fix(storage): add samples for bucket encryption enforcement config

[bajajneha27]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces support for bucket encryption enforcement configurations (GMEK, CMEK, and CSEK) and removes the effectiveTime field from metadata parsing and serialization in both REST and gRPC paths. It also adds a new example file for managing these enforcement policies. Feedback focuses on ensuring consistent error handling for StatusOr objects and correcting logic in the update example to avoid overwriting existing configurations with hardcoded values.

[gemini-code-assist]

The StatusOr<T> returned by GetBucketMetadata should be checked for an error before being dereferenced. While dereferencing a StatusOr with an error will throw an exception, the idiomatic and recommended approach is to check its status explicitly, as is done in other examples in this file. This ensures consistent error handling and makes the code's intent clearer.

    StatusOr<gcs::BucketMetadata> original = client.GetBucketMetadata(bucket_name);
    if (!original) throw std::move(original).status();

    gcs::BucketMetadata updated_metadata = *original;

[gemini-code-assist]

The comment on these lines is misleading, and the code is incorrect if the intention is to preserve the existing configuration for CSEK. The encryption object is initialized with the bucket's existing configuration. By not modifying encryption.customer_supplied_encryption_enforcement_config, its value is preserved. These lines overwrite the preserved value with a hardcoded one and should be removed.

[codecov]

Codecov Report

❌ Patch coverage is 94.95798% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.96%. Comparing base (2708d95) to head (8f7680d).

Files with missing lines	Patch %	Lines
...s/storage_bucket_encryption_enforcement_samples.cc	95.61%	5 Missing ⚠️
google/cloud/storage/bucket_metadata.cc	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           v2.47.x   #16062   +/-   ##
========================================
  Coverage    92.96%   92.96%           
========================================
  Files         2460     2461    +1     
  Lines       228901   228990   +89     
========================================
+ Hits        212807   212890   +83     
- Misses       16094    16100    +6     

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