fix(storage): Fix Resume() to use append_object_spec instead of write_object_spec for resumed appendable uploads by shubham-up-47 · Pull Request #15558

fix(storage): Fix Resume() to use append_object_spec instead of write_object_spec for resumed appendable uploads by shubham-up-47 · Pull Request #15558 · googleapis/google-cloud-cpp

This PR corrects the logic in AsyncWriterConnectionResumedState::Resume() where it incorrectly assumed initial_request_ would always contain an write_object_spec. This assumption fails when resuming an upload that was initiated with ResumeAppendableObjectUpload, which uses append_object_spec, which leads to passing the bucket and object names empty.

The fix introduces a check to determine whether initial_request_ contains a write_object_spec or an append_object_spec, and then correctly extracts the bucket and object names from the available spec. This approach aligns with the pattern already used in WriteResultFactory for handling these two types of specifications.

This change is