Hypertext Transfer Protocol Hypertext Transfer Protocol

HTTP
Hypertext Transfer Protocol

HTTP 2
What It Is
 Protocol for transfer of various data
formats between server and client
– Plaintext
– Hypertext
– Images
– Video
– Sound
 Meta-information also transferred

HTTP 3
Uniform Resources
 URL
– Uniform Resource Locator
– Refers to an existing protocol
 http:, wais:, ftp:, mailto:, gopher:, news:
– Points to a document on a specific server
 URN
– Uniform Resource Name
– Globally unique, persistent identifier
 Independent of location

HTTP 4
Uniform Resources
 URI
– Uniform Resource Identifier
– Collection of URL’s and URN’s

HTTP 5
URL
 <scheme> : //<host> :<port>
/<path> ;<parameters> ?<query>
#<fragment>
– scheme
 The protocol you are using
– host
 Host name or ip number
– port
 TCP port number that protocol server is using
– path
 Path and filename reference of object on server

HTTP 6
URL
 <scheme> : //<host> :<port>
/<path> ;<parameters> ?<query>
#<fragment>
– parameters
 Any specific parameters that object needs
– query
 Query string for a CGI program
– fragment
 Reference to a subset of an object

HTTP 7
URL and HTTP
 All parts of URL, except parameters,
used with http
 Scheme and host can be omitted when
referenced object is on same machine
as referring document
 Port can be omitted so long as
referenced host is running on port listed
in your /etc/services file
– Usually port 80

HTTP 8
URL and HTTP
 Full path used when referring to
another server
– Relative path on same server
 Reference with relative path is a partial URL
 Query passes parameters to CGI
 Fragment jumps to labels within a page
– http://www.x.y/z#foo

HTTP 9
Web Documents
– html
– ASCII text
– Preformatted
 postscript
– Images
 GIF
 JPEG
– Video
 MPEG
– VRML
– Java

HTTP 10
Communication
 Server tells client what type of
information is coming before
information arrives
– File extensions
 .html .htm
 .txt
 .ps
 .au
 .gif .tiff .jpeg
 .mpeg
 .vrml .wrl
 .java

HTTP 11
Communication
 Text and inline images
– Separate objects
 Client browser may optionally send a
list of formats it can accept
 Document can be a program
– Web server executes program and sends
results to client
– Generic term for this program is script,
gateway, or gateway script

HTTP 12
Scripts
 Translates input from client
 Calls other programs
 Translates output from programs and
returns it to client

HTTP 13
Gateways
 Translates from one protocol or service
to another
– HTTP / database query
– Database query results / HTTP

HTTP 14
HTTP 1.0
 Berners Lee, Fielding, Nielsen - 1995
 Used in hypermedia systems distributed
across networks
 Defines request-response conversation
– Requesting program (client) establishes
connection with receiving program (server)
– Client sends request to server
 HTTP specifies syntax

HTTP 15
HTTP 1.0
 Defines request-response conversation
– Server replies with response
 http specifies syntax
 Does not handle network connectivity
or how information is transmitted
 TCP/IP does this

HTTP 16
HTTP 1.0
 HTTP request
– Method
– URI
– Protocol version
– Optional other information
– Method [Request URI] HTTP/1.0 <CRLF>

HTTP 17
HTTP 1.0
 Method
– Get
 Returns object
– Head
 Returns information about object
– Post
 Sends information to be stored on server or as
input to script

HTTP 18
HTTP 1.0
 Method
– Put
 Sends new copy of existing object to server
 Usually not allowed
– Delete
 Deletes object
 Usually not allowed

HTTP 19
HTTP 1.0
 Other information
– User Agent
 Kind of browser
– If-Modified-Since
 Returns object only if more recent than given
date
 Otherwise returns status code 304

HTTP 20
HTTP 1.0
– Accept
 Mime types which browser can accept
– Multipurpose Internet Mail Extension
 text/plain
 text/html
 application/postscript
 image/gif
 image/jpeg
 audio/basic
 video/mpeg
 x-world/x-vrml

HTTP 21
HTTP 1.0
– Authorization
 User password
GET /X/Y/Z.HTML HTTP 1.0
User Agent: Prodigy-WB/1.3e
Accept: text/plain
Accept: text/html
Accept: application/postscript
Accept: image/gif
– Accept: */*

HTTP 22
HTTP 1.0
 HTTP response
– Status line
 HTTP-version Status-code Reason
 Status-codes 1xx - Informational
– Reserved for future use

HTTP 23
HTTP 1.0
 HTTP response
– Status line
 Status-codes 2xx - Success
– The action was successfully received, understood,
and accepted
 200 OK
 201 POST command successful
 202 Request accepted
 203 GET or HEAD request fulfilled
 204 No content

HTTP 24
HTTP 1.0
 HTTP response
– Status line
 Status-codes 3xx - Redirection
– Further action must be taken in order to complete
request
 300 Resource found at multiple locations
 301 Resource moved permanently
 302 Resource moved temporarily
 304 Resource has not modified (since date)

HTTP 25
HTTP 1.0
 HTTP response
– Status line
 Status-codes 4xx - Client error
– The request contains bad syntax or cannot be
fulfilled
 400 Bad request from client
 401 Unauthorized request
 402 Payment required for request
 403 Resource access forbidden
 404 Resource not found
 405 Method not allowed for resource
 406 Resource type not acceptable

HTTP 26
HTTP 1.0
 HTTP response
– Status line
 Status-codes 5xx - Server error
– The server failed to fulfill an apparently valid request
 500 Internal server error
 501 Method not implemented
 502 Bad gateway or server overload
 503 Service unavailable / gateway timeout
 504 Secondary gateway / server timeout

HTTP 27
HTTP 1.0
 HTTP response
– Description of information
 Server Type of server
 Date Date and time
 Content-Length Number of bytes
 Content-Type Mime type
 Content-Language English, for example
 Content-Encoding Data compression
 Last-Modified Date when last modified
 Expires Date when file becomes
invalid

HTTP 28
HTTP 1.0
 Problems
– HTTP is stateless
 Each request requires separate TCP connection
 Server doesn’t remember previous requests

HTTP 29
Evolution of HTTP
 HTTP/0.9 - 1990
– Request method + URI + crlf
 GET /pets/index.html
 Just file contents sent back
– No header information
 Gopher influence
– Media types
 Single character indicated one of ten types

HTTP 30
Evolution of HTTP
 HTTP/1.0 - 1995
– Meta-information between client and
server
 Media types
– MIME type/subtype
 Status codes
 This information influenced the development of
web search engines
– Caching
– Authorization

HTTP 31
Evolution of HTTP
 HTTP/1.0 - 1995
– Problems
 Scalability
– High number of clients visit server for short time
 Flash crowd
 Bandwidth

HTTP 32
Evolution of HTTP
 HTTP/1.1
– Byte ranges
 Request of a document subset
– Adobe's Portable Document Format
– Streaming multimedia
 Eliminates unnecessary client/server
communication
 An interrupted transfer which is restarted can
be more efficient

HTTP 33
Evolution of HTTP
 HTTP/1.1
– Content negotiation with quality factors
 Quality factors
– Real numbers between 0 and 1
 Default is 1
 Accept-Language: fr, en-gb; q=0.8, en; q=0.7

HTTP 34
Evolution of HTTP
 HTTP/1.1
– Chunked encoding
 Transmission of streaming multimedia
– One frame varies in size and composition from the
next
 Streaming video
– Entire image transmitted in first chunk and
differences to the previous image are transmitted in
the next chunk

HTTP 35
Evolution of HTTP
 HTTP/1.1
– Protocol switching
 Client can specify another protocol more suited
to data being transferred
– Message integrity checks
– Digest authentication
 In HTTP/1.0, user sent username and password
over the network
 In HTTP/1.1, the client and the server never
send the actual username or password over the
network

HTTP 36
Evolution of HTTP
 HTTP/1.1
– Persistent connections
 In HTTP/1.0, if a single page includes inline
images, multiple frames, animation, and other
external references, to browse this page would
require many reconnections
 In HTTP/1.1 there are multiple
request/response transactions per connection
 Clients can pipeline requests to the server by
sending multiple requests at start of session

HTTP 37
Evolution of HTTP
 HTTP/1.1
– Cache management with entity tags
 When body of URI changes, so does its entity
tag
– Useful for maintaining caches, as updated URI
information would have a different entity tag
 Can tell if same resource is being cached from
multiple URI's as it would have same entity tag
 Strong entity tag
– Changes when any portion of resource changes
 One or more bytes change
 Weak entity tag
– Changes only when semantics of entity-body
changes

HTTP 38
Evolution of HTTP
 HTTP/1.1
– Software multihoming
 Number of available IP addresses is a concern
 In HTTP/1.0, server could have multiple DNS
entries and IP addresses, each corresponding
to different document tree
 In HTTP/1.1, server could have multiple DNS
entries and only a single IP address

HTTP 39
The Future
 HTTP-Next Generation
– Many channels
 One TCP connection carries multiple channels
for parallel communication
 Different protocols on each channel
– Traditional way
 Multiple TCP connections between same client
and server
 Pages contain images, video, audio, and html

HTTP 40
The Future
 Extensibility
– Adding new MIME headers has been the
traditional way of extending http
– Drawbacks
 No indication whether receiving end
understands these extensions
 No indication whether extension is intended for
all parties along message path or only for
certain intermediaries
 No indication of order in which extensions
should be interpreted

HTTP 41
The Future
 Extensibility
– PEP
 Protocol Extension Protocol

HTTP 42
The Future
 Performance
– Parsing MIME headers wastes resources
– Sticky headers
 Persistent state between multiple http requests
 Not all headers have to be included in every
http message
 Distributed authoring
– Event notification

HTTP 43
The Future
 Caching and replication
– Popular sites are really popular
– Flash crowds happen
– Hot spots on the net are dynamic
– Amount of dynamic data is increasing

HTTP 44
The Future
 QoS
– Quality of service
– Not everything must be treated with same
QoS
– Required QoS should be made at the user-
interface

HTTP 45
The Future
 Real-time protocols and the web
– Streaming protocols
 Audio/video-on-demand

Hypertext Transfer Protocol Hypertext Transfer Protocol

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