Improve error handling for SOCKS proxy.

Author: aaugustin

docs/reference/exceptions.rst

@@ -34,14 +34,16 @@ also reported by :func:`~websockets.asyncio.server.serve` in logs.
 
 .. autoexception:: SecurityError
 
-.. autoexception:: InvalidMessage
-
-.. autoexception:: InvalidStatus
+.. autoexception:: ProxyError
 
 .. autoexception:: InvalidProxyMessage
 
 .. autoexception:: InvalidProxyStatus
 
+.. autoexception:: InvalidMessage
+
+.. autoexception:: InvalidStatus
+
 .. autoexception:: InvalidHeader
 
 .. autoexception:: InvalidHeaderFormat

src/websockets/__init__.py

@@ -49,6 +49,7 @@
     "NegotiationError",
     "PayloadTooBig",
     "ProtocolError",
+    "ProxyError",
     "SecurityError",
     "WebSocketException",
     # .frames
@@ -112,6 +113,7 @@
         NegotiationError,
         PayloadTooBig,
         ProtocolError,
+        ProxyError,
         SecurityError,
         WebSocketException,
     )
@@ -173,6 +175,7 @@
             "NegotiationError": ".exceptions",
             "PayloadTooBig": ".exceptions",
             "ProtocolError": ".exceptions",
+            "ProxyError": ".exceptions",
             "SecurityError": ".exceptions",
             "WebSocketException": ".exceptions",
             # .frames

src/websockets/asyncio/client.py

@@ -12,7 +12,7 @@
 
 from ..client import ClientProtocol, backoff
 from ..datastructures import HeadersLike
-from ..exceptions import InvalidMessage, InvalidStatus, SecurityError
+from ..exceptions import InvalidMessage, InvalidStatus, ProxyError, SecurityError
 from ..extensions.base import ClientExtensionFactory
 from ..extensions.permessage_deflate import enable_client_permessage_deflate
 from ..headers import validate_subprotocols
@@ -148,7 +148,9 @@ def process_exception(exc: Exception) -> Exception | None:
     That exception will be raised, breaking out of the retry loop.
 
     """
-    if isinstance(exc, (OSError, asyncio.TimeoutError)):
+    # This catches python-socks' ProxyConnectionError and ProxyTimeoutError.
+    # Remove asyncio.TimeoutError when dropping Python < 3.11.
+    if isinstance(exc, (OSError, TimeoutError, asyncio.TimeoutError)):
         return None
     if isinstance(exc, InvalidMessage) and isinstance(exc.__cause__, EOFError):
         return None
@@ -266,6 +268,7 @@ class connect:
 
     Raises:
         InvalidURI: If ``uri`` isn't a valid WebSocket URI.
+        InvalidProxy: If ``proxy`` isn't a valid proxy.
         OSError: If the TCP connection fails.
         InvalidHandshake: If the opening handshake fails.
         TimeoutError: If the opening handshake times out.
@@ -622,7 +625,15 @@ async def connect_socks_proxy(
             proxy.password,
             SOCKS_PROXY_RDNS[proxy.scheme],
         )
-        return await socks_proxy.connect(ws_uri.host, ws_uri.port, **kwargs)
+        # connect() is documented to raise OSError.
+        # socks_proxy.connect() doesn't raise TimeoutError; it gets canceled.
+        # Wrap other exceptions in ProxyError, a subclass of InvalidHandshake.
+        try:
+            return await socks_proxy.connect(ws_uri.host, ws_uri.port, **kwargs)
+        except OSError:
+            raise
+        except Exception as exc:
+            raise ProxyError("failed to connect to SOCKS proxy") from exc
 
 except ImportError:
 

src/websockets/exceptions.py

@@ -9,11 +9,12 @@
     * :exc:`InvalidProxy`
     * :exc:`InvalidHandshake`
         * :exc:`SecurityError`
+        * :exc:`ProxyError`
+            * :exc:`InvalidProxyMessage`
+            * :exc:`InvalidProxyStatus`
         * :exc:`InvalidMessage`
         * :exc:`InvalidStatus`
         * :exc:`InvalidStatusCode` (legacy)
-        * :exc:`InvalidProxyMessage`
-        * :exc:`InvalidProxyStatus`
         * :exc:`InvalidHeader`
             * :exc:`InvalidHeaderFormat`
             * :exc:`InvalidHeaderValue`
@@ -48,10 +49,11 @@
     "InvalidProxy",
     "InvalidHandshake",
     "SecurityError",
-    "InvalidMessage",
-    "InvalidStatus",
+    "ProxyError",
     "InvalidProxyMessage",
     "InvalidProxyStatus",
+    "InvalidMessage",
+    "InvalidStatus",
     "InvalidHeader",
     "InvalidHeaderFormat",
     "InvalidHeaderValue",
@@ -206,46 +208,53 @@ class SecurityError(InvalidHandshake):
     """
 
 
-class InvalidMessage(InvalidHandshake):
+class ProxyError(InvalidHandshake):
     """
-    Raised when a handshake request or response is malformed.
+    Raised when failing to connect to a proxy.
 
     """
 
 
-class InvalidStatus(InvalidHandshake):
+class InvalidProxyMessage(ProxyError):
     """
-    Raised when a handshake response rejects the WebSocket upgrade.
+    Raised when an HTTP proxy response is malformed.
+
+    """
+
+
+class InvalidProxyStatus(ProxyError):
+    """
+    Raised when an HTTP proxy rejects the connection.
 
     """
 
     def __init__(self, response: http11.Response) -> None:
         self.response = response
 
     def __str__(self) -> str:
-        return (
-            f"server rejected WebSocket connection: HTTP {self.response.status_code:d}"
-        )
+        return f"proxy rejected connection: HTTP {self.response.status_code:d}"
 
 
-class InvalidProxyMessage(InvalidHandshake):
+class InvalidMessage(InvalidHandshake):
     """
-    Raised when a proxy response is malformed.
+    Raised when a handshake request or response is malformed.
 
     """
 
 
-class InvalidProxyStatus(InvalidHandshake):
+class InvalidStatus(InvalidHandshake):
     """
-    Raised when a proxy rejects the connection.
+    Raised when a handshake response rejects the WebSocket upgrade.
 
     """
 
     def __init__(self, response: http11.Response) -> None:
         self.response = response
 
     def __str__(self) -> str:
-        return f"proxy rejected connection: HTTP {self.response.status_code:d}"
+        return (
+            f"server rejected WebSocket connection: HTTP {self.response.status_code:d}"
+        )
 
 
 class InvalidHeader(InvalidHandshake):

src/websockets/sync/client.py

@@ -9,6 +9,7 @@
 
 from ..client import ClientProtocol
 from ..datastructures import HeadersLike
+from ..exceptions import ProxyError
 from ..extensions.base import ClientExtensionFactory
 from ..extensions.permessage_deflate import enable_client_permessage_deflate
 from ..headers import validate_subprotocols
@@ -420,7 +421,14 @@ def connect_socks_proxy(
             SOCKS_PROXY_RDNS[proxy.scheme],
         )
         kwargs.setdefault("timeout", deadline.timeout())
-        return socks_proxy.connect(ws_uri.host, ws_uri.port, **kwargs)
+        # connect() is documented to raise OSError and TimeoutError.
+        # Wrap other exceptions in ProxyError, a subclass of InvalidHandshake.
+        try:
+            return socks_proxy.connect(ws_uri.host, ws_uri.port, **kwargs)
+        except (OSError, TimeoutError, socket.timeout):
+            raise
+        except Exception as exc:
+            raise ProxyError("failed to connect to SOCKS proxy") from exc
 
 except ImportError:
 

tests/asyncio/test_client.py

@@ -17,6 +17,7 @@
     InvalidProxy,
     InvalidStatus,
     InvalidURI,
+    ProxyError,
     SecurityError,
 )
 from websockets.extensions.permessage_deflate import PerMessageDeflate
@@ -379,24 +380,16 @@ def remove_accept_header(self, request, response):
 
     async def test_timeout_during_handshake(self):
         """Client times out before receiving handshake response from server."""
-        gate = asyncio.get_running_loop().create_future()
-
-        async def stall_connection(self, request):
-            await gate
-
-        # The connection will be open for the server but failed for the client.
-        # Use a connection handler that exits immediately to avoid an exception.
-        async with serve(*args, process_request=stall_connection) as server:
-            try:
-                with self.assertRaises(TimeoutError) as raised:
-                    async with connect(get_uri(server) + "/no-op", open_timeout=2 * MS):
-                        self.fail("did not raise")
-                self.assertEqual(
-                    str(raised.exception),
-                    "timed out during handshake",
-                )
-            finally:
-                gate.set_result(None)
+        # Replace the WebSocket server with a TCP server that does't respond.
+        with socket.create_server(("localhost", 0)) as sock:
+            host, port = sock.getsockname()
+            with self.assertRaises(TimeoutError) as raised:
+                async with connect(f"ws://{host}:{port}", open_timeout=MS):
+                    self.fail("did not raise")
+            self.assertEqual(
+                str(raised.exception),
+                "timed out during handshake",
+            )
 
     async def test_connection_closed_during_handshake(self):
         """Client reads EOF before receiving handshake response from server."""
@@ -570,11 +563,14 @@ class ProxyClientTests(unittest.IsolatedAsyncioTestCase):
     async def socks_proxy(self, auth=None):
         if auth:
             proxyauth = "hello:iloveyou"
-            proxy_uri = "http://hello:iloveyou@localhost:1080"
+            proxy_uri = "http://hello:iloveyou@localhost:51080"
         else:
             proxyauth = None
-            proxy_uri = "http://localhost:1080"
-        async with async_proxy(mode=["socks5"], proxyauth=proxyauth) as record_flows:
+            proxy_uri = "http://localhost:51080"
+        async with async_proxy(
+            mode=["socks5@51080"],
+            proxyauth=proxyauth,
+        ) as record_flows:
             with patch_environ({"socks_proxy": proxy_uri}):
                 yield record_flows
 
@@ -602,14 +598,62 @@ async def test_authenticated_socks_proxy(self):
                     self.assertEqual(client.protocol.state.name, "OPEN")
         self.assertEqual(len(proxy.get_flows()), 1)
 
+    async def test_socks_proxy_connection_error(self):
+        """Client receives an error when connecting to the SOCKS5 proxy."""
+        from python_socks import ProxyError as SocksProxyError
+
+        async with self.socks_proxy(auth=True) as proxy:
+            with self.assertRaises(ProxyError) as raised:
+                async with connect(
+                    "ws://example.com/",
+                    proxy="socks5h://localhost:51080",  # remove credentials
+                ):
+                    self.fail("did not raise")
+        self.assertEqual(
+            str(raised.exception),
+            "failed to connect to SOCKS proxy",
+        )
+        self.assertIsInstance(raised.exception.__cause__, SocksProxyError)
+        self.assertEqual(len(proxy.get_flows()), 0)
+
+    async def test_socks_proxy_connection_fails(self):
+        """Client fails to connect to the SOCKS5 proxy."""
+        from python_socks import ProxyConnectionError as SocksProxyConnectionError
+
+        with self.assertRaises(OSError) as raised:
+            async with connect(
+                "ws://example.com/",
+                proxy="socks5h://localhost:51080",  # nothing at this address
+            ):
+                self.fail("did not raise")
+        # Don't test str(raised.exception) because we don't control it.
+        self.assertIsInstance(raised.exception, SocksProxyConnectionError)
+
+    async def test_socks_proxy_connection_timeout(self):
+        """Client times out while connecting to the SOCKS5 proxy."""
+        # Replace the proxy with a TCP server that does't respond.
+        with socket.create_server(("localhost", 0)) as sock:
+            host, port = sock.getsockname()
+            with self.assertRaises(TimeoutError) as raised:
+                async with connect(
+                    "ws://example.com/",
+                    proxy=f"socks5h://{host}:{port}/",
+                    open_timeout=MS,
+                ):
+                    self.fail("did not raise")
+        self.assertEqual(
+            str(raised.exception),
+            "timed out during handshake",
+        )
+
     async def test_explicit_proxy(self):
         """Client connects to server through a proxy set explicitly."""
-        async with async_proxy(mode=["socks5"]) as proxy:
+        async with async_proxy(mode=["socks5@51080"]) as proxy:
             async with serve(*args) as server:
                 async with connect(
                     get_uri(server),
                     # Take this opportunity to test socks5 instead of socks5h.
-                    proxy="socks5://localhost:1080",
+                    proxy="socks5://localhost:51080",
                 ) as client:
                     self.assertEqual(client.protocol.state.name, "OPEN")
         self.assertEqual(len(proxy.get_flows()), 1)
@@ -626,13 +670,13 @@ async def test_ignore_proxy_with_existing_socket(self):
 
     async def test_unsupported_proxy(self):
         """Client connects to server through an unsupported proxy."""
-        with patch_environ({"ws_proxy": "other://localhost:1080"}):
+        with patch_environ({"ws_proxy": "other://localhost:51080"}):
             with self.assertRaises(InvalidProxy) as raised:
                 async with connect("ws://example.com/"):
                     self.fail("did not raise")
         self.assertEqual(
             str(raised.exception),
-            "other://localhost:1080 isn't a valid proxy: scheme other isn't supported",
+            "other://localhost:51080 isn't a valid proxy: scheme other isn't supported",
         )
 
 

tests/asyncio/test_server.py

@@ -65,9 +65,9 @@ async def test_connection_handler_raises_exception(self):
     async def test_existing_socket(self):
         """Server receives connection using a pre-existing socket."""
         with socket.create_server(("localhost", 0)) as sock:
-            async with serve(handler, sock=sock, host=None, port=None):
-                uri = "ws://{}:{}/".format(*sock.getsockname())
-                async with connect(uri) as client:
+            host, port = sock.getsockname()
+            async with serve(handler, sock=sock):
+                async with connect(f"ws://{host}:{port}/") as client:
                     await self.assertEval(client, "ws.protocol.state.name", "OPEN")
 
     async def test_select_subprotocol(self):