add a comment just before </body> tag to any HTTP response

You could also do this more efficiently using a stream profile versus buffering the full payload with HTTP::collect. You'd need to add a blank stream profile and a custom HTTP profile with response chunking set to rechunk.

when HTTP_REQUEST {

 Javascript to inject in text responses (wrap in curly braces to avoid having to escape meta-characters).
set js {my javascript goes here...}

 Disable the stream filter by default 
STREAM::disable 
} 
 
when HTTP_RESPONSE { 
 
 Check for text responses
if {[HTTP::header value Content-Type] contains "text"} {

 Replace  closing tag with $js
STREAM::expression "@@$js@"
STREAM::enable 
}
}

Aaron