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An HTTP Status Code to Report Legal ObstaclesTextualitytbray@textuality.comhttp://www.tbray.org/ongoing/
Applications and Real-Time
HTTPHTTPThis document specifies a Hypertext Transfer Protocol (HTTP)
status code for use when resource access is denied as a
consequence of legal demands.
Discussion of this draft takes place on the HTTPBIS working group mailing list
(ietf-http-wg@w3.org), which is archived at .
Working Group information can be found at
and ; source code and issues
list for this draft can be found at
.
This document specifies a Hypertext Transfer Protocol (HTTP)
status code for use when a server operator has received a legal
demand to deny access to a resource or to a set of resources which
includes the requested resource.This status code can be used to provide transparency
in circumstances where issues of law or public policy affect server
operations. This transparency may be beneficial both to these operators
and to end users. discusses the forces working
against transparent operation of the Internet; these clearly include
legal interventions to restrict access to content. As that document
notes, and as Section 4 of states, such
restrictions should be made explicit.Feedback should occur on the ietf-http-wg@w3.org mailing list.The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL
NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in
this document are to be interpreted as described in .This status code indicates that the server is denying access
to the resource as a consequence of a legal demand.The server in question might not be an origin server. This type of
legal demand typically most directly affects the operations of ISPs and
search engines.Responses using this status code SHOULD include an explanation,
in the response body, of the details of the legal demand: the party
making it, the applicable legislation or regulation, and what classes of
person and resource it applies
to. For example:
HTTP/1.1 451 Unavailable For Legal Reasons
Link: <https://spqr.example.org/legislatione>; rel=”blocked-by”
Content-Type: text/html
<html>
<head><title>Unavailable For Legal Reasons</title></head>
<body>
<h1>Unavailable For Legal Reasons</h1>
<p>This 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.</p>
</body>
</html>The use of the 451 status code implies neither the existence nor
non-existence of the resource named in the request. That is to say,
it is possible that if the legal demands were removed,
a request for the resource still might not succeed.Note that in many cases clients can still access the denied resource by
using technical countermeasures such as a VPN or the Tor network.A 451 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls; see .As noted above, when an attempt to access a resource fails
with status 451, the entity blocking access might or might not be the
origin server. There are a variety of entities in the resource-access
path which could choose to deny access, for example ISPs,
cache providers, and DNS servers.It is useful, when legal blockages occur, to be able to identify the
entities actually implementing the blocking.When an entity blocks access to a resource and returns status 451, it
SHOULD include a “Link” HTTP header field
whose value is a URI reference
identifying itself. When used for this purpose, the “Link” header field
MUST have a “rel” parameter whose value is “blocked-by”.The intent is that the header be used to identify the entity actually
implementing blockage, not any other entity mandating it. A
human readable response body, as discussed above, is the appropriate
location for discussion of administrative and policy issues.Clients cannot rely upon the use of the 451 status code.
It is possible that certain legal authorities might wish
to avoid transparency, and not only demand the restriction of access
to certain resources, but also avoid disclosing that the demand
was made. The HTTP Status Codes Registry should be updated with the
following entry:Code: 451Description: Unavailable for Legal ReasonsSpecification: [ this document ]The Link Relation Type Registry should updated with the
following entry:Relation Name: blocked-byDescription: Identifies the entity blocking access to a resource
folllowing on receipt of a legal demand.Reference: This document
&rfc2119;
&rfc4084;
&rfc4924;
&rfc7234;
&rfc3986;
&rfc5988;
Thanks to Terence Eden, who observed that the existing
status code 403 was not really suitable for this situation, and
suggested the creation of a new status code.Thanks also to Ray Bradbury.