.heldCertificate(localhostCertificate)
        .build();
    MockWebServer server = new MockWebServer();
    server.useHttps(serverCertificates.sslSocketFactory(), false);
    server.enqueue(new MockResponse());

    HandshakeCertificates clientCertificates = new HandshakeCertificates.Builder()
        .addTrustedCertificate(localhostCertificate.certificate())
        .build();

    MockWebServer server = new MockWebServer();
    server.setServerSocketFactory(new UnixDomainServerSocketFactory(socketFile));
    server.setProtocols(Collections.singletonList(Protocol.H2_PRIOR_KNOWLEDGE));
    server.enqueue(new MockResponse().setBody("hello"));
    server.start();

    OkHttpClient client = new OkHttpClient.Builder()
        .socketFactory(new UnixDomainSocketFactory(socketFile))

      .build();

  public void run() throws Exception {
    Request washingtonPostRequest = new Request.Builder()
        .url("https://www.washingtonpost.com/")
        .build();
    client.newCall(washingtonPostRequest).enqueue(new Callback() {
      @Override public void onFailure(Call call, IOException e) {
      }

      @Override public void onResponse(Call call, Response response) throws IOException {

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://publicobject.com/helloworld.txt")
        .build();

    client.newCall(request).enqueue(new Callback() {
      @Override public void onFailure(Call call, IOException e) {
        e.printStackTrace();
      }

      @Override public void onResponse(Call call, Response response) throws IOException {

 */
public final class Crawler {
  private final OkHttpClient client;
  private final Set<HttpUrl> fetchedUrls = Collections.synchronizedSet(new LinkedHashSet<>());
  private final LinkedBlockingQueue<HttpUrl> queue = new LinkedBlockingQueue<>();
  private final ConcurrentHashMap<String, AtomicInteger> hostnames = new ConcurrentHashMap<>();

  public Crawler(OkHttpClient client) {
    this.client = client;
  }