[wp-trac] [WordPress Trac] #7696: Pingback URI discovery broken for some URIs

[WordPress Trac]

#7696: Pingback URI discovery broken for some URIs
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 Reporter:  Inquisitus  |       Owner:  anonymous                                                   
     Type:  defect      |      Status:  new                                                         
 Priority:  normal      |   Milestone:                                                              
Component:  General     |     Version:  2.7                                                         
 Severity:  normal      |    Keywords:  pingback discovery uri url redirect headers header has-patch
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 Under some circumstances the `discover_pingback_server_uri` function will
 fail due to a 301 redirection being issued by the server.

 This can happen when the request URI points to a directory on the
 recipient server but has no trailing slash. For example, if some blog
 system is installed at http://foo.com/bar/ (and this URI is pingback-
 enabled), then requesting http://foo.com/bar (no trailing slash) will
 result in Apache on the recipient server issuing a 301 redirect to
 http://foo.com/bar/ (with trailing slash). In this case, the
 `discover_pingback_server_uri` function will fail as it will not follow
 the redirection.

 This is perfectly normal behaviour for Apache and so it should really be
 accounted for, even if it's unlikely to manifest itself as a problem. See
 here for a more complete description of what happens:
 http://dmiessler.com/study/hyperlink_trailing_slash/

 My proposed fix involves checking the HTTP status code before looking for
 the `X-Pingback` header. If it's a 301, we extract the `Location` header
 and recursively call `discover_pingback_server_uri` again with that URI.
 Stack overflows are prevented by means of a redirection limit parameter
 for the function; default is 3.

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Ticket URL: <http://trac.wordpress.org/ticket/7696>
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