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Connect 是一个基于 HTTP 服务器的工具集，成为中间件（middleware）。

中间件，其实就是一个简单的 JavaScript 函数。除了处理 req 和 res 对象之外，还接受一个 next 函数来做流控制。

一个简单的网站

初始化：

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var http = require("http");
var connect = require("connect");
var serveStatic = require("serve-static");
var path = require("path");

var app = connect();

app.use(serveStatic(path.join(__dirname, "public-optimized")));
app.use(serveStatic(path.join(__dirname, "public")));

// respond to all requests
app.use(function(req, res) {
  res.end("Hello from Connect!\n");
});

//create node.js http server and listen on port
http.createServer(app).listen(3000);

中间件的使用，模拟登录登出：

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var http = require("http");
var connect = require("connect");
var morgan = require("morgan");
var bodyParser = require("body-parser");
var cookieParser = require("cookie-parser");
var session = require("express-session");

var users = require("./config/users.json");

var app = connect();

// logger
app.use(morgan("dev"));

// parse an HTML body into a string
app.use(bodyParser());

app.use(cookieParser());

app.use(
  session({
    secret: "my site secret"
  })
);

app.use(function(req, res, next) {
  if ("/" == req.url && req.session.logged_in) {
    res.writeHead(200, { "Content-Type": "text/html" });
    res.end(
      `Welcome back, <b>${req.session.name}</b><a href="/logout">Logout</a>`
    );
  } else {
    next();
  }
});

app.use(function(req, res, next) {
  if ("/" == req.url && "GET" == req.method) {
    res.writeHead(200, { "Content-Type": "text/html" });
    res.end(
      [
        '<form method="POST" action="/login">',
        "<h1>Login</h1>",
        "<fieldset>",
        "<label>Please log in</label>",
        'Username: <input type="text" name="user" /><br>',
        'Password: <input type="password" name="password" />',
        "<p><button>Submit</button></p>",
        "</fieldset>",
        "</form>"
      ].join("")
    );
  } else {
    next();
  }
});

app.use(function(req, res, next) {
  if ("/login" == req.url && "POST" == req.method) {
    res.writeHead(200, { "Content-Type": "text/html" });
    if (
      !users[req.body.user] ||
      req.body.password != users[req.body.user].password
    ) {
      res.end('Bad username/password<br><a href="/">Back</a>');
    } else {
      req.session.logged_in = true;
      req.session.name = users[req.body.user].name;
      res.end("Success!");
    }
  } else {
    next();
  }
});

app.use(function(req, res, next) {
  if ("/logout" == req.url) {
    req.session.logged_in = false;
    res.writeHead(200);
    res.end("Logged out!");
  } else {
    next();
  }
});

//create node.js http server and listen on port
http.createServer(app).listen(3000);
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