impl(rest): map http code 504 to kUnavailable

[scotthart]

Upcoming RAB feature considers 504 retryable. Additionally, improve returned error status when no payload is available.

[gemini-code-assist]

Code Review

This pull request introduces the kGatewayTimeout (504) HTTP status code and maps it to StatusCode::kUnavailable. It also updates the AsStatus function to include the HTTP status code in the ErrorInfo metadata when the response payload is empty, with corresponding test updates. Feedback suggests consolidating the status mapping logic to include kBadGateway for consistency with existing tests and optimizing the AsStatus implementation by avoiding redundant string conversions of the status code.

[gemini-code-assist]

These checks can be combined for better readability. Additionally, it appears kBadGateway (502) is also expected to be mapped to kUnavailable based on the test cases (see line 83 of google/cloud/internal/rest_response_test.cc), but it is currently missing from this function. Consider adding it here.

  if (code == HttpStatusCode::kServiceUnavailable ||
      code == HttpStatusCode::kGatewayTimeout ||
      code == HttpStatusCode::kBadGateway) {
    return StatusCode::kUnavailable;
  }

[gemini-code-assist]

The HTTP status code is converted to a string twice. Consider converting it once to improve efficiency. Additionally, ensure to use std::move when passing the local ErrorInfo object to the Status constructor to avoid unnecessary copies, as per repository best practices.

    auto code_str = std::to_string(http_status_code);
    ErrorInfo error_info{{}, {}, {{"http_status_code", code_str}}};
    return Status(status_code, "Received HTTP status code: " + code_str,
                  std::move(error_info));

References

1. When passing a local object to a method that takes it by value, use std::move to avoid unnecessary copies.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.67%. Comparing base (7bc7f71) to head (39cd67c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16077   +/-   ##
=======================================
  Coverage   92.67%   92.67%           
=======================================
  Files        2343     2343           
  Lines      217117   217123    +6     
=======================================
+ Hits       201214   201221    +7     
+ Misses      15903    15902    -1     

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