Fix logger to log exceptions

this is similar to the fix in taskworker

box.js

@@ -10,15 +10,29 @@ const dockerProxy = require('./src/dockerproxy.js'),
     safe = require('safetydance'),
     server = require('./src/server.js');
 
-function setupLogging() {
+let logFd;
+
+async function setupLogging() {
     if (process.env.BOX_ENV === 'test') return;
 
-    const logfileStream = fs.createWriteStream(paths.BOX_LOG_FILE, { flags:'a' });
-    process.stdout.write = process.stderr.write = logfileStream.write.bind(logfileStream);
+    logFd = fs.openSync(paths.BOX_LOG_FILE, 'a');
+    // we used to write using a stream before but it caches internally and there is no way to flush it when things crash
+    process.stdout.write = process.stderr.write = function (...args) {
+        const callback = typeof args[args.length-1] === 'function' ? args.pop() : function () {}; // callback is required for fs.write
+        fs.write.apply(fs, [logFd, ...args, callback]);
+    };
+}
+
+// this is also used as the 'uncaughtException' handler which can only have synchronous functions
+function exitSync(status) {
+    if (status.error) fs.write(logFd, status.error.stack + '\n', function () {});
+    fs.fsyncSync(logFd);
+    fs.closeSync(logFd);
+    process.exit(status.code);
 }
 
 async function startServers() {
-    setupLogging();
+    await setupLogging();
     await server.start(); // do this first since it also inits the database
     await proxyAuth.start();
     await ldap.start();
@@ -27,10 +41,7 @@ async function startServers() {
 
 async function main() {
     const [error] = await safe(startServers());
-    if (error) {
-        console.log('Error starting server', error);
-        process.exit(1);
-    }
+    if (error) return exitSync({ error: new Error(`Error starting server: ${JSON.stringify(error)}`), code: 1 });
 
     // require those here so that logging handler is already setup
     require('supererror');
@@ -56,10 +67,7 @@ async function main() {
         setTimeout(process.exit.bind(process), 3000);
     });
 
-    process.on('uncaughtException', function (error) {
-        console.error((error && error.stack) ? error.stack : error);
-        setTimeout(process.exit.bind(process, 1), 3000);
-    });
+    process.on('uncaughtException', (error) => exitSync({ error, code: 1 }));
 
     console.log(`Cloudron is up and running. Logs are at ${paths.BOX_LOG_FILE}`); // this goes to journalctl
 }