Pass backend tracebacks through to error pages

utils/request.js

@@ -2,12 +2,32 @@
 // @ts-ignore
 const fetch = require("node-fetch")
 
-function request(url, options = {}) {
+async function request(url, options = {}) {
 	if (!options.headers) options.headers = {}
 	options.headers = {
 		"user-agent": "CloudTubeBackend/1.0"
 	}
-	return fetch(url, options)
+	const res = await fetch(url, options)
+
+	if (res.status >= 400) {
+		if (res.status == 500) {
+			let body = await res.text();
+
+			const traceback_start = '<pre id="traceback">';
+			const traceback_end = '</pre>';
+
+			const si = body.indexOf(traceback_start)
+			if (si >= 0) body = body.slice(si + traceback_start.length);
+
+			const ei = body.indexOf(traceback_end)
+			if (ei >= 0) body = body.slice(0, ei);
+
+			throw new Error(`Unexpected error in backend:\n\n${body}`);
+		} else {
+			throw new Error(`Unexpected response from backend: ${res.status} ${res.statusText}`);
+		}
+	}
+	return res
 }
 
 module.exports.request = request