feat(fusion-cli): add graceful shutdown to start command

fusion-cli-tests/test/e2e/dynamic-import-app/test.js

@@ -259,7 +259,8 @@ test('`fusion build` app with Safari user agent and same-origin', async () => {
   await cmd(`build --dir=${dir} --production`, {env});
 
   // Run puppeteer test to ensure that page loads with dynamic content.
-  const {proc, port} = await start(`--dir=${dir}`, {env});
+  const {proc, port, promise} = await start(`--dir=${dir}`, {env});
+  promise.catch(console.error);
 
   const browser = await puppeteer.launch({
     args: ['--no-sandbox', '--disable-setuid-sandbox'],

fusion-cli-tests/test/e2e/utils.js

@@ -66,10 +66,11 @@ function cmd(args /*: any */, options /*: any */) {
 
 async function start(args /*: any */, options /*: any */) {
   const port = await getPort();
+  const promise = cmd(`start --port=${port} ${args}`, options);
   // $FlowFixMe
-  const {proc} = cmd(`start --port=${port} ${args}`, options);
+  const {proc} = promise;
   const res = await waitForServer(port);
-  return {proc, res, port};
+  return {proc, res, port, promise};
 }
 
 async function dev(args /*: any */, options /*: any */) {

fusion-cli/commands/start.js

@@ -12,6 +12,28 @@ const fs = require('fs');
 const path = require('path');
 const cp = require('child_process');
 
+// Gracefully shuts down server when it receives signals
+function listenForShutdown(server, ...signals) {
+  let closing = false;
+
+  const shutDown = (signalName, signal) => {
+    if (closing) {
+      return;
+    }
+    closing = true;
+
+    console.info(`Received ${signalName}, draining open connections`);
+    server.close(() => {
+      console.info(`Drained connections, stopping server`);
+      process.exit(128 + signal);
+    });
+  };
+
+  signals.forEach(signal => {
+    process.once(signal, shutDown);
+  });
+}
+
 exports.run = async function({dir = '.', environment, port, debug} /*: any */) {
   if (debug && !process.env.__FUSION_DEBUGGING__) {
     const command = process.argv.shift();
@@ -39,7 +61,14 @@ exports.run = async function({dir = '.', environment, port, debug} /*: any */) {
     const entry = getEntry(env);
     // $FlowFixMe
     const {start} = require(entry);
-    return start({dir, port: port || process.env.PORT_HTTP || 3000}); // handle server bootstrap errors (e.g. port already in use)
+    const server = await start({
+      dir,
+      port: port || process.env.PORT_HTTP || 3000,
+    }); // handle server bootstrap errors (e.g. port already in use)
+
+    listenForShutdown(server, 'SIGTERM', 'SIGINT');
+
+    return server;
   } else {
     throw new Error(`App can't start. JS isn't compiled`); // handle compilation errors
   }