SignalRecording.java

@@ -16,6 +16,10 @@ import java.util.TreeSet;
  * feature on and off, changes a setting). It keeps what changed, when, and per value how
  * often and through which values, so the value that follows the action stands out: it
  * changes a few times, at the moments the driver noted.
+ *
+ * Besides the captures (polled), it keeps the change events of the properties the recorder
+ * listens to ({@link #event}): how many per property and through which values. A value the
+ * head unit only fills while someone listens shows up there and nowhere else.
  * Pure Java, unit-tested.
  */
 final class SignalRecording {
@@ -31,6 +35,10 @@ final class SignalRecording {
     private final List<String> notes = new ArrayList<>();
     private final Map<String, Integer> changes = new HashMap<>();
     private final Map<String, LinkedHashSet<String>> seen = new HashMap<>();
+    private int events;
+    private final Map<String, String> lastEvent = new HashMap<>();
+    private final Map<String, Integer> eventCounts = new HashMap<>();
+    private final Map<String, LinkedHashSet<String>> eventValues = new HashMap<>();
 
     static String time(long ms) {
         return new SimpleDateFormat("HH:mm:ss", Locale.US).format(new Date(ms));
@@ -65,6 +73,45 @@ final class SignalRecording {
         notes.add(time(ms) + "  " + what);
     }
 
+    /**
+     * A change event from a property listened to. Every one is counted; the timeline gets a
+     * line only when the value differs from that property's last event.
+     */
+    synchronized void event(long ms, String key, String value) {
+        events++;
+        eventCounts.merge(key, 1, Integer::sum);
+        String before = lastEvent.put(key, value);
+        if (value.equals(before)) return;
+        lines.add(time(ms) + "  heard " + key + " = " + value);
+        LinkedHashSet<String> values = eventValues.computeIfAbsent(key, k -> new LinkedHashSet<>());
+        if (values.size() < VALUES_KEPT) values.add(shorten(value));
+    }
+
+    synchronized int events() {
+        return events;
+    }
+
+    /**
+     * Every property that sent events: first those that sent different values, the fewest
+     * events first (the leads), then those that only ever repeated one value.
+     */
+    synchronized List<String> heard() {
+        List<String> keys = new ArrayList<>(eventCounts.keySet());
+        keys.sort((a, b) -> {
+            boolean va = eventValues.get(a).size() > 1, vb = eventValues.get(b).size() > 1;
+            if (va != vb) return va ? -1 : 1;
+            int c = Integer.compare(eventCounts.get(a), eventCounts.get(b));
+            return c != 0 ? c : a.compareTo(b);
+        });
+        List<String> out = new ArrayList<>();
+        for (String key : keys) {
+            LinkedHashSet<String> values = eventValues.get(key);
+            out.add(key + "  " + eventCounts.get(key) + " events  " + String.join(" → ", values)
+                    + (values.size() >= VALUES_KEPT ? " …" : ""));
+        }
+        return out;
+    }
+
     /** The notes alone, in order. */
     synchronized List<String> notes() {
         return new ArrayList<>(notes);

app/src/main/java/com/evsuite/abrp/StylePalette.java

@@ -18,7 +18,8 @@ final class StylePalette {
             case SCIFI: return R.style.ThemeOverlay_EV_Style_SciFi;
             case CARTOON: return R.style.ThemeOverlay_EV_Style_Cartoon;
             case NIXIE: return R.style.ThemeOverlay_EV_Style_Nixie;
-            case GRID: return R.style.ThemeOverlay_EV_Style_Grid;
+            case GRID:
+            case GRID_MAP: return R.style.ThemeOverlay_EV_Style_Grid;
             case TIME_CIRCUITS: return R.style.ThemeOverlay_EV_Style_TimeCircuits;
             case QUEST: return R.style.ThemeOverlay_EV_Style_Quest;
             case VISOR: return R.style.ThemeOverlay_EV_Style_Visor;

app/src/main/res/values/strings.xml

@@ -136,6 +136,7 @@
     <string name="overview_style_terminal">Terminal</string>
     <string name="accent_original">Original</string>
     <string name="overview_style_grid">Grid</string>
+    <string name="overview_style_grid_map">Grid with map</string>
     <string name="overview_style_time_circuits">Time circuits</string>
     <string name="overview_style_quest">Quest</string>
     <string name="overview_style_visor">Visor</string>
@@ -222,11 +223,11 @@
     <string name="drive_mode_unreadable">Not changed: speed or gear unreadable.</string>
     <string name="drive_mode_unknown">an unknown mode (%1$s)</string>
     <string name="label_signal_recorder">Signal recorder</string>
-    <string name="signal_recorder_hint">Records every value the head unit offers for 3 minutes, plus the steering-wheel keys it reports, and lists what changed, the rarest first. To find a signal: start it, note the times you switch the feature on and off or change it, and look for the values that changed then. With a USB stick plugged in, the whole recording is saved on it too (Android/data/…/files).</string>
+    <string name="signal_recorder_hint">Records every value the head unit offers for 3 minutes, listens to the driver-assistance properties for every change they report, and notes the steering-wheel keys; then lists what changed, the rarest first. To find a signal: start it, note the times you switch the feature on and off or change it, and look for the values that changed then. With a USB stick plugged in, the whole recording is saved on it too (Android/data/…/files).</string>
     <string name="btn_signal_record">Record 3 minutes</string>
     <string name="btn_signal_stop">Stop recording</string>
-    <string name="signal_recorder_running">Recording: %1$d:%2$02d of 3:00, %3$d captures. Keys reported, then values changed so far, the rarest first:</string>
-    <string name="signal_recorder_done">Recording from %1$s: %2$d captures, %3$s. Keys reported, then values changed, the rarest first:</string>
+    <string name="signal_recorder_running">Recording: %1$d:%2$02d of 3:00, %3$d captures, %4$d change events heard. Keys reported, then assistance properties heard, then values changed so far, the rarest first:</string>
+    <string name="signal_recorder_done">Recording from %1$s: %2$d captures, %3$d change events heard, %4$s. Keys reported, then assistance properties heard, then values changed, the rarest first:</string>
     <string name="call_log_empty">No upload attempted yet.</string>
     <string name="update_log_title">Updates, newest first:</string>
     <string name="btn_flush_now">Upload now</string>

app/src/test/java/com/evsuite/abrp/MapGeometryTest.java

@@ -0,0 +1,65 @@
+package com.evsuite.abrp;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/** The Grid map's tile arithmetic and the server's road tiles — pure JVM. */
+public class MapGeometryTest {
+
+    @Test
+    public void tilesMatchTheServer() {
+        // Alexanderplatz, Berlin: the tile the server tests use too.
+        assertEquals(8802, MapGeometry.tileX(13.4125));
+        assertEquals(5373, MapGeometry.tileY(52.5219));
+        long key = MapGeometry.key(8802, 5373);
+        assertEquals(8802, MapGeometry.keyX(key));
+        assertEquals(5373, MapGeometry.keyY(key));
+    }
+
+    @Test
+    public void metresPerUnitShrinkTowardsThePoles() {
+        // A zoom-14 tile is about 2.4 km across at the equator, in 4096 units.
+        assertEquals(0.597, MapGeometry.metresPerUnit(0), 0.001);
+        assertEquals(0.363, MapGeometry.metresPerUnit(52.52), 0.001);
+    }
+
+    @Test
+    public void unusablePositions() {
+        assertFalse(MapGeometry.usable(Double.NaN, 13));
+        assertFalse(MapGeometry.usable(0, 0)); // a GPS that has nothing yet
+        assertFalse(MapGeometry.usable(89, 13));
+        assertTrue(MapGeometry.usable(52.52, 13.41));
+    }
+
+    @Test
+    public void roadTilesParse() {
+        RoadTile t = RoadTile.parse("{\"z\":14,\"x\":8802,\"y\":5373,\"extent\":4096,\"ways\":["
+                + "{\"c\":1,\"p\":[-115,1236,82,1080,100,1000]},{\"c\":3,\"p\":[0,0,10,10]}]}", 8802, 5373);
+        assertNotNull(t);
+        assertEquals(2, t.classes.length);
+        assertEquals(1, t.classes[0]);
+        assertEquals(6, t.points[0].length);
+        assertEquals(-115, t.bounds[0][0]);
+        assertEquals(1000, t.bounds[0][1]);
+        assertEquals(100, t.bounds[0][2]);
+        assertEquals(1236, t.bounds[0][3]);
+    }
+
+    @Test
+    public void badRoadTilesAreNoTile() {
+        String head = "{\"z\":14,\"x\":1,\"y\":2,\"extent\":4096,\"ways\":";
+        assertNotNull(RoadTile.parse(head + "[]}", 1, 2));
+        assertNull("another tile", RoadTile.parse(head + "[]}", 1, 3));
+        assertNull("another zoom", RoadTile.parse("{\"z\":13,\"x\":1,\"y\":2,\"extent\":4096,\"ways\":[]}", 1, 2));
+        assertNull("unknown class", RoadTile.parse(head + "[{\"c\":7,\"p\":[0,0,1,1]}]}", 1, 2));
+        assertNull("one point", RoadTile.parse(head + "[{\"c\":1,\"p\":[0,0]}]}", 1, 2));
+        assertNull("odd count", RoadTile.parse(head + "[{\"c\":1,\"p\":[0,0,1]}]}", 1, 2));
+        assertNull("far outside", RoadTile.parse(head + "[{\"c\":1,\"p\":[0,0,99999,1]}]}", 1, 2));
+        assertNull("not JSON", RoadTile.parse("<html>", 1, 2));
+    }
+}

app/src/test/java/com/evsuite/abrp/OverviewStyleTest.java

@@ -63,5 +63,8 @@ public class OverviewStyleTest {
         assertEquals(R.style.ThemeOverlay_EV_Style_Retro,
                 StylePalette.appOverlay(OverviewStyle.RETRO, true, AccentColor.HOLBORN_BLUE));
         assertEquals("original_colours_RETRO", OverviewStyle.RETRO.originalKey());
+        // Grid with map shares the Grid's choice.
+        assertEquals(OverviewStyle.GRID.originalKey(), OverviewStyle.GRID_MAP.originalKey());
+        assertEquals(StylePalette.overlay(OverviewStyle.GRID), StylePalette.overlay(OverviewStyle.GRID_MAP));
     }
 }

app/src/test/java/com/evsuite/abrp/SignalRecordingTest.java

@@ -63,4 +63,22 @@ public class SignalRecordingTest {
         assertTrue(r.lines().get(4).endsWith("key 287 down"));
         assertEquals(1, r.notes().size());
     }
+
+    @Test
+    public void heardPropertiesWithChangingValuesComeFirst() {
+        SignalRecording r = new SignalRecording();
+        for (int i = 0; i < 5; i++) r.event(i * 1000, "CPM 0x2140A10A/0", "1"); // repeats one value
+        r.event(1000, "CPM 0x2160A15B/0", "0.0");
+        r.event(2000, "CPM 0x2160A15B/0", "101.0");
+        r.event(3000, "CPM 0x2160A15B/0", "101.0");
+        r.event(4000, "CPM 0x2160A15B/0", "90.0");
+        List<String> heard = r.heard();
+        assertEquals(2, heard.size());
+        assertEquals("CPM 0x2160A15B/0  4 events  0.0 → 101.0 → 90.0", heard.get(0));
+        assertEquals("CPM 0x2140A10A/0  5 events  1", heard.get(1));
+        assertEquals(9, r.events());
+        // The timeline holds only the changes: 0.0, 101.0, 90.0 and the first 1.
+        long lines = r.lines().stream().filter(l -> l.contains("heard ")).count();
+        assertEquals(4, lines);
+    }
 }

app/src/unstable/java/com/evsuite/abrp/OtaInstallResultReceiver.java

@@ -16,10 +16,17 @@ import android.widget.Toast;
  * STATUS_PENDING_USER_ACTION is the case worth understanding: the platform is saying it will
  * install, but wants the driver to confirm. That happens when the app is not granted a silent
  * install, and the only correct response is to launch the confirmation activity it hands us.
+ *
+ * Any other failure — on the car the session is refused, "Not allowed to install non-system
+ * apps on internal storage", and that answer can come here rather than as an exception — opens
+ * Android's installer screen with the verified APK, as {@link OtaUpdater#install} does for an
+ * immediate refusal. Only a cancel by the driver ends there.
  */
 public final class OtaInstallResultReceiver extends BroadcastReceiver {
 
     static final String ACTION_INSTALL_RESULT = "com.stinnesbeck.nilsmg4.OTA_INSTALL_RESULT";
+    static final String EXTRA_APK = "com.stinnesbeck.nilsmg4.extra.APK";
+    static final String EXTRA_SESSION = "com.stinnesbeck.nilsmg4.extra.SESSION";
 
     private static final String TAG = "EVABRP.Update";
 
@@ -31,12 +38,16 @@ public final class OtaInstallResultReceiver extends BroadcastReceiver {
         Log.i(TAG, "OTA install result: status=" + status + " msg=" + message);
         UpdateLog.record(context, "Install result: status " + status
                 + (message != null ? ", " + message : ""));
+        int session = intent.getIntExtra(EXTRA_SESSION, -1);
+        if (session >= 0) OtaUpdater.noteAnswer(session);
+        String apkPath = intent.getStringExtra(EXTRA_APK);
 
         switch (status) {
             case PackageInstaller.STATUS_PENDING_USER_ACTION:
                 Intent confirm = intent.getParcelableExtra(Intent.EXTRA_INTENT);
                 if (confirm == null) {
-                    toast(context, context.getString(R.string.ota_install_failed, "no confirm intent"));
+                    UpdateLog.record(context, "No confirmation screen offered");
+                    openInstallerScreen(context, apkPath, "no confirm intent");
                     return;
                 }
                 confirm.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
@@ -44,23 +55,52 @@ public final class OtaInstallResultReceiver extends BroadcastReceiver {
                     context.startActivity(confirm);
                 } catch (Throwable t) {
                     Log.e(TAG, "OTA confirm UI failed: " + t.getMessage());
-                    toast(context, context.getString(R.string.ota_install_failed,
-                            t.getClass().getSimpleName()));
+                    UpdateLog.record(context, "Confirmation screen failed: " + t.getClass().getSimpleName());
+                    openInstallerScreen(context, apkPath, t.getClass().getSimpleName());
                 }
                 break;
             case PackageInstaller.STATUS_SUCCESS:
                 toast(context, context.getString(R.string.ota_install_success));
                 break;
+            case PackageInstaller.STATUS_FAILURE_ABORTED:
+                // The driver cancelled: nothing opens again.
+                toast(context, context.getString(R.string.ota_install_failed,
+                        message != null ? message : "cancelled"));
+                break;
             default:
                 // The status message is the package manager's own words — INSTALL_FAILED_*
-                // and friends. Surfaced verbatim, because guessing at it is what made the
-                // previous failure unreadable.
-                toast(context, context.getString(R.string.ota_install_failed,
-                        message != null ? message : "status " + status));
+                // and friends — kept verbatim in the update log, because guessing at it is what
+                // made an earlier failure unreadable. Then the installer screen, which the car
+                // allows where it refuses the session.
+                openInstallerScreen(context, apkPath, message != null ? message : "status " + status);
                 break;
         }
     }
 
+    /**
+     * Opens Android's installer screen for the APK at [apkPath] off the main thread (it is
+     * copied to Downloads first); a toast with [why] when there is none or it cannot open.
+     */
+    private void openInstallerScreen(Context context, String apkPath, String why) {
+        java.io.File apk = apkPath == null ? null : new java.io.File(apkPath);
+        if (apk == null || !apk.isFile()) {
+            toast(context, context.getString(R.string.ota_install_failed, why));
+            return;
+        }
+        PendingResult pending = goAsync();
+        Context app = context.getApplicationContext();
+        new Thread(() -> {
+            try {
+                if (!OtaUpdater.openInstallerScreen(app, apk)) {
+                    new android.os.Handler(android.os.Looper.getMainLooper()).post(() ->
+                            toast(app, app.getString(R.string.ota_install_failed, why)));
+                }
+            } finally {
+                pending.finish();
+            }
+        }, "ota-fallback").start();
+    }
+
     private static void toast(Context context, String text) {
         Toast.makeText(context.getApplicationContext(), text, Toast.LENGTH_LONG).show();
     }

app/src/unstable/java/com/evsuite/abrp/OtaUpdater.java

@@ -464,23 +464,59 @@ final class OtaUpdater {
     static InstallResult install(Context context, File apk) {
         if (!archiveIsThisPackage(context, apk)) return InstallResult.UNREADABLE_ARCHIVE;
         try {
-            commitSession(context, apk);
+            int sessionId = commitSession(context, apk);
+            watchForAnswer(context, sessionId, apk);
             return InstallResult.SESSION_STARTED;
         } catch (Throwable t) {
             Log.w(TAG, "OTA session install failed; trying system install UI", t);
             UpdateLog.record(context, "Installer session failed: " + t);
-            try {
-                launchInstallerActivity(context, apk);
-                UpdateLog.record(context, "Opened the system installer instead");
-                return InstallResult.INSTALL_UI_STARTED;
-            } catch (Throwable fallback) {
-                Log.w(TAG, "OTA install UI failed", fallback);
-                UpdateLog.record(context, "System installer failed too: " + fallback);
-                return InstallResult.SESSION_FAILED;
-            }
+            return openInstallerScreen(context, apk) ? InstallResult.INSTALL_UI_STARTED : InstallResult.SESSION_FAILED;
         }
     }
 
+    /** The installer screen for [apk], as the fallback; false if even that could not open. */
+    static boolean openInstallerScreen(Context context, File apk) {
+        try {
+            launchInstallerActivity(context, apk);
+            UpdateLog.record(context, "Opened the system installer instead");
+            return true;
+        } catch (Throwable fallback) {
+            Log.w(TAG, "OTA install UI failed", fallback);
+            UpdateLog.record(context, "System installer failed too: " + fallback);
+            return false;
+        }
+    }
+
+    /** How long a committed session may stay silent before the installer screen is opened. */
+    private static final long ANSWER_WAIT_MS = 20_000L;
+    /** Sessions the platform has answered (any status), so the watch knows to stand down. */
+    private static final java.util.Set<Integer> answered =
+            java.util.Collections.synchronizedSet(new java.util.HashSet<>());
+
+    /** The platform said something about [sessionId]; called by {@link OtaInstallResultReceiver}. */
+    static void noteAnswer(int sessionId) {
+        answered.add(sessionId);
+    }
+
+    /**
+     * A committed session normally answers within a second or two: installed (the app
+     * restarts), refused, or "confirm on screen". If it says nothing at all, the update would
+     * end silently after its download, so the installer screen is opened instead.
+     */
+    private static void watchForAnswer(Context context, int sessionId, File apk) {
+        Context app = context.getApplicationContext();
+        new android.os.Handler(android.os.Looper.getMainLooper()).postDelayed(() -> {
+            if (answered.contains(sessionId)) return;
+            UpdateLog.record(app, "No answer from the installer after " + ANSWER_WAIT_MS / 1000 + " s");
+            try {
+                app.getPackageManager().getPackageInstaller().abandonSession(sessionId);
+            } catch (Throwable ignored) {
+                // already gone
+            }
+            new Thread(() -> openInstallerScreen(app, apk), "ota-fallback").start();
+        }, ANSWER_WAIT_MS);
+    }
+
     /**
      * True if the archive parses and declares our own package name.
      *
@@ -510,7 +546,8 @@ final class OtaUpdater {
         }
     }
 
-    private static void commitSession(Context context, File apk) throws Exception {
+    /** Commits [apk] to a new installer session and returns its id. */
+    private static int commitSession(Context context, File apk) throws Exception {
         PackageInstaller installer = context.getPackageManager().getPackageInstaller();
         PackageInstaller.SessionParams params = new PackageInstaller.SessionParams(
                 PackageInstaller.SessionParams.MODE_FULL_INSTALL);
@@ -533,7 +570,10 @@ final class OtaUpdater {
             }
             Intent callback = new Intent(context, OtaInstallResultReceiver.class)
                     .setAction(OtaInstallResultReceiver.ACTION_INSTALL_RESULT)
-                    .setPackage(context.getPackageName());
+                    .setPackage(context.getPackageName())
+                    // Where the verified APK is, for the installer screen if the session fails.
+                    .putExtra(OtaInstallResultReceiver.EXTRA_APK, apk.getAbsolutePath())
+                    .putExtra(OtaInstallResultReceiver.EXTRA_SESSION, sessionId);
             // MUTABLE: the platform fills in EXTRA_STATUS and, when it wants the driver to
             // confirm, EXTRA_INTENT. An immutable PendingIntent would arrive empty.
             PendingIntent pending = PendingIntent.getBroadcast(context, sessionId, callback,
@@ -543,6 +583,7 @@ final class OtaUpdater {
             session.commit(pending.getIntentSender());
             committed = true;
             Log.i(TAG, "OTA session " + sessionId + " committed (" + apk.length() + " bytes)");
+            return sessionId;
         } finally {
             // Abandon failed staging, but always close our local handle after a commit too.
             if (!committed) {

k8s/server.yaml

@@ -1,5 +1,21 @@
 # The car server (Go). One replica on purpose: pending pairing requests and the wrong-password
 # counters are kept in memory.
+# The roads of the app's Grid map, fetched on demand, are kept on this small volume.
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mg4-server-maps
+  namespace: mg4
+  labels:
+    app.kubernetes.io/name: mg4-server
+    app.kubernetes.io/part-of: mg4
+spec:
+  accessModes: ["ReadWriteOnce"]
+  # No storageClassName: the cluster's default class is used.
+  resources:
+    requests:
+      storage: 1Gi
+---
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -25,12 +41,13 @@ spec:
         runAsNonRoot: true
         runAsUser: 65532
         runAsGroup: 65532
+        fsGroup: 65532
         seccompProfile:
           type: RuntimeDefault
       containers:
         - name: server
-          # 2.6.2, pinned by digest so a re-pushed tag cannot change what runs.
-          image: git.stinnesbeck.com/nils/mg4-server@sha256:e4de1e75958d58ece8430a1913f9c1614d8ea1bf566f2e1ec5b449ef51844f77
+          # Pinned by digest so a re-pushed tag cannot change what runs (version in SPECS.md).
+          image: git.stinnesbeck.com/nils/mg4-server@sha256:8b8d94e0562833d196162866b7fdc6910d5dd219f6eb84572d4d5c91b74f7ff1
           ports:
             - name: http
               containerPort: 8080
@@ -50,6 +67,12 @@ spec:
               value: https://git.stinnesbeck.com
             - name: FORGE_REPO
               value: nils/mg4
+            # The roads for the app's Grid map: OpenStreetMap vector tiles, fetched only for the
+            # tiles a car asks for and kept on the volume below; "off" switches maps off.
+            - name: MAP_TILES_URL
+              value: https://tiles.openfreemap.org/planet
+            - name: MAP_CACHE_DIR
+              value: /var/cache/mg4-maps
             - name: INFLUX_TOKEN
               valueFrom:
                 secretKeyRef:
@@ -81,6 +104,13 @@ spec:
             readOnlyRootFilesystem: true
             capabilities:
               drop: ["ALL"]
+          volumeMounts:
+            - name: maps
+              mountPath: /var/cache/mg4-maps
+      volumes:
+        - name: maps
+          persistentVolumeClaim:
+            claimName: mg4-server-maps
 ---
 apiVersion: v1
 kind: Service

server/README.md

@@ -23,6 +23,8 @@ Environment only; the server refuses to start when a required value is missing.
 | `APPROVAL_PASSWORD` | optional, at least 12 characters; switches pairing on (see below) |
 | `PUBLIC_URL` | the address a phone uses, for the pairing QR code; derived from the request if empty |
 | `FORGE_URL`, `FORGE_REPO`, `FORGE_TOKEN` | optional; app updates (below). The token only needs to read the repository |
+| `MAP_TILES_URL` | a TileJSON naming the vector tiles the map's roads come from; default OpenFreeMap's `https://tiles.openfreemap.org/planet`, `off` switches maps off, otherwise https only |
+| `MAP_CACHE_DIR` | where fetched map tiles are kept across restarts (the manifest mounts a volume there); empty keeps them in memory only |
 | `LISTEN_ADDR` | default `:8080` |
 
 ## Endpoints
@@ -57,6 +59,26 @@ shared ingest token): `update check` (how many releases, the newest pre-release)
 download started` (file, size), then `update handed out` (bytes sent, time taken) or `update
 download cut short`. The forge's address and token never appear in the log.
 
+## Map roads
+
+`POST /v1/map/roads` `{z, x, y}`, with the car's token: the drivable roads (motorway to minor
+streets) of one web-mercator tile at zoom 14, for the app's "Grid with map" style. The car names
+the tile, not its position, and in the body, so it stays out of access logs. The answer is
+`{z, x, y, extent: 4096, ways: [{c, p: [x, y, …]}]}`: per road its class (0 motorway and trunk,
+1 primary and secondary, 2 tertiary, 3 minor streets) and its points in tile units, simplified to
+about 1.5 m; gzipped when the car accepts it (10–15 KB a tile in a city before that).
+
+The roads are fetched **only for the tiles a car asks for**: the OpenStreetMap vector tile
+(OpenMapTiles schema) of that square from the TileJSON at `MAP_TILES_URL` (by default
+OpenFreeMap: free, no key, no request limits; its template moves with each weekly build and is
+looked up every 6 hours), decoded by a small reader of our own (`mvt.go`, the `transportation`
+layer only). Each tile is fetched once and kept for 30 days in `MAP_CACHE_DIR` (and the last 300
+in memory); at most two fetches run at once. A request waits up to 6 s; a slower fetch goes on
+and is kept, and the car hears 503 with `Retry-After: 10` and gets the tile on its next try.
+400 for anything but zoom 14 or a tile outside it, 503 when the tile host fails (not cached),
+404 when maps are off. The log says `map tile fetched` with the size, never the tile.
+Map data © OpenStreetMap contributors (ODbL), tiles © OpenMapTiles, served by OpenFreeMap.
+
 ## Settings from a phone
 
 The ABRP credentials are long to type on the car. With pairing on, the car (with its own token)

server/api.go

@@ -20,6 +20,7 @@ import (
 //	GET  /v1/health                              unauthenticated liveness probe
 //	     /v1/settings/…, /settings                settings typed on a phone (handoff_http.go)
 //	GET  /v1/app/…                               app updates from the forge (releases.go)
+//	POST /v1/map/roads                           the roads of one map tile (maps.go)
 //
 // A car authenticates with the shared INGEST_TOKEN or with its own token from pairing
 // (pairing_http.go).
@@ -31,6 +32,8 @@ type API struct {
 	Handoff *Handoff
 	// Releases relays the app's releases from the private forge to the car (releases.go).
 	Releases *Releases
+	// Maps serves the roads for the Overview's map from OpenStreetMap vector tiles (maps.go); nil is off.
+	Maps *Maps
 	// PublicURL is the server's address as a phone reaches it, for the pairing QR code;
 	// derived from the request when empty.
 	PublicURL string
@@ -50,6 +53,7 @@ func (a *API) Routes() http.Handler {
 	a.pairingRoutes(mux)
 	a.handoffRoutes(mux)
 	a.releaseRoutes(mux)
+	a.mapRoutes(mux)
 	return mux
 }
 

server/main.go

@@ -34,6 +34,8 @@ type config struct {
 	forgeURL     string
 	forgeRepo    string
 	forgeToken   string
+	mapTilesURL  string
+	mapCacheDir  string
 }
 
 // loadConfig reads the environment and fails closed: a missing InfluxDB setting or a
@@ -51,6 +53,8 @@ func loadConfig(getenv func(string) string) (config, error) {
 		forgeURL:     getenv("FORGE_URL"),
 		forgeRepo:    getenv("FORGE_REPO"),
 		forgeToken:   getenv("FORGE_TOKEN"),
+		mapTilesURL:  getenv("MAP_TILES_URL"),
+		mapCacheDir:  getenv("MAP_CACHE_DIR"),
 	}
 	if c.listenAddr == "" {
 		c.listenAddr = ":8080"
@@ -73,6 +77,18 @@ func loadConfig(getenv func(string) string) (config, error) {
 	if c.forgeURL != "" && !strings.HasPrefix(c.forgeURL, "https://") {
 		return config{}, errors.New("FORGE_URL must be an https URL")
 	}
+	// The map's roads come from vector tiles named by a TileJSON: OpenFreeMap unless another is
+	// named, none with "off". Only https, like the forge.
+	switch c.mapTilesURL {
+	case "":
+		c.mapTilesURL = DefaultMapTilesURL
+	case "off":
+		c.mapTilesURL = ""
+	default:
+		if !strings.HasPrefix(c.mapTilesURL, "https://") {
+			return config{}, errors.New("MAP_TILES_URL must be an https URL or \"off\"")
+		}
+	}
 	if c.approvalPass != "" && len(c.approvalPass) < minApprovalPasswordLength {
 		return config{}, fmt.Errorf("APPROVAL_PASSWORD must be at least %d characters", minApprovalPasswordLength)
 	}
@@ -102,6 +118,15 @@ func main() {
 	releases := &Releases{ForgeURL: cfg.forgeURL, Repo: cfg.forgeRepo, Token: cfg.forgeToken}
 	api := &API{Store: store, IngestToken: cfg.ingestToken, Pairing: pairing, Handoff: NewHandoff(),
 		Releases: releases, PublicURL: cfg.publicURL}
+	if cfg.mapTilesURL != "" {
+		if cfg.mapCacheDir != "" {
+			if err := os.MkdirAll(cfg.mapCacheDir, 0o700); err != nil {
+				slog.Error("map cache directory not usable", "error", err)
+				os.Exit(1)
+			}
+		}
+		api.Maps = NewMaps(cfg.mapTilesURL, cfg.mapCacheDir, mapUserAgent)
+	}
 
 	srv := &http.Server{
 		Addr:              cfg.listenAddr,
@@ -116,7 +141,8 @@ func main() {
 	defer stop()
 	go func() {
 		slog.Info("listening", "addr", cfg.listenAddr, "bucket", cfg.influxBucket,
-			"pairing", pairing.Enabled(), "pairedDevices", len(devices), "appUpdates", releases.enabled())
+			"pairing", pairing.Enabled(), "pairedDevices", len(devices), "appUpdates", releases.enabled(),
+			"maps", api.Maps != nil)
 		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			slog.Error("server failed", "error", err)
 			os.Exit(1)

server/maps.go

@@ -0,0 +1,426 @@
+package main
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"math"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+// Maps serves the roads around the car for the Overview's map (the "Grid with map" style). It
+// fetches only the tiles a car asks for, as OpenStreetMap vector tiles (OpenMapTiles schema,
+// by default from OpenFreeMap), keeps their roads and stores them, so each tile is fetched
+// once and the car only ever talks to this server.
+//
+//	POST /v1/map/roads   {"z":14,"x":…,"y":…}
+//	                     → {"z","x","y","extent":4096,"ways":[{"c":class,"p":[x,y,x,y,…]}]}
+//
+// The car names a web-mercator tile at zoom 14 (about 1.5 km across in central Europe), not
+// its position, and in the body so the tile stays out of access logs. Points are tile-local
+// in 0..4096 (a little beyond at the edges), simplified to about 1.5 m. Classes: 0 motorway and
+// trunk, 1 primary and secondary, 2 tertiary, 3 minor streets (residential, unclassified,
+// living streets).
+//
+// A fetch runs to its end even when the car stops waiting (the car gives up after a few
+// seconds), so its next try finds the tile. Tiles are kept in memory (the last mapMemoryTiles)
+// and, with a cache directory, on disk for mapCacheAge. The tile's coordinates never appear
+// in the log.
+type Maps struct {
+	// TileJSONURL names the vector tiles: a TileJSON document whose first "tiles" template is
+	// used (OpenFreeMap moves its template with every weekly build).
+	TileJSONURL string
+	// CacheDir keeps fetched tiles across restarts; empty keeps them in memory only.
+	CacheDir  string
+	UserAgent string
+	Client    *http.Client
+
+	mu       sync.Mutex
+	memory   map[mapTile]mapEntry
+	inflight map[mapTile]*mapFlight
+	template string
+	tmplAt   time.Time
+	// slots limits fetches running at once.
+	slots chan struct{}
+}
+
+const (
+	mapZoom        = 14
+	mapExtent      = 4096
+	mapMemoryTiles = 300
+	mapCacheAge    = 30 * 24 * time.Hour
+	maxTileBytes   = 8 << 20
+	mapFetchTime   = 60 * time.Second
+	templateAge    = 6 * time.Hour
+	// The simplification tolerance in tile units (about 0.37 m each at 52° N).
+	mapTolerance = 4.0
+	// DefaultMapTilesURL is OpenFreeMap's TileJSON: free OpenStreetMap vector tiles, no key.
+	DefaultMapTilesURL = "https://tiles.openfreemap.org/planet"
+	// mapUserAgent names this service to the tile host.
+	mapUserAgent = "nils-mg4-server/2.8 (private car dashboard; roads for an in-car map)"
+)
+
+// mapWait is how long a request waits for a fetch: less than the car's own 8 s.
+var mapWait = 6 * time.Second
+
+type mapTile struct{ Z, X, Y int }
+
+type mapEntry struct {
+	body []byte
+	at   time.Time
+}
+
+type mapFlight struct {
+	done chan struct{}
+	body []byte
+	err  error
+}
+
+// roadClasses maps the OpenMapTiles transportation classes to the four the car draws; the
+// rest (service, track, path, rail, ferry…) are left out.
+var roadClasses = map[string]int{
+	"motorway": 0, "trunk": 0,
+	"primary": 1, "secondary": 1,
+	"tertiary": 2,
+	"minor":    3,
+}
+
+type roadTile struct {
+	Z      int    `json:"z"`
+	X      int    `json:"x"`
+	Y      int    `json:"y"`
+	Extent int    `json:"extent"`
+	Ways   []road `json:"ways"`
+}
+
+type road struct {
+	C int   `json:"c"`
+	P []int `json:"p"`
+}
+
+func NewMaps(tileJSONURL, cacheDir, userAgent string) *Maps {
+	return &Maps{TileJSONURL: tileJSONURL, CacheDir: cacheDir, UserAgent: userAgent}
+}
+
+func (m *Maps) client() *http.Client {
+	if m.Client != nil {
+		return m.Client
+	}
+	return &http.Client{Timeout: mapFetchTime}
+}
+
+// Tile returns the tile's roads as JSON and whether it came from a cache. Waiting ends with
+// ctx; the fetch itself goes on and is kept.
+func (m *Maps) Tile(ctx context.Context, t mapTile) ([]byte, bool, error) {
+	if body, ok := m.cached(t); ok {
+		return body, true, nil
+	}
+	m.mu.Lock()
+	if m.inflight == nil {
+		m.inflight = map[mapTile]*mapFlight{}
+		m.slots = make(chan struct{}, 2)
+	}
+	f, running := m.inflight[t]
+	if !running {
+		f = &mapFlight{done: make(chan struct{})}
+		m.inflight[t] = f
+		go m.run(t, f)
+	}
+	m.mu.Unlock()
+	select {
+	case <-f.done:
+		return f.body, false, f.err
+	case <-ctx.Done():
+		return nil, false, errors.New("still fetching")
+	}
+}
+
+func (m *Maps) run(t mapTile, f *mapFlight) {
+	defer func() {
+		m.mu.Lock()
+		delete(m.inflight, t)
+		m.mu.Unlock()
+		close(f.done)
+	}()
+	m.slots <- struct{}{}
+	defer func() { <-m.slots }()
+	ctx, cancel := context.WithTimeout(context.Background(), mapFetchTime)
+	defer cancel()
+	raw, err := m.fetch(ctx, t)
+	if err == nil {
+		f.body, err = buildTile(t, raw)
+	}
+	if err != nil {
+		f.err = err
+		return
+	}
+	m.store(t, f.body)
+	slog.Info("map tile fetched", "ways", strings.Count(string(f.body), `"c":`), "bytes", len(f.body))
+}
+
+func (m *Maps) cachePath(t mapTile) string {
+	return filepath.Join(m.CacheDir, fmt.Sprintf("%d_%d_%d.json", t.Z, t.X, t.Y))
+}
+
+func (m *Maps) cached(t mapTile) ([]byte, bool) {
+	m.mu.Lock()
+	e, ok := m.memory[t]
+	m.mu.Unlock()
+	if ok && time.Since(e.at) <= mapCacheAge {
+		return e.body, true
+	}
+	if m.CacheDir == "" {
+		return nil, false
+	}
+	info, err := os.Stat(m.cachePath(t))
+	if err != nil || time.Since(info.ModTime()) > mapCacheAge {
+		return nil, false
+	}
+	body, err := os.ReadFile(m.cachePath(t))
+	if err != nil || !json.Valid(body) {
+		return nil, false
+	}
+	m.remember(t, body, info.ModTime())
+	return body, true
+}
+
+func (m *Maps) store(t mapTile, body []byte) {
+	m.remember(t, body, time.Now())
+	if m.CacheDir == "" {
+		return
+	}
+	tmp := m.cachePath(t) + ".tmp"
+	if err := os.WriteFile(tmp, body, 0o600); err != nil {
+		slog.Warn("map tile not stored", "error", err)
+		return
+	}
+	if err := os.Rename(tmp, m.cachePath(t)); err != nil {
+		slog.Warn("map tile not stored", "error", err)
+	}
+}
+
+// remember keeps the tile in memory, dropping the oldest when full.
+func (m *Maps) remember(t mapTile, body []byte, at time.Time) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.memory == nil {
+		m.memory = map[mapTile]mapEntry{}
+	}
+	if _, ok := m.memory[t]; !ok && len(m.memory) >= mapMemoryTiles {
+		var oldest mapTile
+		var first time.Time
+		for k, e := range m.memory {
+			if first.IsZero() || e.at.Before(first) {
+				oldest, first = k, e.at
+			}
+		}
+		delete(m.memory, oldest)
+	}
+	m.memory[t] = mapEntry{body: body, at: at}
+}
+
+func (m *Maps) get(ctx context.Context, u string, limit int64) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("User-Agent", m.UserAgent)
+	resp, err := m.client().Do(req)
+	if err != nil {
+		// The URL holds the tile: name the failure, not the request.
+		if errors.Is(err, context.DeadlineExceeded) || errors.Is(ctx.Err(), context.DeadlineExceeded) {
+			return nil, errors.New("tile host timed out")
+		}
+		return nil, errors.New("tile host could not be reached")
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 1<<16))
+		return nil, fmt.Errorf("tile host answered %d", resp.StatusCode)
+	}
+	body, err := io.ReadAll(io.LimitReader(resp.Body, limit+1))
+	if err != nil {
+		return nil, errors.New("tile host answer could not be read")
+	}
+	if int64(len(body)) > limit {
+		return nil, errors.New("tile host answer is too large")
+	}
+	return body, nil
+}
+
+// tileTemplate is the current {z}/{x}/{y} URL from the TileJSON, looked up every few hours.
+func (m *Maps) tileTemplate(ctx context.Context) (string, error) {
+	m.mu.Lock()
+	tmpl, at := m.template, m.tmplAt
+	m.mu.Unlock()
+	if tmpl != "" && time.Since(at) < templateAge {
+		return tmpl, nil
+	}
+	body, err := m.get(ctx, m.TileJSONURL, 1<<20)
+	if err != nil {
+		return "", err
+	}
+	var doc struct {
+		Tiles []string `json:"tiles"`
+	}
+	if err := json.Unmarshal(body, &doc); err != nil || len(doc.Tiles) == 0 {
+		return "", errors.New("tile index has no tiles")
+	}
+	tmpl = doc.Tiles[0]
+	u, err := url.Parse(strings.NewReplacer("{z}", "0", "{x}", "0", "{y}", "0").Replace(tmpl))
+	if err != nil || u.Scheme != "https" || u.Host == "" ||
+		!strings.Contains(tmpl, "{z}") || !strings.Contains(tmpl, "{x}") || !strings.Contains(tmpl, "{y}") {
+		return "", errors.New("tile index names no usable https template")
+	}
+	m.mu.Lock()
+	m.template, m.tmplAt = tmpl, time.Now()
+	m.mu.Unlock()
+	return tmpl, nil
+}
+
+func (m *Maps) fetch(ctx context.Context, t mapTile) ([]byte, error) {
+	tmpl, err := m.tileTemplate(ctx)
+	if err != nil {
+		return nil, err
+	}
+	u := strings.NewReplacer("{z}", strconv.Itoa(t.Z), "{x}", strconv.Itoa(t.X), "{y}", strconv.Itoa(t.Y)).Replace(tmpl)
+	raw, err := m.get(ctx, u, maxTileBytes)
+	if err != nil {
+		return nil, err
+	}
+	// Some hosts send the tile gzipped whatever the request said.
+	if len(raw) > 2 && raw[0] == 0x1f && raw[1] == 0x8b {
+		zr, err := gzip.NewReader(bytes.NewReader(raw))
+		if err != nil {
+			return nil, errors.New("tile is not readable")
+		}
+		raw, err = io.ReadAll(io.LimitReader(zr, maxTileBytes+1))
+		if err != nil || len(raw) > maxTileBytes {
+			return nil, errors.New("tile is not readable")
+		}
+	}
+	return raw, nil
+}
+
+// buildTile keeps the roads of the vector tile's transportation layer, in the car's format.
+func buildTile(t mapTile, raw []byte) ([]byte, error) {
+	lines, err := decodeRoads(raw)
+	if err != nil {
+		return nil, err
+	}
+	out := roadTile{Z: t.Z, X: t.X, Y: t.Y, Extent: mapExtent, Ways: []road{}}
+	for _, l := range lines {
+		pts := simplify(l.points, mapTolerance)
+		if len(pts) < 2 {
+			continue
+		}
+		flat := make([]int, 0, len(pts)*2)
+		for _, p := range pts {
+			flat = append(flat, p[0], p[1])
+		}
+		out.Ways = append(out.Ways, road{C: l.class, P: flat})
+	}
+	return json.Marshal(out)
+}
+
+// simplify is Douglas–Peucker: the points that keep the line within tol of the original.
+func simplify(pts [][2]int, tol float64) [][2]int {
+	if len(pts) < 3 {
+		return pts
+	}
+	keep := make([]bool, len(pts))
+	keep[0], keep[len(pts)-1] = true, true
+	type span struct{ a, b int }
+	stack := []span{{0, len(pts) - 1}}
+	for len(stack) > 0 {
+		s := stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+		best, at := 0.0, -1
+		for i := s.a + 1; i < s.b; i++ {
+			if d := segmentDistance(pts[i], pts[s.a], pts[s.b]); d > best {
+				best, at = d, i
+			}
+		}
+		if at >= 0 && best > tol {
+			keep[at] = true
+			stack = append(stack, span{s.a, at}, span{at, s.b})
+		}
+	}
+	var out [][2]int
+	for i, k := range keep {
+		if k {
+			out = append(out, pts[i])
+		}
+	}
+	return out
+}
+
+func segmentDistance(p, a, b [2]int) float64 {
+	px, py := float64(p[0]), float64(p[1])
+	ax, ay, bx, by := float64(a[0]), float64(a[1]), float64(b[0]), float64(b[1])
+	dx, dy := bx-ax, by-ay
+	if dx == 0 && dy == 0 {
+		return math.Hypot(px-ax, py-ay)
+	}
+	u := ((px-ax)*dx + (py-ay)*dy) / (dx*dx + dy*dy)
+	u = max(0, min(1, u))
+	return math.Hypot(px-ax-u*dx, py-ay-u*dy)
+}
+
+func (a *API) mapRoutes(mux *http.ServeMux) {
+	mux.HandleFunc("POST /v1/map/roads", a.ingest(a.mapRoads))
+}
+
+func (a *API) mapRoads(w http.ResponseWriter, r *http.Request, c caller, body []byte) error {
+	if a.Maps == nil {
+		writeJSON(w, http.StatusNotFound, map[string]string{"error": "maps are not enabled"})
+		return nil
+	}
+	var req struct {
+		Z, X, Y *int
+	}
+	if err := json.Unmarshal(body, &req); err != nil || req.Z == nil || req.X == nil || req.Y == nil {
+		return invalid("z, x and y are required")
+	}
+	if *req.Z != mapZoom {
+		return invalid("z must be %d", mapZoom)
+	}
+	limit := 1 << mapZoom
+	if *req.X < 0 || *req.X >= limit || *req.Y < 0 || *req.Y >= limit {
+		return invalid("x and y must be within the zoom level")
+	}
+	// The car waits a few seconds at most; the fetch goes on without it.
+	wait, cancel := context.WithTimeout(r.Context(), mapWait)
+	defer cancel()
+	data, _, err := a.Maps.Tile(wait, mapTile{Z: *req.Z, X: *req.X, Y: *req.Y})
+	if err != nil {
+		slog.Warn("map tile not available yet", "installation", who(c), "error", err)
+		w.Header().Set("Retry-After", "10")
+		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "map data not available yet, try again shortly"})
+		return nil
+	}
+	w.Header().Set("Content-Type", "application/json")
+	if strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
+		var buf bytes.Buffer
+		zw := gzip.NewWriter(&buf)
+		_, _ = zw.Write(data)
+		_ = zw.Close()
+		w.Header().Set("Content-Encoding", "gzip")
+		data = buf.Bytes()
+	}
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write(data)
+	return nil
+}

server/maps_test.go

@@ -0,0 +1,361 @@
+package main
+
+import (
+	"bytes"
+	"compress/gzip"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// A tile in central Berlin.
+var testTile = mapTile{Z: 14, X: 8802, Y: 5373}
+
+// ---------- A minimal vector-tile encoder for the tests ----------
+
+func pbVarint(v uint64) []byte {
+	var b []byte
+	for v >= 0x80 {
+		b = append(b, byte(v)|0x80)
+		v >>= 7
+	}
+	return append(b, byte(v))
+}
+
+func pbKey(num, wire int) []byte { return pbVarint(uint64(num<<3 | wire)) }
+
+func pbBytes(num int, data []byte) []byte {
+	return append(append(pbKey(num, 2), pbVarint(uint64(len(data)))...), data...)
+}
+
+func pbUint(num int, v uint64) []byte { return append(pbKey(num, 0), pbVarint(v)...) }
+
+func pbPacked(num int, vs []uint32) []byte {
+	var d []byte
+	for _, v := range vs {
+		d = append(d, pbVarint(uint64(v))...)
+	}
+	return pbBytes(num, d)
+}
+
+func zz(v int) uint32 { return uint32((v << 1) ^ (v >> 31)) }
+
+// lineCmds encodes line strings as MoveTo/LineTo commands with relative moves.
+func lineCmds(lines ...[][2]int) []uint32 {
+	var out []uint32
+	x, y := 0, 0
+	for _, l := range lines {
+		out = append(out, 1|1<<3, zz(l[0][0]-x), zz(l[0][1]-y))
+		x, y = l[0][0], l[0][1]
+		out = append(out, uint32(2|(len(l)-1)<<3))
+		for _, p := range l[1:] {
+			out = append(out, zz(p[0]-x), zz(p[1]-y))
+			x, y = p[0], p[1]
+		}
+	}
+	return out
+}
+
+type testFeature struct {
+	class    int // index into the values below
+	geomType uint64
+	geometry []uint32
+}
+
+// testVectorTile has a water layer (ignored) and a transportation layer with the given extent.
+func testVectorTile(extent uint64) []byte {
+	values := []string{"primary", "minor", "service", "motorway"}
+	features := []testFeature{
+		// A primary road with a needless middle point.
+		{0, 2, lineCmds([][2]int{{100, 100}, {200, 200}, {300, 300}})},
+		// A minor street in two pieces.
+		{1, 2, lineCmds([][2]int{{0, 500}, {400, 500}}, [][2]int{{600, 500}, {900, 520}})},
+		// A service road and a motorway as a polygon: neither is drawn.
+		{2, 2, lineCmds([][2]int{{10, 10}, {20, 20}})},
+		{3, 3, lineCmds([][2]int{{10, 10}, {20, 20}})},
+	}
+	var layer []byte
+	layer = append(layer, pbUint(15, 2)...)
+	layer = append(layer, pbBytes(1, []byte("transportation"))...)
+	for _, f := range features {
+		var feat []byte
+		feat = append(feat, pbPacked(2, []uint32{0, uint32(f.class)})...)
+		feat = append(feat, pbUint(3, f.geomType)...)
+		feat = append(feat, pbPacked(4, f.geometry)...)
+		layer = append(layer, pbBytes(2, feat)...)
+	}
+	layer = append(layer, pbBytes(3, []byte("class"))...)
+	for _, v := range values {
+		layer = append(layer, pbBytes(4, pbBytes(1, []byte(v)))...)
+	}
+	layer = append(layer, pbUint(5, extent)...)
+
+	water := append(pbBytes(1, []byte("water")), pbUint(5, 4096)...)
+	return append(pbBytes(3, water), pbBytes(3, layer)...)
+}
+
+// ---------- A fake tile host ----------
+
+type fakeHost struct {
+	*httptest.Server
+	tiles  atomic.Int32
+	status int
+	delay  time.Duration
+	gzip   bool
+}
+
+func newFakeHost(t *testing.T) *fakeHost {
+	t.Helper()
+	h := &fakeHost{status: http.StatusOK}
+	mux := http.NewServeMux()
+	mux.HandleFunc("GET /planet", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, `{"tilejson":"3.0.0","tiles":["%s/planet/build1/{z}/{x}/{y}.pbf"]}`, h.URL)
+	})
+	mux.HandleFunc("GET /planet/build1/{z}/{x}/{y}", func(w http.ResponseWriter, r *http.Request) {
+		h.tiles.Add(1)
+		if !strings.Contains(r.UserAgent(), "nils-mg4-server") {
+			t.Errorf("user agent %q", r.UserAgent())
+		}
+		time.Sleep(h.delay)
+		if h.status != http.StatusOK {
+			http.Error(w, "busy", h.status)
+			return
+		}
+		body := testVectorTile(4096)
+		if h.gzip {
+			var buf bytes.Buffer
+			zw := gzip.NewWriter(&buf)
+			_, _ = zw.Write(body)
+			_ = zw.Close()
+			body = buf.Bytes()
+		}
+		_, _ = w.Write(body)
+	})
+	h.Server = httptest.NewTLSServer(mux)
+	return h
+}
+
+func mapsAPIWith(host *fakeHost, cacheDir string) http.Handler {
+	api, _ := newTestAPI()
+	api.Maps = NewMaps(host.URL+"/planet", cacheDir, mapUserAgent)
+	api.Maps.Client = host.Client()
+	return api.Routes()
+}
+
+func tileBody(t mapTile) string {
+	return fmt.Sprintf(`{"z":%d,"x":%d,"y":%d}`, t.Z, t.X, t.Y)
+}
+
+func decodeAnswer(t *testing.T, rec *httptest.ResponseRecorder) roadTile {
+	t.Helper()
+	if rec.Code != 200 {
+		t.Fatalf("%d %s", rec.Code, rec.Body)
+	}
+	var got roadTile
+	if err := json.Unmarshal(rec.Body.Bytes(), &got); err != nil {
+		t.Fatal(err)
+	}
+	return got
+}
+
+// ---------- Tests ----------
+
+func TestVectorTileRoadsAreClassifiedSplitAndSimplified(t *testing.T) {
+	lines, err := decodeRoads(testVectorTile(4096))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(lines) != 3 || lines[0].class != 1 || lines[1].class != 3 || lines[2].class != 3 {
+		t.Fatalf("lines %+v", lines)
+	}
+	if fmt.Sprint(lines[1].points) != "[[0 500] [400 500]]" || fmt.Sprint(lines[2].points) != "[[600 500] [900 520]]" {
+		t.Fatalf("pieces %v %v", lines[1].points, lines[2].points)
+	}
+	// Another extent is scaled to 4096.
+	half, err := decodeRoads(testVectorTile(8192))
+	if err != nil || fmt.Sprint(half[0].points[2]) != "[150 150]" {
+		t.Fatalf("scaled %v %v", half, err)
+	}
+	body, err := buildTile(testTile, testVectorTile(4096))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(body), `{"c":1,"p":[100,100,300,300]}`) {
+		t.Fatalf("the straight road keeps only its ends: %s", body)
+	}
+}
+
+func TestMalformedVectorTilesAreRefused(t *testing.T) {
+	good := testVectorTile(4096)
+	for name, raw := range map[string][]byte{
+		"cut short":       good[:len(good)-7],
+		"bad wire type":   {0x1f, 0x00},
+		"length too long": {0x1a, 0x7f, 0x01},
+	} {
+		if _, err := decodeRoads(raw); err == nil {
+			t.Errorf("%s: accepted", name)
+		}
+	}
+	if lines, err := decodeRoads(nil); err != nil || len(lines) != 0 {
+		t.Fatalf("an empty tile is an empty map: %v %v", lines, err)
+	}
+}
+
+func TestMapTilesAreFetchedOnceAndKeptOnDisk(t *testing.T) {
+	host := newFakeHost(t)
+	host.gzip = true // some hosts gzip whatever was asked
+	defer host.Close()
+	dir := t.TempDir()
+	h := mapsAPIWith(host, dir)
+	if rec := do(t, h, "POST", "/v1/map/roads", "", tileBody(testTile)); rec.Code != 401 {
+		t.Fatalf("without the car's token: %d", rec.Code)
+	}
+	got := decodeAnswer(t, do(t, h, "POST", "/v1/map/roads", testToken, tileBody(testTile)))
+	if got.Extent != 4096 || got.X != testTile.X || got.Y != testTile.Y || len(got.Ways) != 3 {
+		t.Fatalf("tile %+v", got)
+	}
+	decodeAnswer(t, do(t, h, "POST", "/v1/map/roads", testToken, tileBody(testTile)))
+	// A restart: a new server with the same directory asks the host nothing.
+	decodeAnswer(t, do(t, mapsAPIWith(host, dir), "POST", "/v1/map/roads", testToken, tileBody(testTile)))
+	if n := host.tiles.Load(); n != 1 {
+		t.Fatalf("tile fetched %d times", n)
+	}
+}
+
+func TestASlowTileIsFinishedForTheCarsNextTry(t *testing.T) {
+	previous := mapWait
+	mapWait = 50 * time.Millisecond
+	defer func() { mapWait = previous }()
+	host := newFakeHost(t)
+	host.delay = 300 * time.Millisecond
+	defer host.Close()
+	h := mapsAPIWith(host, "")
+	rec := do(t, h, "POST", "/v1/map/roads", testToken, tileBody(testTile))
+	if rec.Code != 503 || rec.Header().Get("Retry-After") == "" {
+		t.Fatalf("the car should hear 'try again': %d", rec.Code)
+	}
+	time.Sleep(600 * time.Millisecond)
+	decodeAnswer(t, do(t, h, "POST", "/v1/map/roads", testToken, tileBody(testTile)))
+	if n := host.tiles.Load(); n != 1 {
+		t.Fatalf("tile fetched %d times", n)
+	}
+}
+
+func TestMapTilesAreGzippedWhenTheCarAcceptsIt(t *testing.T) {
+	host := newFakeHost(t)
+	defer host.Close()
+	req := httptest.NewRequest("POST", "/v1/map/roads", strings.NewReader(tileBody(testTile)))
+	req.Header.Set("Authorization", "Bearer "+testToken)
+	req.Header.Set("Accept-Encoding", "gzip")
+	rec := httptest.NewRecorder()
+	mapsAPIWith(host, "").ServeHTTP(rec, req)
+	if rec.Code != 200 || rec.Header().Get("Content-Encoding") != "gzip" {
+		t.Fatalf("%d %v", rec.Code, rec.Header())
+	}
+	zr, err := gzip.NewReader(rec.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	plain, _ := io.ReadAll(zr)
+	if !bytes.Contains(plain, []byte(`"extent":4096`)) {
+		t.Fatalf("%s", plain)
+	}
+}
+
+func TestMapRequestsAreChecked(t *testing.T) {
+	host := newFakeHost(t)
+	defer host.Close()
+	h := mapsAPIWith(host, "")
+	for _, body := range []string{`{}`, `{"z":15,"x":1,"y":1}`, `{"z":14,"x":-1,"y":1}`,
+		`{"z":14,"x":1,"y":16384}`, `not json`} {
+		if rec := do(t, h, "POST", "/v1/map/roads", testToken, body); rec.Code != 400 {
+			t.Errorf("%s: %d", body, rec.Code)
+		}
+	}
+	if host.tiles.Load() != 0 {
+		t.Fatal("a bad request reached the tile host")
+	}
+}
+
+func TestAFailingHostIsATemporaryFailureAndNotCached(t *testing.T) {
+	var logged bytes.Buffer
+	previous := slog.Default()
+	slog.SetDefault(slog.New(slog.NewTextHandler(&logged, nil)))
+	defer slog.SetDefault(previous)
+
+	host := newFakeHost(t)
+	host.status = http.StatusBadGateway
+	defer host.Close()
+	h := mapsAPIWith(host, t.TempDir())
+	for i := 0; i < 2; i++ {
+		if rec := do(t, h, "POST", "/v1/map/roads", testToken, tileBody(testTile)); rec.Code != 503 {
+			t.Fatalf("%d", rec.Code)
+		}
+	}
+	if n := host.tiles.Load(); n != 2 {
+		t.Fatalf("a failure was cached: %d fetches", n)
+	}
+	// Where the car is stays out of the log.
+	out := logged.String()
+	if !strings.Contains(out, "tile host answered 502") || strings.Contains(out, "8802") ||
+		strings.Contains(out, "5373") {
+		t.Fatalf("log:\n%s", out)
+	}
+}
+
+func TestATileIndexWithoutHttpsIsRefused(t *testing.T) {
+	index := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"tiles":["http://tiles.example.com/{z}/{x}/{y}.pbf"]}`))
+	}))
+	defer index.Close()
+	api, _ := newTestAPI()
+	api.Maps = NewMaps(index.URL, "", mapUserAgent)
+	api.Maps.Client = index.Client()
+	if rec := do(t, api.Routes(), "POST", "/v1/map/roads", testToken, tileBody(testTile)); rec.Code != 503 {
+		t.Fatalf("%d", rec.Code)
+	}
+}
+
+func TestMapsAreOffWithoutATileSource(t *testing.T) {
+	api, _ := newTestAPI()
+	if rec := do(t, api.Routes(), "POST", "/v1/map/roads", testToken, tileBody(testTile)); rec.Code != 404 {
+		t.Fatalf("%d", rec.Code)
+	}
+}
+
+func TestMapTilesURLConfiguration(t *testing.T) {
+	base := map[string]string{"INFLUX_URL": "http://influx", "INFLUX_TOKEN": "t", "INFLUX_ORG": "o",
+		"INGEST_TOKEN": "0123456789abcdef01234567"}
+	load := func(tiles string) (config, error) {
+		return loadConfig(func(k string) string {
+			if k == "MAP_TILES_URL" {
+				return tiles
+			}
+			return base[k]
+		})
+	}
+	if c, err := load(""); err != nil || c.mapTilesURL != DefaultMapTilesURL {
+		t.Fatalf("default: %q %v", c.mapTilesURL, err)
+	}
+	if c, err := load("off"); err != nil || c.mapTilesURL != "" {
+		t.Fatalf("off: %q %v", c.mapTilesURL, err)
+	}
+	if _, err := load("http://tiles.example.com/planet"); err == nil {
+		t.Fatal("plain http accepted")
+	}
+}
+
+func TestSimplification(t *testing.T) {
+	line := [][2]int{{0, 0}, {10, 1}, {20, 0}, {30, 40}}
+	got := simplify(line, 4)
+	if len(got) != 3 || got[1] != [2]int{20, 0} {
+		t.Fatalf("%v", got)
+	}
+}

server/mvt.go

@@ -0,0 +1,278 @@
+package main
+
+import (
+	"errors"
+	"math"
+)
+
+// The roads of a Mapbox Vector Tile (spec 2.1) in the OpenMapTiles schema: the line features
+// of the "transportation" layer whose "class" the car draws (roadClasses), scaled to
+// mapExtent. A minimal protobuf reader, enough for that and nothing more; anything malformed
+// is an error, never a guess.
+
+type roadLine struct {
+	class  int
+	points [][2]int
+}
+
+var errBadTile = errors.New("vector tile is malformed")
+
+// pbReader walks protobuf fields.
+type pbReader struct {
+	b []byte
+	i int
+}
+
+func (r *pbReader) done() bool { return r.i >= len(r.b) }
+
+func (r *pbReader) varint() (uint64, error) {
+	var v uint64
+	for shift := uint(0); shift < 64; shift += 7 {
+		if r.i >= len(r.b) {
+			return 0, errBadTile
+		}
+		c := r.b[r.i]
+		r.i++
+		v |= uint64(c&0x7f) << shift
+		if c < 0x80 {
+			return v, nil
+		}
+	}
+	return 0, errBadTile
+}
+
+// field reads one field's key and, for length-delimited ones, its bytes.
+func (r *pbReader) field() (num int, wire int, val uint64, data []byte, err error) {
+	key, err := r.varint()
+	if err != nil {
+		return 0, 0, 0, nil, err
+	}
+	num, wire = int(key>>3), int(key&7)
+	switch wire {
+	case 0:
+		val, err = r.varint()
+	case 1:
+		if r.i+8 > len(r.b) {
+			return 0, 0, 0, nil, errBadTile
+		}
+		r.i += 8
+	case 2:
+		var n uint64
+		n, err = r.varint()
+		if err == nil {
+			if n > uint64(len(r.b)-r.i) {
+				return 0, 0, 0, nil, errBadTile
+			}
+			data = r.b[r.i : r.i+int(n)]
+			r.i += int(n)
+		}
+	case 5:
+		if r.i+4 > len(r.b) {
+			return 0, 0, 0, nil, errBadTile
+		}
+		r.i += 4
+	default:
+		return 0, 0, 0, nil, errBadTile
+	}
+	return num, wire, val, data, err
+}
+
+// packed reads a repeated uint32 field, packed or not.
+func packed(wire int, val uint64, data []byte, into []uint32) ([]uint32, error) {
+	if wire == 0 {
+		return append(into, uint32(val)), nil
+	}
+	if wire != 2 {
+		return nil, errBadTile
+	}
+	r := pbReader{b: data}
+	for !r.done() {
+		v, err := r.varint()
+		if err != nil {
+			return nil, err
+		}
+		into = append(into, uint32(v))
+	}
+	return into, nil
+}
+
+// decodeRoads returns the drawable roads of the tile.
+func decodeRoads(tile []byte) ([]roadLine, error) {
+	r := pbReader{b: tile}
+	for !r.done() {
+		num, _, _, data, err := r.field()
+		if err != nil {
+			return nil, err
+		}
+		if num != 3 { // layers
+			continue
+		}
+		lines, isRoads, err := decodeLayer(data)
+		if err != nil {
+			return nil, err
+		}
+		if isRoads {
+			return lines, nil
+		}
+	}
+	return nil, nil // a tile without roads (sea, desert) is an empty one
+}
+
+type rawFeature struct {
+	tags     []uint32
+	geomType uint64
+	geometry []uint32
+}
+
+func decodeLayer(layer []byte) ([]roadLine, bool, error) {
+	r := pbReader{b: layer}
+	var name string
+	var keys []string
+	var values []string // only string values matter for "class"
+	var features []rawFeature
+	extent := uint64(4096)
+	for !r.done() {
+		num, wire, val, data, err := r.field()
+		if err != nil {
+			return nil, false, err
+		}
+		switch num {
+		case 1:
+			name = string(data)
+		case 2:
+			f, err := decodeFeature(data)
+			if err != nil {
+				return nil, false, err
+			}
+			features = append(features, f)
+		case 3:
+			keys = append(keys, string(data))
+		case 4:
+			values = append(values, valueString(data))
+		case 5:
+			if wire != 0 || val == 0 {
+				return nil, false, errBadTile
+			}
+			extent = val
+		}
+	}
+	if name != "transportation" {
+		return nil, false, nil
+	}
+	scale := float64(mapExtent) / float64(extent)
+	var lines []roadLine
+	for _, f := range features {
+		if f.geomType != 2 { // LINESTRING
+			continue
+		}
+		class, ok := -1, false
+		for i := 0; i+1 < len(f.tags); i += 2 {
+			k, v := int(f.tags[i]), int(f.tags[i+1])
+			if k >= len(keys) || v >= len(values) {
+				return nil, false, errBadTile
+			}
+			if keys[k] == "class" {
+				class, ok = roadClasses[values[v]]
+				if !ok {
+					class = -1
+				}
+			}
+		}
+		if class < 0 {
+			continue
+		}
+		parts, err := lineGeometry(f.geometry, scale)
+		if err != nil {
+			return nil, false, err
+		}
+		for _, p := range parts {
+			lines = append(lines, roadLine{class: class, points: p})
+		}
+	}
+	return lines, true, nil
+}
+
+func decodeFeature(data []byte) (rawFeature, error) {
+	var f rawFeature
+	r := pbReader{b: data}
+	for !r.done() {
+		num, wire, val, d, err := r.field()
+		if err != nil {
+			return f, err
+		}
+		switch num {
+		case 2:
+			if f.tags, err = packed(wire, val, d, f.tags); err != nil {
+				return f, err
+			}
+		case 3:
+			f.geomType = val
+		case 4:
+			if f.geometry, err = packed(wire, val, d, f.geometry); err != nil {
+				return f, err
+			}
+		}
+	}
+	if len(f.tags)%2 != 0 {
+		return f, errBadTile
+	}
+	return f, nil
+}
+
+// valueString is a Value's string_value, "" for any other kind.
+func valueString(data []byte) string {
+	r := pbReader{b: data}
+	for !r.done() {
+		num, _, _, d, err := r.field()
+		if err != nil {
+			return ""
+		}
+		if num == 1 {
+			return string(d)
+		}
+	}
+	return ""
+}
+
+// lineGeometry follows the MoveTo/LineTo commands of a (multi)line string.
+func lineGeometry(cmds []uint32, scale float64) ([][][2]int, error) {
+	var parts [][][2]int
+	var cur [][2]int
+	x, y := 0, 0
+	zig := func(v uint32) int { return int(int32(v>>1) ^ -int32(v&1)) }
+	at := func() [2]int {
+		return [2]int{int(math.Round(float64(x) * scale)), int(math.Round(float64(y) * scale))}
+	}
+	for i := 0; i < len(cmds); {
+		id, count := cmds[i]&7, int(cmds[i]>>3)
+		i++
+		switch id {
+		case 1, 2: // MoveTo, LineTo
+			if i+2*count > len(cmds) {
+				return nil, errBadTile
+			}
+			for k := 0; k < count; k++ {
+				x += zig(cmds[i])
+				y += zig(cmds[i+1])
+				i += 2
+				if id == 1 {
+					if len(cur) >= 2 {
+						parts = append(parts, cur)
+					}
+					cur = [][2]int{at()}
+				} else {
+					if p := at(); len(cur) == 0 || cur[len(cur)-1] != p {
+						cur = append(cur, p)
+					}
+				}
+			}
+		case 7: // ClosePath, not in a line; ignored
+		default:
+			return nil, errBadTile
+		}
+	}
+	if len(cur) >= 2 {
+		parts = append(parts, cur)
+	}
+	return parts, nil
+}