determining the url of a request

[Jeff Kaufman]

If I have a ngx_http_request_t, is there a built-in way to get the
full url for the request? r->uri has "/path/to/page.html" but is there
a way to get a full "scheme://host[:port]/path/to/page.html"?

Some background: I'm working on ngx_pagespeed [1], a port of
mod_pagespeed to nginx.  The idea is to automatically rewrite webpages
and their resources to make pages load faster.  The pagespeed code
needs to know what url has been requested so it can do things like
turn absolute urls into relative urls.

Jeff

[1] https://github.com/pagespeed/ngx_pagespeed