gcs-s3-compat-acl-rejection

name	gcs-s3-compat-acl-rejection
description	Fix S3 "InvalidArgument" errors when using Google Cloud Storage S3-compatible API with ObjectCannedAcl::PublicRead or x-amz-acl headers. Use when: (1) put_object or upload_blob fails with InvalidArgument on GCS, (2) Using aws-sdk-s3 Rust crate with GCS endpoint (storage.googleapis.com), (3) Bucket has uniform bucket-level access enabled (GCS default since 2023), (4) S3 operations work on MinIO/AWS but fail on GCS. GCS rejects per-object ACLs when uniform bucket-level access is enabled.
author	Claude Code
version	1.0.0
date	"2026-03-21T00:00:00.000Z"

GCS S3-Compatible API ACL Rejection

Problem

S3 put_object calls fail with InvalidArgument when targeting Google Cloud Storage via its S3-compatible API, despite working correctly with MinIO or AWS S3.

Context / Trigger Conditions

• Using aws-sdk-s3 (Rust) or any S3 SDK with GCS endpoint
• AWS_ENDPOINT=https://storage.googleapis.com
• Error: Error { code: "InvalidArgument", message: "Invalid argument." }
• Stack trace shows S3BlobStore::put_temp or similar S3 put operation
• The GCS bucket has uniform bucket-level access enabled (GCS default)

Solution

Remove ObjectCannedAcl::PublicRead from put_object calls when using GCS:

// BEFORE (fails on GCS with uniform bucket-level access)
self.client
    .put_object()
    .body(body)
    .bucket(&self.s3_bucket)
    .key(key)
    .acl(ObjectCannedAcl::PublicRead)  // This causes InvalidArgument
    .send()
    .await?;

// AFTER (works with GCS)
self.client
    .put_object()
    .body(body)
    .bucket(&self.s3_bucket)
    .key(key)
    // Remove .acl() — use bucket-level IAM instead
    .send()
    .await?;

For public read access, configure the bucket IAM policy instead:

gsutil iam ch allUsers:objectViewer gs://YOUR_BUCKET

Or disable uniform bucket-level access (not recommended):

gsutil ubla set off gs://YOUR_BUCKET

Verification

After removing the .acl() call, upload should succeed:

curl -X POST "$PDS_URL/xrpc/com.atproto.repo.uploadBlob" \
  -H "Authorization: Bearer $JWT" \
  -H "Content-Type: video/mp4" \
  --data-binary @test.mp4

Notes

• GCS uniform bucket-level access has been the default since 2023
• The copy_object call in move_object() also uses .acl(PublicRead) and will fail
• This affects rsky-pds blob storage: rsky-pds/src/actor_store/aws/s3.rs lines 69, 97, 212
• MinIO doesn't enforce this restriction, so local dev works but production GCS fails
• The same issue applies to put_permanent() and move_object() methods