How do web servers process HTTP requests?

Web servers process HTTP requests by receiving the request, interpreting it, and returning the requested resource or error message.

When a client, such as a web browser, sends an HTTP request to a web server, the server first receives the request. This request is typically sent over the internet using the TCP/IP protocol. The server listens on a specific port (usually port 80 for HTTP and port 443 for HTTPS) for incoming requests.

Once the server receives the request, it needs to interpret it. The HTTP request contains various pieces of information that the server uses to understand what is being asked. This includes the request method (such as GET, POST, PUT, DELETE), the URL, and possibly additional data in the form of headers or a message body. The server analyses this information to determine what resource the client is asking for and how to process the request.

After interpreting the request, the server will attempt to fulfil it. If the client has requested a specific file or page, the server will locate that resource on its system. If the resource exists and the client has the necessary permissions, the server will send the resource back to the client in the body of an HTTP response. The response also includes a status code and headers, which provide additional information about the result of the request.

However, not all requests can be fulfilled. If the requested resource does not exist, the server will return a 404 Not Found status code. If the client does not have the necessary permissions, the server will return a 403 Forbidden status code. There are many other possible status codes, each indicating a different outcome of the request.

In addition to processing individual requests, web servers also need to handle multiple simultaneous connections. This is typically done using a combination of multi-threading and multiplexing. The server may also use caching to store the results of common requests, reducing the amount of work needed to process these requests in the future.

In summary, the process of handling an HTTP request involves receiving the request, interpreting it, and returning the requested resource or an error message. This process is fundamental to the operation of the World Wide Web.