feat(storage): log additional bytes received from GCS in read path

[nidhiii-27]

When the GCS client requests a specific range of bytes but the transport provides more bytes than expected, we now emit a warning log. This matches the behavior of other GCS client libraries and aids in debugging. Decompressed objects are ignored because their wire size varies from the requested size.

Fixes: #475824752

[Generated-by: AI]

[gemini-code-assist]

Code Review

This pull request introduces tracking of the total bytes received during GCS object reads in ObjectReadStreambuf to log a warning if more bytes are received than requested. The review feedback highlights three main areas for improvement: first, total_bytes_received_ is only updated in xsgetn() and must also be updated in underflow() to prevent under-counting; second, a defensive check is needed to ensure range.end > range.begin to avoid incorrect negative expected byte calculations; and finally, for consistency, the member variable transformation_ should be accessed directly instead of using the transformation() accessor.

[gemini-code-assist]

The total_bytes_received_ counter is only updated here in xsgetn(). However, ObjectReadStreambuf also overrides underflow() to handle buffered/single-character reads (e.g., via std::getline or operator>>). If a user reads from the stream using those methods, underflow() will read from the source but total_bytes_received_ will not be incremented, leading to an under-count and missed warnings.

Please ensure total_bytes_received_ is also updated in underflow(), or refactor the byte-tracking logic into a common helper method called by both xsgetn() and underflow().

[gemini-code-assist]

If ReadRange is configured such that range.end <= range.begin (or if it represents an open-ended range where end is not set/defaults to 0), range.end - range.begin will be negative or zero. This would cause total_bytes_received_ > *expected_bytes_ to evaluate to true incorrectly, triggering false warning logs.

We should defensively check that range.end > range.begin before returning the difference.

  if (request.HasOption<ReadRange>()) {
    auto const& range = request.GetOption<ReadRange>().value();
    if (range.end > range.begin) {
      return range.end - range.begin;
    }
    return absl::nullopt;
  }

References

1. Prefer defensive code, such as explicit checks, even if they seem redundant based on the current implementation of a framework, as the framework's contract may change in the future.

[gemini-code-assist]

For consistency with how other member variables (like expected_bytes_, total_bytes_received_, bucket_name_, and object_name_) are accessed in this function and in xsgetn(), we should access the member variable transformation_ directly instead of calling the accessor method transformation().

    if (!transformation_.has_value()) {

[nidhiii-27]

Addressed all PR review comments.