Build a Node.js HTTP server
The previous article introduced the most basic Node.js program. While the "Hello World" program is good, Node.js is more commonly used to create highly scalable server applications. This article introduces a simple HTTP server built on Node.js.
Key Points
- Node.js allows to create a simple HTTP server, the key step is to create a new file, insert the appropriate code and run the server. The server can be accessed through a web browser through localhost or the machine's IP address. The functionality of the
- server is built on the
require()method (loading the module) and thehttpmethod of thecreateServer()module (creating the server and executing the callback function for each new request). The callback function uses two parameters (request and response) to process client requests and return data.
The - The server uses the
response.writeHead()method to send the HTTP status code and response header back to the client, writes it to the HTML page usingresponse.write(), and ends the response usingresponse.end(). The server uses thelisten()method to listen for incoming connections. Currently, the server can only return a single HTML page, and future enhancements may include reading web pages from the file system and integrating HTTP authentication.
Running the server
First, create a new file named "web_server.js". Insert the following code into the file and save:
var http = require("http");
var server = http.createServer(function(request, response) {
response.writeHead(200, {"Content-Type": "text/html"});
response.write("<!DOCTYPE html>");
response.write("<html>");
response.write("<head>");
response.write("<title>Hello World Page</title>");
response.write("</head>");
response.write("<body>");
response.write("Hello World!");
response.write("</body>");
response.write("</html>");
response.end();
});
server.listen(80);
console.log("Server is listening");
To start the server, type the following command. If everything works fine, you will see a message indicating that the server is listening. Note that the sample server tries to bind to port 80 (standard HTTP port). If this port has been used or is restricted on your machine, you will encounter an error.
node web_server.js
The next step is to use a web browser to connect to the server. Launch the browser of your choice and direct it to any of the following links. In network terms, localhost (and its IP address 127.0.0.1) refers to the machine you are currently using. Your browser should display "Hello World!".
<code>http://localhost http://127.0.0.1</code>
How the server works
Now that the server is up and running, it's time to analyze the code. The first thing to note is the require() call on line 1. Node.js provides a simple module system with a huge developer community. The Node.js program can use the require() method to load a single module. While many modules have to be downloaded, some modules (e.g. http) are included in the Node.js installation. On line 2, use the http method of the createServer() module to create an HTTP server. Like most Node.js functions, createServer() takes the callback function as an argument. This callback function is executed every time the server receives a new request. The callback function accepts two parameters: request and response. The request object contains information about client requests, such as URLs, HTTP headers, etc. Similarly, the response object is used to return data to the client. The callback function first calls the response.writeHead() method. This method sends the HTTP status code and a set of response headers back to the client. The status code is used to indicate the result of the request. For example, everyone has encountered a 404 error before, indicating that the page cannot be found. The sample server returns code 200, indicating success. In addition to the status code, the server returns many HTTP headers that define the parameters of the response. If you do not specify headers, Node.js will send them implicitly for you. The sample server only specifies the Content-Type header. This specific header defines the MIME type of the response. For HTML responses, the MIME type is "text/html". Next, the server performs several calls to response.write(). These calls are used to write to HTML pages. By default, UTF-8 character encoding is used. Technically, all of these calls can be combined into a single call for performance improvement. However, for such a simple example, performance is sacrificed for the readability of the code. After writing to the HTML page, the response.end() method will be called. By calling this method, we tell the server that the response header and body have been sent and that the request has been completed. The sample server calls end() without parameters. However, if you only need to call once, end() can also be called like write(). The listen() call on line 15 causes the server to bind to the port and listen for incoming connections. Computers have thousands of ports that act as communication endpoints. In order to connect to the server, the client must know exactly which port the server is listening on. The port is identified by the port number, and the HTTP server usually listens to port 80.
Conclusion
This article introduces a very basic HTTP server. In its current state, the server can only return a single HTML page. In the next few weeks, we will dive into the world of Node.js, exploring other features such as reading web pages from file systems and integrating HTTP authentication.
FAQ for creating HTTP servers (FAQ)
What is the purpose of the ‘http.createServer()’ method in Node.js?
Thehttp.createServer() method is a built-in function in Node.js to create a new instance of the HTTP server. This server listens for incoming requests and sends a response. It takes a requestListener function as an argument, which is automatically added to the "request" event. This function is called every time the server receives a request. The requestListener function has two parameters: request (an instance of http.IncomingMessage) and response (an instance of http.ServerResponse).
How does the ‘response.writeHead()’ method in Node.js work?
Theresponse.writeHead() method is a function in Node.js that sends response headers to requests. This method accepts two parameters: the status code and a normal object representing the response header. The status code is a 3-bit HTTP status code, and the second parameter is an object where each key-value pair represents a header name and its value. This method must be called before response.end() and can only be called once per response.
What is the difference between ‘write’ and ‘writeHead’ in Node.js?
The and write methods in writeHeadNode.js are used to send server responses. The writeHead method is used to send an HTTP status code and a set of response headers, while the write method is used to send a response body to the client. The writeHead method should be called before write, both should be called before end, and end signals the server that all response headers and body have been sent.
How to use the ‘node-http-server’ package in Node.js?
node-http-server is a simple and easy-to-configure HTTP or HTTPS server for Node.js. To use it, you first need to install it using npm (Node package manager) by running npm install node-http-server. After installation, you can introduce it in the Node.js file and start the server using its deploy method. The deploy method takes the configuration object as a parameter where you can specify server options such as port, root, and serverIndex.
How to handle HTTP requests and responses in Node.js?
In Node.js, you can use the http module to handle HTTP requests and responses. First, you need to create an HTTP server using the http.createServer() method. This method takes the callback function as a parameter, which is executed every time the server receives a request. The callback function has two parameters: request and response. The request object can be used to get information about client requests, such as URLs, HTTP headers, and payloads. The response object is used to send a response to the client. You can set the HTTP status code and header using the response.writeHead() method, write the response body using the response.write() method, and end the response using the response.end() method.
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