Fixes UnixSocketAddress desynchronization bug on MacOS after calling UnixDatagramChannel#receive

src/main/java/jnr/unixsocket/Native.java

@@ -217,6 +217,10 @@ public static int recvfrom(int fd, ByteBuffer dst, SockAddrUnix addr) throws IOE
             n = libsocket().recvfrom(fd, dst, dst.remaining(), 0, addr, addrlen);
         } while (n < 0 && Errno.EINTR.equals(getLastError()));
 
+        if (n >= 0 && addr != null && addrlen != null) {
+            addr.updatePath(addrlen.getValue());
+        }
+
         if (n > 0) {
             dst.position(dst.position() + n);
         }

src/main/java/jnr/unixsocket/SockAddrUnix.java

@@ -101,6 +101,8 @@ void updatePath(final int len) {
                     cachedPath = cachedPath.substring(0, slen);
                 }
             }
+            // Sync the struct field with the normalized cachedPath
+            getPathField().set(cachedPath);
         }
     }
 

src/test/java/jnr/unixsocket/UnixDatagramChannelRoundTripTest.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2026
+ *
+ * This file is part of the JNR project.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package jnr.unixsocket;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+
+import org.junit.Test;
+
+public class UnixDatagramChannelRoundTripTest {
+
+    private static UnixSocketAddress tempAddress() throws IOException {
+        File socketFile = Files.createTempFile("jnr-unixsocket-roundtrip", ".sock").toFile();
+        socketFile.delete();
+        socketFile.deleteOnExit();
+        return new UnixSocketAddress(socketFile);
+    }
+
+    @Test
+    public void receiveAddressRoundTripCanBeUsedAsReplyTarget() throws Exception {
+        final UnixSocketAddress serverAddress = tempAddress();
+        final UnixSocketAddress clientAddress = tempAddress();
+
+        final byte[] message = "hello".getBytes(StandardCharsets.UTF_8);
+        final int iterations = 1000;
+
+        try (UnixDatagramChannel server = UnixDatagramChannel.open().bind(serverAddress);
+             UnixDatagramChannel client = UnixDatagramChannel.open().bind(clientAddress)) {
+
+            for (int i = 0; i < iterations; i++) {
+                ByteBuffer tx = ByteBuffer.wrap(message);
+                int sent = client.send(tx, serverAddress);
+                assertTrue("client->server send should send > 0 bytes", sent > 0);
+
+                ByteBuffer rx = ByteBuffer.allocate(64);
+                UnixSocketAddress receivedFrom = server.receive(rx);
+                assertEquals("received sender path should match bound client path", clientAddress.humanReadablePath(), receivedFrom.humanReadablePath());
+
+                // If receivedFrom contains trailing garbage bytes, this send may fail
+                // with ENOENT (No such file or directory).
+                ByteBuffer reply = ByteBuffer.wrap(message);
+
+                int echoed = server.send(reply, receivedFrom);
+                assertTrue("server reply send should send > 0 bytes", echoed > 0);
+
+                ByteBuffer clientRx = ByteBuffer.allocate(64);
+                UnixSocketAddress echoedFrom = client.receive(clientRx);
+                assertEquals("server path should be stable", serverAddress.path(), echoedFrom.path());
+            }
+        }
+    }
+}
+