Potential internal CF Pages issue: Error 500 on first post request but not subsequent ones

The pages worker seems to fail to process the first post request, but a try catch on the entire backend doesn't catch it and it happens even if there is no backend code other than just returning OK directly.

I suspect that there is an issue at Cloudlfare Pages, SvelteKit or the Cloudflare Pages Adapter for SvelteKit.

The Error 500:

Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Unexpected token '<', "<!DOCTYPE "... is not valid JSON
or

JSON.parse: unexpected character at line 1 column 1 of the JSON data

JSON.parse: unexpected character at line 1 column 1 of the JSON data

JSON.parse: unexpected character at line 1 column 1 of the JSON data

JSON.parse: unexpected character at line 1 column 1 of the JSON data

2funOP•3/29/24, 1:28 AM

Is there a way to get the stacktrace to know exactly where it happens?

2funOP•3/29/24, 1:43 AM

This doesn't happen running the page locally using the node adapter for SvelteKit or using the

wrangler pages dev

wrangler pages dev

command

2funOP•3/29/24, 1:43 AM

Therefore I strongly think it is a Cloudflare Pages internal issue

2funOP•3/29/24, 3:02 AM

Fixed the issue with this code:

import { browser } from '$app/environment';

if (browser) {
    let loaded = sessionStorage.getItem('form_page_reload');
    if (!loaded) { // Fixes weird Cloudflare Pages "Error 500 on initial post" issue
        sessionStorage.setItem('form_page_reload', 'true');
        location.reload();
    }
}

import { browser } from '$app/environment';

if (browser) {
    let loaded = sessionStorage.getItem('form_page_reload');
    if (!loaded) { // Fixes weird Cloudflare Pages "Error 500 on initial post" issue
        sessionStorage.setItem('form_page_reload', 'true');
        location.reload();
    }
}

It just refreshes the page once to "skip" the initial phase I guess. Weird

2funOP•8/23/24, 5:55 PM

After some debugging, I found in the wrangler logs that there is no GET request initially. So instead of using svelte's goto(url) function I just did window.location.href = url instead

2funOP•8/23/24, 5:55 PM

Seems to have fixed it

Matix•8/24/24, 7:11 PM

hi @2fun im experiencing a similar issue. How did you access the wranger logs?

Matix•8/24/24, 7:21 PM

Nvm, I think I figured out.. But the logs are not really helpful aswell

import { browser } from '$app/environment'; if (browser) { let loaded = sessionStorage.getItem('form_page_reload'); if (!loaded) { // Fixes weird Cloudflare Pages "Error 500 on initial post" issue sessionStorage.setItem('form_page_reload', 'true'); location.reload(); } }

Potential internal CF Pages issue: Error 500 on first post request but not subsequent ones

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