HTTP Protocol

• Designed to transfer hypertext

• Designed as a request-response Application layer protocol where a client requests hypertext from a server

• HTML Entity

  • A way of telling the browser to display those characters it would otherwise look at as a tag or part of the programming itself

  Reserved Character in HTML	HTML Entity Version
  "	"
  '	'
  &	&
  <	<
  >	>

HTML Request Methods

• GET Method

  • retrieves whatever information is identified by the Request-URI

  • Visible in a browser

  • can also be used to send data (problem is that it adds the data to the URL)

    • For example: http://www.example.com/checkout?7568.asp/credit1234567890123456

• HEAD Method

  • the server does not have to return a message-body in the response

  • usually used for testing hypertext links for validity, accessibility and recent modification

  • Also used to request headers and metadata

• POST Method

  • Used to request that a web server accepts the data enclosed in the body of the request message, usually by just storing it

  • It is a better and safer method than GET to submit data to a resource for processing

  • Safer because admins can make it so it is not stored in browser history or in the server logs

  • Does not display returned data in the URL

  • Visible with a Wireshark capture

• PUT Method

  • Requests that the enclosed entity be stored under the supplied Request-URI

  • If it points to an existing resource - the enclosed entity should be considered as a modified version of the one already on the origin server

  • If it points to a resource that does not exist - the origin server creates the resource

• DELETE Method

  • Requests that the origin server delete the resource identified by the Request-URI

• TRACE Method

  • Used to invoke a remote, Application layer loopback of the request message

  • Final recipient of the request should reflect the message received back to the client as a 200 (OK) response

• CONNECT Method

  • Reserved for use with a proxy that can dynamically switch to being a tunnel

HTTP Response Messages

• The first digit of the Status Code defines the class or response

• The last two digits do not have any categorization role but define the response intent

  • 1xx: Informational - Request received, continuing process

  • 2xx: Success - Successfully received, understood and accepted

  • 3xx: Redirection - Action has to be taken to complete the request

  • 4xx: Client Error - Request contains bad syntax or cannot be fulfilled

  • 5xx: Server Error - Server failed to fulfill an apparently valid request