Fix binding multiple sockets failed on MacOS

Author: kzhdev

CHANGELOG

@@ -5,7 +5,8 @@
 - Fix MacOS build
 - Fix example log macros doesn't work without format args
 - Added socket binding (lines 165-176) - Bind to a local address before setting multicast options. This is required on some platforms like macOS for multicast senders.
-- Fixed setsockopt calls (lines 180, 189, 203) - Changed from passing raw pointer to using reinterpret_cast<const char*>(&value). While this is technically the same thing, it's more explicit about the expected type.
+- Fixed setsockopt calls (lines 180, 189, 203) - Changed from passing raw pointer to using reinterpret_cast<const char*>(&value). While this is technically the same thing, it's more explicit about the expected type
+- Fix binding multiple sockts failed on MacOS 
 
 #1.0.0.0 - [09/26/2025]
 - Initial Release

include/slick/socket/multicast_receiver_unix.h

@@ -203,8 +203,18 @@ bool MulticastReceiverBase<DerivedT>::setup_multicast_options()
         if (setsockopt(socket_, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0)
         {
             int error = errno;
-            LOG_WARN("Failed to set address reuse. error={} ({})", error, strerror(error));
+            LOG_WARN("Failed to set SO_REUSEADDR. error={} ({})", error, strerror(error));
         }
+
+#ifdef SO_REUSEPORT
+        // On BSD-derived systems (macOS, FreeBSD), SO_REUSEPORT is required
+        // to allow multiple sockets to bind to the same port
+        if (setsockopt(socket_, SOL_SOCKET, SO_REUSEPORT, &reuse, sizeof(reuse)) < 0)
+        {
+            int error = errno;
+            LOG_WARN("Failed to set SO_REUSEPORT. error={} ({})", error, strerror(error));
+        }
+#endif
     }
 
     // Bind to the multicast port

tests/multicast_receiver_tests.cpp

@@ -146,16 +146,16 @@ TEST_F(MulticastReceiverTest, MultipleReceiversSameGroup) {
     // Test that multiple receivers can listen to the same multicast group
     auto receiver1 = std::make_unique<TestMulticastReceiver>("TestReceiver1", config_);
     auto receiver2 = std::make_unique<TestMulticastReceiver>("TestReceiver2", config_);
-    
-    // Both should be able to start (due to reuse_address = true)
+
+    // Both should be able to start (due to reuse_address = true and SO_REUSEPORT)
     EXPECT_TRUE(receiver1->start());
     EXPECT_TRUE(receiver2->start());
-    
+
     std::this_thread::sleep_for(std::chrono::milliseconds(100));
-    
+
     EXPECT_TRUE(receiver1->is_running());
     EXPECT_TRUE(receiver2->is_running());
-    
+
     receiver1->stop();
     receiver2->stop();
 }