Implement concurrent downloads and resumable chunked uploads for GCS #31
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- Enable parallel downloads with 4MB chunks and 5 concurrent workers for improved performance on large objects
- putOnce renamed as putResumable - chunk size set to 100MB by default as in fog client - eventhough chunking the upload, still serial no concurrency
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Context
The GCS client currently performs single-threaded downloads and uploads, which is inefficient for large files. Additionally, upload failures require retrying the entire file, wasting bandwidth on unreliable networks.
Solution
Concurrent Downloads
Implemented parallel downloads using transfermanager.NewDownloader with 5 concurrent workers and 4MB chunks
Also for encrypted objects falls back to single-stream (transfermanager incompatibility)
Resumable Chunked Uploads
Configured GCS Writer with 100MB chunk size (matching fog-google client). Enables automatic per-chunk retry instead of whole-file retry. Uploads remain sequential (GCS SDK limitation - no NewUploader equivalent)
Chunking provides resumability and memory efficiency, not speed improvement for uploads.