Add presigned URL support for direct S3 downloads (#48)

backend/app/storage.py

@@ -450,6 +450,46 @@ class S3Storage:
         except ClientError:
             return False
 
+    def generate_presigned_url(
+        self,
+        s3_key: str,
+        expiry: Optional[int] = None,
+        response_content_type: Optional[str] = None,
+        response_content_disposition: Optional[str] = None,
+    ) -> str:
+        """
+        Generate a presigned URL for downloading an object.
+
+        Args:
+            s3_key: The S3 key of the object
+            expiry: URL expiry in seconds (defaults to settings.presigned_url_expiry)
+            response_content_type: Override Content-Type header in response
+            response_content_disposition: Override Content-Disposition header in response
+
+        Returns:
+            Presigned URL string
+        """
+        if expiry is None:
+            expiry = settings.presigned_url_expiry
+
+        params = {
+            "Bucket": self.bucket,
+            "Key": s3_key,
+        }
+
+        # Add response header overrides if specified
+        if response_content_type:
+            params["ResponseContentType"] = response_content_type
+        if response_content_disposition:
+            params["ResponseContentDisposition"] = response_content_disposition
+
+        url = self.client.generate_presigned_url(
+            "get_object",
+            Params=params,
+            ExpiresIn=expiry,
+        )
+        return url
+
 
 # Singleton instance
 _storage = None