HTTP

1
HTTP
2
Introduction

• Client-Server communication protocol
• Request-response
• Version 1.0
• Stateless
• Version 1.1 adds
• the ability to keep connections open
• virtual hosting
• etc

3
Request/Response

• General Structure
• Start_LineltCRLFgt
• Message HeaderltCRLFgt
• ltCRLFgt
• Message BodyltCRLFgt

4
More Details

• Start_line (Request or Response)
• Request
• MethodltSPgtRequest-URIltSPgtHTTP-VersionltCRLFgt
• Response
• HTTP-VersionltSPgtStatus-codeltSPgtResponse-PhraseltCRL
  Fgt
• Message Header
• Field_nameltSPgtField_value, Field_value
• Message Body
• Binary data

5
HTTP Request Methods

• GET Retrieve the URL
• POST Give information to server
• HEAD Retrieve the header for the URL
• OPTIONS Request available options
• PUT Store document at specified URL
• DELETE Delete specified URL
• and many others

6
Typical Request

• Version 1.0
• Version 1.1

GET /path/file.html HTTP/1.0 From
someuser_at_jmarshall.com User-Agent HTTPTool/1.0
blank line here
GET /path/file.html HTTP/1.1 Host
www.host1.com80 blank line here
7
The GET Method

• Retrieves a URL
• General case is very simple
• Can send information along with URL
• URL?name1value1name2value2
• No Message Body

8
The POST Method

• Send information in the Message Body
• Information is free format

POST /path/script.cgi HTTP/1.0 From
frog_at_jmarshall.com User-Agent HTTPTool/1.0
Content-Type application/x-www-form-urlencoded
Content-Length 32 homeCosbyfavoriteflavorf
lies
9
The HTTP Response

• Status-Line
• HTTP-Version Status-Code Response-Phrase
• Headers
• Content-Type mime-type
• Blank line
• Message Body

10
Status Line

• The HTTP version is in the format "HTTP/x.x".
• The status code is meant to be computer-readable
  the reason phrase is meant to be human-readable,
  and may vary.
• The status code is a three-digit integer
• 1xx indicates an informational message only
• 2xx indicates success of some kind
• 3xx redirects the client to another URL
• 4xx indicates an error on the client's part
• 5xx indicates an error on the server's part

11
Some Status Codes

• 200 OK
• The request succeeded, and the resulting resource
  (e.g. file or script output) is returned in the
  message body
• 404 Not Found
• 301 Moved Permanently
• 302 Moved Temporarily
• 303 See Other (HTTP 1.1 only)
• The resource has moved to another URL (given by
  the Location response header), and should be
  automatically retrieved by the client. This is
  often used by a CGI script to redirect the
  browser to an existing file.
• 500 Server Error

12
Typical Response
HTTP/1.0 200 OK Date Fri, 31 Dec 1999 235959
GMT Content-Type text/html Content-Length
1354 lthtmlgt ltbodygt lth1gtHappy New
Millennium!lt/h1gt (more file contents) . . .
lt/bodygt lt/htmlgt
13
HTTP 1.1

• Additional Headers
• Sockets stay open
• Time-out connection, or
• Connection close header
• Host header is required
• Host www.servername.domain
• Chunked Data