Node.js靜態文件伺服器（改進版）

首先還是先感謝github，感謝github上提供此段源碼的作者。跟昨晚看的靜態文件伺服器來比今天的靜態文件伺服器稍微複雜些，可以學到很多新的東西。
仔細會發現這次的代碼多了一個fs.stat函數和ReadStream對象的pipe函數，stat這個函數是用來獲取文件信息。第一個參數是傳入文件路徑，第二個則是回調函數，回調函數的第二個參數stats的屬性為文件的基本信息。pipe函數用於將這個可讀流和destination目標可寫流連接起來，傳入這個流中的數據將會寫入到destination流中。通過在必要時暫停和恢復流，來源流和目的流得以保持同步。

該靜態文件伺服器的改進點在於使用了Last-Modified和If-Modified-Since報文頭，可以不必要給瀏覽器返回它已經存在的文件。順便可以根據瀏覽器請求資源的壓縮方式返回給資源進行gzip或者deflate壓縮。

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);
                    //獲得文件的修改時間    
                    var lastModified = stats.mtime.toUTCString();
                    var ifModifiedSince = "If-Modified-Since".toLowerCase();
                    //設置Last-Modified
                    //伺服器給瀏覽器返迴文件最後一次修改時間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);
                    }
                    //伺服器接收瀏覽器發送過來的If-Modified-Since報文頭
                    //日期相同表示該資源沒有變化則返回304
                    //告訴瀏覽器該資源你已經有了,不需要再請求了
                    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欄位聲明瞭一個網頁或URL地址不再被瀏覽器緩存的時間，一旦超過了這個時間，瀏覽器都應該聯繫原始伺服器。這裡設置失效時間為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"
};

枚舉各種資源的類型，可根據擴展名設置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"
};