Fix race condition in replication

app/replication.py

@@ -308,7 +308,8 @@ class ReplicationManager:
 
             logger.info(f"Replicating {bucket_name}/{object_key}: Size={file_size}, ContentType={content_type}")
 
-            try:
+            def do_put_object() -> None:
+                """Helper to upload object."""
                 with path.open("rb") as f:
                     s3.put_object(
                         Bucket=rule.target_bucket,
@@ -318,32 +319,37 @@ class ReplicationManager:
                         ContentType=content_type or "application/octet-stream",
                         Metadata=metadata or {}
                     )
+
+            try:
+                do_put_object()
             except (ClientError, S3UploadFailedError) as e:
-                is_no_bucket = False
+                error_code = None
                 if isinstance(e, ClientError):
-                    if e.response['Error']['Code'] == 'NoSuchBucket':
-                        is_no_bucket = True
+                    error_code = e.response['Error']['Code']
                 elif isinstance(e, S3UploadFailedError):
                     if "NoSuchBucket" in str(e):
-                        is_no_bucket = True
+                        error_code = 'NoSuchBucket'
 
-                if is_no_bucket:
+                # Handle NoSuchBucket - create bucket and retry
+                if error_code == 'NoSuchBucket':
                     logger.info(f"Target bucket {rule.target_bucket} not found. Attempting to create it.")
+                    bucket_ready = False
                     try:
                         s3.create_bucket(Bucket=rule.target_bucket)
-                        # Retry upload
-                        with path.open("rb") as f:
-                            s3.put_object(
-                                Bucket=rule.target_bucket,
-                                Key=object_key,
-                                Body=f,
-                                ContentLength=file_size,
-                                ContentType=content_type or "application/octet-stream",
-                                Metadata=metadata or {}
-                            )
-                    except Exception as create_err:
-                        logger.error(f"Failed to create target bucket {rule.target_bucket}: {create_err}")
-                        raise e # Raise original error
+                        bucket_ready = True
+                        logger.info(f"Created target bucket {rule.target_bucket}")
+                    except ClientError as bucket_err:
+                        # BucketAlreadyExists or BucketAlreadyOwnedByYou means another thread created it - that's OK!
+                        if bucket_err.response['Error']['Code'] in ('BucketAlreadyExists', 'BucketAlreadyOwnedByYou'):
+                            logger.debug(f"Bucket {rule.target_bucket} already exists (created by another thread)")
+                            bucket_ready = True
+                        else:
+                            logger.error(f"Failed to create target bucket {rule.target_bucket}: {bucket_err}")
+                            raise e  # Raise original NoSuchBucket error
+                    
+                    if bucket_ready:
+                        # Retry the upload now that bucket exists
+                        do_put_object()
                 else:
                     raise e
             
@@ -354,3 +360,4 @@ class ReplicationManager:
             logger.error(f"Replication failed for {bucket_name}/{object_key}: {e}")
         except Exception:
             logger.exception(f"Unexpected error during replication for {bucket_name}/{object_key}")
+