Question

How to write this socket stream on local file system client in Java?

Python works:

# Echo server program
import socket,os

s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
try:
    os.remove("/tmp/socketname")
except OSError:
    pass
s.bind("/tmp/socketname")
s.listen(1)
conn, addr = s.accept()
while 1:
    data = conn.recv(1024)
    if not data: break
    conn.send(data)
conn.close()


# Echo client program
import socket
s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
s.connect("/tmp/socketname")
s.send('Hello, world')
data = s.recv(1024)
s.close()
print 'Received', repr(data)

Java:

  /* Client: how do you mention the /tmp/socketname? */
  public static String localsendTCPBytes(String bytes) throws IOException {
    String downloaded = null;
    Socket socket = new Socket("localhost", 58888);
    DataOutputStream upload = new DataOutputStream(socket.getOutputStream());
    BufferedReader download = new BufferedReader(new InputStreamReader(socket.getInputStream()));

    String caps = bytes;
    upload.writeBytes(caps);
    upload.flush();
    String get;
    downloaded = download.readLine();
    System.out.println("[TCP]: downloading: " + downloaded);
    socket.close();
    return downloaded;
  }

Follow up:

1) Import jar and attach to the project:

JUnixsocket – download JAR

2) Unitest Java client code

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.newsclub.net.unix.AFUNIXSocket;
import org.newsclub.net.unix.AFUNIXSocketAddress;
import org.newsclub.net.unix.AFUNIXSocketException;

public class SimpleTestClient {
  public static void main(String[] args) throws IOException {
    final File socketFile = new File("/tmp/socketname");
    AFUNIXSocket sock = AFUNIXSocket.newInstance();
    try {
      sock.connect(new AFUNIXSocketAddress(socketFile));
    } catch (AFUNIXSocketException e) {
      System.out.println("Cannot connect to server. Have you started it?");
      System.out.flush();
      throw e;
    }
    System.out.println("Connected");
    InputStream is = sock.getInputStream();
    OutputStream os = sock.getOutputStream();
    byte[] buf = new byte[128];
    int read = is.read(buf);
    System.out.println("Server says: " + new String(buf, 0, read));
    System.out.println("Replying to server...");
    os.write("Hello Server".getBytes());
    os.flush();
    os.close();
    is.close();
    sock.close();
    System.out.println("End of communication.");
  }
}

3) Build/compile problem:

java.lang.UnsatisfiedLinkError: Could not load junixsocket library, tried [/opt/newsclub/lib-native/libjunixsocket-linux-1.6-amd64.so, /opt/newsclub/lib-native/libjunixsocket-linux-1.5-amd64.so, lib:junixsocket-linux-1.6-amd64, lib:junixsocket-linux-1.5-amd64]; please define system property org.newsclub.net.unix.library.path
    at org.newsclub.net.unix.NativeUnixSocket.load(NativeUnixSocket.java:95)
    at org.newsclub.net.unix.NativeUnixSocket.<clinit>(NativeUnixSocket.java:105)
    at org.newsclub.net.unix.AFUNIXSocket.<init>(AFUNIXSocket.java:36)
    at org.newsclub.net.unix.AFUNIXSocket.newInstance(AFUNIXSocket.java:50)
    at unixdomainsocket.SimpleTestClient.main(SimpleTestClient.java:26)
Caused by: java.lang.UnsatisfiedLinkError: no junixsocket-linux-1.5-amd64 in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1681)
    at java.lang.Runtime.loadLibrary0(Runtime.java:840)
    at java.lang.System.loadLibrary(System.java:1047)
    at org.newsclub.net.unix.NativeUnixSocket.load(NativeUnixSocket.java:77)
    ... 4 more
Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class org.newsclub.net.unix.NativeUnixSocket
    at org.newsclub.net.unix.AFUNIXSocketImpl.connect(AFUNIXSocketImpl.java:125)
    at org.newsclub.net.unix.AFUNIXSocket.connect(AFUNIXSocket.java:97)
    at org.newsclub.net.unix.AFUNIXSocket.connect(AFUNIXSocket.java:87)
    at unixdomainsocket.SimpleTestClient.main(SimpleTestClient.java:28)
Java Result: 1

4) Solution:

-Djava.library.path=/usr/lib/jni -Djava.library.path=/usr/lib/rxtx -Djava.security.policy=applet.policy -Djava.library.path=/var/tmp/screwyou/jar/lib-native

Works!

Answer 1

You can’t use Unix domain sockets from the Java JDK. You would need an external package, if you can find one.