Refactor startup/shutdown for tests

* `src/node/server.js` can now be run as a script (for normal
    operation) or imported as a module (for tests).
  * Move shutdown actions to `src/node/server.js` to be close to the
    startup actions.
  * Put startup and shutdown in functions so that tests can call them.
  * Use `await` instead of callbacks.
  * Block until the HTTP server is listening to avoid races during
    test startup.
  * Add a new `shutdown` hook.
  * Use the `shutdown` hook to:
      * close the HTTP server
      * call `end()` on the stats collection to cancel its timers
      * call `terminate()` on the Threads.Pool to stop the workers
  * Exit with exit code 0 (instead of 1) on SIGTERM.
  * Export the HTTP server so that tests can get the HTTP server's
    port via `server.address().port` when `settings.port` is 0.

src/node/hooks/express.js

@@ -5,18 +5,20 @@ var fs = require('fs');
 var path = require('path');
 var npm = require("npm/lib/npm.js");
 var  _ = require("underscore");
+const util = require('util');
 
-var server;
 var serverName;
 
-exports.createServer = function () {
+exports.server = null;
+
+exports.createServer = async () => {
   console.log("Report bugs at https://github.com/ether/etherpad-lite/issues")
 
   serverName = `Etherpad ${settings.getGitCommit()} (https://etherpad.org)`;
 
   console.log(`Your Etherpad version is ${settings.getEpVersion()} (${settings.getGitCommit()})`);
 
-  exports.restartServer();
+  await exports.restartServer();
 
   if (settings.ip === "") {
     // using Unix socket for connectivity
@@ -38,10 +40,10 @@ exports.createServer = function () {
   }
 }
 
-exports.restartServer = function () {
-  if (server) {
+exports.restartServer = async () => {
+  if (exports.server) {
     console.log("Restarting express server");
-    server.close();
+    await util.promisify(exports.server.close).bind(exports.server)();
   }
 
   var app = express(); // New syntax for express v3
@@ -65,10 +67,10 @@ exports.restartServer = function () {
     }
 
     var https = require('https');
-    server = https.createServer(options, app);
+    exports.server = https.createServer(options, app);
   } else {
     var http = require('http');
-    server = http.createServer(app);
+    exports.server = http.createServer(app);
   }
 
   app.use(function(req, res, next) {
@@ -110,7 +112,12 @@ exports.restartServer = function () {
   }
 
   hooks.callAll("expressConfigure", {"app": app});
-  hooks.callAll("expressCreateServer", {"app": app, "server": server});
+  hooks.callAll('expressCreateServer', {app, server: exports.server});
 
-  server.listen(settings.port, settings.ip);
-}
+  await util.promisify(exports.server.listen).bind(exports.server)(settings.port, settings.ip);
+};
+
+exports.shutdown = async (hookName, context) => {
+  if (!exports.server) return;
+  await util.promisify(exports.server.close).bind(exports.server)();
+};

src/node/hooks/express/adminsettings.js

@@ -46,11 +46,10 @@ exports.socketio = function (hook_name, args, cb) {
       });
     });
 
-    socket.on("restartServer", function () {
+    socket.on('restartServer', async () => {
       console.log("Admin request to restart server through a socket on /admin/settings");
       settings.reloadSettings();
-      hooks.aCallAll("restartServer", {}, function () {});
-
+      await hooks.aCallAll('restartServer');
     });
 
   });

src/node/hooks/express/errorhandling.js

@@ -1,39 +1,5 @@
-var os = require("os");
-var db = require('../../db/DB');
 var stats = require('ep_etherpad-lite/node/stats')
 
-
-exports.onShutdown = false;
-exports.gracefulShutdown = function(err) {
-  if(err && err.stack) {
-    console.error(err.stack);
-  } else if(err) {
-    console.error(err);
-  }
-
-  // ensure there is only one graceful shutdown running
-  if (exports.onShutdown) {
-    return;
-  }
-
-  exports.onShutdown = true;
-
-  console.log("graceful shutdown...");
-
-  // do the db shutdown
-  db.doShutdown().then(function() {
-    console.log("db sucessfully closed.");
-
-    process.exit(0);
-  });
-
-  setTimeout(function() {
-    process.exit(1);
-  }, 3000);
-}
-
-process.on('uncaughtException', exports.gracefulShutdown);
-
 exports.expressCreateServer = function (hook_name, args, cb) {
   exports.app = args.app;
 
@@ -46,28 +12,4 @@ exports.expressCreateServer = function (hook_name, args, cb) {
     console.error(err.stack? err.stack : err.toString());
     stats.meter('http500').mark()
   });
-
-  /*
-   * Connect graceful shutdown with sigint and uncaught exception
-   *
-   * Until Etherpad 1.7.5, process.on('SIGTERM') and process.on('SIGINT') were
-   * not hooked up under Windows, because old nodejs versions did not support
-   * them.
-   *
-   * According to nodejs 6.x documentation, it is now safe to do so. This
-   * allows to gracefully close the DB connection when hitting CTRL+C under
-   * Windows, for example.
-   *
-   * Source: https://nodejs.org/docs/latest-v6.x/api/process.html#process_signal_events
-   *
-   *   - SIGTERM is not supported on Windows, it can be listened on.
-   *   - SIGINT from the terminal is supported on all platforms, and can usually
-   *     be generated with <Ctrl>+C (though this may be configurable). It is not
-   *     generated when terminal raw mode is enabled.
-   */
-  process.on('SIGINT', exports.gracefulShutdown);
-
-  // when running as PID1 (e.g. in docker container)
-  // allow graceful shutdown on SIGTERM c.f. #3265
-  process.on('SIGTERM', exports.gracefulShutdown);
 }