* cannot do TLS over domain sockets.
 */
public class ClientAndServer {
  public void run() throws Exception {
    File socketFile = new File("/tmp/ClientAndServer.sock");
    socketFile.delete(); // Clean up from previous runs.

    MockWebServer server = new MockWebServer();
    server.setServerSocketFactory(new UnixDomainServerSocketFactory(socketFile));
    server.setProtocols(Collections.singletonList(Protocol.H2_PRIOR_KNOWLEDGE));

  public void fetch(HttpUrl url) throws IOException {
    // Skip hosts that we've visited many times.
    AtomicInteger hostnameCount = new AtomicInteger();
    AtomicInteger previous = hostnames.putIfAbsent(url.host(), hostnameCount);
    if (previous != null) hostnameCount = previous;
    if (hostnameCount.incrementAndGet() > 100) return;

    Request request = new Request.Builder()
        .url(url)
        .build();