注意：对于所有这些示例，我使用的应用程序结构如下：

.
├── app.js
└── public
    ├── protected
    │   └── file.txt  <-- contains text "protected file"
    └── regular
        └── file.txt  <-- contains text "regular file"

您有两种选择。最简单的方法是让Express 在公共中间件 之前 通过路由器路由请求，从而使您可以截获请求：

var express = require('express');
var http = require('http');
var path = require('path');

var app = express();

// use app.router before express.static
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));

function userIsAllowed(callback) {
  // this function would contain your logic, presumably asynchronous,
  // about whether or not the user is allowed to see files in the
  // protected directory; here, we'll use a default value of "false"
  callback(false);
};

app.get('/', function(req, res, next) {
  res.end('Home page');
});

app.get('/protected/*', function(req, res, next) {
  userIsAllowed(function(allowed) {
    if (allowed) {
      next(); // call the next handler, which in this case is express.static
    } else {
      res.end('You are not allowed!');
    }
  });
});

http.createServer(app).listen(3000, function(){
  console.log('Express server listening on port 3000');
});

结果：

http://localhost:3000/regular/file.txt # regular file
http://localhost:3000/protected/file.txt # You are not allowed!

这种方法的问题在于，在提供静态文件之前，请求必须一直通过应用程序的路由器进行处理，虽然效率不高，但可以满足您的需求（您需要采取一些措施）测量并自己找出）。

另一个选择是在中间件链中插入一个基本功能相同的小功能，但不需要在整个应用路由器中运行：

var express = require('express');
var http = require('http');
var path = require('path');

function userIsAllowed(callback) {
  // this function would contain your logic, presumably asynchronous,
  // about whether or not the user is allowed to see files in the
  // protected directory; here, we'll use a default value of "false"
  callback(false);
};

// This function returns a middleware function
var protectPath = function(regex) {
  return function(req, res, next) {
    if (!regex.test(req.url)) { return next(); }

    userIsAllowed(function(allowed) {
      if (allowed) {
        next(); // send the request to the next handler, which is express.static
      } else {
        res.end('You are not allowed!');
      }
    });
  };
};

var app = express();

app.use(protectPath(/^\/protected\/.*$/));
app.use(express.static(path.join(__dirname, 'public')));

app.get('/', function(req, res, next) {
  res.end('Home page');
});

http.createServer(app).listen(3000, function(){
  console.log('Express server listening on port 3000');
});

这执行的逻辑基本相同，但是它不是在 整个
应用路由器中路由每个请求，而是在每个请求的开头运行一个小功能，以检查所请求的URL是否与您传入的正则表达式匹配。它运行检查以查看用户是否可以访问该文件。

结果：

http://localhost:3000/regular/file.txt # regular file
http://localhost:3000/protected/file.txt # You are not allowed!