socket_mode Connection: Add support for IPv6

[KostyaEsmukov]

Summary

The current implementation uses hardcoded AF_INET (IPv4) family and a first DNS record for connection. This doesn't work in IPv6-only environments (via NAT64):

ERROR:slack_sdk.rtm_v2:Failed to establish a connection (session id: <STRIPPED>, error: [Errno -2] Name or service not known)
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/slack_sdk/socket_mode/builtin/connection.py", line 116, in connect
    trace_enabled=self.trace_enabled,
  File "/usr/lib/python3/dist-packages/slack_sdk/socket_mode/builtin/internals.py", line 123, in _establish_new_socket_connection
    sock.connect((server_hostname, server_port))
  File "/usr/lib/python3.6/ssl.py", line 1109, in connect
    self._real_connect(addr, False)
  File "/usr/lib/python3.6/ssl.py", line 1096, in _real_connect
    socket.connect(self, addr)
socket.gaierror: [Errno -2] Name or service not known

This is fixed here by switching to the socket.create_connection function, which correctly handles IPv4+IPv6 families and additionally iterates through all DNS records until the connection is made.

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.models (UI component builders)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.scim (SCIM API client)
• slack_sdk.rtm (RTM client)
• slack_sdk.signature (Request Signature Verifier)
• /docs-src (Documents, have you run ./docs.sh?)
• /docs-src-v2 (Documents, have you run ./docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python setup.py validate after making the changes. [Some e2e tests don't pass with a ConnectionResetError: [Errno 54] Connection reset by peer error]

[codecov]

Codecov Report

Merging #1036 (aa19a09) into main (32d8ae9) will increase coverage by 0.07%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##             main    #1036      +/-   ##
==========================================
+ Coverage   84.34%   84.41%   +0.07%     
==========================================
  Files          95       95              
  Lines        8877     8869       -8     
==========================================
  Hits         7487     7487              
+ Misses       1390     1382       -8     

Impacted Files	Coverage Δ
slack_sdk/socket_mode/builtin/internals.py	48.43% <20.00%> (+0.37%)	⬆️
slack_sdk/socket_mode/client.py	72.56% <0.00%> (+2.65%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 32d8ae9...aa19a09. Read the comment docs.

[seratch]

Hi @KostyaEsmukov, thanks for taking the time to make this pull request! It looks great to me but I would like to verify the behavior with proxy before merging this change (As codecov pointed out, the pattern with proxy is not covered by unit tests yet).

The integration tests have a few proxy examples. I will manually check the behavior later in my timezone (+09:00) https://github.com/slackapi/python-slack-sdk/blob/main/integration_tests/samples/socket_mode/builtin_proxy_example.py

[seratch]

Thanks a lot for the perfect work. I've manually verified if there is no regression with this change with the proxy settings. Looks great to me 👍