Question

Another central module is called "http" . It provides functionality for running HTTP servers and making HTTP requests.

This is all it takes to start a simple HTTP server:

var http = require("http");
var server = http.createServer(function(request, response) {
  response.writeHead(200, {"Content-Type": "text/html"});
  response.write("<h1>Hello!</h1><p>You asked for <code>" +
                 request.url + "</code></p>");
  response.end();
});
server.listen(8000);

If you run this script on your own machine, you can point your web browser at http://localhost:8000/hello to make a request to your server. It will respond with a small HTML page.

The function passed as an argument to createServer is called every time a client tries to connect to the server. The request and response variables are objects representing the incoming and outgoing data. The first contains information about the request, such as its url property, which tells us to what URL the request was made.

To send something back, you call methods on the response object. The first, writeHead , will write out the response headers (see Chapter 17 ). You give it the status code (200 for “OK” in this case) and an object that contains header values. Here we tell the client that we will be sending back an HTML document.

Next, the actual response body (the document itself) is sent with response.write . You are allowed to call this method multiple times if you want to send the response piece by piece, possibly streaming data to the client as it becomes available. Finally, response.end signals the end of the response.

The call to server.listen causes the server to start waiting for connections on port 8000. This is the reason you have to connect to localhost:8000, rather than just localhost (which would use the default port, 80), to speak to this server.

To stop running a Node script like this, which doesn’t finish automatically because it is waiting for further events (in this case, network connections), press Ctrl-C.

A real web server usually does more than the one in the previous example—it looks at the request’s method (the method property) to see what action the client is trying to perform and at the request’s URL to find out which resource this action is being performed on. You’ll see a more advanced server later in this chapter .

To act as an HTTP client, we can use the request function in the "http" module.

var http = require("http");
var request = http.request({
  hostname: "eloquentjavascript.net",
  path: "/20_node.html",
  method: "GET",
  headers: {Accept: "text/html"}
}, function(response) {
  console.log("Server responded with status code",
              response.statusCode);
});
request.end();

The first argument to request configures the request, telling Node what server to talk to, what path to request from that server, which method to use, and so on. The second argument is the function that should be called when a response comes in. It is given an object that allows us to inspect the response, for example to find out its status code.

Just like the response object we saw in the server, the object returned by request allows us to stream data into the request with the write method and finish the request with the end method. The example does not use write because GET requests should not contain data in their request body.

To make requests to secure HTTP (HTTPS) URLs, Node provides a package called https , which contains its own request function, similar to http.request .

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.