Examine the structure of HTTP requests and responses, including methods, URLs, headers, and bodies.
The entire communication on the web is based on the HTTP request/response cycle. Understanding the anatomy of these messages is crucial for any web developer. An HTTP request, sent by a client (like a browser), has several key components. The Request Line is the first line and contains three parts: the HTTP method (e.g., `GET`, `POST`), the URL of the requested resource (e.g., `/users/123`), and the HTTP version (e.g., `HTTP/1.1`). Following the request line are the Headers, which are a series of key-value pairs that provide additional information about the request. Common request headers include `Host` (the domain of the server), `User-Agent` (information about the client browser), `Accept` (what content types the client can handle), and `Authorization` (for sending authentication credentials). Finally, for methods like `POST` or `PUT`, the request can have a Body, which contains the data being sent to the server (e.g., JSON data for creating a new user). An HTTP response, sent back by the server, has a similar structure. The Status Line is the first line and contains the HTTP version, a status code (e.g., `200`), and a status message (e.g., `OK`). Following this are the response Headers, which provide information about the response. Common response headers include `Content-Type` (the MIME type of the response body, e.g., `application/json`), `Content-Length`, and `Date`. Finally, the response often includes a Body, which contains the actual resource requested (e.g., the HTML of a webpage or the JSON data from an API).