Expose a shutdown API to support clean shutdown on Windows

Windows can't send signals like SIGINT/SIGTERM to arbitrary processes in
a way that can support clean shutdown. With Docker, we have quite a bit
of cleanup to do, and clean shutdown becomes more important, so it's
useful to expose an API that the desktop app can use to trigger this
directly.

Author: pimterry

src/api-server.ts

@@ -17,6 +17,7 @@ import { buildInterceptors, Interceptor, ActivationError } from './interceptors'
 import { ALLOWED_ORIGINS } from './constants';
 import { delay } from './util/promise';
 import { getDnsServer } from './dns-server';
+import { shutdown } from './shutdown';
 
 const ENABLE_PLAYGROUND = false;
 
@@ -61,6 +62,7 @@ const typeDefs = `
             proxyPort: Int!
         ): Boolean!
         triggerUpdate: Void
+        shutdown: Void
     }
 
     type InterceptionConfig {
@@ -177,6 +179,13 @@ const buildResolvers = (
             },
             triggerUpdate: () => {
                 eventEmitter.emit('update-requested');
+            },
+            // On Windows, there's no clean way to send signals between processes to trigger graceful
+            // shutdown. To handle that, we use HTTP from the desktop shell, instead of inter-process
+            // signals. This completely shuts down the server, not just a single proxy endpoint, and
+            // should only be called once the app is fully exiting.
+            shutdown: () => {
+                shutdown('API call');
             }
         },
 

src/shutdown.ts

@@ -5,16 +5,16 @@ type ShutdownHandler = () => Promise<unknown>;
 const shutdownHandlers: Array<ShutdownHandler> = [];
 
 export function registerShutdownHandler() {
-    process.on('SIGTERM', shutdown);
-    process.on('SIGINT', shutdown);
+    process.on('SIGTERM', () => shutdown('SIGTERM'));
+    process.on('SIGINT', () => shutdown('SIGINT'));
 }
 
 export function addShutdownHandler(handler: ShutdownHandler) {
     shutdownHandlers.push(handler);
 }
 
-async function shutdown() {
-    console.log('Shutting down...');
+export async function shutdown(cause: string) {
+    console.log(`Shutting down after ${cause}...`);
 
     const shutdownPromises = Promise.all(shutdownHandlers.map(
         async (handler) => {