Module download 

Streaming download implementation.

Protocol

1. Acquire a scoped resource lock via LockRegistry.
2. Emit transfer:state { state: running }.
3. Issue GetObject — obtain content_length and the body ByteStream.
4. Open <dest>.partial for writing (atomic rename on success).
5. Stream 256 KB chunks; for each chunk: write to file, increment transferred_bytes, call emit_progress (throttled).
6. Poll the cancel receiver between chunks.
7. On cancel: delete .partial, emit Canceled, release lock with Cancel.
8. On success: rename .partial → final, emit Done, release lock.
9. On I/O or S3 error: delete .partial, emit Failed, release lock.

OCP contract

The atomic .partial rename pattern and lock acquire/release sequence are reusable for any downloaded asset. Upload (task 32) acquires the same lock registry with a different op_name.

Constants

CHUNK_SIZE 🔒

Bytes per read chunk — 256 KB.

Functions

cleanup_on_error 🔒

Error path: delete .partial (if any), emit Failed, release lock.

download_object

Stream-download key from bucket and write it atomically to dest_path.

handle_cancel 🔒

Cancel path: delete .partial, emit Canceled, release lock.

now_ms 🔒

now_secs 🔒