fix(storage): allow setting full checksum at finalize for appendable uploads

[v-pratap]

Fixes the checksum validation logic at the end of appendable uploads so users can provide a final expected CRC.

[gemini-code-assist]

Code Review

This pull request updates the AsyncWriterConnectionImpl::Finalize method to handle manual CRC32C checksum injection via UseCrc32cValueOption and to avoid sending partial CRCs for appendable uploads. The reviewer identified a critical inconsistency in how current_options and options_ are checked for the CRC option, which could lead to the option being ignored or the upload failing. A consistent check across both option sources was suggested to resolve this issue.

[gemini-code-assist]

There is an inconsistency in how current_options and options_ are checked. If UseCrc32cValueOption is provided via the connection's options_ but not in the thread-local current_options, the first if condition is skipped, and the else if condition is also skipped (since options_->has<...>() is true). This results in action remaining kFinalizeWithChecksum without actually setting the CRC on the request, which will cause the upload to fail or ignore the user-provided CRC.

We should check both current_options and options_ consistently for the CRC option.

  auto const& current_options = google::cloud::internal::CurrentOptions();
  auto has_crc_option = current_options.has<google::cloud::storage::UseCrc32cValueOption>() ||
                        options_->has<google::cloud::storage::UseCrc32cValueOption>();

  // Default to letting the internal hash function compute and send the checksum.
  auto action = PartialUpload::kFinalizeWithChecksum;

  if (has_crc_option) {
    // The user provided a final CRC. We manually inject it into the request.
    // We use kFinalize so the internal hash function doesn't overwrite it.
    auto crc = current_options.has<google::cloud::storage::UseCrc32cValueOption>()
                   ? current_options.get<google::cloud::storage::UseCrc32cValueOption>()
                   : options_->get<google::cloud::storage::UseCrc32cValueOption>();
    write.mutable_object_checksums()->set_crc32c(crc);
    action = PartialUpload::kFinalize;
  } else if (is_append) {
    // For appendable uploads, the internal hash function only sees the chunks uploaded
    // in this stream, not the full object. We use kFinalize to avoid sending this
    // partial CRC, which would otherwise fail validation.
    action = PartialUpload::kFinalize;
  }

[codecov]

Codecov Report

❌ Patch coverage is 98.05825% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.26%. Comparing base (4d78d42) to head (bf842c3).

Files with missing lines	Patch %	Lines
...rage/internal/async/writer_connection_impl_test.cc	97.84%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16251   +/-   ##
=======================================
  Coverage   92.26%   92.26%           
=======================================
  Files        2214     2214           
  Lines      206307   206406   +99     
=======================================
+ Hits       190348   190447   +99     
  Misses      15959    15959           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.