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Text of the page (random words):
this action which non malicious bots would not make one example of this occurring in practice was during the short lived google web accelerator beta which prefetched arbitrary urls on the page a user was viewing causing records to be automatically altered or deleted en masse the beta was suspended only weeks after its first release following widespread criticism 40 idempotent method edit see also idempotence computer science meaning a request method is idempotent if multiple identical requests with that method have the same effect as a single such request the methods put and delete and safe methods are defined as idempotent safe methods are trivially idempotent since they are intended to have no effect on the server whatsoever the put and delete methods meanwhile are idempotent since successive identical requests will be ignored a website might for instance set up a put endpoint to modify a user s recorded email address if this endpoint is configured correctly any requests which ask to change a user s email address to the same email address which is already recorded e g duplicate requests following a successful request will have no effect similarly a request to delete a certain user will have no effect if that user has already been deleted in contrast the methods post connect and patch are not necessarily idempotent and therefore sending an identical post request multiple times may further modify the state of the server or have further effects such as sending multiple emails in some cases this is the desired effect but in other cases it may occur accidentally a user might for example inadvertently send multiple post requests by clicking a button again if they were not given clear feedback that the first click was being processed while web browsers may show alert dialog boxes to warn users in some cases where reloading a page may re submit a post request it is generally up to the web application to handle cases where a post request should not be submitted more than once note that whether or not a method is idempotent is not enforced by the protocol or web server it is perfectly possible to write a web application in which for example a database insert or other non idempotent action is triggered by a get or other request to do so against recommendations however may result in undesirable consequences if a user agent assumes that repeating the same request is safe when it is not cacheable method edit see also web cache a request method is cacheable if responses to requests with that method may be stored for future reuse the methods get head and post are defined as cacheable in contrast the methods put delete connect options trace and patch are not cacheable response edit a response is sent to the client by the server the start line of a response consists of the protocol version a status code and optionally a reason phrase with fields separated by a single space character 4 2 1 the following response start line specifies protocol version http 1 1 status code 400 and reason phrase bad request http 1 1 400 bad request response header fields allow the server to pass additional information beyond the status line acting as response modifiers they give information about the server or about further access to the target resource or related resources each response header field has a defined meaning which can be further refined by the semantics of the request method or response status code status code edit see also list of http status codes the status code is a three digit decimal integer value that represents the disposition of the server s attempt to satisfy the client s request generally a client handles a response primarily based on the status code and secondarily on response header fields a client may not understand each status code that a server reports but it must understand the class as indicated by the first digit and treat an unrecognized code as equivalent to the x00 code of that class the classes are as follows 1xx informational the request was received continuing process 2xx successful the request was successfully received understood and accepted 3xx redirection further action needs to be taken in order to complete the request 4xx client error the request cannot be fulfilled due to an issue that the client might be able to control 5xx server error the server failed to fulfill an apparently valid request reason phrase edit the standard reason phrases are only recommendations a web server is allowed to use a localized equivalent if a status code indicates a problem the user agent might display the reason phrase to the user to provide further information about the nature of the problem the standard also allows the user agent to attempt to interpret the reason phrase though this might be unwise since the standard explicitly specifies that status codes are machine readable and reason phrases are human readable example edit the following demonstrates an http 1 1 request response transaction for a server at www example com port 80 http 1 0 would use the same messages except for a few missing headers http 2 and http 3 would use the same request response mechanism but with different representations for http headers the following is a request with no body it consists of a start line 6 header fields and a blank line each terminated with a carriage return and line feed sequence the host header field distinguishes between various dns names sharing a single ip address allowing name based virtual hosting while optional in http 1 0 it is mandatory in http 1 1 get http 1 1 host www example com user agent mozilla 5 0 accept text html application xhtml xml application xml q 0 9 image avif image webp q 0 8 accept language en gb en q 0 5 accept encoding gzip deflate br connection keep alive although not clear in the representation above due to limitations of this wiki the blank line at the end results in ending in two line terminator sequences represented as a stream of characters a shorted version of above shows this more clearly with crlf representing a line terminator sequence get http 1 1 crlf host www example com crlf crlf in the following response the etag entity tag header field is used to determine if a cached version of the requested resource is identical to the current version of the resource on the server the content type header field specifies the internet media type of the data conveyed by the http message and content length indicates its length in bytes the http 1 1 webserver publishes its ability to respond to requests for a byte range of the resource by including accept ranges bytes this is useful if the client needs to have only certain portions 41 of a resource sent by the server which is called byte serving when connection close is sent it means that the web server will close the tcp connection immediately after the end of the transfer of this response 4 9 1 most of the header fields are optional but some are mandatory when header content length is missing from a response with a body then this should be considered an error in http 1 0 but it may not be an error in http 1 1 if header transfer encoding chunked is present chunked transfer encoding uses a chunk size of 0 to mark the end of the content some old implementations of http 1 0 omitted the header content length when the length of the body was not known at the beginning of the response and so the transfer of data to client continued until server closed the socket content encoding gzip informs the client that the body is compressed per the gzip algorithm http 1 1 200 ok date mon 23 may 2005 22 38 34 gmt content type text html charset utf 8 content length 155 last modified wed 08 jan 2003 23 11 55 gmt server apache 1 3 3 7 unix red hat linux etag 3f80f 1b6 3e1cb03b accept ranges bytes connection close html head title an example page title head body p hello world this is a very simple html document p body html similar protocols edit gopher protocol a content delivery protocol that was displaced by http in the early 1990s spdy protocol an alternative to http developed at google superseded by http 2 gemini protocol a gopher inspired protocol which mandates privacy related features history edit tim berners lee tim berners lee and his team at cern are credited with inventing http along with html and the associated technology for a web server and a client user interface called web browser berners lee designed http in order to help with the adoption of his other idea the worldwideweb project which was first proposed in 1989 now known as the world wide web development of http was initiated in 1989 and summarized in a simple document describing the behavior of a client and a server using the first http version named 0 9 42 that version was subsequently developed eventually becoming the public 1 0 43 development of early http request for comments rfc documents started a few years later in a coordinated effort by the internet engineering task force ietf and the world wide web consortium w3c with work later moving to the ietf the first web server went live in 1990 44 45 the protocol used had only one method namely get which would request a page from a server 46 the response from the server was always an html page 42 http 0 9 edit in 1991 the first documented official version of http was written as a plain document less than 700 words long and this version was named http 0 9 which supported only get method allowing clients to only retrieve html documents from the server but not supporting any other file formats or information upload 42 http 1 0 draft edit since 1992 a new document was written to specify the evolution of the basic protocol towards its next full version it supported both the simple request method of the 0 9 version and the full get request that included the client http version this was the first of the many unofficial http 1 0 drafts that preceded the final work on http 1 0 43 w3c http working group edit after having decided that new features of http protocol were required and that they had to be fully documented as official rfc documents in early 1995 the http working group http wg led by dave raggett was constituted with the aim to standardize and expand the protocol with extended operations extended negotiation richer meta information tied with a security protocol which became more efficient by adding additional methods and header fields 47 48 the http wg planned to revise and publish new versions of the protocol as http 1 0 and http 1 1 within 1995 but because of the many revisions that timeline lasted much more than one year 49 the http wg planned also to specify a far future version of http called http ng http next generation that would have solved all remaining problems of previous versions related to performances low latency responses etc but this work started only a few years later and it was never completed http 1 0 edit in may 1996 rfc 1945 3 was published as a final http 1 0 revision of what had been used in previous 4 years as a pre standard http 1 0 draft which was already used by many web browsers and web servers in early 1996 developers started to even include unofficial extensions of the http 1 0 protocol i e keep alive connections etc into their products by using drafts of the upcoming http 1 1 specifications 20 http 1 1 edit since early 1996 major web browsers and web server developers also started to implement new features specified by pre standard http 1 1 drafts specifications end user adoption of the new versions of browsers and servers was rapid in march 1996 one web hosting company reported that over 40 of browsers in use on the internet used the new http 1 1 header host to enable virtual hosting and that by june 1996 65 of all browsers accessing their servers were pre standard http 1 1 compliant 50 in january 1997 rfc 2068 51 was officially released as http 1 1 specifications in june 1999 rfc 2616 34 was released to include all improvements and updates based on previous obsolete http 1 1 specifications w3c http ng working group edit resuming the old 1995 plan of previous http working group in 1997 an http ng working group was formed to develop a new http protocol named http ng http new generation a few proposals drafts were produced for the new protocol to use multiplexing of http transactions inside a single tcp ip connection but in 1999 the group stopped its activity passing the technical problems to ietf 52 ietf http working group restarted edit in 2007 the ietf http working group http wg bis or httpbis was restarted firstly to revise and clarify previous http 1 1 specifications and secondly to write and refine future http 2 specifications named httpbis 53 54 spdy edit main article spdy in 2009 google announced spdy a binary protocol they developed to speed up web traffic between browsers and servers in many tests using spdy was indeed faster than using http 1 1 spdy was integrated into google s chromium and then into other major web browsers 55 some of the ideas about multiplexing http streams over a single tcp connection were taken from various sources including the work of w3c http ng working group http 2 edit main article http 2 in 2012 http working group httpbis announced the need for a new protocol initially considering aspects of spdy 56 57 and eventually deciding to derive the new protocol from spdy 58 in may 2015 http 2 was published as rfc 7540 59 the protocol was quickly adopted by web browsers already supporting spdy and more slowly by web servers 2014 updates to http 1 1 edit in june 2014 the http working group released an updated six part http 1 1 specification obsoleting rfc 2616 34 rfc 7230 hypertext transfer protocol http 1 1 message syntax and routing 60 obsolete rfc 7231 hypertext transfer protocol http 1 1 semantics and content 61 obsolete rfc 7232 hypertext transfer protocol http 1 1 conditional requests 62 obsolete rfc 7233 hypertext transfer protocol http 1 1 range requests 63 obsolete rfc 7234 hypertext transfer protocol http 1 1 caching 64 obsolete rfc 7235 hypertext transfer protocol http 1 1 authentication 65 obsolete http 0 9 deprecation edit in 2014 http 0 9 was deprecated for servers supporting version http 1 1 and higher 60 appendix a since http 0 9 did not support header fields in a request there is no mechanism for it to support name based virtual hosts selection of resource by inspection of the host header field any server that implements name based virtual hosts ought to disable support for http 0 9 most requests that appear to be http 0 9 are in fact badly constructed http 1 x requests caused by a client failing to properly encode the request target since 2016 many product managers and developers of user agents browsers etc and web servers have begun planning to gradually deprecate and dismiss support for http 0 9 protocol mainly for the following reasons 66 it is so simple that an rfc document was never written there is only the original document 42 it has no http headers and lacks many other f...
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