id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
7696	Pingback URI discovery broken for some URIs	Inquisitus	anonymous	"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."	defect (bug)	closed	normal		General		normal	duplicate	pingback discovery uri url redirect headers header has-patch