HTTP Hypertext Transfer Protocol. HTTP2 What It Is n Protocol for transfer of various data formats between server and client –Plaintext –Hypertext –Images

HTTPHTTP

Hypertext Transfer Hypertext Transfer ProtocolProtocol

HTTP 2

What It IsWhat It Is

Protocol for transfer of various data Protocol for transfer of various data formats between server and clientformats between server and client– PlaintextPlaintext– HypertextHypertext– ImagesImages– VideoVideo– SoundSound

Meta-information also transferredMeta-information also transferred

HTTP 3

Uniform ResourcesUniform Resources

URLURL– Uniform Resource LocatorUniform Resource Locator– Refers to an existing protocolRefers to an existing protocol

http:, wais:, ftp:, mailto:, gopher:, news:http:, wais:, ftp:, mailto:, gopher:, news:

– Points to a document on a specific serverPoints to a document on a specific server URNURN

– Uniform Resource NameUniform Resource Name– Globally unique, persistent identifierGlobally unique, persistent identifier

Independent of locationIndependent of location

HTTP 4

Uniform ResourcesUniform Resources

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

HTTP 5

URLURL <scheme> : //<host> :<port> /<path> <scheme> : //<host> :<port> /<path>

;<parameters> ?<query> ;<parameters> ?<query> #<fragment>#<fragment>– schemescheme

The protocol you are usingThe protocol you are using– hosthost

Host name or ip numberHost name or ip number– portport

TCP port number that protocol server is usingTCP port number that protocol server is using– pathpath

Path and filename reference of object on serverPath and filename reference of object on server

HTTP 6

URLURL

<scheme> : //<host> :<port> <scheme> : //<host> :<port> /<path> ;<parameters> ?/<path> ;<parameters> ?<query> #<fragment><query> #<fragment>– parametersparameters

Any specific parameters that object Any specific parameters that object needsneeds

– queryquery Query string for a CGI programQuery string for a CGI program

– fragmentfragment Reference to a subset of an objectReference to a subset of an object

HTTP 7

URL and HTTPURL and HTTP

All parts of URL, except parameters, All parts of URL, except parameters, used with httpused with http

Scheme and host can be omitted Scheme and host can be omitted when referenced object is on same when referenced object is on same machine as referring documentmachine as referring document

Port can be omitted so long as Port can be omitted so long as referenced host is running on port referenced host is running on port listed in your /etc/services filelisted in your /etc/services file– Usually port 80Usually port 80

HTTP 8

URL and HTTPURL and HTTP

Full path used when referring to Full path used when referring to another serveranother server– Relative path on same serverRelative path on same server

Reference with relative path is a Reference with relative path is a partialpartial URLURL

Query passes parameters to CGIQuery passes parameters to CGI Fragment jumps to labels within a Fragment jumps to labels within a

pagepage– http://www.x.y/z#foohttp://www.x.y/z#foo

HTTP 9

Web DocumentsWeb Documents

– htmlhtml– ASCII textASCII text– PreformattedPreformatted

postscriptpostscript– ImagesImages

GIFGIF JPEGJPEG

– VideoVideo MPEGMPEG

– VRMLVRML– JavaJava

HTTP 10

CommunicationCommunication Server tells client what type of Server tells client what type of

information is coming before information is coming before information arrivesinformation arrives– File extensionsFile extensions

.html .htm.html .htm .txt.txt .ps.ps .au.au .gif .tiff .jpeg.gif .tiff .jpeg .mpeg.mpeg .vrml .wrl.vrml .wrl .java.java

HTTP 11

CommunicationCommunication

Text and inline imagesText and inline images– Separate objectsSeparate objects

Client browser may optionally send a Client browser may optionally send a list of formats it can acceptlist of formats it can accept

Document can be a programDocument can be a program– Web server executes program and sends Web server executes program and sends

results to clientresults to client– Generic term for this program is Generic term for this program is scriptscript, ,

gatewaygateway, or , or gateway scriptgateway script

HTTP 12

ScriptsScripts

Translates input from clientTranslates input from client Calls other programsCalls other programs Translates output from programs Translates output from programs

and returns it to clientand returns it to client

HTTP 13

GatewaysGateways

Translates from one protocol or Translates from one protocol or service to anotherservice to another– HTTP / database queryHTTP / database query– Database query results / HTTPDatabase query results / HTTP

HTTP 14

HTTP 1.0HTTP 1.0

Berners Lee, Fielding, Nielsen - 1995Berners Lee, Fielding, Nielsen - 1995 Used in hypermedia systems Used in hypermedia systems

distributed across networksdistributed across networks Defines request-response Defines request-response

conversationconversation– Requesting program (client) establishes Requesting program (client) establishes

connection with receiving program connection with receiving program (server)(server)

– Client sends request to serverClient sends request to server HTTP specifies syntaxHTTP specifies syntax

HTTP 15

HTTP 1.0HTTP 1.0

Defines request-response Defines request-response conversationconversation– Server replies with responseServer replies with response

http specifies syntaxhttp specifies syntax

Does not handle network Does not handle network connectivity or how information is connectivity or how information is transmittedtransmitted

TCP/IP does thisTCP/IP does this

HTTP 16

HTTP 1.0HTTP 1.0

HTTP requestHTTP request– MethodMethod– URIURI– Protocol versionProtocol version– Optional other informationOptional other information– Method [Request URI] HTTP/1.0 Method [Request URI] HTTP/1.0

<CRLF><CRLF>

HTTP 17

HTTP 1.0HTTP 1.0

MethodMethod– GetGet

Returns objectReturns object

– HeadHead Returns information about objectReturns information about object

– PostPost Sends information to be stored on server Sends information to be stored on server

or as input to scriptor as input to script

HTTP 18

HTTP 1.0HTTP 1.0

MethodMethod– PutPut

Sends new copy of existing object to Sends new copy of existing object to serverserver

Usually not allowedUsually not allowed

– DeleteDelete Deletes objectDeletes object Usually not allowedUsually not allowed

HTTP 19

HTTP 1.0HTTP 1.0

Other informationOther information– User AgentUser Agent

Kind of browserKind of browser

– If-Modified-SinceIf-Modified-Since Returns object only if more recent than Returns object only if more recent than

given dategiven date Otherwise returns status code 304Otherwise returns status code 304

HTTP 20

HTTP 1.0HTTP 1.0

Other informationOther information– AcceptAccept

Mime types which browser can acceptMime types which browser can accept– Multipurpose Internet Mail ExtensionMultipurpose Internet Mail Extension

text/plaintext/plain text/htmltext/html application/postscriptapplication/postscript image/gifimage/gif image/jpegimage/jpeg audio/basicaudio/basic video/mpegvideo/mpeg x-world/x-vrmlx-world/x-vrml

HTTP 21

HTTP 1.0HTTP 1.0

Other informationOther information– AuthorizationAuthorization

User passwordUser passwordGET /X/Y/Z.HTML HTTP 1.0GET /X/Y/Z.HTML HTTP 1.0

User Agent: Prodigy-WB/1.3eUser Agent: Prodigy-WB/1.3e

Accept: text/plainAccept: text/plain

Accept: text/htmlAccept: text/html

Accept: application/postscriptAccept: application/postscript

Accept: image/gifAccept: image/gif

– Accept: */*Accept: */*

HTTP 22

HTTP 1.0HTTP 1.0

HTTP responseHTTP response– Status lineStatus line

HTTP-version Status-code ReasonHTTP-version Status-code Reason Status-codes 1xx - InformationalStatus-codes 1xx - Informational

– Reserved for future useReserved for future use

HTTP 23

HTTP 1.0HTTP 1.0


Status-codes 2xx - SuccessStatus-codes 2xx - Success– The action was successfully received, The action was successfully received,

understood, and acceptedunderstood, and accepted 200 OK200 OK 201201 POST command POST command

successfulsuccessful 202202 Request acceptedRequest accepted 203203 GET or HEAD request GET or HEAD request

fulfilledfulfilled 204204 No contentNo content

HTTP 24

HTTP 1.0HTTP 1.0


Status-codes 3xx - RedirectionStatus-codes 3xx - Redirection– Further action must be taken in order to Further action must be taken in order to

complete requestcomplete request 300300 Resource found at Resource found at

multiple locationsmultiple locations 301 Resource moved permanently301 Resource moved permanently 302 Resource moved temporarily302 Resource moved temporarily 304 Resource has not modified (since 304 Resource has not modified (since

date)date)

HTTP 25

HTTP 1.0HTTP 1.0


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

400400 Bad request from clientBad request from client 401401 Unauthorized requestUnauthorized request 402402 Payment required for requestPayment required for request 403403 Resource access forbiddenResource access forbidden 404404 Resource not foundResource not found 405405 Method not allowed for Method not allowed for

resourceresource 406406 Resource type not acceptableResource type not acceptable

HTTP 26

HTTP 1.0HTTP 1.0


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

500500 Internal server errorInternal server error 501501 Method not implementedMethod not implemented 502502 Bad gateway or server Bad gateway or server

overloadoverload 503503 Service unavailable / Service unavailable /

gateway timeoutgateway timeout 504504 Secondary gateway / server Secondary gateway / server

timeouttimeout

HTTP 27

HTTP 1.0HTTP 1.0

HTTP responseHTTP response– Description of informationDescription of information

Server Server Type of server Type of server Date Date Date and time Date and time Content-LengthContent-Length Number of bytes Number of bytes Content-TypeContent-Type Mime type Mime type Content-LanguageContent-Language English, for example English, for example Content-EncodingContent-Encoding Data compression Data compression Last-ModifiedLast-Modified Date when last modified Date when last modified ExpiresExpires Date when file becomes Date when file becomes

invalidinvalid

HTTP 28

HTTP 1.0HTTP 1.0

ProblemsProblems– HTTP is statelessHTTP is stateless

Each request requires separate TCP Each request requires separate TCP connectionconnection

Server doesn’t remember previous Server doesn’t remember previous requestsrequests

HTTP 29

Evolution of HTTPEvolution of HTTP

HTTP/0.9 - 1990HTTP/0.9 - 1990– Request method + URI + crlfRequest method + URI + crlf

GET /pets/index.htmlGET /pets/index.html Just file contents sent backJust file contents sent back

– No header informationNo header information

Gopher influenceGopher influence– Media typesMedia types

Single character indicated one of ten Single character indicated one of ten typestypes

HTTP 30


HTTP/1.0 - 1995HTTP/1.0 - 1995– Meta-information between client and Meta-information between client and

serverserver Media typesMedia types

– MIME type/subtypeMIME type/subtype Status codesStatus codes This information influenced the development This information influenced the development

of web search enginesof web search engines

– CachingCaching– AuthorizationAuthorization

HTTP 31


HTTP/1.0 - 1995HTTP/1.0 - 1995– ProblemsProblems

ScalabilityScalability– High number of clients visit server for short High number of clients visit server for short

timetime Flash crowdFlash crowd

BandwidthBandwidth

HTTP 32


HTTP/1.1HTTP/1.1– Byte rangesByte ranges

Request of a document subsetRequest of a document subset– Adobe's Portable Document FormatAdobe's Portable Document Format– Streaming multimediaStreaming multimedia

Eliminates unnecessary client/server Eliminates unnecessary client/server communicationcommunication

An interrupted transfer which is restarted An interrupted transfer which is restarted can be more efficientcan be more efficient

HTTP 33


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

factorsfactors Quality factorsQuality factors

– Real numbers between 0 and 1Real numbers between 0 and 1 Default is 1Default is 1

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

HTTP 34


HTTP/1.1HTTP/1.1– Chunked encodingChunked encoding

Transmission of streaming multimediaTransmission of streaming multimedia– One frame varies in size and composition from One frame varies in size and composition from

the nextthe next Streaming videoStreaming video

– Entire image transmitted in first chunk and Entire image transmitted in first chunk and differences to the previous image are differences to the previous image are transmitted in the next chunktransmitted in the next chunk

HTTP 35


HTTP/1.1HTTP/1.1– Protocol switchingProtocol switching

Client can specify another protocol more Client can specify another protocol more suited to data being transferredsuited to data being transferred

– Message integrity checksMessage integrity checks– Digest authenticationDigest authentication

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

In HTTP/1.1, the client and the server never In HTTP/1.1, the client and the server never send the actual username or password over send the actual username or password over the networkthe network

HTTP 36


HTTP/1.1HTTP/1.1– Persistent connectionsPersistent connections

In HTTP/1.0, if a single page includes inline In HTTP/1.0, if a single page includes inline images, multiple frames, animation, and images, multiple frames, animation, and other external references, to browse this other external references, to browse this page would require many reconnectionspage would require many reconnections

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

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

HTTP 37

Evolution of HTTPEvolution of HTTP HTTP/1.1HTTP/1.1

– Cache management with entity tagsCache management with entity tags When body of URI changes, so does its entity When body of URI changes, so does its entity

tagtag– Useful for maintaining caches, as updated URI Useful for maintaining caches, as updated URI

information would have a different entity taginformation would have a different entity tag Can tell if same resource is being cached from Can tell if same resource is being cached from

multiple URI's as it would have same entity tagmultiple URI's as it would have same entity tag Strong entity tagStrong entity tag

– Changes when any portion of resource changesChanges when any portion of resource changes One or more bytes changeOne or more bytes change

Weak entity tagWeak entity tag– Changes only when semantics of entity-body Changes only when semantics of entity-body

changeschanges

HTTP 38


HTTP/1.1HTTP/1.1– Software multihomingSoftware multihoming

Number of available IP addresses is a Number of available IP addresses is a concernconcern

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

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

HTTP 39

The FutureThe Future

HTTP-Next GenerationHTTP-Next Generation– Many channelsMany channels

One TCP connection carries multiple One TCP connection carries multiple channels for parallel communicationchannels for parallel communication

Different protocols on each channelDifferent protocols on each channel

– Traditional wayTraditional way Multiple TCP connections between same Multiple TCP connections between same

client and serverclient and server Pages contain images, video, audio, and Pages contain images, video, audio, and

htmlhtml

HTTP 40


ExtensibilityExtensibility– Adding new MIME headers has been Adding new MIME headers has been

the traditional way of extending httpthe traditional way of extending http– DrawbacksDrawbacks

No indication whether receiving end No indication whether receiving end understands these extensionsunderstands these extensions

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

No indication of order in which extensions No indication of order in which extensions should be interpretedshould be interpreted

HTTP 41


ExtensibilityExtensibility– PEPPEP

Protocol Extension ProtocolProtocol Extension Protocol

HTTP 42


PerformancePerformance– Parsing MIME headers wastes resourcesParsing MIME headers wastes resources– Sticky headersSticky headers

Persistent state between multiple http Persistent state between multiple http requestsrequests

Not all headers have to be included in every Not all headers have to be included in every http messagehttp message

Distributed authoringDistributed authoring– Event notificationEvent notification

HTTP 43


Caching and replicationCaching and replication– Popular sites are Popular sites are really really popularpopular– Flash crowds happenFlash crowds happen– Hot spots on the net are dynamicHot spots on the net are dynamic– Amount of dynamic data is increasingAmount of dynamic data is increasing

HTTP 44


QoSQoS– Quality of serviceQuality of service– Not everything must be treated with Not everything must be treated with

same QoSsame QoS– Required QoS should be made at the Required QoS should be made at the

user-interfaceuser-interface

HTTP 45


Real-time protocols and the webReal-time protocols and the web– Streaming protocolsStreaming protocols

Audio/video-on-demandAudio/video-on-demand