content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.net;
  
  import android.annotation.NonNull;
  import android.util.Log;
  
  import java.io.IOException;
  import java.net.InetSocketAddress;
  
  import javax.net.SocketFactory;
  import javax.net.ssl.SSLSocket;
  import javax.net.ssl.SSLSocketFactory;
  
  /**
   * Class for testing connectivity to DNS-over-TLS servers.
   * {@hide}
   */
  public class PrivateDnsConnectivityChecker {
      private static final String TAG = "NetworkUtils";
  
      private static final int PRIVATE_DNS_PORT = 853;
      private static final int CONNECTION_TIMEOUT_MS = 5000;
  
      private PrivateDnsConnectivityChecker() { }
  
      /**
       * checks that a provided host can perform a TLS handshake on port 853.
       * @param hostname host to connect to.
       */
      public static boolean canConnectToPrivateDnsServer(@NonNull String hostname) {
          final SocketFactory factory = SSLSocketFactory.getDefault();
          TrafficStats.setThreadStatsTag(TrafficStats.TAG_SYSTEM_APP);
  
          try (SSLSocket socket = (SSLSocket) factory.createSocket()) {
              socket.setSoTimeout(CONNECTION_TIMEOUT_MS);
              socket.connect(new InetSocketAddress(hostname, PRIVATE_DNS_PORT));
              if (!socket.isConnected()) {
                  Log.w(TAG, String.format("Connection to %s failed.", hostname));
                  return false;
              }
              socket.startHandshake();
              Log.w(TAG, String.format("TLS handshake to %s succeeded.", hostname));
              return true;
          } catch (IOException e) {
              Log.w(TAG, String.format("TLS handshake to %s failed.", hostname), e);
              return false;
          }
      }
  }
  