UnixSocketFactory.java

package okhttp3;

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import javax.net.SocketFactory;

public class UnixSocketFactory extends SocketFactory implements Dns {
  private final Map<String, String> pathToHostname = new LinkedHashMap<>();
  private final Map<String, String> hostnameToPath = new LinkedHashMap<>();
  private int nextId = 1;

  public HttpUrl urlForPath(String path) {
    return new HttpUrl.Builder()
        .scheme("http")
        .host(hostnameForPath(path))
        .build();
  }

  private synchronized String hostnameForPath(String path) {
    String hostname = pathToHostname.get(path);
    if (hostname == null) {
      hostname = "p" + (nextId++) + ".socket";
      pathToHostname.put(path, hostname);
      hostnameToPath.put(hostname, path);
    }
    return hostname;
  }

  private synchronized String pathForInetAddress(InetAddress inetAddress) {
    return hostnameToPath.get(inetAddress.getHostName());
  }

  @Override public List<InetAddress> lookup(String hostname) throws UnknownHostException {
    return hostname.endsWith(".socket")
        ? Arrays.asList(InetAddress.getByAddress(hostname, new byte[] {0, 0, 0, 0}))
        : Dns.SYSTEM.lookup(hostname);
  }

  @Override public Socket createSocket() throws IOException {
    return new UnixSocket();
  }

  class UnixSocket extends Socket {
    @Override public void connect(SocketAddress endpoint, int timeout) throws IOException {
      String path = pathForInetAddress(((InetSocketAddress) endpoint).getAddress());

      System.out.println(path);
    }
  }

  @Override public Socket createSocket(InetAddress inetAddress, int i) {
    throw new UnsupportedOperationException();
  }

  @Override public Socket createSocket(String s, int i) {
    throw new UnsupportedOperationException();
  }

  @Override public Socket createSocket(String s, int i, InetAddress inetAddress, int i1) {
    throw new UnsupportedOperationException();
  }

  @Override
  public Socket createSocket(InetAddress inetAddress, int i, InetAddress inetAddress1, int i1) {
    throw new UnsupportedOperationException();
  }
}

Alternately, instead of using a map to track the hostname and path, you could just hex encode the path string. That makes this stateless, which is nice. But it imposes a limit on the length of the path.