Allow serving npm linked modules using tools/serve

Developing modules in external repositories can be a bit tedious if you
need to bundle up the external module every time you want to test it.
This allows module authors to use `npm link` to make their development
source code accessible to `tools/serve`.

Author: nickstenning

tools/serve

@@ -33,12 +33,36 @@ app.use('/api/token', function(request, response) {
 });
 
 app.use('/bundle/annotator.js', browserify('index.js', {standalone: 'annotator'}));
+
+// Serve files locally from src/ext/
 app.use('/bundle/ext', function (req, res, next) {
   // browserify-middleware expects req.path to be set
   req.path = req.url;
   browserify('src/ext/')(req, res, next);
 });
 
+// Serve any browserifiable module. Useful when developing external modules. If
+// you are developing the "annotator-widgets" module you can run
+//
+//     npm link
+//
+// in the annotator-widgets repository, followed by
+//
+//     npm link annotator-widgets
+//
+// in the annotator repository, and then you can load
+//
+//     /bundle/ext/annotator-widgets.js
+//
+// from this server.
+app.use('/bundle/ext', function (req, res, next) {
+  if (req.url.slice(0, 1) !== '/' || req.url.slice(-3) !== '.js') {
+    next();
+  }
+  var moduleName = req.url.slice(1, -3);
+  browserify([moduleName])(req, res, next);
+});
+
 // Static files
 app.use(connect.static(process.cwd()));