fix: allow system to generate random port when desired (#319) (#328)

Co-authored-by: Justin Beckwith <beckwith@google.com>

Author: rrthomas

src/index.ts

@@ -1,5 +1,6 @@
 import {EventEmitter} from 'events';
 import {URL} from 'url';
+import {AddressInfo} from 'net';
 import * as http from 'http';
 import * as path from 'path';
 import {Readable} from 'stream';
@@ -81,13 +82,17 @@ export class LinkChecker extends EventEmitter {
     let server: http.Server | undefined;
     const hasHttpPaths = options.path.find(x => x.startsWith('http'));
     if (!hasHttpPaths) {
-      const port = options.port || 5000 + Math.round(Math.random() * 1000);
+      let port = options.port;
       server = await startWebServer({
         root: options.serverRoot!,
         port,
         markdown: options.markdown,
         directoryListing: options.directoryListing,
       });
+      if (port === undefined) {
+        const addr = server.address() as AddressInfo;
+        port = addr.port;
+      }
       for (let i = 0; i < options.path.length; i++) {
         if (options.path[i].startsWith('/')) {
           options.path[i] = options.path[i].slice(1);

src/server.ts

@@ -1,3 +1,4 @@
+import {AddressInfo} from 'net';
 import * as http from 'http';
 import * as path from 'path';
 import * as fs from 'fs';
@@ -16,7 +17,7 @@ export interface WebServerOptions {
   // The local path that should be mounted as a static web server
   root: string;
   // The port on which to start the local web server
-  port: number;
+  port?: number;
   // If markdown should be automatically compiled and served
   markdown?: boolean;
   // Should directories automatically serve an inde page
@@ -33,8 +34,12 @@ export async function startWebServer(options: WebServerOptions) {
   return new Promise<http.Server>((resolve, reject) => {
     const server = http
       .createServer((req, res) => handleRequest(req, res, root, options))
-      .listen(options.port, () => resolve(server))
+      .listen(options.port || 0, () => resolve(server))
       .on('error', reject);
+    if (!options.port) {
+      const addr = server.address() as AddressInfo;
+      options.port = addr.port;
+    }
     enableDestroy(server);
   });
 }

test/test.server.ts

@@ -1,22 +1,23 @@
 import * as assert from 'assert';
 import {describe, it, before, after} from 'mocha';
 import {startWebServer} from '../src/server';
+import {AddressInfo} from 'net';
 import {Server} from 'http';
 import {request} from 'gaxios';
 import * as fs from 'fs';
 
 describe('server', () => {
   let server: Server;
-  const port = 5000 + Math.round(Math.random() * 1000);
-  const rootUrl = `http://localhost:${port}`;
+  let rootUrl: string;
   const contents = fs.readFileSync('test/fixtures/server/index.html', 'utf-8');
   before(async () => {
     server = await startWebServer({
-      port,
       directoryListing: true,
       markdown: true,
       root: 'test/fixtures/server',
     });
+    const addr = server.address() as AddressInfo;
+    rootUrl = `http://localhost:${addr.port}`;
   });
   after(() => server.destroy());