final OkHttpClient client = new OkHttpClient();

  String post(String url, String json) throws IOException {
    RequestBody body = RequestBody.create(json, JSON);
    Request request = new Request.Builder()
        .url(url)
        .post(body)
        .build();
    try (Response response = client.newCall(request).execute()) {
      return response.body().string();
    }

  }

  @Override public Socket createSocket(InetAddress host, int port) throws IOException {
    Socket result = createSocket();

    try {
      result.connect(new InetSocketAddress(host, port));
    } catch (IOException e) {
      result.close();
      throw e;
    }
    return result;
  }

  @Override public Socket createSocket(

      // Deserialize HTTP response to concrete type.
      ResponseBody body = response.body();
      List<Contributor> contributors = CONTRIBUTORS_JSON_ADAPTER.fromJson(body.source());

      // Sort list by the most contributions.
      Collections.sort(contributors, (c1, c2) -> c2.contributions - c1.contributions);

      // Output list of contributors.
      for (Contributor contributor : contributors) {