HEAD requests the headers that would be returned if the
HEAD request's URL was instead requested with the HTTP
GET method. For example, if a URL might produce a large download, a
HEAD request could read its
Content-Length header to check the filesize without actually downloading the file.
Warning: A response to a
HEAD method should not have a body. If it has one anyway, that body must be ignored: any representation headers that might describe the erroneous body are instead assumed to describe the response which a similar
GET request would have received.
If the response to a
HEAD request shows that a cached URL response is now outdated, the cached copy is invalidated even if no
GET request was made.