Method start

java/src/test/java/com/github/copilot/CapiProxy.java:81–165

Starts the proxy server and returns its URL. @return the proxy URL (e.g., "http://localhost:12345") @throws IOException if the server fails to start @throws InterruptedException if the startup is interrupted

()

     *             if the startup is interrupted
     */
    public String start() throws IOException, InterruptedException {
        if (proxyUrl != null) {
            return proxyUrl;
        }

        // Find the repo root by looking for the test/harness directory
        Path harnessDir = findHarnessDirectory();
        if (harnessDir == null) {
            throw new IOException("Could not find test/harness directory. "
                    + "Make sure you are running from within the copilot-sdk repository.");
        }

        // Start the harness server using npx tsx
        // On Windows, npx is installed as npx.cmd which requires cmd /c to launch
        boolean isWindows = System.getProperty("os.name").toLowerCase().contains("win");
        var pb = isWindows
                ? new ProcessBuilder("cmd", "/c", "npx", "tsx", "server.ts")
                : new ProcessBuilder("npx", "tsx", "server.ts");
        pb.directory(harnessDir.toFile());
        pb.redirectErrorStream(false);
        // Tell the replaying proxy to fail fast on unmatched requests rather than
        // forwarding them to the real API. Without this, unmatched requests hit the
        // live API with a fake token and crash the proxy's JSON parser.
        pb.environment().put("GITHUB_ACTIONS", "true");

        process = pb.start();

        // Read stdout to get the listening URL
        // Note: We keep the reader open to avoid closing the process input stream
        stdoutReader = new BufferedReader(new InputStreamReader(process.getInputStream()));

        // Also consume stderr in a background thread to prevent blocking
        Thread stderrThread = new Thread(() -> {
            try (BufferedReader errReader = new BufferedReader(new InputStreamReader(process.getErrorStream()))) {
                String errLine;
                while ((errLine = errReader.readLine()) != null) {
                    System.err.println("[CapiProxy stderr] " + errLine);
                }
            } catch (IOException e) {
                // Ignore
            }
        });
        stderrThread.setDaemon(true);
        stderrThread.start();

        String line = stdoutReader.readLine();
        if (line == null) {
            // Try to get error info
            StringBuilder errInfo = new StringBuilder();
            try (BufferedReader errReader = new BufferedReader(new InputStreamReader(process.getErrorStream()))) {
                String errLine;
                while ((errLine = errReader.readLine()) != null) {
                    errInfo.append(errLine).append("\n");
                }
            }
            process.destroyForcibly();
            throw new IOException("Failed to read proxy URL - server may have crashed. Stderr: " + errInfo);
        }