fix: auto-detect GCS endpoint for correct V4 signature config#635
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May 30, 2026 03:26
GCS S3-compatible API requires: - virtual-hosted-style addressing (not path-style) - region_name='auto' for V4 signatures Previously both clients were hardcoded to path-style addressing and used the raw S3_REGION value (often empty), causing SignatureDoesNotMatch on every put_object. Now _boto_config() auto-detects storage.googleapis.com and applies the correct settings, while MinIO and other S3 backends keep path-style addressing unchanged.
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Problem
GCS S3-compatible API continues to reject put_object with SignatureDoesNotMatch even after setting ContentType explicitly.
Root Cause
The boto3/aiobotocore clients were hardcoded to:
addressing_style: "path"— GCS S3 API requiresvirtual-hosted-styleregion_name: used rawS3_REGIONenv var (often empty) — GCS requires"auto"for V4 signaturesWith path-style addressing, GCS computes the signature over a different canonical request than what boto3 signs, causing an unrecoverable mismatch.
Fix
_boto_config()method used by both sync and async clientsstorage.googleapis.comin endpoint URL via_is_gcs()addressing_style=virtual,region_name=autopathstyle, user-specified region)Verification
Existing test
test_s3_backend_passes_max_pool_connectionspasses. The test creates a mock S3Backend — GCS detection is endpoint-based and only activates whenstorage.googleapis.comappears in the URL.