The document describes the structure and components of HTTP request and response messages. It explains that an HTTP request contains a request line with the method, URL and HTTP version, header lines with additional fields like Host and User-Agent, and an optional message body. A response contains a status line with the protocol version, status code and message, header lines including Date, Server and Content-Type, and a message body containing the requested object. Common status codes like 200, 301 and 404 are also defined.

1. Chapter 2
Application Layer
Computer Networking: A
Top Down Approach,
4th edition.
Jim Kurose, Keith Ross
Addison-Wesley, July
2007.

2. HTTP Request Message
Two types of HTTP messages:
Request, Response
HTTP request message:
Human-readable format
A typical HTTP request message
GET /somedir/page.html HTTP/1.1
Host: www.someschool.edu
User-agent: Mozilla/4.0
Connection: close
Accept-language:fr
(Blank Line)
Body

3. HTTP Request Message
• Request Line
 First Line of HTTP request message
 The request line has three fields
 Method field can take on several values
GET,POST, PUT, DELETE etc
Majority of HTTP request messages use GET
 URL field
 HTTP version field
• Header Lines
– Host: Host on which the object resides
– User-agent: Identifies the client program e.g. Mozilla/4.0
– Connection: Shows whether the connection should be closed
or not
– Accept-language: Shows the language the client prefers

4. HTTP Request Message
• Body is empty with GET
method
• Used with the POST
method
– Web page often
includes form input
– Input is sent to
server in body
PUT method:
• To upload objects to
web server
DELETE method
• Allows a user or an
application to delete
an object on web
server
Find out about OPTIONS, TRACE, HEAD?

5. HTTP Response Message
HTTP/1.1 200 OK
Connection: close
Date: Thu, 06 Aug 1998 12:00:15
GMT
Server: Apache/1.3.0 (Unix)
Last-Modified: Mon, 22 Jun 1998
Content-Length: 6821
Content-Type: text/html
Body contains Requested Object

6. HTTP Response Message
• Status Line
– Protocol Version
– Status Code and Status Message
 The status code and associated phrase indicate the result of the request
• Header Line
 Connection: Shows whether the connection should be
closed or not
 Date and time: When the HTTP response was created
 Server: Analogous to user-agent in request message
 Last-modified: When the Object was last created or
modified
 Content-length: Number of bytes in object being sent
 Content-Type: Indicates the object type (HTML text etc.)

7. HTTP Response Status Codes
The status code and associated phrase indicate the
result of the request
200 OK
– Request succeeded and information is returned
in response
301 Moved Permanently
– Requested object moved, new location specified
later in this message (Location:)
404 Not Found
– Requested document not found on this server
505 Version not supported
– HTTP version is not supported by the server