Merge pull request #299 from hypfvieh/issue-298

Issue 298

Author: hypfvieh

README.md

@@ -74,7 +74,7 @@ The library will remain open source and MIT licensed and can still be used, fork
    - **Minimum Java version: 21**
    - **Removed** all methods, members and classes marked as deprecated
    - Update JUnit to Version 6
-   - Remove `throws IOException` from `AbstractConnectionBase.close()` (Issue #287)
+   - Remove `throws IOException` from `AbstractConnectionBase.close()` ([#287](https://github.com/hypfvieh/dbus-java/issues/287))
    - Support usage of `Struct`s as return value (as alternative to `Tuple` with generics) (based on discussion in #285)
    - Updated dependencies and plugins
    - Added support to use `Struct` datatypes as return values instead of `Tuple`#
@@ -87,6 +87,8 @@ The library will remain open source and MIT licensed and can still be used, fork
      - This can be enabled using the `DBusConnectionBuilder`, example: `DBusConnection sessionConnection = DBusConnectionBuilder.forSystemBus().receivingThreadConfig().withAllVirtualThreads(true).connectionConfig().build()`
      - Virtual-Threads can be enabled/disabled for each of the different executor services used in `ReceivingService`: `SIGNAL`, `ERROR`, `METHODCALL`, `METHODRETURN`
      - default remains native threads on all executors
+   - Fixed possible NullPointerException in SASL auth ([#294](https://github.com/hypfvieh/dbus-java/issues/294))
+   - Fixed SASL authentication issue when running in server mode in combination with unix sockets ([#298](https://github.com/hypfvieh/dbus-java/issues/298)) 
 
 ##### Changes in 5.2.0 (2025-12-21):
    - removed properties from dbus-java.version which causes issues with reproducable builds ([PR#279](https://github.com/hypfvieh/dbus-java/issues/279)) 

dbus-java-core/src/main/java/org/freedesktop/dbus/connections/SASL.java

@@ -598,24 +598,18 @@ public boolean auth(SocketChannel _sock, AbstractTransport _transport) throws IO
             case SERVER:
                 switch (state) {
                     case INITIAL_STATE:
-                        ByteBuffer buf = ByteBuffer.allocate(1);
-                        if (_sock != null) {
-                            _sock.read(buf); // 0
+                        try {
+                            int kuid = -1;
+                            if (_transport instanceof AbstractUnixTransport aut) {
+                                kuid = aut.getUid(_sock);
+                            }
+                            if (kuid >= 0) {
+                                kernelUid = stupidlyEncode("" + kuid);
+                            }
                             state = SaslAuthState.WAIT_AUTH;
-                        } else {
-                            try {
-                                int kuid = -1;
-                                if (_transport instanceof AbstractUnixTransport aut) {
-                                    kuid = aut.getUid(null);
-                                }
-                                if (kuid >= 0) {
-                                    kernelUid = stupidlyEncode("" + kuid);
-                                }
-                                state = SaslAuthState.WAIT_AUTH;
 
-                            } catch (SocketException _ex) {
-                                state = SaslAuthState.FAILED;
-                            }
+                        } catch (SocketException _ex) {
+                            state = SaslAuthState.FAILED;
                         }
                     break;
                     case WAIT_AUTH:

dbus-java-core/src/main/java/org/freedesktop/dbus/connections/transports/AbstractTransport.java

@@ -249,6 +249,9 @@ public void setPreConnectCallback(Consumer<AbstractTransport> _run) {
      * @throws IOException on any error
      */
     private void authenticate(SocketChannel _sock) throws IOException {
+        if (_sock == null) {
+            throw new IOException("SocketChannel instance required");
+        }
         SASL sasl = new SASL(config.getSaslConfig());
         try {
             if (!sasl.auth(_sock, this)) {

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

@@ -13,9 +13,17 @@ 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
      */
@@ -27,7 +35,12 @@ public static int getUid(SocketChannel _sock) throws IOException {
         UnixDomainPrincipal creds = _sock.getOption(ExtendedSocketOptions.SO_PEERCRED);
         UserPrincipal user = creds.user();
 
-        return Integer.parseInt(user.getName());
+        int uid = -1;
+        if (user != null && user.hashCode() != user.getName().hashCode()) {
+            uid = user.hashCode();
+        }
+
+        return uid;
     }
 
 }