middleware.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
var path = require("path");
var MemoryFileSystem = require("memory-fs");
var mime = require("mime");

// constructor for the middleware
module.exports = function(compiler, options) {
	if(!options) options = {};
	if(options.watchDelay === undefined) options.watchDelay = 200;
	if(typeof options.stats === "undefined") options.stats = {};
	if(!options.stats.context) options.stats.context = process.cwd();

	// store our files in memory
	var files = {};
	var fs = compiler.outputFileSystem = new MemoryFileSystem();

	compiler.plugin("done", function(stats) {
		// We are now on valid state
		state = true;
		// Do the stuff in nextTick, because bundle may be invalidated
		//  if a change happend while compiling
		process.nextTick(function() {
			// check if still in valid state
			if(!state) return;
			// print webpack output
			var displayStats = (!options.quiet && options.stats !== false);
			if(displayStats &&
				!(stats.hasErrors() || stats.hasWarnings()) &&
				options.noInfo)
				displayStats = false;
			if(displayStats) {
				console.log(stats.toString(options.stats));
			}
			if (!options.noInfo && !options.quiet)
				console.info("webpack: bundle is now VALID.");

			// execute callback that are delayed
			var cbs = callbacks;
			callbacks = [];
			cbs.forEach(function continueBecauseBundleAvailible(cb) {
				cb();
			});
		});

		// In lazy mode, we may issue another rebuild
		if(forceRebuild) {
			forceRebuild = false;
			rebuild();
		}
	});

	// on compiling
	function invalidPlugin() {
		if(state && (!options.noInfo && !options.quiet))
			console.info("webpack: bundle is now INVALID.");
		// We are now in invalid state
		state = false;
	}
	compiler.plugin("invalid", invalidPlugin);
	compiler.plugin("compile", invalidPlugin);

	// the state, false: bundle invalid, true: bundle valid
	var state = false;

	// in lazy mode, rebuild automatically
	var forceRebuild = false;

	// delayed callback
	var callbacks = [];

	// wait for bundle valid
	function ready(fn, req) {
		if(state) return fn();
		if(!options.noInfo && !options.quiet)
			console.log("webpack: wait until bundle finished: " + req.url);
		callbacks.push(fn);
	}

	// start watching
	if(!options.lazy) {
		var watching = compiler.watch(options.watchDelay, function(err) {
			if(err) throw err;
		});
	} else {
		state = true;
	}

	function rebuild() {
		if(state) {
			state = false;
			compiler.run(function(err) {
				if(err) throw err;
			});
		} else {
			forceRebuild = true;
		}
	}

	function pathJoin(a, b) {
		return a == "/" ? "/" + b : (a||"") + "/" + b;
	}

	function getFilenameFromUrl(url) {
		// localPreview is the folder our bundle should be in

		var localPrefixes = options.publicPath || ["/"];
    var filename;

    if (typeof localPrefixes == 'string') {
      localPrefixes = [ localPrefixes ];
    }

    for (var i in localPrefixes) {
      var localPrefix = localPrefixes[i];
      if(url.indexOf(localPrefix) !== 0) {
        if(/^(https?:)?\/\//.test(localPrefix)) {
          localPrefix = "/" + localPrefix.replace(/^(https?:)?\/\/[^\/]+\//, "");
          // fast exit if another directory requested
          if(url.indexOf(localPrefix) !== 0) continue;
        } else continue;
      }

      // get filename from request
      filename = url.substr(localPrefix.length);
      if(filename.indexOf("?") >= 0) {
        filename = filename.substr(0, filename.indexOf("?"));
      }
    }

    if (!filename) {
      return false;
    }

		return filename ? pathJoin(compiler.outputPath, filename) : compiler.outputPath;
	}

	// The middleware function
	function webpackDevMiddleware(req, res, next) {
		var filename = getFilenameFromUrl(req.url);
		if (filename === false) return next();


		// in lazy mode, rebuild on bundle request
		if(options.lazy && filename === pathJoin(compiler.outputPath, options.filename))
			rebuild();
		// delay the request until we have a vaild bundle
		ready(function() {
			try {
				var stat = fs.statSync(filename);
				if(!stat.isFile()) {
					if (stat.isDirectory()) {
						filename = path.join(filename, "index.html");
						stat = fs.statSync(filename);
						if(!stat.isFile()) throw "next";
					} else {
						throw "next";
					}
				}
			} catch(e) {
				return next();
			}

			// server content
			var content = fs.readFileSync(filename);
			res.setHeader("Access-Control-Allow-Origin", "*"); // To support XHR, etc.
			res.setHeader("Content-Type", mime.lookup(filename));
			if(options.headers) {
				for(var name in options.headers) {
					res.setHeader(name, options.headers[name]);
				}
			}
			res.end(content);
		}, req);
	}

	webpackDevMiddleware.getFilenameFromUrl = getFilenameFromUrl;

	webpackDevMiddleware.invalidate = function() {
		if(watching) watching.invalidate();
	};
	webpackDevMiddleware.close = function(callback) {
		callback = callback || function(){};
		if(watching) watching.close(callback);
		else callback();
	};

	webpackDevMiddleware.fileSystem = fs;

	return webpackDevMiddleware;
}