Forum OpenACS Q&A: How to return 304s for ADP pages?

You could put something like this in a filter

set mtime [ns_httptime [file mtime [$filename]
set none_header [ns_set iget [ns_conn headers] If-None-Match]
set since_header [ns_set iget [ns_conn headers] If-Modified-Since]

if {$none_header == $mtime || $since_header == $mtime} {
    ns_return 304 html/text
} else {
    ns_set put [ns_conn outputheaders] ETag $mtime
}

Since the nsd.tcl's

    ns_param   checkmodifiedsince   true  

appears to not work for ADP pages, and I haven't found a way to enable nsd's checking of the Not-Modified-Since header for ADP pages, I took Carl's suggestion and wrote a proc to do it.

The site I wrote it for is OpenACS 3.x so I am invoking it at the top of ad_serve_adp_page:

# code from ad_serve_adp_page
if {[jt_return_304_p]} {
	ns_return 304 text/plain ""
	return
}

Here's the code for jt_return_304_p...

proc jt_return_304_p {} {

    set return_304_p 0

    # ad_conn only works for abstract urls
    set path [ad_conn file]

    if {[string equal "" $path]} {
	# ns_conn doesn't work for abstract urls
	set path "[ns_normalizepath [ns_info pageroot][ns_conn url]]"
    }

    if { [file exists $path]} {
	set modified_time [file mtime $path]

	# googlebot doesn't use ETags;
	#set none_header [ns_set iget [ns_conn headers] If-None-Match]

	# NS 4.x SGI sends If-Modified-Since with "; length=xx"
	# If-Modified-Since = Thu, 21 Aug 2003 04:37:53 GMT
	# If-Modified-Since = Tue, 30 Sep 2003 22:28:53 GMT; length=885
	set since_header_maybe_length [ns_set iget [ns_conn headers] If-Modified-Since]
	
	if {![string equal "" $since_header_maybe_length]} {
	    # If-Modified-Since header sent

	   # remove the ;length=xx part if present
	    set since_header [lindex [split $since_header_maybe_length ";"] 0]

 	   # convert date string to epoch time
	    set since_time [clock scan $since_header]
	
	    if {$modified_time < $since_time} {
		# file hasn't changed
		set return_304_p 1
	    }
	}
    }
        
    return $return_304_p
}

To test it, telnet to your Web server's port 80:

$ telnet jamesthornton.com 80
Trying 209.164.72.61...
Connected to jamesthornton.com.
Escape character is '^]'.

... and send someting similar to the following HTTP commands (make sure not to begin with a blank line, but terminate with a blank line)...

GET /index.html HTTP/1.0
User-Agent: Googlebot/2.1 (+http://www.googlebot.com/bot.html)
From:  googlebot(at)googlebot.com
Accept: text/html,text/plain,application/*
Host: jamesthornton.com
If-Modified-Since: Thu, 21 Aug 2010 23:44:54 GMT

You should get something back like this:

HTTP/1.0 304 Not Modified
Set-Cookie: ad_browser_id=6789763; Path=/; Expires=Fri, 01-Jan-2010 01:00:00 GMT
Set-Cookie: ad_session_id=6789764,0,Y3ajJELPiYQI8bsl.KCRGRRjLVjV1izs,1064970966; Path=/; Max-Age=86400
Set-Cookie: last_visit=1064970966; path=/; expires=Fri, 01-Jan-2010 01:00:00 GMT
Set-Cookie: CurriculumProgress=start; path=/; expires=Fri, 01-Jan-2010 01:00:00 GMT
Content-Type: text/plain; charset=iso-8859-1
MIME-Version: 1.0
Date: Wed, 01 Oct 2003 01:16:07 GMT
Server: AOLserver/3.3.1+ad13
Connection: close

Connection closed by foreign host.

A simple hack would be to touch the file when a user posts a comment or adds other dynamic content.