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Network Fundamentals

# Introduction
Let's start with a typical example of an HTTP response message:


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 3 parts: an initial **status line**, some **header lines** and an **entity body**.

>**Note: 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 client error
  - 5xx is 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 requested object doesn't exist on the server.
  - **`400 Bad Request`**: generic error code that indicates that the request was in a format that the server could not comprehend.
  - **`500 HTTP Internal Server Error`**: the request could not be completed because the server encountered some unexpected error.

  - **`505 HTTP Version Not Supported`**: the requested HTTP version is not supported by the server.


Have a look at pages 39 and 40 of [RFC 2616](https://www.ietf.org/rfc/rfc2616.txt) for a comprehensive list.

Let's look at what HTTP response messages look like!

HTTP: Response Messages

Introduction