add `server_connect_error` hook (#6806)

* Add server connection error hook

* Add new hook to api-events doc

* Rename and add test

* Forgot to commit

* Small fix

* [autofix.ci] apply automated fixes

* fixed test_server.py

* fixed 'Import block is un-sorted or un-formatted'

* [autofix.ci] apply automated fixes

* test++, doc++

* add CHANGELOG entry

* [autofix.ci] apply automated fixes

* fix authors

* fix test

* [autofix.ci] apply automated fixes

---------

Co-authored-by: haanhvu <haanh6594@gmail.com>
Co-authored-by: spacewasp <spacewasp1982@gmail.com>

CHANGELOG.md

@@ -9,6 +9,8 @@
 
 * Add support for editing non text files in a hex editor
   ([#6768](https://github.com/mitmproxy/mitmproxy/pull/6768), @wnyyyy)
+* Add `server_connect_error` hook that is triggered when connection establishment fails.
+  ([#6806](https://github.com/mitmproxy/mitmproxy/pull/6806), @haanhvu, @spacewasp, @mhils)
 * Add section in mitmweb for rendering, adding and removing a comment
   ([#6709](https://github.com/mitmproxy/mitmproxy/pull/6709), @lups2000)
 * Fix multipart form content view being unusable.

docs/scripts/api-events.py

@@ -97,6 +97,7 @@ with outfile.open("w") as f, contextlib.redirect_stdout(f):
             server_hooks.ServerConnectHook,
             server_hooks.ServerConnectedHook,
             server_hooks.ServerDisconnectedHook,
+            server_hooks.ServerConnectErrorHook,
         ],
     )
 

mitmproxy/proxy/server.py

@@ -196,6 +196,7 @@ class ConnectionHandler(metaclass=abc.ABCMeta):
             self.log(
                 f"server connection to {human.format_address(command.connection.address)} killed before connect: {err}"
             )
+            await self.handle_hook(server_hooks.ServerConnectErrorHook(hook_data))
             self.server_event(
                 events.OpenConnectionCompleted(command, f"Connection killed: {err}")
             )
@@ -224,6 +225,7 @@ class ConnectionHandler(metaclass=abc.ABCMeta):
                     err = "connection cancelled"
                 self.log(f"error establishing server connection: {err}")
                 command.connection.error = err
+                await self.handle_hook(server_hooks.ServerConnectErrorHook(hook_data))
                 self.server_event(events.OpenConnectionCompleted(command, err))
                 if isinstance(e, asyncio.CancelledError):
                     # From https://docs.python.org/3/library/asyncio-exceptions.html#asyncio.CancelledError:
@@ -237,8 +239,11 @@ class ConnectionHandler(metaclass=abc.ABCMeta):
                 command.connection.state = ConnectionState.OPEN
                 command.connection.peername = writer.get_extra_info("peername")
                 command.connection.sockname = writer.get_extra_info("sockname")
-                self.transports[command.connection].reader = reader
-                self.transports[command.connection].writer = writer
+                self.transports[command.connection] = ConnectionIO(
+                    handler=asyncio.current_task(),
+                    reader=reader,
+                    writer=writer,
+                )
 
                 assert command.connection.peername
                 if command.connection.address[0] != command.connection.peername[0]:

mitmproxy/proxy/server_hooks.py

@@ -63,3 +63,14 @@ class ServerDisconnectedHook(commands.StartHook):
     """
 
     data: ServerConnectionHookData
+
+
+@dataclass
+class ServerConnectErrorHook(commands.StartHook):
+    """
+    Mitmproxy failed to connect to a server.
+
+    Every server connection will receive either a server_connected or a server_connect_error event, but not both.
+    """
+
+    data: ServerConnectionHookData

test/mitmproxy/proxy/test_server.py

@@ -0,0 +1,66 @@
+import asyncio
+import collections
+from unittest import mock
+
+import pytest
+
+from mitmproxy import options
+from mitmproxy.connection import Server
+from mitmproxy.proxy import commands
+from mitmproxy.proxy import server
+from mitmproxy.proxy import server_hooks
+from mitmproxy.proxy.mode_specs import ProxyMode
+
+
+class MockConnectionHandler(server.SimpleConnectionHandler):
+    hook_handlers: dict[str, mock.Mock]
+
+    def __init__(self):
+        super().__init__(
+            reader=mock.Mock(),
+            writer=mock.Mock(),
+            options=options.Options(),
+            mode=ProxyMode.parse("regular"),
+            hooks=collections.defaultdict(lambda: mock.Mock()),
+        )
+
+
+@pytest.mark.parametrize("result", ("success", "killed", "failed"))
+async def test_open_connection(result, monkeypatch):
+    handler = MockConnectionHandler()
+    server_connect = handler.hook_handlers["server_connect"]
+    server_connected = handler.hook_handlers["server_connected"]
+    server_connect_error = handler.hook_handlers["server_connect_error"]
+    server_disconnected = handler.hook_handlers["server_disconnected"]
+
+    match result:
+        case "success":
+            monkeypatch.setattr(
+                asyncio,
+                "open_connection",
+                mock.AsyncMock(return_value=(mock.MagicMock(), mock.MagicMock())),
+            )
+            monkeypatch.setattr(
+                MockConnectionHandler, "handle_connection", mock.AsyncMock()
+            )
+        case "failed":
+            monkeypatch.setattr(
+                asyncio, "open_connection", mock.AsyncMock(side_effect=OSError)
+            )
+        case "killed":
+
+            def _kill(d: server_hooks.ServerConnectionHookData) -> None:
+                d.server.error = "do not connect"
+
+            server_connect.side_effect = _kill
+
+    await handler.open_connection(
+        commands.OpenConnection(connection=Server(address=("server", 1234)))
+    )
+
+    assert server_connect.call_args[0][0].server.address == ("server", 1234)
+
+    assert server_connected.called == (result == "success")
+    assert server_connect_error.called == (result != "success")
+
+    assert server_disconnected.called == (result == "success")