web server in node.js

webserver.js

// A very basic web server in node.js
// Stolen from: Node.js for Front-End Developers by Garann Means (p. 9-10)

var port = 8000;
var serverUrl = "127.0.0.1";

var http = require("http");
var path = require("path");
var fs = require("fs");
var checkMimeType = true;

console.log("Starting web server at " + serverUrl + ":" + port);

http.createServer( function(req, res) {

	var now = new Date();

	var filename = req.url || "index.html";
	var ext = path.extname(filename);
	var localPath = __dirname;
	var validExtensions = {
		".html" : "text/html",
		".js": "application/javascript",
		".css": "text/css",
		".txt": "text/plain",
		".jpg": "image/jpeg",
		".gif": "image/gif",
		".png": "image/png",
		".woff": "application/font-woff",
		".woff2": "application/font-woff2"
	};

	var validMimeType = true;
	var mimeType = validExtensions[ext];
	if (checkMimeType) {
		validMimeType = validExtensions[ext] != undefined;
	}

	if (validMimeType) {
		localPath += filename;
		fs.exists(localPath, function(exists) {
			if(exists) {
				console.log("Serving file: " + localPath);
				getFile(localPath, res, mimeType);
			} else {
				console.log("File not found: " + localPath);
				res.writeHead(404);
				res.end();
			}
		});

	} else {
		console.log("Invalid file extension detected: " + ext + " (" + filename + ")")
	}

}).listen(port, serverUrl);

function getFile(localPath, res, mimeType) {
	fs.readFile(localPath, function(err, contents) {
		if(!err) {
			res.setHeader("Content-Length", contents.length);
			if (mimeType != undefined) {
				res.setHeader("Content-Type", mimeType);
			}
			res.statusCode = 200;
			res.end(contents);
		} else {
			res.writeHead(500);
			res.end();
		}
	});
}

In case this might be useful for some, below a more up to date version (as of 2019) of how to serve files with node.js in only 30 lines of code, especially when using node 11.x which deprecated tons of things and now recommends tons of others things.

var http = require('http');
var url = require('url');
var fs = require('fs');
var path = require('path');
var baseDirectory = __dirname;   // or whatever base directory you want

var port = 8080;

http.createServer(function (request, response) {
    try {
        var requestUrl = url.parse(request.url);

        // need to use path.normalize so people can't access directories underneath baseDirectory
        var fsPath = baseDirectory+path.normalize(requestUrl.pathname);

        var fileStream = fs.createReadStream(fsPath);
        fileStream.pipe(response);
        fileStream.on('open', function() {
            response.writeHead(200);
        });
        fileStream.on('error',function(e) {
            response.writeHead(404) ;    // assume the file doesn't exist
            response.end();
        });
    } catch(e) {
        response.writeHead(500);
        response.end() ;    // end the response so browsers don't hang
        console.log(e.stack);
    }
}).listen(port);

console.log("listening on port "+port);

Obviously, it can be implemented a MIME restriction.

This code is not mine. All credits go to Ole Haugset and B T who did it on Stackoverflow for a beginner.

I checked a bit the code, it runs smoothly on node 11.14.0-alpine, follows some recommandations of the official documentation.
For example:

The fs.readFile() function buffers the entire file. To minimize memory costs, when possible prefer streaming via fs.createReadStream().

Line 61: res.setHeader("Content-Length", contents.length); is incorrect.

It can mislead the actual length computation which depends on the data encoding.
Use Buffer.byteLength(string, [encoding]) to solve this.

Ref: Documentation
Ref: Stackoverflow