How to protect public dynamic folder in nodejs

Note. For all these examples, I use an application structured as follows:

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

You have several options. The simplest one is to Express route the request through your router before the public middleware, allowing you to intercept the request:

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');
});

Results:

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

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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');
});

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:

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