feat(web-server): allow injection of custom middleware.

docs/config/01-configuration-file.md

@@ -280,6 +280,35 @@ httpsServerOptions: {
 **Description:** A list of log appenders to be used. See the documentation for [log4js] for more information.
 
 
+## middleware
+**Type:** Array
+
+**Default:** `[]`
+
+**Description:** List of names of additional middleware you want the karma server to use. Middleware will be used in the order listed.
+
+You must have installed the middleware via a plugin/framework (either inline or via NPM). Additional information can be found in [plugins].
+
+The plugin must provide an express/connect middleware function (details about this can be found in [the Express docs](http://expressjs.com/guide/using-middleware.html). An example of custom inline middleware is shown below.
+
+**Example:**
+```javascript
+var CustomMiddlewareFactory = function (config) {
+  return function (request, response, /* next */) {
+    response.writeHead(200)
+    return response.end("content!")
+  }
+}
+```
+
+```javascript
+middleware: ['custom']
+plugins: [
+  {'middleware:custom': ['factory', CustomMiddlewareFactory]}
+  ...
+]
+```
+
 ## plugins
 **Type:** Array
 

lib/web-server.js

@@ -63,9 +63,16 @@ var createWebServer = function (injector, emitter, fileList) {
     // TODO(vojta): remove, this is only here because of karma-dart
     // we need a better way of custom handlers
     .use(injector.invoke(createCustomHandler))
-    .use(function (request, response) {
-      common.serve404(response, request.url)
+
+  if (config.middleware) {
+    config.middleware.forEach(function (middleware) {
+      handler.use(injector.get('middleware:' + middleware))
     })
+  }
+
+  handler.use(function (request, response) {
+    common.serve404(response, request.url)
+  })
 
   var serverClass = http
   var serverArguments = [handler]

test/unit/web-server.spec.js

@@ -32,7 +32,7 @@ describe('web-server', () => {
   var m = mocks.loadFile(__dirname + '/../../lib/web-server.js', _mocks, _globals)
 
   var customFileHandlers = server = emitter = null
-
+  var middlewareActive = false
   var servedFiles = (files) => {
     emitter.emit('file_list_modified', {included: [], served: files})
   }
@@ -41,16 +41,31 @@ describe('web-server', () => {
     beforeEach(() => {
       customFileHandlers = []
       emitter = new EventEmitter()
+      var config = {
+        basePath: '/base/path',
+        urlRoot: '/',
+        middleware: ['custom'],
+        middlewareResponse: 'hello middleware!'
+      }
 
       var injector = new di.Injector([{
-        config: ['value', {basePath: '/base/path', urlRoot: '/'}],
+        config: ['value', config],
         customFileHandlers: ['value', customFileHandlers],
         emitter: ['value', emitter],
         fileList: ['value', {files: {served: [], included: []}}],
         capturedBrowsers: ['value', null],
         reporter: ['value', null],
         executor: ['value', null],
-        proxies: ['value', null]
+        proxies: ['value', null],
+        'middleware:custom': ['factory', function (config) {
+          return function (request, response, next) {
+            if (middlewareActive) {
+              response.writeHead(222)
+              return response.end(config.middlewareResponse)
+            }
+            next()
+          }
+        }]
       }])
 
       server = injector.invoke(m.createWebServer)
@@ -81,6 +96,25 @@ describe('web-server', () => {
         .expect(200, 'new-js-source')
     })
 
+    describe('middleware', () => {
+      beforeEach(() => {
+        servedFiles(new Set([new File('/base/path/one.js')]))
+        middlewareActive = true
+      })
+
+      it('should use injected middleware', () => {
+        return request(server)
+          .get('/base/other.js')
+          .expect(222, 'hello middleware!')
+      })
+
+      it('should inject middleware behind served files', () => {
+        return request(server)
+          .get('/base/one.js')
+          .expect(200, 'js-source')
+      })
+    })
+
     it('should serve no files when they are not available yet', () => {
       return request(server)
         .get('/base/new.js')