Getting raw exceptions instead of httpcore.ConnectError when using trio

[florimondmanca]

Description

Looks like we're missing an edge case in our trio backend — getting an OSError, socket.gaierror, etc, instead of a properly wrapped httpcore.ConnectError when requesting an unknown host.

Reproduces when using backend="anyio" too, as well as various versions of trio (0.17.*, 0.16.*), and on Python 3.8 and Python 3.9.

To reproduce

Assuming there's no server running on localhost:8000, run this script…

import httpcore
import trio

@trio.run
async def main() -> None:
 async with httpcore.AsyncConnectionPool() as http:
 method = b"GET"
 url = (b"http", b"localhost", 8000, b"/")
 await http.arequest(method, url)

Expected behavior

Should be like when running on asyncio, i.e. raise a proper httpcore.ConnectError():

import asyncio
import httpcore

async def main() -> None:
 async with httpcore.AsyncConnectionPool() as http:
 method = b"GET"
 url = (b"http", b"localhost", 8000, b"/")
 await http.arequest(method, url)

asyncio.run(main())

Traceback (most recent call last):
 File "/Users/florimond/Developer/python-projects/httpcore/debug/client.py", line 14, in <module>
 asyncio.run(main())
 File "/Users/florimond/.pyenv/versions/3.9.0/lib/python3.9/asyncio/runners.py", line 44, in run
 return loop.run_until_complete(main)
 File "/Users/florimond/.pyenv/versions/3.9.0/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
 return future.result()
 File "/Users/florimond/Developer/python-projects/httpcore/debug/client.py", line 11, in main
 await http.arequest(method, url)
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection_pool.py", line 218, in arequest
 response = await connection.arequest(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection.py", line 92, in arequest
 self.socket = await self._open_socket(timeout)
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection.py", line 118, in _open_socket
 return await self.backend.open_tcp_stream(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_backends/auto.py", line 44, in open_tcp_stream
 return await self.backend.open_tcp_stream(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_backends/asyncio.py", line 243, in open_tcp_stream
 return SocketStream(
 File "/Users/florimond/.pyenv/versions/3.9.0/lib/python3.9/contextlib.py", line 135, in __exit__
 self.gen.throw(type, value, traceback)
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_exceptions.py", line 12, in map_exceptions
 raise to_exc(exc) from None
httpcore.ConnectError: Multiple exceptions: [Errno 61] Connect call failed ('127.0.0.1', 8000), [Errno 61] Connect call failed ('::1', 8000, 0, 0), [Errno 61] Connect call failed ('fe80::1', 8000, 0, 1)

Actual behavior

We get a raw OSError:

trio.MultiError: ConnectionRefusedError(61, 'Error in connect: Connection refused'), ConnectionRefusedError(61, 'Error in connect: Connection refused'), ConnectionRefusedError(61, 'Error in connect: Connection refused')

Details of embedded exception 1:

 Traceback (most recent call last):
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_highlevel_open_tcp_stream.py", line 332, in attempt_connect
 await sock.connect(sockaddr)
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_socket.py", line 682, in connect
 raise OSError(err, "Error in connect: " + os.strerror(err))
 ConnectionRefusedError: [Errno 61] Error in connect: Connection refused

Details of embedded exception 2:

 Traceback (most recent call last):
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_highlevel_open_tcp_stream.py", line 332, in attempt_connect
 await sock.connect(sockaddr)
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_socket.py", line 682, in connect
 raise OSError(err, "Error in connect: " + os.strerror(err))
 ConnectionRefusedError: [Errno 61] Error in connect: Connection refused

Details of embedded exception 3:

 Traceback (most recent call last):
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_highlevel_open_tcp_stream.py", line 332, in attempt_connect
 await sock.connect(sockaddr)
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_socket.py", line 682, in connect
 raise OSError(err, "Error in connect: " + os.strerror(err))
 ConnectionRefusedError: [Errno 61] Error in connect: Connection refused

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
 File "/Users/florimond/Developer/python-projects/httpcore/debug/client.py", line 6, in <module>
 async def main() -> None:
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_core/_run.py", line 1928, in run
 raise runner.main_task_outcome.error
 File "/Users/florimond/Developer/python-projects/httpcore/debug/client.py", line 10, in main
 await http.arequest(method, url)
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection_pool.py", line 218, in arequest
 response = await connection.arequest(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection.py", line 92, in arequest
 self.socket = await self._open_socket(timeout)
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_async/connection.py", line 118, in _open_socket
 return await self.backend.open_tcp_stream(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_backends/auto.py", line 44, in open_tcp_stream
 return await self.backend.open_tcp_stream(
 File "/Users/florimond/Developer/python-projects/httpcore/httpcore/_backends/trio.py", line 154, in open_tcp_stream
 stream: trio.abc.Stream = await trio.open_tcp_stream(
 File "/Users/florimond/Developer/python-projects/httpcore/venv/lib/python3.9/site-packages/trio/_highlevel_open_tcp_stream.py", line 367, in open_tcp_stream
 raise OSError(msg) from trio.MultiError(oserrors)
OSError: all attempts to connect to localhost:8000 failed

If we change the URL to point to an external host, like doesnotexistatall.org, we get a socket.gaierror:

[...]
socket.gaierror: [Errno 8] nodename nor servname provided, or not known