| 词条 | HTTP 451 |
| 释义 |
In computer networking, HTTP 451 Unavailable For Legal Reasons is an error status code of the HTTP protocol to be displayed when the user requests a resource which cannot be served for legal reasons, such as a web page censored by a government. The number 451 is a reference to Ray Bradbury's 1953 dystopian novel Fahrenheit 451, in which books are outlawed.[2] 451 could be described as a more explanatory variant of 403 Forbidden.[3] This status code is standardized in RFC 7725. Examples of situations where an HTTP 451 error code could be displayed include web pages deemed a danger to national security, or web pages deemed to violate copyright, privacy, blasphemy laws, or any other law or court order. The RFC is specific that a 451 response does not indicate whether the resource exists but requests for it have been blocked, if the resource has been removed for legal reasons and no longer exists, or even if the resource has never existed, but any discussion of its topic has been legally forbidden (see superinjunction).[4] Some sites have previously returned HTTP 404 (Not Found) or similar if they are not legally permitted to disclose that the resource has been removed. Such a tactic is used in the United Kingdom by some internet service providers utilising the Internet Watch Foundation blacklist, returning a 404 message or another error message instead of showing a message indicating the site is blocked.[5][6] The status code was formally proposed in 2013 by Tim Bray, following earlier informal proposals by Chris Applegate[7] in 2008 and Terence Eden[8] in 2012. It was approved by the IESG on December 18, 2015.[9] It was published as RFC 7725 in February 2016. HTTP 451 was mentioned by the BBC's From Our Own Correspondent program, as an indication of the effects of sanctions on Sudan and the inability to access Airbnb, iOS's App Store, or other Western web services.[10] After introduction of the GDPR in European Economic Area (EEA) many websites located outside EEA started to serve HTTP 451 instead of trying to comply with this new privacy law.[11] UsageWhen an entity intercepts the request and returns status 451, it should include a "Link" HTTP header field whose value is a URI reference identifying itself. The "Link" header field must then have a "rel" parameter whose value is "blocked-by". This is intended to identify the entity implementing the blocking (an ISP, DNS provider, caching system, etc.), not the legal authority mandating the block.[12] At an IETF hackathon, participants used a web crawler to discover that several implementations misunderstood this header and gave the legal authority instead.[13] ExampleHTTP/1.1 451 Unavailable For Legal Reasons Link: Content-Type: text/html Unavailable For Legal ReasonsThis request may not be serviced in the Roman Province of Judea due to the Lex Julia Majestatis, which disallows access to resources hosted on servers deemed to be operated by the People's Front of Judea. See also
References1. ^{{cite web|url=https://www.attorneygeneral.gov/taking-action/press-releases/attorney-general-shapiro-governor-wolf-state-police-successfully-block-access-to-3d-downloadable-guns-in-pennsylvania/|title=Attorney General Shapiro, Governor Wolf, State Police Successfully Block Access to 3D Downloadable Guns in Pennsylvania }} 2. ^{{cite news| url = https://www.theguardian.com/books/2012/jun/22/ray-bradbury-internet-error-message-451| title = Call for Ray Bradbury to be honoured with internet error message| last = Flood| first = Alison| date = June 22, 2012| newspaper = The Guardian| accessdate = June 22, 2012}} 3. ^{{cite web| url = https://nakedsecurity.sophos.com/2013/08/19/http-error-code-451-unavailable-for-legal-reasons/| title = HTTP error code 451: "Unavailable For Legal Reasons"| last = Ducklin| first = Paul| date = August 19, 2013| website = Naked Security| publisher = Sophos| accessdate = }} 4. ^RFC 7725, §3 5. ^"If the request is for the blocked content then the proxy server will return a 404 error page to the customer" https://wiki.openrightsgroup.org/wiki/Cleanfeed 6. ^"TCP Reset is sent back to the customer instead of content." https://www.theguardian.com/technology/blog/2008/dec/08/internet-censorship-wikipedia-diagram 7. ^{{cite web|url=http://www.qwghlm.co.uk/2008/12/09/there-is-no-http-code-for-censorship/|title=There is no HTTP code for censorship|date=December 9, 2008|access-date=December 23, 2015}} 8. ^{{cite web|url=http://motherboard.vice.com/read/the-http-451-error-code-for-censorship-is-now-an-internet-standard|title=The HTTP 451 Error Code for Censorship Is Now an Internet Standard|last=Byrne|first=Michael|date=21 December 2015|work=Vice|accessdate=21 December 2015}} 9. ^{{cite web|url=https://www.mnot.net/blog/2015/12/18/451|title=Why 451?|date=December 18, 2015|access-date=December 20, 2015}} 10. ^{{Cite radio |title=From Our Own Correspondent |type=radio |publisher=BBC Radio 4 |author= Sally Hayden |date=28 September 2017 |url=http://www.bbc.co.uk/programmes/b095tcx0}} 11. ^{{cite news |author=Matt Burgess |title=The tyranny of GDPR popups and the websites failing to adapt |url=https://www.wired.co.uk/article/gdpr-cookies-eprivacy-regulation-popups |work=WIRED |date=2018-08-29 |access-date=2018-10-01}} 12. ^{{cite web|url=https://tools.ietf.org/html/rfc7725|title=An HTTP Status Code to Report Legal Obstacles|author=Tim Bray|website=IETF Tools|date=February 2016|access-date=2018-01-16}} 13. ^{{cite web|url=https://www.rfc-editor.org/errata/eid5181|title=RFC Errata Report|author=Stéphane Bortzmeyer|website=IETF Tools|date=11 November 2017|access-date=2018-12-03}} External links
2 : Hypertext Transfer Protocol status codes|Internet censorship |
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