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Web Development Interview Handbook

HTTP: Response Messages

Explore HTTP response messages to understand their structure, including status lines, headers, and the response body. Learn how status codes communicate request results and how headers like Cache-Control and ETag manage caching and security. This lesson equips you to recognize key HTTP response components essential for web development and debugging.

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Introduction

Let’s start with a typical example of an HTTP response message:

Shell
HTTP/1.1 200 OK
Connection: close
Date: Tue, 18 Aug 2015 15: 44 : 04 GMT
Server: Apache/2.2.3 (CentOS)
Last-Modified: Tue, 18 Aug 2015 15:11:03 GMT 
Content-Length: 6821
Content-Type: text/html
[The object that was requested]

It has three parts: an initial status line, some header lines, and an entity body.

📝 HTTP response messages don’t have the URL or the method fields. Those are strictly for request messages.

Status line

  • HTTP response status lines start with the HTTP version.

Status code

  • The status code comes next, which tells the client if the request succeeded or failed.
  • There are a lot of status codes:
    • 1xx codes fall in the informational category
    • 2xx codes fall in the success category
    • 3xx codes are for redirection
    • 4xx is a client error
    • 5xx is a server error

Here is a list of some common status codes and their meanings:

  • 200 OK: the request was successful, and the result is appended with the response message.

  • 404 File Not Found: the ...