Getting/Setting HTTP Headers

[jakecjacobson]

I need to write a feed parser that takes a url for any Atom or RSS
feed and transform it into an Atom feed.  I done the transformation
part but I want to support conditional HTTP requests.  I have not been
able to find any examples that show:

1.  How to read the Last_Modified or ETag header value from the
requester
2.  How to set the corresponding HTTP header value, either a 302 not
modified or the new Last_Modified date and/or ETag values