Building and Managing Web Sites

1
Building and Managing Web Sites

• HTTP Fundamentals

2
HTTP Introduction

• HTTP -- Hypertext Transfer Protocol
• HTTP is the protocol that WWW requests are based
  upon.
• Standard maintained by W3C at http//www.w3.org/Pr
  otocols/
• HTTP specification defines how client requests
  content from a server and how a server returns a
  response to the client.

3
HTTP Introduction

• Two different versions, 1.0 and 1.1
• Version 1.1 more efficient with larger pages.
• HTTP supports many request types
• PUT and DELETE not commonly used
• GET and POST are primary types.

4
Web Server Fundamentals

• A webserver is software that does the following
• Server receives requests from browser/client for
  resources
• A resource is any chunk of information that can
  be identified by a URL like HMTL or image files,
  scripts, streaming media, etc.
• Server retrieves and/or processes the resource
• Server sends the resource back to the client
• Server logs the transaction
• Responses/requests occur using the HTTP protocol,
  typically on port 80

5
Sample HTTP Exchange

• To retrieve the resource at http//www.host.com/pa
  th/file.html
• Browser sends request to host www.host.com, port
  80
• GET /path/file.html HTTP/1.0
• From 105.123.456.789
• User-Agent Mozilla/4.01
• The server sends a response back to the client
• HTTP/1.0 200 OK
• Date Fri, 31 Dec 1999 235959 GMT
• Content-Type text/html
• Content-Length 1354
• lthtmlgtltbodygtlth1gtHappy New Millenium!lt/h1gt
• (more file contents)
• lt/bodygt
• lt/htmlgt

6
Response Status Line

• Includes three parts separated by spaces
• the HTTP version
• a response status code that gives the result of
  the request
• An English reason phrase describing the status
  code.
• Typical status lines are
• HTTP/1.0 200 OK or
• HTTP/1.0 404 Not Found

7
Common Response Status Codes

• 200 OK - Request succeeded, resulting resource is
  returned in the message body
• 404 Not Found --The requested resource doesn't
  exist.
• 301 Moved Permanently
• 302 Moved Temporarily
• 303 See Other (HTTP 1.1 only) Resource has moved
  to another URL (given by the Location response
  header), and should be automatically retrieved by
  the client.
• 500 Server Error -- Unexpected server error.
  Common caused by a server-side script that has
  bad syntax, fails, or otherwise can't run
  correctly.

8
Response Content-Type

• Response header includes Content-Type to tell
  client/browser how to handle the resource
  (display a browser or launch an
  application/plug-in)
• Based on MIME types for email attachments
• Broad types text, image, audio, video,
  application
• Many different subtypes, always new ones.
• E.g., Content-Type text/html
• Most webservers software have a list of common
  types must define new subtypes on webserver

9
FrontPage and HTTP

• FrontPage uses the HTTP commands PUT and DELETE
• FrontPage can be sensitive to Proxy Servers that
  intercept HTTP requests.
• Can also attach via FTP.