fix: send multipart encoding when using gcs_uri (fixes 400 error)

FastAPI requires multipart/form-data for endpoints with File()/Form()
parameters. When gcs_uri is used without a file upload, requests
defaulted to x-www-form-urlencoded, causing a 400 Bad Request.

Fix: send a dummy empty file field to force multipart encoding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: beveradb

audio_separator/remote/api_client.py

@@ -149,9 +149,14 @@ def separate_audio(
 
         try:
             # Increase timeout for large files (5 minutes)
+            # When using gcs_uri (no file upload), we still need multipart/form-data
+            # encoding because FastAPI requires it for endpoints with File()/Form() params.
+            # Passing a dummy empty file field forces requests to use multipart encoding.
+            if not files:
+                files = {"file": ("", b"", "application/octet-stream")}
             response = self.session.post(
                 f"{self.api_url}/separate",
-                files=files if files else None,
+                files=files,
                 data=data,
                 timeout=300,
             )

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]
 name = "audio-separator"
-version = "0.44.0"
+version = "0.44.1"
 description = "Easy to use audio stem separation, using various models from UVR trained primarily by @Anjok07"
 authors = ["Andrew Beveridge <andrew@beveridge.uk>"]
 license = "MIT"

tests/unit/test_remote_api_client.py

@@ -536,9 +536,10 @@ def test_separate_audio_with_gcs_uri(self, mock_post, api_client):
 
         assert result["task_id"] == "test-task-gcs"
 
-        # Verify gcs_uri was sent in form data, no file upload
+        # Verify gcs_uri was sent in form data
         call_args = mock_post.call_args
-        assert call_args[1]["files"] is None
+        # A dummy empty file is sent to force multipart encoding (FastAPI requires it)
+        assert call_args[1]["files"]["file"][0] == ""  # empty filename
         assert call_args[1]["data"]["gcs_uri"] == "gs://my-bucket/path/to/audio.flac"
 
     def test_separate_audio_requires_file_or_gcs_uri(self, api_client):