Support for server-side rendering (#118)

If `options.serverSideRender` is true, the middleware will set the `stat` object, which is generated by webpack, to `res`, and all requests will wait for building.

Author: wuct

README.md

@@ -41,7 +41,7 @@ app.use(webpackMiddleware(webpack({
 		// but it will work with other paths too.
 	}
 }), {
-	// publicPath is required, whereas all other options are optional 
+	// publicPath is required, whereas all other options are optional
 
 	noInfo: false,
 	// display no info to console (only warnings and errors)
@@ -70,6 +70,9 @@ app.use(webpackMiddleware(webpack({
 		colors: true
 	}
 	// options for formating the statistics
+
+	serverSideRender: false,
+	// Turn off the server-side rendering mode. See Server-Side Rendering part for more info.
 }));
 ```
 
@@ -109,3 +112,18 @@ This part shows how you might interact with the middleware during runtime:
 	  console.log('Package is in a valid state');
 	});
 	```
+
+## Server-Side Rendering
+In order to develop a server-side rendering application, we need access to the [`stats`](https://github.com/webpack/docs/wiki/node.js-api#stats), which is generated with the latest build.
+
+In the server-side rendering mode, __webpack-dev-middleware__ sets the `stat` to `res.locals.webpackStats`, then call `next()` to trigger the next middleware, where we can render pages and response to clients. During the webpack building process, all requests will be pending until the build is finished and the `stat` is available.
+
+```JavaScript
+app.use(webpackMiddleware(compiler, { serverSideRender: true })
+
+// The following middleware would not be invoked until the latest build is finished.
+app.use((req, res) => {
+  const  assetsByChunkName = res.locals.webpackStats.toJson().assetsByChunkName
+  // then use `assetsByChunkName` for server-sider rendering
+})
+```

middleware.js

@@ -58,6 +58,8 @@ module.exports = function(compiler, options) {
 	compiler.plugin("done", function(stats) {
 		// We are now on valid state
 		state = true;
+		webpackStats = stats
+
 		// Do the stuff in nextTick, because bundle may be invalidated
 		// if a change happened while compiling
 		process.nextTick(function() {
@@ -108,6 +110,8 @@ module.exports = function(compiler, options) {
 	// the state, false: bundle invalid, true: bundle valid
 	var state = false;
 
+	var webpackStats;
+
 	// in lazy mode, rebuild automatically
 	var forceRebuild = false;
 
@@ -194,12 +198,20 @@ module.exports = function(compiler, options) {
 
 	// The middleware function
 	function webpackDevMiddleware(req, res, next) {
+		function goNext() {
+			if(!options.serverSideRender) return next()
+			ready(function() {
+				res.locals.webpackStats = webpackStats
+				next()
+			}, req)
+		}
+
 		if(req.method !== 'GET') {
-			return next();
+			return goNext();
 		}
 
 		var filename = getFilenameFromUrl(req.url);
-		if(filename === false) return next();
+		if(filename === false) return goNext();
 
 		// in lazy mode, rebuild on bundle request
 		if(options.lazy && (!options.filename || options.filename.test(filename)))
@@ -229,7 +241,7 @@ module.exports = function(compiler, options) {
 					}
 				}
 			} catch(e) {
-				return next();
+				return goNext();
 			}
 
 			// server content