Equivalent anyio code raises SSLSyscallError

[Bluenix2]

I've been having super weird issues with closing up an AnyIO socket, no matter what I do. It doesn't want me to receive any more data, I can't send, and when I try to close the socket I get an error ¯_(ツ)_/¯

Here is the socket code:

import json
import random
import socket
import ssl
from sys import platform
from time import sleep

import certifi
from wsproto.events import AcceptConnection, Request, TextMessage, CloseConnection
from wsproto import WSConnection, ConnectionType

TOKEN = ...  # IMPORTANT: Replace this

RECV_SIZE = 65536

SERVER_NAME = 'gateway.discord.gg'
SERVER_PORT = 443

def receive_event(ws, connection):
    while True:
        data = connection.recv(RECV_SIZE)
        assert data  # We should've gotten data (not empty)
        ws.receive_data(data)

        for event in ws.events():
            if not isinstance(event, TextMessage):
                # We don't really care about any other event
                continue

            return json.loads(event.data)

# Configure TLS context for WebSocket *Secure*
ctx = ssl.create_default_context(cafile=certifi.where())

# Open the underlying socket
sock = socket.create_connection((SERVER_NAME, SERVER_PORT))
sock = ctx.wrap_socket(sock, server_hostname=SERVER_NAME)

# WSProto handles the actual WebSocket connection for us
conn = WSConnection(ConnectionType.CLIENT)
sock.send(conn.send(Request(SERVER_NAME, target='/?v=9&encoding=json')))

# Receive until we get the acceptance of the connection
acceptance = None
while acceptance is not None:
    conn.receive_data(sock.recv(RECV_SIZE))
    for acceptance in conn.events():
        assert isinstance(acceptance, AcceptConnection)
        break

# Receive the HELLO event
hello = receive_event(conn, sock)
print(hello)

# Send the IDENTIFY command
sock.send(conn.send(TextMessage(
    json.dumps({
        'op': 2,
        'd': {
            'token': TOKEN,
            'intents': 0,
            'properties': {
                '$os': platform,
                '$browser': 'Testing',
                '$device': 'Testing'
            }
    }})
)))

# We should now be receiving the READY event
ready = receive_event(conn, sock)
print(ready)

# After this, because we don't HEARTBEAT and IDENTIFied with no intents, we
# should be getting no more events. Discord will eventually disconnect us
# after roughly a minute, this is the bug-part.
event = None
while event is None:
    conn.receive_data(sock.recv(RECV_SIZE))
    for event in conn.events():
        assert isinstance(event, CloseConnection)

        # In the WebSocket protocol a closure requires both sides to respond
        # to the closure.
        sock.send(conn.send(event.response()))
        break

# We have responded to the WebSocket close frame, we now need to shut down
# the socket
print('Closing connection')
sock.shutdown(socket.SHUT_WR)
sock.close()

But then when I try to migrate to AnyIO, like this:

import anyio
import json
import random
import ssl
from sys import platform
from time import sleep

import certifi
from wsproto.events import AcceptConnection, Request, TextMessage, CloseConnection
from wsproto import WSConnection, ConnectionType

TOKEN = ...  # IMPORTANT: Replace this

RECV_SIZE = 65536

SERVER_NAME = 'gateway.discord.gg'
SERVER_PORT = 443

async def receive_event(ws, connection):
    while True:
        data = await connection.receive(RECV_SIZE)
        assert data  # We should've gotten data (not empty)
        ws.receive_data(data)

        for event in ws.events():
            if not isinstance(event, TextMessage):
                # We don't really care about any other event
                continue

            return json.loads(event.data)

sock = await anyio.connect_tcp(SERVER_NAME, SERVER_PORT, tls=True)

# WSProto handles the actual WebSocket connection for us
conn = WSConnection(ConnectionType.CLIENT)
await sock.send(conn.send(Request(SERVER_NAME, target='/?v=9&encoding=json')))

# Receive until we get the acceptance of the connection
acceptance = None
while acceptance is not None:
    conn.receive_data(await sock.receive(RECV_SIZE))
    for acceptance in conn.events():
        assert isinstance(acceptance, AcceptConnection)
        break

# Receive the HELLO event
hello = await receive_event(conn, sock)
print(hello)

# Send the IDENTIFY command
await sock.send(conn.send(TextMessage(
    json.dumps({
        'op': 2,
        'd': {
            'token': TOKEN,
            'intents': 0,
            'properties': {
                '$os': platform,
                '$browser': 'Testing',
                '$device': 'Testing'
            }
    }})
)))

# We should now be receiving the READY event
ready = await receive_event(conn, sock)
print(ready)

# After this, because we don't HEARTBEAT and IDENTIFied with no intents, we
# should be getting no more events. Discord will eventually disconnect us
# after roughly a minute, this is the bug-part.
event = None
while event is None:
    conn.receive_data(await sock.receive(RECV_SIZE))
    for event in conn.events():
        assert isinstance(event, CloseConnection)

        # In the WebSocket protocol a closure requires both sides to respond
        # to the closure.
        await sock.send(conn.send(event.response()))
        break

# We have responded to the WebSocket close frame, we now need to shut down
# the socket
await sock.aclose()

I now get the following error:

---------------------------------------------------------------------------
SSLSyscallError                           Traceback (most recent call last)
~\AppData\Local\Programs\Python\Python39\lib\site-packages\anyio\streams\tls.py in _call_sslobject_method(self, func, *args)
    101             try:
--> 102                 result = func(*args)
    103             except ssl.SSLWantReadError:

~\AppData\Local\Programs\Python\Python39\lib\ssl.py in unwrap(self)
    947         """Start the SSL shutdown handshake."""
--> 948         return self._sslobj.shutdown()
    949 

SSLSyscallError: Some I/O error occurred (_ssl.c:2756)

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

BrokenResourceError                       Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_15900/2276960278.py in <module>
     84 # We have responded to the WebSocket close frame, we now need to shut down
     85 # the socket
---> 86 await sock.aclose()

~\AppData\Local\Programs\Python\Python39\lib\site-packages\anyio\streams\tls.py in aclose(self)
    142         if self.standard_compatible:
    143             try:
--> 144                 await self.unwrap()
    145             except BaseException:
    146                 await aclose_forcefully(self.transport_stream)

~\AppData\Local\Programs\Python\Python39\lib\site-packages\anyio\streams\tls.py in unwrap(self)
    134 
    135         """
--> 136         await self._call_sslobject_method(self._ssl_object.unwrap)
    137         self._read_bio.write_eof()
    138         self._write_bio.write_eof()

~\AppData\Local\Programs\Python\Python39\lib\site-packages\anyio\streams\tls.py in _call_sslobject_method(self, func, *args)
    119                 await self.transport_stream.send(self._write_bio.read())
    120             except (ssl.SSLEOFError, ssl.SSLSyscallError) as exc:
--> 121                 raise BrokenResourceError from exc
    122             else:
    123                 # Flush any pending writes first

BrokenResourceError:

This is just a simple reproduceable of my real code on GitHub.

[agronholm]

HTTP connections need tls_standard_compatible=False because such servers abruptly close the connection without performing the closing handshake.