fix(sfu): use concrete WebRTC listen IP for browser-consumable ICE candidates

Backend/.env.example

@@ -17,7 +17,7 @@ MEDIA_PROVIDER=mock
 TURN_URLS=
 TURN_USERNAME=
 TURN_CREDENTIAL=
-MEDIA_WEBRTC_LISTEN_IP=0.0.0.0
+MEDIA_WEBRTC_LISTEN_IP=127.0.0.1
 MEDIA_WEBRTC_ANNOUNCED_IP=
 MEDIA_RTC_MIN_PORT=40000
 MEDIA_RTC_MAX_PORT=49999

Backend/README.md

@@ -38,7 +38,7 @@ Required env vars:
 | `MEDIA_SFU_ENGINE` | SFU engine for `single_server_sfu` mode (`mediasoup` default, `noop` fallback) |
 | `MEDIA_PROVIDER` | Media backend provider (`mock` by default) |
 | `TURN_URLS` / `TURN_USERNAME` / `TURN_CREDENTIAL` | TURN/STUN configuration used by single-server SFU mode |
-| `MEDIA_WEBRTC_LISTEN_IP` / `MEDIA_WEBRTC_ANNOUNCED_IP` | WebRTC transport bind/announce IPs for mediasoup SFU |
+| `MEDIA_WEBRTC_LISTEN_IP` / `MEDIA_WEBRTC_ANNOUNCED_IP` | WebRTC transport bind/announce IPs for mediasoup SFU. Do not leave bind IP as `0.0.0.0` without an announced IP in non-local environments. |
 | `MEDIA_RTC_MIN_PORT` / `MEDIA_RTC_MAX_PORT` | UDP/TCP RTP port range for mediasoup worker |
 | `MEDIA_RECORDINGS_DIR` | Local output directory for server-side recording workers (planned in SFU mode) |
 | `MEDIA_MAX_PUBLISHERS` / `MEDIA_MAX_SUBSCRIBERS_PER_ROOM` | Soft concurrency limits for single-server media mode (planned) |

Backend/media/sfu/mediasoup.ts

@@ -1,4 +1,5 @@
 import { randomUUID } from 'crypto';
+import { networkInterfaces } from 'os';
 
 import { mediaConfig } from '../config';
 import type {
@@ -39,6 +40,45 @@ const parsePort = (value: string | undefined, fallback: number): number => {
   return parsed;
 };
 
+const pickHostIpv4 = (): string | null => {
+  const interfaces = networkInterfaces();
+  for (const addresses of Object.values(interfaces)) {
+    if (!addresses) continue;
+    for (const address of addresses) {
+      if (address.family === 'IPv4' && !address.internal) {
+        return address.address;
+      }
+    }
+  }
+  return null;
+};
+
+const resolveListenAddress = (): { ip: string; announcedAddress?: string } => {
+  const configuredListenIp = (process.env.MEDIA_WEBRTC_LISTEN_IP ?? '').trim();
+  const configuredAnnounced = process.env.MEDIA_WEBRTC_ANNOUNCED_IP?.trim();
+
+  if (configuredListenIp && configuredListenIp !== '0.0.0.0') {
+    return {
+      ip: configuredListenIp,
+      ...(configuredAnnounced ? { announcedAddress: configuredAnnounced } : {}),
+    };
+  }
+
+  const discoveredIp = pickHostIpv4();
+  if (!configuredAnnounced && configuredListenIp === '0.0.0.0') {
+    console.warn(
+      `[sfu] MEDIA_WEBRTC_LISTEN_IP is 0.0.0.0 without MEDIA_WEBRTC_ANNOUNCED_IP. ` +
+      `Using ${discoveredIp ?? '127.0.0.1'} for ICE candidates. Configure both env vars for production.`,
+    );
+  }
+
+  const ip = discoveredIp ?? '127.0.0.1';
+  return {
+    ip,
+    ...(configuredAnnounced ? { announcedAddress: configuredAnnounced } : {}),
+  };
+};
+
 const toTransportOptions = (transport: any): SfuTransportOptions => ({
   id: transport.id,
   iceParameters: transport.iceParameters ?? {},
@@ -105,19 +145,18 @@ export class MediasoupSfuService implements SfuService {
   }
 
   private async createWebRtcTransport(router: any): Promise<any> {
-    const listenIp = process.env.MEDIA_WEBRTC_LISTEN_IP ?? '0.0.0.0';
+    const listenAddress = resolveListenAddress();
-    const announcedAddress = process.env.MEDIA_WEBRTC_ANNOUNCED_IP?.trim();
     return await router.createWebRtcTransport({
       listenInfos: [
         {
           protocol: 'udp',
-          ip: listenIp,
+          ip: listenAddress.ip,
-          ...(announcedAddress ? { announcedAddress } : {}),
+          ...(listenAddress.announcedAddress ? { announcedAddress: listenAddress.announcedAddress } : {}),
         },
         {
           protocol: 'tcp',
-          ip: listenIp,
+          ip: listenAddress.ip,
-          ...(announcedAddress ? { announcedAddress } : {}),
+          ...(listenAddress.announcedAddress ? { announcedAddress: listenAddress.announcedAddress } : {}),
         },
       ],
       enableUdp: true,
@@ -364,4 +403,3 @@ export class MediasoupSfuService implements SfuService {
     return consumerDescriptor;
   }
 }
-