[fix] handle missing server file for an action request

[teemingc]

fixes #7965
fixes #7957

• Returns a 405 response for an action request when no server file exists for a page.
• Adds a JSON body for the "cross-origin POST" and "no actions exist" error responses.

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[dummdidumm]

Thank you - I'm not sure if this is the right fix though. Looking at the linked issue, that error response should have been JSON instead - the "Accept" header clearly states that. So we should fix this on the server instead. Are there other situations besides the reproducible in the issue where you experienced this bug?

[teemingc]

Ah you're right. I wasn't even thinking of the Accept header.

I assumed that the server was returning plain text responses for all errors because it was also failing to parse the 405 error response when no actions exist (this was what I was trying to fix originally). I think it's this line that's causing it?. Should the server return a JSON response body in most if not all cases?

other situations besides the reproducible in the issue where you experienced this bug?

The server returns text/plain when a +page.server.js file exists and there are no actions.
https://stackblitz.com/edit/sveltejs-kit-template-default-oazk46?file=src%2Froutes%2F%2Bpage.svelte

Otherwise, without a +page.server.js file, it returns text/html.
https://stackblitz.com/edit/sveltejs-kit-template-default-siriup

[dummdidumm]

Interesting - thanks for investigating! The Accept header should be honored in these cases, so in the progressive enhancement case where JSON is expected for the response, it should be sent as such.
The offending code is inside actions.js and runtime/server/page/index.js (line 41, the "is action request but no +page.server.js exists" case is unhandled).

[teemingc]

Thanks for the guidance @dummdidumm ! I've added handling for a missing server file using the same "405 POST method not allowed. No actions exist for this page" response. Hopefully I've implemented this correctly.

[dummdidumm]

Thank you! Ok so this brings up another design question: Right now the response is still not JSONified, which it should be, but if we do that, it ideally should honor the App.Error interface. So this should probably use handle_error_and_jsonify and return a JSON response from that (similar to what's happeneing further below in that method).

[teemingc]

Yup, looks much better now.

What about the plain text response from the CSRF check?
Should a JSON response also be made available to prevent the JSON parsing error from enhance?

	if (options.csrf.check_origin) {
		const forbidden =
			request.method === 'POST' &&
			request.headers.get('origin') !== url.origin &&
			is_form_content_type(request);

		if (forbidden) {
			const csrf_error = error(403, `Cross-site ${request.method} form submissions are forbidden`);
			// handle accept: application/json
			if (request.headers.get('accept') === 'application/json') {
				return json(csrf_error.body, { status: csrf_error.status });
			}
			return new Response(csrf_error.body.message, { status: csrf_error.status });
		}
	}

[dummdidumm]

yeah that makes sense 👍

[dummdidumm]

Thank you!