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12 June 2012, 15:21

HTTP Error Status 451 proposed to show legal block

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Network icon Google's developer advocate Tim Bray has proposed a new HTTP Error status code to the IETF as an RFC to bring more transparency to the legal and government blocks and filters of content on the internet. Most blocking systems return a 403 error (Forbidden) when denying a user access; this is regarded as incorrect as the page does exist, it is just not accessible. For example, in the UK, where ISPs are required to block the Pirate Bay, most tend to return a 403 error code. Bray's proposal is that the 451 code should instead be returned with an explanation of why the content was unavailable. He offers the following as an example of such a returned message.

HTTP/1.1 451 Unavailable For Legal Reasons
Content-Type: text/html

<title>Unavailable For Legal Reasons</title>
<h1>Unavailable For Legal Reasons</h1>
<p>This request may not be serviced in the Roman Province of
Judea due to Lex3515, the Legem Ne Subversionem Act of AUC755,
which disallows access to resources hosted on servers deemed
to be operated by the Judean Liberation Front.</p>

If a web server or proxy responded with 451, this would, says Bray, give no information about the actual existence or non-existence of the resource, but merely reflect that there is blocking in place; if the block were removed the resource could still be unavailable. The 451 code would be optional and it is possible that courts, governments or companies blocking content would not return the status code to ensure that the existence of the block was not revealed. The selection of the 451 code is inspired by the book Fahrenheit 451 by the recently deceased Ray Bradbury. It has been noted though that the 4xx set of error codes is defined as referring to situations when it is believed the client has erred.

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