I would like to use a middleware for checking users credentials only for some routes (those that start with /user/), but to my surprise server.use does not take a route as first argument and with restify-namespace server.use effect is still global.
Is there other way better than passing my auth middleware to all routes alongside the controller?
I think I'm going to just use server.use and inside the middleware make the following route check:
if (req.url.indexOf('/user/') !== 0) {
return next();
}
Unfortunately restify doesn't seem to be like express, which support the * operator. Hence, What I would suggest is grouping the routes that you desire together and apply a .use before them.
That is:
server.get('/test', function(req, res, next) {
// no magic here. server.use hasn't been called yet.
});
server.use(function(req, res, next) {
// do your magic here
if(some condition) {
// magic worked!
next(); // call to move on to the next middleware.
} else {
// crap magic failed return error perhaps?
next(new Error('some error')); // to let the error handler handle it.
}
});
server.get('/admin/', function(req, res, next) {
// magic has to be performed prior to getting here!
});
server.get('/admin/users', function(req, res, next) {
// magic has to be performed prior to getting here!
});
However, I would personally advocate the use of express, but choose whatever fits your need.
I'm experimenting with KrakenJS, trying to build an basic API to understand things.
One thing I'm unsure of is the middleware, specifically the 404/500 error handling.
"fileNotFound": {
"enabled": true,
"priority": 130,
"module": {
"name":"path:./lib/exceptions/404"
}
}
This catches any 404 errros, and then I handle that myself in my own configuration. However, why is this fileNotFound thrown? Where is serverError thrown for 500 errors?
I would like to define my own files for other exceptions like a 403, however how would I get this to trigger a middleware?
As #HeadCode mentioned, definitely read up on meddleware to understand how middleware gets loaded a bit better.
That said, we have to go over a few things in order to make what's happening more clear.
Handling 404s
First, let's go over how one would typically register a 404 handler in a plain old express app.
Typically you'd have the final middleware in your middleware continuation chain just assume that, if we made it that far without bailing, we simply cannot find the resource. Here's an example:
var express = require('express');
var app = express();
app.get('/firstRoute', function handler(req, res) { res.send('found me'); });
app.get('/secondRoute', function handler(req, res) { res.send('found me'); });
app.use(function notFoundHandler(req, res, next) {
res.status(404).send('Route Not Found');
});
app.listen(8000, function onListen() { console.log('listening on 8000...'); });
Since routes are resolved in the order they're added in Express 4, as long as your 404 handler is last you can be certain no other route matched.
This pattern is briefly described in the Express FAQs.
Handling 500s
Now let's move on to 500s.
Express has the concept of an error-handling middleware (also described on the Express site). An error handling middleware requires an arity of 4 (i.e., takes four arguments) and that's the only difference. They're only executed if an error is signaled which is done by passing an object into your next call. Easier explained in code:
var express = require('express');
var app = express();
app.get('/firstRoute', function handler(req, res) { res.send('found me'); });
app.get('/secondRoute', function handler(req, res) { throw new Error('oops'); });
app.use(function notFoundHandler(req, res, next) {
res.status(404).send('Route Not Found');
});
app.use(function errorHandler(err, req, res, next) {
res.status(500).send('Broken. :(');
});
app.listen(8000, function onListen() { console.log('listening on 8000...'); });
In the above example, errorHandler will only execute if either 1) another middleware or route handler throws an error or 2) we call next with an argument*, .e.g. next(new Error('oops')).
Go ahead and run that. if you visit /notFound or any random route, you'll correctly get a 404. If you visit /firstRoute you'll get found me, and if you go to secondRoute you'll get Broken. :(.
What about kraken?
Kraken—or more accurately, meddleware—just moves defining your middleware into your config. That little block of json you copied above is basically functionally equivalent to the following in a vanilla express app:
var fileNotFound = require('./lib/exceptions/404');
// ... app.use() everything with a priority lower than 130 ...
app.use(fileNotFound());
// ... app.use() everything with a priority *greater* than 130 ...
I just recently started working on an express.js based application, which also uses the pg module (https://github.com/brianc/node-postgres)
I also spent a significant amount of time, reading about node and express approach error handling, the benefits of properly designing middleware, etc. Yet, a recurring problem is still buzzing me without a solution.
Say, I have the following router method:
app.get("/:someThing/:someId", function(req, res, next) {
pgClient.query("some SQL query", function(err, data) {
if (err) { return next(err); } // some 500 handler will take it
if (data.rows.length == 0) {
next(); // send it over to a 404 handler
}
//finally, here we get the chance to do something with the data.
//and send it over via res.json or something else
});
});
If I've read correctly, this should be the proper way to do it. Yet, I bet you can also admt that it is too much of boilerplate to rewrite over and over ... and over again, even in the very same router method, in case we have multiple nested callbacks.
I've been asking myself what the best way to handle such a situation centrally would be. All of my ideas involve intercepting the pgClient.query method. In one, the query method will simply throw the error instead of passing it to the callback. In another, the call to the pgClient.query will send the router method's next to pgClient. Then the intercepted query method will know how to deal with the next being passed to it.
From what I know, throwing errors around is not really the appropriate way to get it to the 500 handlers. On another hand, passin next as an option to pgClient, gives such a low level a lot of knowledge about the the layers above, which based on my knowledge and experience, can lead to coupling, and is not very good either.
What do you suggest?
You can use connect-domain middleware. It works with connect and express and based on Doman API.
You need to add connect-domain middleware as first middleware in stack. Thats all. Now you can throw errors everywhere in your async code and they will be handled with domain middleware and passed to express error handler.
Simple example:
// Some async function that can throw error
var asyncFunction = function(callback) {
process.nextTick(function() {
if (Math.random() > 0.5) {
throw new Error('Some error');
}
callback();
});
};
var express = require('express');
var connectDomain = require('connect-domain');
var app = express();
app.use(connectDomain());
// We need to add router middleware before custom error handler
app.use(app.router);
// Common error handler (all errors will be passed here)
app.use(function(err, req, res, next){
console.error(err.stack);
res.send(500, 'Something broke!');
});
app.listen(3131);
// Simple route
app.get('/', function(req, res, next) {
asyncFunction(function() {
res.send(200, 'OK');
});
});
I use nodeJS and senchalab's connect middleware (not express!!). I need to catch the static errors (like 404). How do i get these? I tried to check the source, but i could not find a way to pass an error-handler to connect.static.
here is a gist of the general structure i (have to) use:
https://gist.github.com/2397415
Based on your routes:
router.routes['/'] = 'my page';
router.routes['/404'] = '404 test';
I think you meant this:
connect()
.use(connect.static(__dirname + '/public'))
.use(function(req, res, next){
switch (req.url) {
case '/404':
var body = '404 test';
res.statusCode = 404;
res.setHeader('Content-Length', body.length);
res.end(body);
break;
default:
var body = 'my page';
res.setHeader('Content-Length', body.length);
res.end(body);
}
})
.listen(3001);
Also I want to add that in old connect version 1.x you can use 'connect.router', but in 2.x version it was removed and moved to express. If you need useful routing system, use express:
Connect was never meant to be used directly, it exists to support
frameworks like Express
You could add a catch-all routes after static and all your routes:
app.get('*', function(req, res){
//respond with 404 page or something.
})
It will catch all unmatched GET requests.
Almost every Express app I see has an app.use statement for middleware but I haven't found a clear, concise explanation of what middleware actually is and what the app.use statement is doing. Even the express docs themselves are a bit vague on this. Can you explain these concepts for me please?
middleware
I'm halfway through separating the concept of middleware in a new project.
Middleware allows you to define a stack of actions that you should flow through. Express servers themselves are a stack of middlewares.
// express
var app = express();
// middleware
var stack = middleware();
Then you can add layers to the middleware stack by calling .use
// express
app.use(express.static(..));
// middleware
stack.use(function(data, next) {
next();
});
A layer in the middleware stack is a function, which takes n parameters (2 for express, req & res) and a next function.
Middleware expects the layer to do some computation, augment the parameters and then call next.
A stack doesn't do anything unless you handle it. Express will handle the stack every time an incoming HTTP request is caught on the server. With middleware you handle the stack manually.
// express, you need to do nothing
// middleware
stack.handle(someData);
A more complete example :
var middleware = require("../src/middleware.js");
var stack = middleware(function(data, next) {
data.foo = data.data*2;
next();
}, function(data, next) {
setTimeout(function() {
data.async = true;
next();
}, 100)
}, function(data) {
console.log(data);
});
stack.handle({
"data": 42
})
In express terms you just define a stack of operations you want express to handle for every incoming HTTP request.
In terms of express (rather than connect) you have global middleware and route specific middleware. This means you can attach a middleware stack to every incoming HTTP requests or only attach it to HTTP requests that interact with a certain route.
Advanced examples of express & middleware :
// middleware
var stack = middleware(function(req, res, next) {
users.getAll(function(err, users) {
if (err) next(err);
req.users = users;
next();
});
}, function(req, res, next) {
posts.getAll(function(err, posts) {
if (err) next(err);
req.posts = posts;
next();
})
}, function(req, res, next) {
req.posts.forEach(function(post) {
post.user = req.users[post.userId];
});
res.render("blog/posts", {
"posts": req.posts
});
});
var app = express.createServer();
app.get("/posts", function(req, res) {
stack.handle(req, res);
});
// express
var app = express.createServer();
app.get("/posts", [
function(req, res, next) {
users.getAll(function(err, users) {
if (err) next(err);
req.users = users;
next();
});
}, function(req, res, next) {
posts.getAll(function(err, posts) {
if (err) next(err);
req.posts = posts;
next();
})
}, function(req, res, next) {
req.posts.forEach(function(post) {
post.user = req.users[post.userId];
});
res.render("blog/posts", {
"posts": req.posts
});
}
], function(req, res) {
stack.handle(req, res);
});
After simplifying things, a web server can be seen as a function that takes in a request and outputs a response. So if you view a web server as a function, you could organize it into several pieces and separate them into smaller functions so that the composition of them will be the original function.
Middlewares are the smaller functions that you can compose with others and the obvious benefit is that you can reuse them.
I add a late answer to add something not mentioned in the previous answers.
By now it should be clear that middleware is/are function(s) run between the client request and the server answer. The most common middleware functionality needed are error managing, database interaction, getting info from static files or other resources. To move on the middleware stack the next callback must be called, you can see it in the end of middleware function to move to the next step in the flow.
You can use the app.use approach and have a flow like this:
var express = require('express'),
app = express.createServer(),
port = 1337;
function middleHandler(req, res, next) {
console.log("execute middle ware");
next();
}
app.use(function (req, res, next) {
console.log("first middle ware");
next();
});
app.use(function (req, res, next) {
console.log("second middle ware");
next();
});
app.get('/', middleHandler, function (req, res) {
console.log("end middleware function");
res.send("page render finished");
});
app.listen(port);
console.log('start server');
but you can also use another approach and pass each middleware as function arguments. Here is a example from the MooTools Nodejs website where midleware gets the Twitter, Github and Blog flow before the response is sent back to the client. Note how the functions are passed as arguments in app.get('/', githubEvents, twitter, getLatestBlog, function(req, res){. Using app.get will only be called for GET requests, app.use will be called for all requests.
// github, twitter & blog feeds
var githubEvents = require('./middleware/githubEvents')({
org: 'mootools'
});
var twitter = require('./middleware/twitter')();
var blogData = require('./blog/data');
function getLatestBlog(req, res, next){
blogData.get(function(err, blog) {
if (err) next(err);
res.locals.lastBlogPost = blog.posts[0];
next();
});
}
// home
app.get('/', githubEvents, twitter, getLatestBlog, function(req, res){
res.render('index', {
title: 'MooTools',
site: 'mootools',
lastBlogPost: res.locals.lastBlogPost,
tweetFeed: res.locals.twitter
});
});
expressjs guide has pretty neat answer to your question, I highly recommend you to read that, I am posting a short snippet of the guide, the guide is quite good.
Writing middleware for use in Express apps
Overview
Middleware functions are functions that have access to the request object (req), the response object (res), and the next function in the application’s request-response cycle. The next function is a function in the Express router which, when invoked, executes the middleware succeeding the current middleware.
Middleware functions can perform the following tasks:
Execute any code.
Make changes to the request and the response objects.
End the request-response cycle.
Call the next middleware in the stack.
If the current middleware function does not end the request-response cycle, it must call next() to pass control to the next middleware function. Otherwise, the request will be left hanging.
Example
Here is an example of a simple “Hello World” Express application. The remainder of this article will define and add two middleware functions to the application: one called myLogger that prints a simple log message and another called requestTime1 that displays the timestamp of the HTTP request.
var express = require('express')
var app = express()
app.get('/', function (req, res) {
res.send('Hello World!')
})
app.listen(3000)
Middleware function myLogger
Here is a simple example of a middleware function called “myLogger”. This function just prints “LOGGED” when a request to the app passes through it. The middleware function is assigned to a variable named myLogger.
var myLogger = function (req, res, next) {
console.log('LOGGED')
next()
}
Notice the call above to next(). Calling this function invokes the next middleware function in the app. The next() function is not a part of the Node.js or Express API, but is the third argument that is passed to the middleware function. The next() function could be named anything, but by convention it is always named “next”. To avoid confusion, always use this convention.
To load the middleware function, call app.use(), specifying the middleware function. For example, the following code loads the myLogger middleware function before the route to the root path (/).
var express = require('express')
var app = express()
var myLogger = function (req, res, next) {
console.log('LOGGED')
next()
}
app.use(myLogger)
app.get('/', function (req, res) {
res.send('Hello World!')
})
app.listen(3000)
Every time the app receives a request, it prints the message “LOGGED” to the terminal.
The order of middleware loading is important: middleware functions that are loaded first are also executed first.
If myLogger is loaded after the route to the root path, the request never reaches it and the app doesn’t print “LOGGED”, because the route handler of the root path terminates the request-response cycle.
The middleware function myLogger simply prints a message, then passes on the request to the next middleware function in the stack by calling the next() function.
This post will only contain myLogger middleware, for further post you could go to the original expressjs guide here.
=====Very very simple explanation=====
Middlewares are often used in the context of Express.js framework and are a fundamental concept for node.js . In a nutshell, Its basically a function that has access to the request and response objects of your application. The way I'd like to think about it, is a series of 'checks/pre-screens' that the request goes through before the it is handled by the application. For e.g, Middlewares would be a good fit to determine if the request is authenticated before it proceeds to the application and return the login page if the request is not authenticated or for logging each request. A lot of third-party middlewares are available that enables a variety of functionality.
Simple Middleware example:
var app = express();
app.use(function(req,res,next)){
console.log("Request URL - "req.url);
next();
}
The above code would be executed for each request that comes in and would log the request url, the next() method essentially allows the program to continue. If the next() function is not invoked, the program would not proceed further and would halt at the execution of the middleware.
A couple of Middleware Gotchas:
The order of middlewares in your application matters, as the request would go through each one in a sequential order.
Forgetting to call the next() method in your middleware function can halt the processing of your request.
Any change the req and res objects in the middleware function, would make the change available to other parts of the application that uses req and res
Middlewares are functions executed in the middle after the input/source then produces an output which could be the final output or could be used by the next middleware until the cycle is complete.
It is like a product that goes through an assembly line where it gets modified as it moves along until it gets completed, evaluated or gets rejected.
A middleware expects some value to work on (i.e. parameter values) and based on some logic the middleware will call or not call the next middleware or send a response back to the client.
If you can't still grasp the middleware concept, it is in a way similar to the Decorator or Chain of command patterns.
Middleware is a subset of chained functions called by the Express js routing layer before the user-defined handler is invoked. Middleware functions have full access to the request and response objects and can modify either of them.
The middleware chain is always called in the exact order in which it has been defined, so it is vital for you to know exactly what a specific piece of middleware is doing. Once a middleware function finishes, it calls the next function in the chain by invoking its next argument as function. After the complete chain gets executed,the user request handler is called.
Keep things simple, man!
Note: the answer is related to the ExpressJS builtin middlware cases, however there are different definitions and use cases of middlewares.
From my point of view, middleware acts as utility or helper functions but its activation and use is fully optional by using the app.use('path', /* define or use builtin middleware */) which don't wants from us to write some code for doing very common tasks which are needed for each HTTP request of our client like processing cookies, CSRF tokens and ..., which are very common in most applications so middleware can help us do these all for each HTTP request of our client in some stack, sequence or order of operations then provide the result of the process as a single unit of client request.
Example:
Accepting clients requests and providing back responses to them according to their requests is the nature of web server technology.
Imagine if we are providing a response with just "Hello, world!" text for a GET HTTP request to our webserver's root URI is very simple scenario and don't needs anything else, but instead if we are checking the currently logged-in user and then responding with "Hello, Username!" needs something more than usual in this case we need a middleware to process all the client request metadata and provide us the identification info grabbed from the client request then according to that info we can uniquely identify our current user and it is possible to response to him/her with some related data.
Hope it to help someone!
In very basic term if i want to explain it like this i learn this from traversymedia youtube channel express crash course.
ok so middle ware is a function who execute after you make a call to your route like this.
var logger = function(req, res, next){
console.log('logging...');
next();
}
app.use(logger);
This logger function execute every time you refresh your page that means you can write anything in it that you required to do after your page get rendered any operation api call, reset things basically anything. and put this middleware before your route function order of middleware is really important or it dons't work