Web UI: sending an image returns HTTP 500 `invalid image source` (v1 API works)

[subin9]

Describe the bug

Sending an image from the built-in web UI (http://localhost:1234/ui) fails with HTTP 500:

invalid image source, expected http https or data url: relative url without a base

Sending the same image directly through the /v1/chat/completions API works fine.

Root cause

The UI uploads the picked image to /api/upload_image, which saves it to the cache dir and returns a relative URL (mistralrs-cli/src/ui/handlers/api.rs):

let url = format!("uploads/{filename}");
(StatusCode::OK, Json(json!({ "path": path, "url": url }))).into_response()

The UI stores that relative string in the message and sends it back as image_url.url to /v1/chat/completions (mistralrs-cli/webui/src/lib/stores/chat.svelte.ts -> image_url: { url }). That endpoint resolves image sources under the ServerRequest media policy, which only accepts http / https / data URLs (mistralrs-server-core/src/media_source.rs):

anyhow::bail!("Invalid {kind} source: expected http, https, or data URL: {err}");

Url::parse("uploads/<uuid>.png") fails with RelativeUrlWithoutBase ("relative url without a base"), producing the 500. The v1 API works because real callers pass a data:/http(s) URL. (The relative URL only works for display, via the /uploads static route.)

The upload flow was added in #1370 / #1364.

Steps to reproduce

1. mistralrs serve -m <any vision model> (UI is on by default at /ui)
2. Open http://localhost:1234/ui, attach an image, send.
3. -> HTTP 500 invalid image source ... relative url without a base.
4. The same image via POST /v1/chat/completions with a data:/http URL succeeds.

Other information

• OS: Linux (WSL2); reproduces regardless of backend (it's a request-layer/URL bug).

Latest commit or version

v0.8.23 / current master.

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I have a fix ready (encode UI images as data: URLs client-side, matching what the working v1 path sends) and will open a PR referencing this issue. Note videos share the identical relative-URL path and are fixed the same way.