[tbnl-devel] Last-Modified / If-Modified-Since Headers

[pete-tbnl-dev at kazmier.com]

Is there any interest in adding functionality that enables TBNL to
automatically send a "304 Not Modified" in response to content that has
not changed?  For example, in the Java Servlet world, a servlet author
can define getLastModified().  What does this buy the servlet author?
Automatic client-side caching.  For those not familiar with the
"Last-Modified/If-Modified-Since" headers, here's a brief overview.

The first time client A visits our servlet page, our servlet is called
to generate some HTML output.  If a servlet author has implemented
getLastModified(), the servlet container invokes this method and inserts
a "Last-Modified" header in the response to the client.  The value of
this header is a date specifying when the page was last modified.  This
value is cached in the client's browser.

The next time client A visits our servlet page, in the HTTP request, the
client's browser includes a "If-Modified-Since" header with the value
that our servlet had previously sent.  When our servlet receives the
request, it notices the "If-Modified-Since" header, and thus invokes our
servlet's getLastModified() method (if defined).  When the time returned
by this method is newer than the time the client sent, the servlet
container proceeds to dispatch the request to our servlet for processing
and generation of output.

Things are more interesting when the value returned from
getLastModified() is the not newer than the value of the
"If-Modified-Since" header.  In this case, the servlet container
bypasses our servlet and simply sends a "304 Not Modified" back to the
client which instructs the browser to display the cached content.  It is
important to note that this servlet container did not dispatch to our
code to generate HTML output, it is completely bypassed and all handled
by the container.

This is the functionality that I would like to add to TBNL.  I'm going
to do it for myself even if its not part of the core; however, I thought
it would be useful for others as well, and thus this post.  How would
one implement this within TBNL?  Would the same approach the Java folks
used suffice?  Provide a special variable, *last-modified-handler*, that
users can set to return a timestamp?  From within that method, users
would have access to *request* so they could return specific times for
various URIs.  This is what I need it for, my entire site will be served
by HTML-TEMPLATEs and I'll use the last time the template file was
modified as my timestamp.

Thoughts?

Thanks,
Pete