1 files changed, 24 insertions, 1 deletions
diff --git a/synapse/app/__init__.py b/synapse/app/__init__.py
index b45adafdd3..f56f5fcc13 100644
--- a/synapse/app/__init__.py
+++ b/synapse/app/__init__.py
@@ -12,15 +12,38 @@
 # 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.
-
+import logging
 import sys
 
 from synapse import python_dependencies  # noqa: E402
 
 sys.dont_write_bytecode = True
 
+logger = logging.getLogger(__name__)
+
 try:
     python_dependencies.check_requirements()
 except python_dependencies.DependencyException as e:
     sys.stderr.writelines(e.message)
     sys.exit(1)
+
+
+def check_bind_error(e, address, bind_addresses):
+    """
+    This method checks an exception occurred while binding on 0.0.0.0.
+    If :: is specified in the bind addresses a warning is shown.
+    The exception is still raised otherwise.
+
+    Binding on both 0.0.0.0 and :: causes an exception on Linux and macOS
+    because :: binds on both IPv4 and IPv6 (as per RFC 3493).
+    When binding on 0.0.0.0 after :: this can safely be ignored.
+
+    Args:
+        e (Exception): Exception that was caught.
+        address (str): Address on which binding was attempted.
+        bind_addresses (list): Addresses on which the service listens.
+    """
+    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