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  Other information – 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  Other information – 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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