首先还是先感谢github，感谢github上提供此段源码的作者。跟昨晚的来比今天的静态文件服务器有点点复杂些，可以学到很多新的东西。

仔细会发现这次的代码多了一个fs.stat函数和ReadStream对象的pipe函数，stat这个函数是用来获取文件信息。第一个参数是传入文件路径，第二个则是回调函数，回调函数的第二个参数stats的属性为文件的基本信息。pipe函数用于将这个可读流和destination目标可写流连接起来，传入这个流中的数据将会写入到destination流中。通过在必要时暂停和恢复流，来源流和目的流得以保持同步。

该静态文件服务器的改进点在于使用了Last-Modified和If-Modified-Since报文头，可以不必要给浏览器返回它已经存在的文件。顺便可以根据浏览器请求资源的压缩方式返回给资源进行gzip或者deflate压缩。

var PORT = 8000;var http = require("http");var url = require("url");var fs = require("fs");var path = require("path");var mime = require("./mime").types;var config = require("./config");var zlib = require("zlib");var server = http.createServer(function(request, response) { response.setHeader("Server", "Node/V5"); var pathname = url.parse(request.url).pathname; console.log("url = " + pathname); if (pathname.slice(-1) === "/") { pathname = pathname + config.Welcome.file; } var realPath = __dirname + "/" + path.join("assets", path.normalize(pathname.replace(/\.\./g, ""))); console.log("realPath = " + realPath); var pathHandle = function (realPath) { fs.stat(realPath, function (err, stats) { if (err) { response.writeHead(404, "Not Found", {'Content-Type': 'text/plain'}); response.write("stats = " + stats); response.write("This request URL " + pathname + " was not found on this server."); response.end(); } else { if (stats.isDirectory()) { realPath = path.join(realPath, "/", config.Welcome.file); pathHandle(realPath); } else { var ext = path.extname(realPath); ext = ext ? ext.slice(1) : 'unknown'; var contentType = mime[ext] || "text/plain"; response.setHeader("Content-Type", contentType); //获得文件的修改时间 var lastModified = stats.mtime.toUTCString(); var ifModifiedSince = "If-Modified-Since".toLowerCase(); //设置Last-Modified //服务器给浏览器返回文件最后一次修改时间Last-Modified response.setHeader("Last-Modified", lastModified); if (ext.match(config.Expires.fileMatch)) { var expires = new Date(); expires.setTime(expires.getTime() + config.Expires.maxAge * 1000); response.setHeader("Expires", expires.toUTCString()); response.setHeader("Cache-Control", "max-age=" + config.Expires.maxAge); } //服务器接收浏览器发送过来的If-Modified-Since报文头 //日期相同表示该资源没有变化则返回304 //告诉浏览器该资源你已经有了,不需要再请求了 if (request.headers[ifModifiedSince] && lastModified == request.headers[ifModifiedSince]) { response.writeHead(304, "Not Modified"); response.end(); } else { var raw = fs.createReadStream(realPath); var acceptEncoding = request.headers['accept-encoding'] || ""; var matched = ext.match(config.Compress.match); if (matched && acceptEncoding.match(/\bgzip\b/)) { response.writeHead(200, "Ok", {'Content-Encoding': 'gzip'}); raw.pipe(zlib.createGzip()).pipe(response); } else if (matched && acceptEncoding.match(/\bdeflate\b/)) { response.writeHead(200, "Ok", {'Content-Encoding': 'deflate'}); raw.pipe(zlib.createDeflate()).pipe(response); } else { response.writeHead(200, "Ok"); raw.pipe(response); } } } } }); }; pathHandle(realPath);});server.listen(PORT);console.log("Server runing at port: " + PORT + ".");

Expires字段声明了一个网页或URL地址不再被浏览器缓存的时间，一旦超过了这个时间，浏览器都应该联系原始服务器。这里设置失效时间为1年。

exports.Expires = { fileMatch: /^(gif|png|jpg|js|css)$/ig, maxAge: 60*60*24*365};exports.Compress = { match: /css|js|html/ig};exports.Welcome = { file: "index.html"};

枚举各种资源的类型，可根据扩展名设置Content-Type。

exports.types = { "css": "text/css", "gif": "image/gif", "html": "text/html", "ico": "image/x-icon", "jpeg": "image/jpeg", "jpg": "image/jpeg", "js": "text/javascript", "json": "application/json", "pdf": "application/pdf", "png": "image/png", "svg": "image/svg+xml", "swf": "application/x-shockwave-flash", "tiff": "image/tiff", "txt": "text/plain", "wav": "audio/x-wav", "wma": "audio/x-ms-wma", "wmv": "video/x-ms-wmv", "xml": "text/xml"};