fix: Improve type annotations in SignatureVerifier

[BHSPitMonkey]

Summary

Receive headers as abstract/immutable collections.abc.Mapping instead of Dict to more accurately declare compatibility with dict-like objects (common for holding headers in HTTP frameworks), and mark timestamp/signature args as Optional in is_valid to reflect reality and fix the typechecker errors in is_valid_request.

Testing

These changes only touch type annotations which have no runtime effects; The only expectation here is that type checks pass.

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)

Requirements

• 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 @BHSPitMonkey to sign the Salesforce Inc. Contributor License Agreement.

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
2	2	0	0

View the top 1 failed test(s) by shortest run time

::tests.slack_sdk.signature.test_signature_verifier

Stack Traces | 0s run time

#x1B[1m#x1B[.../slack_sdk/signature/test_signature_verifier.py#x1B[0m:3: in <module>
    from slack_sdk.signature import SignatureVerifier
#x1B[1m#x1B[31mslack_sdk/signature/__init__.py#x1B[0m:15: in <module>
    class SignatureVerifier:
#x1B[1m#x1B[31mslack_sdk/signature/__init__.py#x1B[0m:30: in SignatureVerifier
    headers: Mapping[str, str],
#x1B[1m#x1B[31mE   TypeError: 'ABCMeta' object is not subscriptable#x1B[0m

View the full list of 1 ❄️ flaky test(s)

::tests.signature.test_signature_verifier

Flake rate in main: 100.00% (Passed 0 times, Failed 57 times)

Stack Traces | 0s run time

#x1B[1m#x1B[31mtests/signature/test_signature_verifier.py#x1B[0m:3: in <module>
    from slack.signature import SignatureVerifier
#x1B[1m#x1B[31mslack/signature/__init__.py#x1B[0m:1: in <module>
    from slack_sdk.signature import SignatureVerifier  # noqa
#x1B[1m#x1B[31mslack_sdk/signature/__init__.py#x1B[0m:15: in <module>
    class SignatureVerifier:
#x1B[1m#x1B[31mslack_sdk/signature/__init__.py#x1B[0m:30: in SignatureVerifier
    headers: Mapping[str, str],
#x1B[1m#x1B[31mE   TypeError: 'ABCMeta' object is not subscriptable#x1B[0m

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[WilliamBergamin]

Hi @BHSPitMonkey thanks for opening this PR 🙏

Love seeing those # type: ignore go away!
Changes seem solid but aren't compatible with python 3.7 and 3.8, I left a comment on how to potentially address it, once resolved we should be good to merge

[WilliamBergamin]

For python 3.7 and 3.8 this Mapping type is not importable from collections.abc causing

slack_sdk/signature/__init__.py:30: in SignatureVerifier
    headers: Mapping[str, str],
E   TypeError: 'ABCMeta' object is not subscriptable

Importing Mapping as follows should fix the issue 🤔

from typing import TYPE_CHECKING,  Dict, Optional, Union

if TYPE_CHECKING:
    from collections.abc import Mapping
else:
    Mapping = Dict

[WilliamBergamin]

If we go this route, it might be a good idea to also include a comment about how this is for python 3.7 and 3.8 backwards compatibility

[BHSPitMonkey]

Argh, old Pythons strike again! But I like your proposed solution - Will push it with a comment shortly.