Allow binds to both :: and 0.0.0.0

Binding on 0.0.0.0 when :: is specified in the bind_addresses is now allowed.
This causes a warning explaining the behaviour.
Configuration changed to match.

See #2232

Signed-off-by: Silke Hofstra <silke@slxh.eu>

synapse/app/homeserver.py

@@ -58,6 +58,7 @@ from twisted.internet import defer, reactor
 from twisted.web.resource import EncodingResourceWrapper, Resource
 from twisted.web.server import GzipEncoderFactory
 from twisted.web.static import File
+from twisted.internet import error
 
 logger = logging.getLogger("synapse.app.homeserver")
 
@@ -131,6 +132,7 @@ class SynapseHomeServer(HomeServer):
 
         if tls:
             for address in bind_addresses:
+                try:
                     reactor.listenSSL(
                         port,
                         SynapseSite(
@@ -142,8 +144,12 @@ class SynapseHomeServer(HomeServer):
                         self.tls_server_context_factory,
                         interface=address
                     )
+                except error.CannotListenError as e:
+                    check_bind_error(e, address, bind_addresses)
+
         else:
             for address in bind_addresses:
+                try:
                     reactor.listenTCP(
                         port,
                         SynapseSite(
@@ -154,6 +160,8 @@ class SynapseHomeServer(HomeServer):
                         ),
                         interface=address
                     )
+                except error.CannotListenError as e:
+                    check_bind_error(e, address, bind_addresses)
         logger.info("Synapse now listening on port %d", port)
 
     def _configure_named_resource(self, name, compress=False):
@@ -232,6 +240,7 @@ class SynapseHomeServer(HomeServer):
                 bind_addresses = listener["bind_addresses"]
 
                 for address in bind_addresses:
+                    try:
                         reactor.listenTCP(
                             listener["port"],
                             manhole(
@@ -241,9 +250,12 @@ class SynapseHomeServer(HomeServer):
                             ),
                             interface=address
                         )
+                    except error.CannotListenError as e:
+                        check_bind_error(e, address, bind_addresses)
             elif listener["type"] == "replication":
                 bind_addresses = listener["bind_addresses"]
                 for address in bind_addresses:
+                    try:
                         factory = ReplicationStreamProtocolFactory(self)
                         server_listener = reactor.listenTCP(
                             listener["port"], factory, interface=address
@@ -251,6 +263,8 @@ class SynapseHomeServer(HomeServer):
                         reactor.addSystemEventTrigger(
                             "before", "shutdown", server_listener.stopListening,
                         )
+                    except error.CannotListenError as e:
+                        check_bind_error(e, address, bind_addresses)
             else:
                 logger.warn("Unrecognized listener type: %s", listener["type"])
 
@@ -284,6 +298,13 @@ class SynapseHomeServer(HomeServer):
         return db_conn
 
 
+def check_bind_error(e, address, bind_addresses):
+    if address == '0.0.0.0' and '::' in bind_addresses:
+        logger.warn('Failed to listen on 0.0.0.0, continuing because listening on [::]')
+    else:
+        raise e
+
+
 def setup(config_options):
     """
     Args:

synapse/config/server.py

@@ -220,14 +220,12 @@ class ServerConfig(Config):
             port: %(bind_port)s
 
             # Local addresses to listen on.
-            # On Linux and Mac OS, this will listen on all IPv4 and IPv6
+            # On Linux and Mac OS, `::` will listen on all IPv4 and IPv6
             # addresses by default. For most other OSes, this will only listen
             # on IPv6.
             bind_addresses:
               - '::'
-              # For systems other than Linux or Mac OS, uncomment the next line
-              # to also listen on IPv4.
-              #- '0.0.0.0'
+              - '0.0.0.0'
 
             # This is a 'http' listener, allows us to specify 'resources'.
             type: http
@@ -265,7 +263,7 @@ class ServerConfig(Config):
           # For when matrix traffic passes through loadbalancer that unwraps TLS.
           - port: %(unsecure_port)s
             tls: false
-            bind_addresses: ['::']
+            bind_addresses: ['::', '0.0.0.0']
             type: http
 
             x_forwarded: false