Add an express server which serves the package's contents.

Add an express server which serve's the package's contents in a manner
similar to unpkg:

 - The '/' route serves the package's entry point script

 - Other routes serve files from the package

This can be used together with the CLIENT_URL setting in the Hypothesis
service to configure the service to serve the local development version
of the client instead of the production version.

gulpfile.js

@@ -22,6 +22,7 @@ var through = require('through2');
 
 var createBundle = require('./scripts/gulp/create-bundle');
 var manifest = require('./scripts/gulp/manifest');
+var servePackage = require('./scripts/gulp/serve-package');
 var vendorBundles = require('./scripts/gulp/vendor-bundles');
 
 var IS_PRODUCTION_BUILD = process.env.NODE_ENV === 'production';
@@ -286,11 +287,15 @@ gulp.task('watch-manifest', function () {
   }));
 });
 
-gulp.task('start-live-reload-server', function () {
+gulp.task('serve-live-reload', function () {
   var LiveReloadServer = require('./scripts/gulp/live-reload-server');
   liveReloadServer = new LiveReloadServer(3000, 'http://localhost:5000');
 });
 
+gulp.task('serve-package', function () {
+  servePackage(3001);
+});
+
 gulp.task('build',
           ['build-js',
            'build-css',
@@ -299,7 +304,8 @@ gulp.task('build',
           generateManifest);
 
 gulp.task('watch',
-          ['start-live-reload-server',
+          ['serve-package',
+           'serve-live-reload',
            'watch-js',
            'watch-css',
            'watch-fonts',

package.json

@@ -43,6 +43,7 @@
     "eslint": "^3.0.1",
     "eslint-config-hypothesis": "^1.0.0",
     "exorcist": "^0.4.0",
+    "express": "^4.14.1",
     "extend": "^2.0.0",
     "gulp": "^3.9.1",
     "gulp-batch": "^1.0.5",

scripts/gulp/serve-package.js

+'use strict';
+
+var express = require('express');
+var { log } = require('gulp-util');
+var { readFileSync } = require('fs');
+
+/**
+ * An express server which serves the contents of the package.
+ *
+ * The server behaves similarly to npm CDNs, such as unpkg.com. The '/' route
+ * returns the contents of the package's entry point. Other routes return the
+ * contents of the specified file within the package.
+ *
+ * When developing the client, the Hypothesis service should be configured to
+ * use the URL of this service as the client URL, so that the boot script is
+ * returned by the service's '/embed.js' route and included in the '/app.html'
+ * app.
+ */
+function servePackage(port) {
+  var app = express();
+
+  app.get('/', function (req, res) {
+    var entryPath = require.resolve('../..');
+    var entryScript = readFileSync(entryPath).toString('utf-8');
+    res.send(entryScript);
+  });
+
+  app.use(express.static('.'));
+
+  app.listen(port, function () {
+    log(`Package served at http://localhost:${port}`);
+  });
+}
+
+module.exports = servePackage;