Support Google Discovery `mediaUpload` endpoints in generated clients

[KeremTurgutlu]

Fastspec currently parses Google Discovery methods as normal JSON operations and ignores supportsMediaUpload / mediaUpload metadata. For Gemini’s media.upload method, this causes the generated client to call POST /v1beta/files with JSON like {"file": "/path/to/file.mp4"}, which fails because Gemini expects upload bytes via /upload/v1beta/files or /resumable/upload/v1beta/files. The Discovery spec already includes the required upload protocol paths and metadata, so fastspec should preserve this in OpSpec and route media upload operations through multipart/simple or resumable upload handling instead of ordinary JSON request serialization.

[KeremTurgutlu]

It’s an easy-to-moderate change, but not as simple as swapping path to the resumable path.

For Google Discovery mediaUpload, the normal op path:

/v1beta/files

is the metadata-create endpoint. The media upload path:

/resumable/upload/v1beta/files

requires a resumable upload protocol, not just a different URL.

Roughly, the flow is:

1. Start upload session:

POST /resumable/upload/v1beta/files
X-Goog-Upload-Protocol: resumable
X-Goog-Upload-Command: start
X-Goog-Upload-Header-Content-Length: <bytes>
X-Goog-Upload-Header-Content-Type: video/mp4
Content-Type: application/json

Body:

{"file": {"display_name": "ox1Tt2HBjRk.mp4"}}

2. Read response header:

X-Goog-Upload-URL: ...

3. Upload bytes to that URL:

POST <upload-url>
X-Goog-Upload-Offset: 0
X-Goog-Upload-Command: upload, finalize
Content-Length: <bytes>

Body: raw file bytes.

So if fastspec just changes the op path to /resumable/upload/v1beta/files, it will still fail, because it’ll send JSON rather than the resumable upload headers/body.

The clean design would be:

• Extend OpSpec with something like:

media_upload: dict = field(default_factory=dict)
supports_media_upload: bool = False

• In discovery_to_ops, preserve supportsMediaUpload and mediaUpload.
• In OpFunc.__call__, if the op has supports_media_upload and the user passes a file/path, route to a special helper:

await self._google_resumable_upload(path, metadata=body)

• Otherwise keep the normal JSON behavior.

I would not replace the path globally, because some calls may be metadata-only or may not include a local file. Treat media upload as a special execution path.

For now, a local helper just for Gemini uploads is probably faster than making fastspec fully generic. But as a library improvement, supporting Google Discovery mediaUpload via resumable upload is very reasonable and not huge.