App 2.4.0: pair with the server by QR code

The Server tab gets "Pair with phone" right under the server URL, which
is now pre-filled with https://car.stinnesbeck.com. It opens a dialog
with a QR code and the short code, polls the server, and on approval
saves this car's own token like Save would — nothing to type in the
car. Denied, expired, and pairing switched off on the server are each
reported. PairingClient is tested against a stand-in for the server.

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

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

@@ -0,0 +1,132 @@
+package com.evsuite.abrp;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+/** The car's pairing client against a stand-in that answers like the Go server. */
+public class PairingClientTest {
+
+    private ServerSocket socket;
+    private Thread thread;
+    private String url;
+    private final Deque<Integer> pollStatuses = new ArrayDeque<>();
+    private volatile int startStatus = 201;
+    private volatile String lastStartBody;
+
+    @Before
+    public void setUp() throws Exception {
+        socket = new ServerSocket(0, 10, InetAddress.getLoopbackAddress());
+        url = "http://127.0.0.1:" + socket.getLocalPort();
+        thread = new Thread(() -> {
+            while (!socket.isClosed()) {
+                try (Socket client = socket.accept()) {
+                    handle(client);
+                } catch (Exception ignored) {
+                    // socket closed in tearDown
+                }
+            }
+        });
+        thread.start();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        socket.close();
+        thread.join(2000);
+    }
+
+    /** Minimal HTTP/1.1: one request per connection, body by Content-Length. */
+    private void handle(Socket client) throws Exception {
+        BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream(), StandardCharsets.UTF_8));
+        String requestLine = in.readLine();
+        int length = 0;
+        for (String line = in.readLine(); line != null && !line.isEmpty(); line = in.readLine()) {
+            if (line.toLowerCase(java.util.Locale.US).startsWith("content-length:")) {
+                length = Integer.parseInt(line.substring(15).trim());
+            }
+        }
+        char[] body = new char[length];
+        int read = 0;
+        while (read < length) read += in.read(body, read, length - read);
+        String path = requestLine.split(" ")[1];
+        int status;
+        String response;
+        if (path.equals("/v1/pair/start")) {
+            lastStartBody = new String(body);
+            status = startStatus;
+            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\"}";
+        } else {
+            Integer next;
+            synchronized (pollStatuses) { next = pollStatuses.poll(); }
+            status = next == null ? 410 : next;
+            response = status == 200 ? "{\"token\":\"car-token-0123456789abcdefghij\",\"deviceId\":\"d1\"}"
+                    : status == 202 ? "{\"status\":\"authorization_pending\"}" : "{\"error\":\"x\"}";
+        }
+        byte[] bytes = response.getBytes(StandardCharsets.UTF_8);
+        OutputStream out = client.getOutputStream();
+        out.write(("HTTP/1.1 " + status + " X\r\nContent-Type: application/json\r\nContent-Length: " + bytes.length
+                + "\r\nConnection: close\r\n\r\n").getBytes(StandardCharsets.UTF_8));
+        out.write(bytes);
+        out.flush();
+    }
+
+    @Test
+    public void startSendsTheInstallationAndReadsTheCodes() throws Exception {
+        long before = System.currentTimeMillis();
+        PairingClient.Request request = PairingClient.start(url, "6f1a2b3c-4d5e-4f60-8a9b-0c1d2e3f4a5b");
+        assertTrue(lastStartBody, lastStartBody.contains("6f1a2b3c-4d5e-4f60-8a9b-0c1d2e3f4a5b"));
+        assertEquals("dev-code", request.deviceCode);
+        assertEquals("K7F-3QX", request.userCode);
+        assertEquals("https://car.example.com/pair?code=K7F-3QX", request.verificationUriComplete);
+        assertEquals(5000L, request.intervalMs);
+        assertTrue(request.expiresAtMs >= before + 600_000L);
+    }
+
+    @Test
+    public void pollMapsEveryServerAnswer() throws Exception {
+        synchronized (pollStatuses) {
+            pollStatuses.add(202);
+            pollStatuses.add(200);
+            pollStatuses.add(403);
+            pollStatuses.add(410);
+        }
+        PairingClient.PollResult pending = PairingClient.poll(url, "dev-code");
+        assertEquals(PairingClient.Outcome.PENDING, pending.outcome);
+        assertNull(pending.token);
+        PairingClient.PollResult approved = PairingClient.poll(url, "dev-code");
+        assertEquals(PairingClient.Outcome.APPROVED, approved.outcome);
+        assertEquals("car-token-0123456789abcdefghij", approved.token);
+        assertEquals(PairingClient.Outcome.DENIED, PairingClient.poll(url, "dev-code").outcome);
+        assertEquals(PairingClient.Outcome.EXPIRED, PairingClient.poll(url, "dev-code").outcome);
+    }
+
+    @Test
+    public void pairingSwitchedOffOnTheServerIsReportedAsSuch() throws Exception {
+        startStatus = 404;
+        try {
+            PairingClient.start(url, "6f1a2b3c-4d5e-4f60-8a9b-0c1d2e3f4a5b");
+            fail("expected NotEnabledException");
+        } catch (PairingClient.NotEnabledException expected) {
+            // the dialog says pairing is off instead of a generic failure
+        }
+    }
+}