What is the purpose of the HTTP header field “Content-Location”?

Question

Confused/inspired by a comment to my question Do search engines respect the HTTP header field “Content-Location”?, I’d like to know, what the exact purpose of the Content-Lo

Answer 1

Content-Location HTTP header is supposed to declare unique location of the resource that was used for a response to HTTP GET (e.g. request was GET /frontpage HTTP/1.1, the server may add HTTP header Content-Location: http://domain.com/frontpage.english.msie-optimized informing the user agent that if this specific response is needed later, the provided location should be used because the original location may depend on various things, which should then be explained via the "Vary" header).

However, note that HTTP Content-Location header is problematic in real world usage because different browsers (user agents) handle it differently: http://mail.python.org/pipermail/web-sig/2004-October/000985.html

This is because of RFC 2616 section 14.14 which says that "The value of Content-Location also defines the base URI for the entity". In short, a comforming user agent will compute the BASE URL for the fetched document using the Content-Location header which may result in different relative URLs being used if the fetched document does not define BASE url and real fetched URL and Content-Location differ enough (the "directory"/"path" part of the URL is different).

In addition, I've yet to see any advantage for using HTTP Content-Location (I once hoped that this could be used for hinting about permanent bookmark location in case currently viewed URL was volatile, such as domain.com/news/latest but that doesn't seem to be the case).

My current advice is forget about Content-Location for HTTP but you may use it for MIME email.