No exceptions on missing error webpages

- Create a `safeReadFileSync()` function in `src/utils.js` to wrap around `fs.readFileSync()`
- Migrate error-webpage loads to use `safeReadFileSync()`, with default values of an empty string
- Move the 404 error middleware to explicitly only be called *after* extensions are registered

src/middleware/basicAuth.js

@@ -5,13 +5,12 @@
 import { Buffer } from 'node:buffer';
 import storage from 'node-persist';
 import { getAllUserHandles, toKey, getPasswordHash } from '../users.js';
-import { getConfig, getConfigValue } from '../util.js';
-import { readFileSync } from 'node:fs';
+import { getConfig, getConfigValue, safeReadFileSync } from '../util.js';
 
 const PER_USER_BASIC_AUTH = getConfigValue('perUserBasicAuth', false);
 const ENABLE_ACCOUNTS = getConfigValue('enableUserAccounts', false);
 
-const unauthorizedWebpage = readFileSync('./public/error/unauthorized.html', { encoding: 'utf-8' });
+const unauthorizedWebpage = safeReadFileSync('./public/error/unauthorized.html') ?? '';
 const unauthorizedResponse = (res) => {
     res.set('WWW-Authenticate', 'Basic realm="SillyTavern", charset="UTF-8"');
     return res.status(401).send(unauthorizedWebpage);

src/middleware/whitelist.js

@@ -5,13 +5,15 @@ import Handlebars from 'handlebars';
 import ipMatching from 'ip-matching';
 
 import { getIpFromRequest } from '../express-common.js';
-import { color, getConfigValue } from '../util.js';
+import { color, getConfigValue, safeReadFileSync } from '../util.js';
 
 const whitelistPath = path.join(process.cwd(), './whitelist.txt');
 const enableForwardedWhitelist = getConfigValue('enableForwardedWhitelist', false);
 let whitelist = getConfigValue('whitelist', []);
 let knownIPs = new Set();
-const forbiddenWebpage = Handlebars.compile(fs.readFileSync('./public/error/forbidden-by-whitelist.html', 'utf-8'));
+const forbiddenWebpage = Handlebars.compile(
+    safeReadFileSync('./public/error/forbidden-by-whitelist.html') ?? '',
+);
 
 if (fs.existsSync(whitelistPath)) {
     try {

src/util.js

@@ -871,3 +871,14 @@ export class MemoryLimitedMap {
         return this.map[Symbol.iterator]();
     }
 }
+
+/**
+ * A 'safe' version of `fs.readFileSync()`. Returns the contents of a file if it exists, falling back to a default value if not.
+ * @param {string} filePath Path of the file to be read.
+ * @param {Parameters<typeof fs.readFileSync>[1]} options Options object to pass through to `fs.readFileSync()` (default: `{ encoding: 'utf-8' }`).
+ * @returns The contents at `filePath` if it exists, or `null` if not.
+ */
+export function safeReadFileSync(filePath, options = { encoding: 'utf-8' }) {
+    if (fs.existsSync(filePath)) return fs.readFileSync(filePath, options);
+    return null;
+}