server: limit address binding in cluster mode

server/python/cluster_setup.py

@@ -10,7 +10,7 @@ from typing import Any
 
 import rpc
 import rpc_reader
-from typing import TypedDict
+from typing import TypedDict, Callable
 
 
 class ClusterObject(TypedDict):
@@ -21,6 +21,7 @@ class ClusterObject(TypedDict):
     sourceKey: str
     sha256: str
 
+
 def isClusterAddress(address: str):
     return not address or address == os.environ.get("SCRYPTED_CLUSTER_ADDRESS", None)
 
@@ -130,11 +131,8 @@ class ClusterSetup:
                 peer.kill("cluster client killed")
                 writer.close()
 
-        listenAddress = "0.0.0.0" if self.SCRYPTED_CLUSTER_ADDRESS else "127.0.0.1"
-        clusterRpcServer = await asyncio.start_server(
-            handleClusterClient, listenAddress, 0
-        )
-        self.clusterPort = clusterRpcServer.sockets[0].getsockname()[1]
+        clusterRpcServerInfo = await cluster_listen_zero(handleClusterClient)
+        self.clusterPort = clusterRpcServerInfo["port"]
         self.peer.onProxySerialization = lambda value: self.onProxySerialization(
             self.peer, value, None
         )
@@ -238,3 +236,49 @@ class ClusterSetup:
             return newValue
         except Exception as e:
             return value
+
+
+class ClusterServerListener(TypedDict):
+    server: asyncio.Server
+    port: int
+
+
+async def cluster_listen_zero(
+    callback: Callable[[asyncio.StreamReader, asyncio.StreamWriter]]
+) -> ClusterServerListener:
+    SCRYPTED_CLUSTER_ADDRESS = os.getenv("SCRYPTED_CLUSTER_ADDRESS")
+    if not SCRYPTED_CLUSTER_ADDRESS:
+        server = await asyncio.start_server(callback, host=None, port=0)
+        port = server.sockets[0].getsockname()[1]
+        return {
+            "server": server,
+            "port": port,
+        }
+
+    # need to listen on the cluster address and 127.0.0.1 on the same port.
+    retries = 5
+    while retries > 0:
+        cluster_server = await asyncio.start_server(
+            callback, host=SCRYPTED_CLUSTER_ADDRESS, port=0
+        )
+        port = cluster_server.sockets[0].getsockname()[1]
+
+        try:
+            print('trying to bind to port', port)
+            local_server = await asyncio.start_server(
+                callback, host="127.0.0.1", port=port
+            )
+
+            future = asyncio.ensure_future(local_server.wait_closed())
+            future.add_done_callback(lambda: local_server.close())
+
+            return {
+                "server": cluster_server,
+                "port": port,
+            }
+        except:
+            # Port may be in use, keep trying.
+            cluster_server.close()
+            retries -= 1
+
+    raise Exception("failed to bind to cluster address.")

server/python/plugin_repl.py

@@ -198,6 +198,7 @@ async def createREPLServer(sdk: ScryptedStatic, plugin: ScryptedDevice) -> int:
     sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
     sock.settimeout(None)
+    # TODO: this should use an equivalent to cluster_listen_zero
     sock.bind(("0.0.0.0" if os.getenv("SCRYPTED_CLUSTER_ADDRESS") else "127.0.0.1", 0))
     sock.listen()