Requests and responses

Narration uses an AI-generated voice.

[00:00] One question, one answer

By the end of this video, you'll be able to name every part of an HTTP request, and of its response. And you'll know where each part of a web address is used.

Our request has now reached HTTP. HTTP is a conversation of one question, and one answer. The browser sends a request, saying what it wants. The server sends back a response. How it went, and usually, the content. Each exchange stands alone. The server doesn't remember you between requests.

[00:34] A URL, taken apart

Start with the address. It has four parts, each used at a different hop. First, the scheme, https. Encrypt the connection, on port four four three. Next, the host. It's looked up in DNS, then sent again inside the request. Then the path, slash cart. Which page on the site. And the query, after the question mark. Extra values for the server.

[01:02] The request

Now the request itself. Its first line has three parts. The method, POST. That's what you want to do. The path, slash cart. And the HTTP version. Then the headers. Each is a name and a value. The Host header names the site. Others describe the body, or send a cookie. A blank line ends the headers. Then comes the body, here the item for the cart.

[01:29] The Host header

That Host header matters more than it looks. Many sites can share one server, at one IP address. So the address alone can't say which site you meant. The Host header does. The server reads it, and picks the site.

And the method? GET fetches. POST sends data, like that cart item. The next lesson covers the rest.

[01:53] The response

The response has the same shape. First, the status line. The version, then the status, two oh one Created. Three digits that say how it went. Then its headers. Content-Type says the body is JSON. And Set-Cookie asks the browser to store a cookie. Then a blank line, and the body. So every request and response has one shape. A first line, headers, a blank line, then maybe a body. Name the parts, and you can read any of them.

[02:27] One page, many requests

Loading a page is rarely one exchange. The browser fetches the HTML, and reads it. Then it requests every stylesheet, script, image and font the page mentions. Often dozens. To watch them, open the Network tab in your browser's developer tools, and reload.

And since each exchange stands alone, the server can't tell your second request from a stranger's. Unless the request carries something that identifies you. Usually a cookie, which is coming up later in this module.

[03:01] See a real one

You can see a real response yourself. Point curl at a deployed service, asking for just the headers. The first line says HTTP two, two hundred. It answered over HTTP two, with success. Below it are the headers. This body is plain text. HTTP two sends the same parts in a binary format. You read them the same way.

[03:28] Recap

So, a quick recap. A request is a method, a path, headers, and maybe a body. A response is a status, headers, and maybe a body. And the Host header tells a shared server which site you meant.

Now try it. Open the Network tab, reload a page, and pick one request. Name its method, its path, and its status. I'll see you in the next lesson.