Issue 298: Found a way to get the UID using the hashCode

Author: hypfvieh

dbus-java-transport-native-unixsocket/src/main/java/org/freedesktop/dbus/transport/jre/NativeUnixSocketHelper.java

@@ -1,33 +1,46 @@
 package org.freedesktop.dbus.transport.jre;
 
+import jdk.net.ExtendedSocketOptions;
+import jdk.net.UnixDomainPrincipal;
+
 import java.io.IOException;
 import java.nio.channels.SocketChannel;
+import java.nio.file.attribute.UserPrincipal;
 
 public final class NativeUnixSocketHelper {
 
     private NativeUnixSocketHelper() {}
 
     /**
      * Get the UID of peer credentials.
+     * <p>
+     * Gathering the UID of SO_PEERCRED directly is not obvious when it comes to JDK native unix sockets.<br>
+     * based on the implementation in {@code sun.nio.fs.UnixUserPrincipals.User},<br>
+     * calling {@code hashCode()} on the {@link UserPrincipal} will give you either the UID or the hashCode of the name.
+     * </p><p>
+     * This method ensures that a proper UID is returned and not the hashCode of the name.
+     * If there is no UID, -1 is returned.
+     * </p>
      *
      * @param _sock socket to read from
-     * @return UID, -1 if given {@link SocketChannel} was null
+     * @return UID, -1 if given {@link SocketChannel} was {@code null} or UID could not be determined
      *
      * @throws IOException when socket channel fails to read SO_PEERCRED option
      */
     public static int getUid(SocketChannel _sock) throws IOException {
-        // gathering the UID of SO_PEERCRED is currently not possible using pure Java.
-        // The code below will only provide the username, not the UID.
-        // This does not comply with the DBus-Spec which wants UID.
-        return -1;
-//        if (_sock == null) {
-//            return -1;
-//        }
-//
-//        UnixDomainPrincipal creds = _sock.getOption(ExtendedSocketOptions.SO_PEERCRED);
-//        UserPrincipal user = creds.user();
-//
-//        return Integer.parseInt(user.getName());
+        if (_sock == null) {
+            return -1;
+        }
+
+        UnixDomainPrincipal creds = _sock.getOption(ExtendedSocketOptions.SO_PEERCRED);
+        UserPrincipal user = creds.user();
+
+        int uid = -1;
+        if (user != null && user.hashCode() != user.getName().hashCode()) {
+            uid = user.hashCode();
+        }
+
+        return uid;
     }
 
 }