Advanced Servers

Last updated last month

Static File Server

One popular use case is to serve files directly from a directory on our machine.

For this, we will setup a configuration module at config.js that contains:

config.js
'use strict'
module.exports = {
staticPath: __dirname // process.cwd()
}

Which our application will include via require('./config') (extensions are optional).

Read File

The most basic way of accomplishing this, is to use fs.readFile

server-readfile.js
'use strict'
// Requires
const httpUtil = require('http')
const fsUtil = require('fs')
const pathUtil = require('path')
const urlUtil = require('url')
const config = require('./config')
// Server
httpUtil.createServer(function (req, res) {
const file = urlUtil.parse(req.url).pathname
const path = pathUtil.join(config.staticPath, file)
fsUtil.exists(path, function (exists) {
if (!exists) {
res.statusCode = 404
return res.end('404 File Not Found')
}
fsUtil.readFile(path, function (error, data) {
if (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
}
return res.end(data)
})
})
}).listen(8080)

Test it: curl http://localhost:8080/server-static.js

However, readFile will read the entire file, then send the entire file. Take a moment to imagine how this not optimum.

Streams

The next most basic way, is to use a Readable Stream via fs.createReadStream.

server-stream.js
'use strict'
// Requires
const httpUtil = require('http')
const fsUtil = require('fs')
const pathUtil = require('path')
const urlUtil = require('url')
const config = require('./config')
// Server
httpUtil.createServer(function (req, res) {
const file = urlUtil.parse(req.url).pathname
const path = pathUtil.join(config.staticPath, file)
fsUtil.exists(path, function (exists) {
if (!exists) {
res.statusCode = 404
return res.end('404 File Not Found')
}
const read = fsUtil.createReadStream(path)
read.on('error', function (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
})
read.pipe(res)
})
}).listen(8080)

Test it: curl http://localhost:8080/server-static.js

Directories

Getting more advanced here. What about outputting the contents of directories too? For this, we can use fs.readdir

server-static.js
'use strict'
// Requires
const httpUtil = require('http')
const fsUtil = require('fs')
const pathUtil = require('path')
const urlUtil = require('url')
const config = require('./config')
// @TODO
// This is getting a bit big, how can we refactor this?
// Can we abstract it out?
// What considerations do we need to take into account?
// How would we add additional actions if we abstract?
// Server
httpUtil.createServer(function (req, res) {
const file = urlUtil.parse(req.url).pathname
const path = pathUtil.join(config.staticPath, file)
fsUtil.exists(path, function (exists) {
if (!exists) {
res.statusCode = 404
return res.end('404 File Not Found')
}
fsUtil.stat(path, function (error, stat) {
if (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
}
if (stat.isDirectory()) {
fsUtil.readdir(path, function (error, files) {
if (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
}
return res.end(files.join('\n'))
})
}
else {
const read = fsUtil.createReadStream(path)
read.on('error', function (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
})
read.pipe(res)
}
})
})
}).listen(8080)

Test it: curl http://localhost:8080

Applying Abstractions

Considering the static file server example is incredibly common. Lets think of ways we can abstract out the serving of static files so we can re-use that functionality easily.

Desiring a solution like:

server-static-module.js
'use strict'
// Requires
const httpUtil = require('http')
const serveStatic = require('./serve-static')
const config = require('./config')
// Server
httpUtil.createServer(function (req, res) {
serveStatic(config.staticPath, req, res)
}).listen(8080)
// Can even do this, due to the simplicity
// httpUtil.createServer(
// serveStatic.bind(null, config.staticPath)
// ).listen(8080)

One could come up with the following:

serve-static.js
'use strict'
// Requires
const fsUtil = require('fs')
const pathUtil = require('path')
const urlUtil = require('url')
// Serve static
module.exports = function (root, req, res, next) {
const file = urlUtil.parse(req.url).pathname
const path = pathUtil.join(root, file)
fsUtil.exists(path, function (exists) {
if (!exists) {
if (next) return next()
res.statusCode = 404
return res.end('404 File Not Found')
}
fsUtil.stat(path, function (error, stat) {
if (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
}
if (stat.isDirectory()) {
fsUtil.readdir(path, function (error, files) {
if (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
}
return res.end(files.join('\n'))
})
}
else {
const read = fsUtil.createReadStream(path)
read.on('error', function (error) {
console.log('Warning:', error.stack)
res.statusCode = 500
return res.end('500 Internal Server Error')
})
read.pipe(res)
}
})
})
}

Note the introduction of a next callback. This allows us to chain additional or custom functionality.

server-static-custom.js
'use strict'
// Requires
const httpUtil = require('http')
const serveStatic = require('./serve-static')
const config = require('./config')
// Server
httpUtil.createServer(function (req, res) {
serveStatic(config.staticPath, req, res, function () {
res.statusCode = 404
res.end('404 Not Found. 🙁 \n')
})
}).listen(8080)

Introduction to Middlewares

In our previous example of writing the serveStatic what we effectively did was create a middleware, albiet a basic middleware but a middleware nonetheless. Naturally, there are already plenty of other middlewares published as modules by other people. This is helped by the middleware framework Connect originally by TJ Holowaychuk.

Before we can install anything, we need to first initialise our directory as a node.js project:

npm init

That will create a package.json file that will keep track of the dependencies we install.

We can install connect like so:

npm install --save connect

Using connect, our static file server example would become:

connect-static.js
'use strict'
// Requires
const connect = require('connect')
const config = require('./config')
// Server
const app = connect()
// Middlewares
// Use our local static middleware
app.use(require('./serve-static').bind(null, config.staticPath))
// Create the fallback middleware for when the route was not found
app.use(function (req, res) {
res.statusCode = 404
res.end('404 Not Found. 🙁 \n')
})
// Listen
app.listen(8080)

Much simpler. Notice how the middlewares are like a waterfall, it hits the first, then if the first doesn't know what to do, the logic will flow through to the next middleware (accomplished by the previous middleware calling the next callback inside it).

Connect has plenty of other middlewares available for it. Official middlewares for connect are listed on its website with 3rd party middleware listed on GitHub.

There is even existing middlewares for what we've just accomplished. We can install them like so:

npm install --save serve-static serve-index

And consume them like so:

connect-community.js
'use strict'
// Requires
const connect = require('connect')
const config = require('./config')
// Server
const app = connect()
// Middlewares
// Serve the files at the static path
app.use(require('serve-static')(config.staticPath))
// If a directory is requested, serve its index.html file if it has one
app.use(require('serve-index')(config.staticPath))
// If none of the previous middlewares matched, then fallback to 404
app.use(function (req, res) {
res.statusCode = 404
res.end('404 Not Found. 🙁 \n')
})
// Listen
app.listen(8080)

Introduction to Web Frameworks

There are a few web frameworks for node. The most used is Express originally by TJ Holowaychuk.

Perhaps by now you would have noticed the amount of individuals mentioned who have created awesome things, this is very much the case, anyone can have an impact.

Express can be thought of as a layer that sits ontop of connect and node's http module. It provides its own middleware and uses its own request and response objects that inherit from those of node's http module. The benefit over just using connect are:

  • Addition of routing

  • Common functionality provided through a friendly syntax

We can install express like so:

npm install --save express

The following is what a simple hello world server would look like with express:

express-basic.js
'use strict'
// Requires
const express = require('express')
// Application
const app = express()
// Routes
// These make things easier
app.get('/', function (req, res) {
res.send('hello world')
})
// Fallback middleware
app.use(function (req, res) {
res.send(404, '404 Not Found. 🙁 \n')
// ^ this is different from connect
})
// Server
const server = app.listen(8080)

It is important to note that the line var server = app.listen(8080); is the same as doing var server = require('http').createServer(app).listen(8080);. You will need to remember this when interfacing with other modules - some modules like to interface with the express instance app while others like to interface with the node http server instance server instead.

And this is what our static file server will look like with express:

express-static.js
'use strict'
// Requires
const express = require('express')
const config = require('./config')
// Application
const app = express()
// Middlewares
// Use our local one
app.use(require('./serve-static').bind(null, config.staticPath))
// Use the prexisting ones
// app.use(require('serve-static')(config.staticPath))
// app.use(require('serve-index')(config.staticPath))
// Fallback middleware
app.use(function (req, res) {
res.send(404, '404 Not Found. 🙁 \n')
})
// Server
const server = app.listen(8080)

Notice the nicer syntax for setting the status code of the response. Before it was res.statusCode = 404; now it is the first argument of res.send. This is what we meant by express providing a nicer syntax.