File Upload & Processing

Accept files through forms and APIs, store them as assets, and process them safely in the background.

Uploads come in two flavors: a user dropping a file into your page, and a system pushing a file to your API. Both end up as cluster assets, and heavy processing belongs in the queue. This tutorial covers the whole pipeline.

Upload via a Page (User-Facing)

1. Build a form with state_form and a file-capable input from the state elements — see the form pattern in Block Templates.
2. On submit, read the form with state_form_get; the file arrives with its name, type, and size.
3. Store it via the asset upload API (POST /api/v1/_system/assets/stream) or a file-handling block, into public (world-readable) or system_assets (private) — choose per public vs private.
4. Record the asset guid/path on a document so you can find it later (e.g. photo on a profile document).

Upload via an API (Machine-Facing)

1. Register on_startup_register_uri_post with your upload URI — see the upload template.
2. Validate: content type, size limit, required metadata. Reject with a 400 before storing anything.
3. Store as an asset; reply 200 with {"guid": "...", "path": "..."} so the caller can reference it.
4. Scope it deliberately — uploads are never *public by accident; use *loggedin or a custom scope with a secret in the path.

Processing: Do It in the Background

Resizing, parsing, importing, converting — never inline in the request. The pattern:

1. The upload flow stores the file and enqueues a processing job with function_custom_execute_from_queue — see Queue.
2. A queue worker flow picks it up: reads the file with file_from_assets, transforms it (e.g. resize/convert with the image blocks), writes results back to a document or a new asset.
3. Mark progress on the job document (status: queued → processing → done|failed) so users can poll or a page can show state.
4. Log failures to the console and storage — the error-pins pattern from Block Execution.

Safety Rules

• Never trust the client's filename for the stored path — generate your own.
• Cap file size at the API (the asset API rejects oversize with FILE_TOO_BIG) and validate type by content, not extension.
• Keep user uploads out of public unless they are truly public — private folders + scoped serving, per Serving Protected Files.
• Import pipelines should be idempotent: re-running the same file updates the same output document (upsert by source guid).

Next Steps

Assets Asset paths, APIs, and access rules in depth. Queue Background processing for the heavy lifting. Block Templates The upload template this pipeline extends.

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