[BUG 685] Add full multicast support for WSJT-X, so that multiple apps can listen

.env.example

@@ -171,6 +171,9 @@ CLASSIC_ANALOG_CLOCK=false
 WSJTX_ENABLED=true
 WSJTX_UDP_PORT=2237
 
+# Multicast address group for WSJTX. Leave commented if not being used
+# WSJTX_MULTICAST_ADDRESS=224.0.0.1
+
 # Relay key for remote WSJT-X relay agent (cloud deployments)
 # WSJTX_RELAY_KEY=your-secret-relay-key-here
 

README.md

@@ -498,6 +498,14 @@ Live decoded FT8, FT4, JT65, JT9, and WSPR messages from WSJT-X, JTDX, or any co
 2. In WSJT-X: set the UDP Server address to your OpenHamClock machine's IP (e.g., `192.168.1.100`) and port `2237`.
 3. Make sure UDP port 2237 is not blocked by a firewall.
 
+**Network setup (WSJT-X using Multicast):**
+
+While the above configuration works just fine in a majority of cases, if you are running more than one multicast listener on a host (e.g. OpenHamClock and something like GridTracker2), then OpenHamClock needs to configure itself properly as a multicast listener.
+
+Uncomment the `WSJTX_MULTICAST_ADDRESS` line in `.env`, and make sure that the multicast address there matches what you have set in WSJT-X. e.g. `224.0.0.1`
+
+You will need to restart OpenHamCLock after this change.
+
 **Cloud setup (OpenHamClock on a remote server):**
 
 WSJT-X sends data over UDP, which only works on a local network. For cloud deployments (like Railway or openhamclock.com), you need the WSJT-X Relay Agent to bridge the gap. See the [WSJT-X Relay Agent](#wsjt-x-relay-agent) section below.
@@ -773,11 +781,12 @@ All configuration is done through the `.env` file. On first run, this file is au
 
 ### WSJT-X Integration
 
-| Variable          | Default  | Description                                                                                                                                                             |
-| ----------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `WSJTX_ENABLED`   | `true`   | Enable the WSJT-X UDP listener on the server.                                                                                                                           |
-| `WSJTX_UDP_PORT`  | `2237`   | UDP port for receiving WSJT-X decoded messages. Must match the port configured in WSJT-X Settings → Reporting → UDP Server.                                             |
-| `WSJTX_RELAY_KEY` | _(none)_ | Shared secret key for the WSJT-X relay agent. Required only for cloud deployments where WSJT-X can't reach the server directly over UDP. Pick any strong random string. |
+| Variable                  | Default  | Description                                                                                                                                                             |
+| ------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `WSJTX_ENABLED`           | `true`   | Enable the WSJT-X UDP listener on the server.                                                                                                                           |
+| `WSJTX_MULTICAST_ADDRESS` | _(none)_ | Multicast address to listen for messages                                                                                                                                |
+| `WSJTX_UDP_PORT`          | `2237`   | UDP port for receiving WSJT-X decoded messages. Must match the port configured in WSJT-X Settings → Reporting → UDP Server.                                             |
+| `WSJTX_RELAY_KEY`         | _(none)_ | Shared secret key for the WSJT-X relay agent. Required only for cloud deployments where WSJT-X can't reach the server directly over UDP. Pick any strong random string. |
 
 ### DX Cluster
 

server.js

@@ -11023,6 +11023,7 @@ app.get('/api/aprs/stations', (req, res) => {
 
 const WSJTX_UDP_PORT = parseInt(process.env.WSJTX_UDP_PORT || '2237');
 const WSJTX_ENABLED = process.env.WSJTX_ENABLED !== 'false'; // enabled by default
+const WSJTX_MULTICAST_ADDRESS = process.env.WSJTX_MULTICAST_ADDRESS;
 const WSJTX_RELAY_KEY = process.env.WSJTX_RELAY_KEY || ''; // auth key for remote relay agent
 const WSJTX_MAX_DECODES = 500; // max decodes to keep in memory
 const WSJTX_MAX_AGE = 60 * 60 * 1000; // 60 minutes (configurable via client)
@@ -11880,7 +11881,7 @@ app.get('/api/n3fjp/qsos', (req, res) => {
 let wsjtxSocket = null;
 if (WSJTX_ENABLED) {
   try {
-    wsjtxSocket = dgram.createSocket('udp4');
+    wsjtxSocket = dgram.createSocket({ type: 'udp4', reuseAddr: true });
 
     wsjtxSocket.on('message', (buf, rinfo) => {
       const msg = parseWSJTXMessage(buf);
@@ -11894,9 +11895,33 @@ if (WSJTX_ENABLED) {
     wsjtxSocket.on('listening', () => {
       const addr = wsjtxSocket.address();
       console.log(`[WSJT-X] UDP listener on ${addr.address}:${addr.port}`);
+
+      if (WSJTX_MULTICAST_ADDRESS) {
+        try {
+          wsjtxSocket.addMembership(WSJTX_MULTICAST_ADDRESS);
+          console.log(`[WSJT-X] Joined multicast group ${WSJTX_MULTICAST_ADDRESS}`);
+        } catch (e) {
+          console.error(`Failed to join multicast group ${WSJTX_MULTICAST_ADDRESS}`);
+        }
+      }
     });
 
-    wsjtxSocket.bind(WSJTX_UDP_PORT, '0.0.0.0');
+    if (WSJTX_MULTICAST_ADDRESS) {
+      wsjtxSocket.bind(
+        {
+          port: WSJTX_UDP_PORT,
+          exclusive: false,
+        },
+        () => {
+          wsjtxSocket.setMulticastLoopback(true);
+        },
+      );
+    } else {
+      wsjtxSocket.bind({
+        port: WSJTX_UDP_PORT,
+        address: '0.0.0.0',
+      });
+    }
   } catch (e) {
     console.error(`[WSJT-X] Failed to start UDP listener: ${e.message}`);
   }