HTTPHTTP

HypertextHypertext TransferTransfer ProtocolProtocol WhatWhat ItIt IsIs

n ProtocolProtocol forfor transfertransfer ofof variousvarious datadata formatsformats betweenbetween serverserver andand clientclient – Plaintext – Hypertext – Images – Video – Sound n MetaMeta--informationinformation alsoalso transferredtransferred

HTTP 2 UniformUniform ResourcesResources

n URLURL – Uniform Resource Locator – Refers to an existing protocol

n http:, wais:, ftp:, mailto:, gopher:, news: – Points to a document on a specific server n URNURN – Uniform Resource Name – Globally unique, persistent identifier

n Independent of location

HTTP 3 UniformUniform ResourcesResources

n URIURI – Uniform Resource Identifier – Collection of URL’s and URN’s

HTTP 4 URLURL

n :: //// :: // ;; ?? ## – scheme n The protocol you are using – host n Host name or ip number – port n TCP port number that protocol server is using – path n Path and filename reference of object on server HTTP 5 URLURL

n :: //// :: // ;; ?? ## – parameters n Any specific parameters that object needs – query n Query string for a CGI program – fragment n Reference to a subset of an object

HTTP 6 URLURL andand HTTPHTTP

n AllAll partsparts ofof URL,URL, exceptexcept parameters,parameters, usedused withwith httphttp n SchemeScheme andand hosthost cancan bebe omittedomitted whenwhen referencedreferenced objectobject isis onon samesame machinemachine asas referringreferring documentdocument n PortPort cancan bebe omittedomitted soso longlong asas referencedreferenced hosthost isis runningrunning onon portport listedlisted inin youryour /etc/services/etc/services filefile – Usually port 80 HTTP 7 URLURL andand HTTPHTTP

n FullFull pathpath usedused whenwhen referringreferring toto anotheranother serverserver – Relative path on same server

n Reference with relative path is a partial URL n QueryQuery passespasses parametersparameters toto CGICGI n FragmentFragment jumpsjumps toto labelslabels withinwithin aa pagepage – http://www.x.y/z#foo

HTTP 8 WebWeb DocumentsDocuments

– html – ASCII text – Preformatted n postscript – Images n GIF n JPEG – Video n MPEG – VRML – Java HTTP 9 CommunicationCommunication

n ServerServer tellstells clientclient whatwhat typetype ofof informationinformation isis comingcoming beforebefore informationinformation arrivesarrives – File extensions n .html .htm n .txt n .ps n .au n .gif .tiff .jpeg n .mpeg n .vrml .wrl n .java HTTP .java 10 CommunicationCommunication

n TextText andand inlineinline imagesimages – Separate objects n ClientClient browserbrowser maymay optionallyoptionally sendsend aa listlist ofof formatsformats itit cancan acceptaccept n DocumentDocument cancan bebe aa programprogram – Web server executes program and sends results to client – Generic term for this program is script, gateway, or gateway script HTTP gateway, or gateway script 11 ScriptsScripts

n TranslatesTranslates inputinput fromfrom clientclient n CallsCalls otherother programsprograms n TranslatesTranslates outputoutput fromfrom programsprograms andand returnsreturns itit toto clientclient

HTTP 12 GatewaysGateways

n TranslatesTranslates fromfrom oneone protocolprotocol oror serviceservice toto anotheranother – HTTP / database query – Database query results / HTTP

HTTP 13 HTTPHTTP 1.01.0

n BernersBerners Lee,Lee, Fielding,Fielding, NielsenNielsen -- 19951995 n UsedUsed inin hypermediahypermedia systemssystems distributeddistributed acrossacross networksnetworks n DefinesDefines requestrequest--responseresponse conversationconversation – Requesting program (client) establishes connection with receiving program (server) – Client sends request to server

n HTTP specifies syntax

HTTP 14 HTTPHTTP 1.01.0

n DefinesDefines requestrequest--responseresponse conversationconversation – Server replies with response

n http specifies syntax n DoesDoes notnot handlehandle networknetwork connectivityconnectivity oror howhow informationinformation isis transmittedtransmitted

n TCP/IP does this

HTTP 15 HTTPHTTP 1.01.0

n HTTPHTTP requestrequest – Method – URI – Protocol version – Optional other information – Method [Request URI] HTTP/1.0

HTTP 16 HTTPHTTP 1.01.0

n MethodMethod – Get

n Returns object – Head

n Returns information about object – Post

n Sends information to be stored on server or as input to script

HTTP 17 HTTPHTTP 1.01.0

n MethodMethod – Put

n Sends new copy of existing object to server

n Usually not allowed – Delete

n Deletes object

n Usually not allowed

HTTP 18 HTTPHTTP 1.01.0

n OtherOther informationinformation – User Agent

n Kind of browser – If-Modified-Since

n Returns object only if more recent than given date

n Otherwise returns status code 304

HTTP 19 HTTPHTTP 1.01.0

n OtherOther informationinformation – Accept

n Mime types which browser can accept – Multipurpose Internet Mail Extension

n text/plain

n text/html

n application/postscript

n image/gif

n image/jpeg

n audio/basic

n video/mpeg

n x-world/x-vrml HTTP 20 HTTPHTTP 1.01.0

n OtherOther informationinformation – Authorization

n 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 21 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Status line

n HTTP-version Status-code Reason

n Status-codes 1xx - Informational – Reserved for future use

HTTP 22 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Status line

n Status-codes 2xx - Success – The action was successfully received, understood, and accepted

n 200 OK

n 201 POST command successful

n 202 Request accepted

n 203 GET or HEAD request fulfilled

n 204 No content

HTTP 23 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Status line

n Status-codes 3xx - Redirection – Further action must be taken in order to complete request

n 300 Resource found at multiple locations

n 301 Resource moved permanently

n 302 Resource moved temporarily

n 304 Resource has not modified (since date)

HTTP 24 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Status line

n Status-codes 4xx - Client error – The request contains bad syntax or cannot be fulfilled

n 400 Bad request from client

n 401 Unauthorized request

n 402 Payment required for request

n 403 Resource access forbidden

n 404 Resource not found

n 405 Method not allowed for resource

HTTP n 406 Resource type not acceptable 25 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Status line

n Status-codes 5xx - Server error – The server failed to fulfill an apparently valid request

n 500 Internal server error

n 501 Method not implemented

n 502 Bad gateway or server overload

n 503 Service unavailable / gateway timeout

n 504 Secondary gateway / server timeout

HTTP 26 HTTPHTTP 1.01.0

n HTTPHTTP responseresponse – Description of information

n Server Type of server

n Date Date and time

n Content-Length Number of bytes

n Content-Type Mime type

n Content-Language English, for example

n Content-Encoding Data compression

n Last-Modified Date when last modified

n Expires Date when file becomes invalid HTTP invalid 27 HTTPHTTP 1.01.0

n ProblemsProblems – HTTP is stateless

n Each request requires separate TCP connection

n Server doesn’t remember previous requests

HTTP 28 EvolutionEvolution ofof HTTPHTTP

n HTTP/0.9HTTP/0.9 -- 19901990 – Request method + URI + crlf

n GET /pets/index.html

n Just file contents sent back – No header information n GopherGopher influenceinfluence – Media types

n Single character indicated one of ten types

HTTP 29 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.0HTTP/1.0 -- 19951995 – Meta-information between client and server

n Media types – MIME type/subtype

n Status codes

n This information influenced the development of web search engines – Caching – Authorization HTTP 30 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.0HTTP/1.0 -- 19951995 – Problems

n Scalability – High number of clients visit server for short time

n Flash crowd

n Bandwidth

HTTP 31 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Byte ranges

n Request of a document subset – Adobe's Portable Document Format – Streaming multimedia

n Eliminates unnecessary client/server communication

n An interrupted transfer which is restarted can be more efficient

HTTP 32 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Content negotiation with quality factors

n Quality factors – Real numbers between 0 and 1

n Default is 1

n Accept-Language: fr, en-gb; q=0.8, en; q=0.7

HTTP 33 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Chunked encoding

n Transmission of streaming multimedia – One frame varies in size and composition from the next

n Streaming video – Entire image transmitted in first chunk and differences to the previous image are transmitted in the next chunk

HTTP 34 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Protocol switching

n Client can specify another protocol more suited to data being transferred – Message integrity checks – Digest authentication

n In HTTP/1.0, user sent username and password over the network

n In HTTP/1.1, the client and the server never send the actual username or password over the network HTTP 35 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Persistent connections

n 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

n In HTTP/1.1 there are multiple request/response transactions per connection

n Clients can pipeline requests to the server by sending multiple requests at start of session

HTTP 36 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Cache management with entity tags n When body of URI changes, so does its entity tag – Useful for maintaining caches, as updated URI information would have a different entity tag n Can tell if same resource is being cached from multiple URI's as it would have same entity tag n Strong entity tag – Changes when any portion of resource changes

n One or more bytes change n Weak entity tag – Changes only when semantics of entity-body HTTP changes 37 EvolutionEvolution ofof HTTPHTTP

n HTTP/1.1HTTP/1.1 – Software multihoming

n Number of available IP addresses is a concern

n In HTTP/1.0, server could have multiple DNS entries and IP addresses, each corresponding to different document tree

n In HTTP/1.1, server could have multiple DNS entries and only a single IP address

HTTP 38 TheThe FutureFuture

n HTTPHTTP--NextNext GenerationGeneration – Many channels

n One TCP connection carries multiple channels for parallel communication

n Different protocols on each channel – Traditional way

n Multiple TCP connections between same client and server

n Pages contain images, video, audio, and html

HTTP 39 TheThe FutureFuture

n ExtensibilityExtensibility – Adding new MIME headers has been the traditional way of extending http – Drawbacks

n No indication whether receiving end understands these extensions

n No indication whether extension is intended for all parties along message path or only for certain intermediaries

n No indication of order in which extensions should be interpreted HTTP 40 TheThe FutureFuture

n ExtensibilityExtensibility – PEP

n Protocol Extension Protocol

HTTP 41 TheThe FutureFuture

n PerformancePerformance – Parsing MIME headers wastes resources – Sticky headers

n Persistent state between multiple http requests

n Not all headers have to be included in every http message n DistributedDistributed authoringauthoring – Event notification

HTTP 42 TheThe FutureFuture

n CachingCaching andand replicationreplication – Popular sites are really popular – Flash crowds happen – Hot spots on the net are dynamic – Amount of dynamic data is increasing

HTTP 43 TheThe FutureFuture

n QoSQoS – Quality of service – Not everything must be treated with same QoS – Required QoS should be made at the user- interface

HTTP 44 TheThe FutureFuture

n RealReal--timetime protocolsprotocols andand thethe webweb – Streaming protocols

n Audio/video-on-demand

HTTP 45