fix infinite looping when socket goes stale in gevent

[abhinavabcd]

Summary

When Running in socket mode using gevent, after a while it just goes into infinite loop and becomes unresponsive.

Technically receive function can raise an exception on broken socket on certains errno,
instead of empty bytes indicating clean closure.

Testing

• Run after gevent patching.
• Disconnect network or let socket go inactive.
• CHeck the process stat, pyspy stuck in 100% cpu.

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)

• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)

• slack_sdk.socket_mode (Socket Mode client)

• slack_sdk.signature (Request Signature Verifier)

• slack_sdk.oauth (OAuth Flow Utilities)

• slack_sdk.models (UI component builders)

• slack_sdk.scim (SCIM API client)

• slack_sdk.audit_logs (Audit Logs API client)

• slack_sdk.rtm_v2 (RTM client)

• /docs (Documents)

• /tutorial (PythOnBoardingBot tutorial)

• tests/integration_tests (Automated tests for this library)

• 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 python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @abhinavabcd to sign the Salesforce Inc. Contributor License Agreement.

[WilliamBergamin]

I'm reluctant to approve these changes since this is a critical section of our project 🤔

Is there any clear documentation on which errno should raise an exception and which should return empty bytes?