Fix for UnknownHostException's caused by TLS support. Enable TLS v1.1 and TLS v1.2 on older platforms <APIv20. NOTE: Internally supported just not enabled.

Snippet.java

// Enable TLS v1.1 and TLS v1.2 on older platforms <APIv20.
// NOTE: Internally supported just not enabled.
if(Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP){
	try{
		X509TrustManager trustManager = systemDefaultTrustManager();
		okHttpBuilder.sslSocketFactory(new TLSSocketFactory(), trustManager);
	}
	catch(GeneralSecurityException e){
		Log.e(TAG, "API security", e);
	}
}

private X509TrustManager systemDefaultTrustManager()
	throws GeneralSecurityException
{
	TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
		TrustManagerFactory.getDefaultAlgorithm());
	trustManagerFactory.init((KeyStore) null);
	TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
	if(trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)){
		throw new IllegalStateException(
			"Unexpected default trust managers:" + Arrays.toString(trustManagers));
	}
	return (X509TrustManager) trustManagers[0];
}

TLSSocketFactory.java

import java.net.InetAddress;
import java.net.Socket;

import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;

/**
 * ref: https://github.com/square/okhttp/issues/1934
 * credit: https://gist.github.com/fkrauthan/ac8624466a4dee4fd02f
 */
public class TLSSocketFactory extends SSLSocketFactory
{
  private SSLSocketFactory internalSSLSocketFactory;


  public TLSSocketFactory()
    throws KeyManagementException, NoSuchAlgorithmException
  {
    SSLContext context = SSLContext.getInstance("TLS");
    context.init(null, null, null);
    internalSSLSocketFactory = context.getSocketFactory();
  }

  @Override
  public String[] getDefaultCipherSuites()
  {
    return internalSSLSocketFactory.getDefaultCipherSuites();
  }

  @Override
  public String[] getSupportedCipherSuites()
  {
    return internalSSLSocketFactory.getSupportedCipherSuites();
  }

  @Override
  public Socket createSocket(Socket s, String host, int port, boolean autoClose)
    throws IOException
  {
    return enableTLSOnSocket(
      internalSSLSocketFactory.createSocket(s, host, port, autoClose));
  }

  @Override
  public Socket createSocket(String host, int port)
    throws IOException
  {
    return enableTLSOnSocket(internalSSLSocketFactory.createSocket(host, port));
  }

  @Override
  public Socket createSocket(String host, int port, InetAddress localHost, int localPort)
    throws IOException
  {
    return enableTLSOnSocket(
      internalSSLSocketFactory.createSocket(host, port, localHost, localPort));
  }

  @Override
  public Socket createSocket(InetAddress host, int port)
    throws IOException
  {
    return enableTLSOnSocket(internalSSLSocketFactory.createSocket(host, port));
  }

  @Override
  public Socket createSocket(InetAddress address, int port, InetAddress localAddress, int localPort)
    throws IOException
  {
    return enableTLSOnSocket(
      internalSSLSocketFactory.createSocket(address, port, localAddress, localPort));
  }

  private Socket enableTLSOnSocket(Socket socket)
  {
    if(socket != null && (socket instanceof SSLSocket)){
      ((SSLSocket) socket).setEnabledProtocols(new String[] { "TLSv1.1", "TLSv1.2" });
    }
    return socket;
  }
}

Original Issue okhttp/issues/1934
Related Gist fkrauthan/ac8624466a4dee4fd02f