Add "--open-private-ports" cmdline option

This is helpful when generating a config file for running synapse under docker.

docs/sample_config.yaml

@@ -209,7 +209,7 @@ listeners:
       - names: [client, federation]
         compress: false
 
-    # example additonal_resources:
+    # example additional_resources:
     #
     #additional_resources:
     #  "/_matrix/my/custom/endpoint":

synapse/config/_base.py

@@ -150,6 +150,7 @@ class Config(object):
         server_name,
         generate_secrets=False,
         report_stats=None,
+        open_private_ports=False,
     ):
         """Build a default configuration file
 
@@ -173,6 +174,9 @@ class Config(object):
             report_stats (bool|None): Initial setting for the report_stats setting.
                 If None, report_stats will be left unset.
 
+            open_private_ports (bool): True to leave private ports (such as the non-TLS
+                HTTP listener) open to the internet.
+
         Returns:
             str: the yaml config file
         """
@@ -185,6 +189,7 @@ class Config(object):
                 server_name=server_name,
                 generate_secrets=generate_secrets,
                 report_stats=report_stats,
+                open_private_ports=open_private_ports,
             )
         )
 
@@ -298,6 +303,14 @@ class Config(object):
                 " stored. Defaults to the current working directory."
             ),
         )
+        generate_group.add_argument(
+            "--open-private-ports",
+            action="store_true",
+            help=(
+                "Leave private ports (such as the non-TLS HTTP listener) open to the"
+                " internet. Do not use this unless you know what you are doing."
+            ),
+        )
 
         config_args, remaining_args = config_parser.parse_known_args(argv)
 
@@ -351,6 +364,7 @@ class Config(object):
                     server_name=server_name,
                     report_stats=(config_args.report_stats == "yes"),
                     generate_secrets=True,
+                    open_private_ports=config_args.open_private_ports,
                 )
 
                 if not cls.path_exists(config_dir_path):

synapse/config/server.py

@@ -307,7 +307,9 @@ class ServerConfig(Config):
     def has_tls_listener(self):
         return any(l["tls"] for l in self.listeners)
 
-    def generate_config_section(self, server_name, data_dir_path, **kwargs):
+    def generate_config_section(
+        self, server_name, data_dir_path, open_private_ports, **kwargs
+    ):
         _, bind_port = parse_and_validate_server_name(server_name)
         if bind_port is not None:
             unsecure_port = bind_port - 400
@@ -320,6 +322,13 @@ class ServerConfig(Config):
         # Bring DEFAULT_ROOM_VERSION into the local-scope for use in the
         # default config string
         default_room_version = DEFAULT_ROOM_VERSION
+
+        unsecure_http_binding = "port: %i\n            tls: false" % (unsecure_port,)
+        if not open_private_ports:
+            unsecure_http_binding += (
+                "\n            bind_addresses: ['::1', '127.0.0.1']"
+            )
+
         return (
             """\
         ## Server ##
@@ -511,9 +520,7 @@ class ServerConfig(Config):
           # If you plan to use a reverse proxy, please see
           # https://github.com/matrix-org/synapse/blob/master/docs/reverse_proxy.rst.
           #
-          - port: %(unsecure_port)s
-            tls: false
-            bind_addresses: ['::1', '127.0.0.1']
+          - %(unsecure_http_binding)s
             type: http
             x_forwarded: true
 
@@ -521,7 +528,7 @@ class ServerConfig(Config):
               - names: [client, federation]
                 compress: false
 
-            # example additonal_resources:
+            # example additional_resources:
             #
             #additional_resources:
             #  "/_matrix/my/custom/endpoint":