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HTTP

    Messages

The formats of the request meassage and response messages contain Headers and body with some other information. Request messages consist of Request line, Headers, A blank line and Body. Response messages consist of Status line, Headers, A blank line and Body.
Request line has following format;

Request type
space
URL
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HTTP version
Status Line ha following format:
HTTP version
space
Status code
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Status phrase


Request type: methods like GET, POST etc.
URL: destination address to which request to be sent.
HTTP Version: version name of HTTP line 1.1.
Status code: code of three digits in the response message like 200, 404.(see table of status code from return from server )
Status phrase: shows more information of status code like 200 means OK, 404 means resources not found.

Headers : it is used to exchange more information between client and server like Date, Connection, MIME type, Accept etc.
There four types of headers
  • General header :

header
Description
Cache-control
Specifies information about caching
Connection
Shows whether connection should be open or closed
Date
Shows current date
Upgrade
Specifies the preferred communication protocol.
Mime-version
Shows the mime version used
  • Request header
Header
Description
Accept
Media format client can accept
Accept-charset
Shows whether connection should be open or closed
Accept-encoding
Shows current date
Accept-language
Specifies the preferred communication protocol.
Form
The e-mail address of the user
Host
Show the host and port number of the client
If-modified-since
Send the document if newer than specified date
If-match
Send the document if it matches given tag
If-non-match
Send the document if it does not match given tag
If-range
Send only the portion of the document that is missing
If-unmodified-since
Send the document if not changed since specified date
Referrer
Specifies the URL of the linked document
User-agent
Identifies the client program
  • Response Header
header
Description
Accept-range
Shows if server accepts the range requested by client
Age
Shows the age of document
Public
Shows the supported list of methods
Retry-after
Specifies the date after which server is available.
Server
Shows server name and version

  • Entity header:  information about body of document. It used in response messages, requests like POST,PUT methods, that contains body.
header
Description
Allow
List valid methods that can be used within URL
Content-encoding

Content-type
Shows media type
Content-language

Content-length

Content-range

Etag
Gives an entity tag
Expires
Gives the date and time when contents may change
Last-modified
Date and time of last change
Location
Location of create and removal document.


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