[unified-server] Dev mode requests for inline JS fail

[timswanson-google]

The Unified Server shows a blank page when running in dev mode. The page JS is never getting loaded due to the way Vite-Express handles the request for inline JS.

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In its current form, the index.html for the unified server contains an inline script.¹

https://github.com/breadboard-ai/breadboard/blob/4904e2a6b5cc486b722fe38b4fbf7f21408922a2/packages/unified-server/index.html

In production mode, this works fine. The JS is built into the compiled HTML and everything works as expected.

In dev mode, however, the Vite dev server moves the inline script into a JS file with a URL that looks like this:

/@id/__x00__/<repo-path>/index.html?html-proxy&index=0.js

The 0.js is a reference to the "first inline JS block in the HTML file". Vite extracts this script from the HTML and serves it separately. Presumably to enable things like hot module reload.

Vite-Express does not handle these URLs correctly. Instead, they fall through to the static routing logic, and index.html is returned again. Since the browser expects JS and gets HTML, it logs this error:

Failed to load module script: Expected a JavaScript module script
but the server responded with a MIME type of "text/html".
Strict MIME type checking is enforced for module scripts per HTML spec.

The JS is never loaded or executed, so the resulting page is blank.

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In the board-server package, we have a hand-written handler for these requests that defer explicitly to the Vite dev server:

breadboard/packages/board-server/src/server/common.ts

Line 94 in 4904e2a

if (pathname.endsWith(".html") && !req.url?.includes("?html-proxy")) {

However, it doesn't look like Vite-Express has any such logic.

Need to dig into why this is happening and what can be done about it.

Footnotes

1. This script was copied more-or-less verbatim from the same file in visual-editor. This is fine for the initial build-out, but will be a maintenance issue going forward, and a separate issue has been created to address it. [unified-server] Create a common bootstrap page for the visual editor #4350 ↩

[timswanson-google]

I've filed an issue with the Vite-Express project to see if this is a known issue or if there's something we can do to configure it.

szymmis/vite-express#158

[dglazkov]

This is now kind of fixed for us, since I moved all the inline code out.