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Debugging logs

Send debugging information in an errored response to a logging service.
export default {
async fetch(request, env, ctx) {
// Service configured to receive logs
const LOG_URL = "https://log-service.example.com/";
async function postLog(data) {
return await fetch(LOG_URL, {
method: "POST",
body: data,
});
}
let response;
try {
response = await fetch(request);
if (!response.ok && !response.redirected) {
const body = await response.text();
throw new Error(
"Bad response at origin. Status: " +
response.status +
" Body: " +
// Ensure the string is small enough to be a header
body.trim().substring(0, 10)
);
}
} catch (err) {
// Without ctx.waitUntil(), your fetch() to Cloudflare's
// logging service may or may not complete
ctx.waitUntil(postLog(err.toString()));
const stack = JSON.stringify(err.stack) || err;
// Copy the response and initialize body to the stack trace
response = new Response(stack, response);
// Add the error stack into a header to find out what happened
response.headers.set("X-Debug-stack", stack);
response.headers.set("X-Debug-err", err);
}
return response;
},
};
interface Env {}
export default {
async fetch(request, env, ctx): Promise<Response> {
// Service configured to receive logs
const LOG_URL = "https://log-service.example.com/";
async function postLog(data) {
return await fetch(LOG_URL, {
method: "POST",
body: data,
});
}
let response;
try {
response = await fetch(request);
if (!response.ok && !response.redirected) {
const body = await response.text();
throw new Error(
"Bad response at origin. Status: " +
response.status +
" Body: " +
// Ensure the string is small enough to be a header
body.trim().substring(0, 10)
);
}
} catch (err) {
// Without ctx.waitUntil(), your fetch() to Cloudflare's
// logging service may or may not complete
ctx.waitUntil(postLog(err.toString()));
const stack = JSON.stringify(err.stack) || err;
// Copy the response and initialize body to the stack trace
response = new Response(stack, response);
// Add the error stack into a header to find out what happened
response.headers.set("X-Debug-stack", stack);
response.headers.set("X-Debug-err", err);
}
return response;
},
} satisfies ExportedHandler<Env>;
import json
import traceback
from pyodide.ffi import create_once_callable
from js import Response, fetch, Headers
async def on_fetch(request, _env, ctx):
# Service configured to receive logs
log_url = "https://log-service.example.com/"
async def post_log(data):
return await fetch(log_url, method="POST", body=data)
response = await fetch(request)
try:
if not response.ok and not response.redirected:
body = await response.text()
# Simulating an error. Ensure the string is small enough to be a header
raise Exception(f'Bad response at origin. Status:{response.status} Body:{body.strip()[:10]}')
except Exception as e:
# Without ctx.waitUntil(), your fetch() to Cloudflare's
# logging service may or may not complete
ctx.waitUntil(create_once_callable(post_log(e)))
stack = json.dumps(traceback.format_exc()) or e
# Copy the response and add to header
response = Response.new(stack, response)
response.headers["X-Debug-stack"] = stack
response.headers["X-Debug-err"] = e
return response