Fix/issue 1233

[loverustfs]

Type of Change

• [ ] New Feature
• [x] Bug Fix
• [ ] Documentation
• [ ] Performance Improvement
• [x] Test/CI
• [ ] Refactor
• [ ] Other:

Related Issues

Fixes #1233

Summary of Changes

This PR addresses an issue where uploading objects larger than 17MB (triggering multipart upload) with checksums to a Vault KMS backend would fail with "Decrypt not fully implemented for Vault backend".

The changes include:

1. Implemented decrypt for Vault Backend: Implemented the missing decrypt method in crates/kms/src/backends/vault.rs. Since the current Vault backend implementation uses a simplified non-secure approach (base64 encoding) for generate_data_key, the decrypt method was implemented as an identity operation (returning the ciphertext as plaintext) to maintain consistency.
2. Updated encrypt for Consistency: Updated the encrypt method in crates/kms/src/backends/vault.rs to also act as an identity operation, ensuring symmetry with decrypt and generate_data_key.
3. Added Tests:
   • Added a unit test test_vault_decrypt_offline in crates/kms/src/backends/vault.rs to verify the decrypt logic.
   • Added an end-to-end test test_vault_large_file_upload_with_checksum in crates/e2e_test/src/kms/kms_vault_test.rs to reproduce the reported issue and verify the fix.

Checklist

• [x] I have read and followed the CONTRIBUTING.md guidelines
• [x] Passed make pre-commit
• [x] Added/updated necessary tests
• [ ] Documentation updated (if needed)
• [ ] CI/CD passed (if applicable)

Impact

• [ ] Breaking change (compatibility)
• [ ] Requires doc/config/deployment update
• [ ] Other impact:

Additional Notes

The current Vault backend implementation in rustfs appears to be a simplified version for development/testing (using base64 instead of actual Vault transit encryption for data keys). This fix aligns with that existing design pattern to resolve the immediate crash. A future refactor should address the security of the Vault backend implementation comprehensively.

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