Integrate Python web apps with Workbench

[seeM]

Following on from #4662, we should update runApplication to detect if we're in Workbench, and if so, find a free port and corresponding proxied URL (possibly related to #4274) and pass them both to getTerminalOptions. Unfortunately, some application frameworks need the proxied URL to be configured as the "URL prefix"/"root path".

[sharon-wang]

I ran a Streamlit app in Workbench and it's displaying in the Viewer successfully! It'd be nice if the proxied path was reflected in the Terminal output, but ctrl+clicking on the Local URL results in the URL getting resolved to the correct proxied path (the one shown at the top of the Viewer).

[sharon-wang]

The Quarto preview Terminal output shows the proxied path in addition to the localhost URL:

The Quarto extension code that outputs "Browse at ": https://github.com/quarto-dev/quarto/blob/49abc46be3dbfd5cbd1eadf3d04cb4a7ac690b5c/apps/vscode/src/providers/preview/preview.ts#L532

[sharon-wang]

Additional testing of Python web apps on Workbench: #4662 (comment)

• Summary:
  • Working: Streamlit, Dash, Flask
  • Not working / partially working: Gradio (styles and images not loading from correct path), FastAPI (request is not proxied properly)

Just to see what would happen, I tried modifying the following to include a call to positron proxy to retrieve the proxied URI. It seemed to fix the issues with Gradio and Fastapi, but Streamlit and Dash stopped working. Flask still remained happy.

positron/extensions/positron-run-app/src/extension.ts

Lines 226 to 235 in 659e073

	if (url) {
	// Convert the url to an external URI.
	const localBaseUri = vscode.Uri.parse(url.toString());
	const localUri = options.urlPath ?
	vscode.Uri.joinPath(localBaseUri, options.urlPath) : localBaseUri;
	const externalUri = await vscode.env.asExternalUri(localUri);
	// Open the server URL in the viewer pane.
	positron.window.previewUrl(externalUri);
	}

It seems like we're in this situation:

App Framework
👇 please provide proxy url, then I'll tell you the app url
👆 please provide app url, then I'll tell you the proxy url
Positron Proxy

@seeM is it possible to preconfigure the app url (host:port) and pass that information to Positron Proxy? I suspect that may involve a bunch of framework-specific handling which may not be preferred. I'll look into what we can do on the Positron Proxy side to provide a proxy url separately from setting up the proxied connection.