App 2.4.2: pairing dialog shows errors instead of closing

- On a failure the pairing dialog stays open and shows the reason in
  red (Cancel becomes Close); before, it closed at once and the reason
  was only in the Server tab's status line.
- "Pairing is not enabled" only when the server says so. Any other 404
  (a server older than 2.1.0, or a proxy's page) is reported as a
  server without pairing.
- Pairing and Test connection name the problem: a server name that
  does not resolve (Test connection used to say "No internet
  connection"), a server that does not answer, or the HTTP status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

app/build.gradle

@@ -34,8 +34,8 @@ android {
         applicationId "com.stinnesbeck.nilsmg4"
         minSdk 27
         targetSdk 36
-        versionCode 59
+        versionCode 60
-        versionName "2.4.1"
+        versionName "2.4.2"
 
         // 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/MainActivity.java

@@ -455,7 +455,7 @@ public class MainActivity extends AppCompatActivity {
                 message = getString(R.string.conn_err_timeout);
                 color = COLOR_ERROR;
             } catch (Exception e) {
-                message = getString(R.string.conn_err_no_internet);
+                message = describeNetworkError(e, url);
                 color = COLOR_ERROR;
             }
             final String m = message;
@@ -514,6 +514,9 @@ public class MainActivity extends AppCompatActivity {
                 .setView(panel)
                 .setNegativeButton(R.string.pair_cancel, null)
                 .create();
+        // Shown only once the server has answered, so a failure leaves no empty QR frame.
+        qr.setVisibility(View.GONE);
+        code.setVisibility(View.GONE);
         dialog.setOnDismissListener(d -> cancelled[0] = true);
         dialog.show();
 
@@ -525,8 +528,12 @@ public class MainActivity extends AppCompatActivity {
                 android.graphics.Bitmap bitmap = QrCode.generate(request.verificationUriComplete, 416);
                 runOnUiThread(() -> {
                     instructions.setText(getString(R.string.pair_scan, request.verificationUri));
-                    if (bitmap != null) qr.setImageBitmap(bitmap);
+                    if (bitmap != null) {
+                        qr.setImageBitmap(bitmap);
+                        qr.setVisibility(View.VISIBLE);
+                    }
                     code.setText(request.userCode);
+                    code.setVisibility(View.VISIBLE);
                     status.setText(R.string.pair_waiting);
                 });
                 PairingClient.PollResult result = null;
@@ -552,26 +559,58 @@ public class MainActivity extends AppCompatActivity {
                 }
             } catch (PairingClient.NotEnabledException e) {
                 outcome = getString(R.string.pair_not_enabled);
+            } catch (PairingClient.HttpStatusException e) {
+                outcome = e.status == 404 ? getString(R.string.pair_err_old_server)
+                        : getString(R.string.err_http, e.status);
             } catch (InterruptedException e) {
                 return;
             } catch (Exception e) {
-                outcome = getString(R.string.pair_error, e.getClass().getSimpleName());
+                outcome = describeNetworkError(e, url);
             }
             final String message = outcome;
             final int c = color;
             runOnUiThread(() -> {
-                if (!cancelled[0]) dialog.dismiss();
+                setConnectionStatus(c, message);
                 if (c == COLOR_OK) {
                     if (consumptionCloudClient != null) consumptionCloudClient.invalidateHistory();
                     showServerConfig();
                     serverTokenLayout.setError(null);
                     refreshStatus();
+                    if (!cancelled[0]) dialog.dismiss();
+                    return;
                 }
-                setConnectionStatus(c, message);
+                if (cancelled[0]) return;
+                // Keep the dialog up with the reason, instead of closing it on a failure the
+                // driver would otherwise only see as a flicker.
+                qr.setVisibility(View.GONE);
+                code.setVisibility(View.GONE);
+                instructions.setVisibility(View.GONE);
+                status.setText(message);
+                status.setTextColor(c);
+                android.widget.Button close = dialog.getButton(android.content.DialogInterface.BUTTON_NEGATIVE);
+                if (close != null) close.setText(R.string.pair_close);
             });
         }, "server-pairing").start();
     }
 
+    /**
+     * A network failure in words the driver can act on: a name that does not resolve, a
+     * server that does not answer, or a status. Shared by Test connection and pairing.
+     */
+    private String describeNetworkError(Exception e, String url) {
+        String host = Uri.parse(url).getHost();
+        if (host == null) host = url;
+        if (e instanceof java.net.UnknownHostException) return getString(R.string.err_dns, host);
+        if (e instanceof java.net.SocketTimeoutException || e instanceof java.net.ConnectException
+                || e instanceof java.net.NoRouteToHostException) {
+            return getString(R.string.err_unreachable, host);
+        }
+        if (e instanceof PairingClient.HttpStatusException) {
+            return getString(R.string.err_http, ((PairingClient.HttpStatusException) e).status);
+        }
+        return getString(R.string.pair_error, e.getClass().getSimpleName());
+    }
+
     private static int httpGet(String url, String token) throws java.io.IOException {
         java.net.HttpURLConnection connection = (java.net.HttpURLConnection) new java.net.URL(url).openConnection();
         try {

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

@@ -52,13 +52,28 @@ final class PairingClient {
     /** Thrown when pairing is switched off on the server (no APPROVAL_PASSWORD). */
     static final class NotEnabledException extends Exception { }
 
+    /** The server answered with a status the flow does not expect. */
+    static final class HttpStatusException extends java.io.IOException {
+        final int status;
+
+        HttpStatusException(int status) {
+            super("HTTP " + status);
+            this.status = status;
+        }
+    }
+
+    /** What the server says when APPROVAL_PASSWORD is unset; any other 404 is a missing route. */
+    static final String NOT_ENABLED_MESSAGE = "pairing is not enabled";
+
     private PairingClient() { }
 
     static Request start(String serverUrl, String installationId) throws Exception {
         Response r = post(serverUrl + "/v1/pair/start",
                 new JSONObject().put("installationId", installationId));
-        if (r.status == 404) throw new NotEnabledException();
+        // Only the server's own answer means "switched off". A 404 without it is a server (or
-        if (r.status != 201) throw new java.io.IOException("HTTP " + r.status);
+        // proxy) that has no pairing route at all, e.g. one older than 2.1.0.
+        if (r.status == 404 && r.body.contains(NOT_ENABLED_MESSAGE)) throw new NotEnabledException();
+        if (r.status != 201) throw new HttpStatusException(r.status);
         JSONObject json = new JSONObject(r.body);
         long now = System.currentTimeMillis();
         return new Request(
@@ -77,7 +92,7 @@ final class PairingClient {
             case 202: return new PollResult(Outcome.PENDING, null);
             case 403: return new PollResult(Outcome.DENIED, null);
             case 410: return new PollResult(Outcome.EXPIRED, null);
-            default: throw new java.io.IOException("HTTP " + r.status);
+            default: throw new HttpStatusException(r.status);
         }
     }
 

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

@@ -66,6 +66,11 @@
     <string name="pair_expired">The code expired — press Pair with phone again</string>
     <string name="pair_not_enabled">Pairing is not enabled on the server (no APPROVAL_PASSWORD)</string>
     <string name="pair_error">Pairing failed: %1$s</string>
+    <string name="pair_close">Close</string>
+    <string name="pair_err_old_server">The server has no pairing (HTTP 404). It needs server version 2.1.0 or newer.</string>
+    <string name="err_dns">Server name %1$s not found. Is it in public DNS?</string>
+    <string name="err_unreachable">Server %1$s not reachable</string>
+    <string name="err_http">Server answered HTTP %1$d</string>
     <string name="pair_cancel">Cancel</string>
     <string name="pair_qr_description">QR code to approve this car on your phone</string>
     <string name="server_err_token">The token must be at least 24 characters, without spaces</string>

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

@@ -27,6 +27,7 @@ public class PairingClientTest {
     private String url;
     private final Deque<Integer> pollStatuses = new ArrayDeque<>();
     private volatile int startStatus = 201;
+    private volatile String startErrorBody = "{\"error\":\"pairing is not enabled\"}";
     private volatile String lastStartBody;
 
     @Before
@@ -73,7 +74,7 @@ public class PairingClientTest {
             response = status == 201
                     ? "{\"deviceCode\":\"dev-code\",\"userCode\":\"K7F-3QX\",\"verificationUri\":\"https://car.example.com/pair\","
                       + "\"verificationUriComplete\":\"https://car.example.com/pair?code=K7F-3QX\",\"expiresIn\":600,\"interval\":5}"
-                    : "{\"error\":\"pairing is not enabled\"}";
+                    : startErrorBody;
         } else {
             Integer next;
             synchronized (pollStatuses) { next = pollStatuses.poll(); }
@@ -119,6 +120,19 @@ public class PairingClientTest {
         assertEquals(PairingClient.Outcome.EXPIRED, PairingClient.poll(url, "dev-code").outcome);
     }
 
+    @Test
+    public void aServerWithoutPairingIsNotMistakenForPairingSwitchedOff() throws Exception {
+        // e.g. server 2.0.0, or a proxy's own 404 page
+        startStatus = 404;
+        startErrorBody = "404 page not found";
+        try {
+            PairingClient.start(url, "6f1a2b3c-4d5e-4f60-8a9b-0c1d2e3f4a5b");
+            fail("expected HttpStatusException");
+        } catch (PairingClient.HttpStatusException expected) {
+            assertEquals(404, expected.status);
+        }
+    }
+
     @Test
     public void pairingSwitchedOffOnTheServerIsReportedAsSuch() throws Exception {
         startStatus = 404;