expires header for images iRule v11.x

Here is an iRule I wrote a while back, hope it helps:

I called it suppress_304, I have not touched it in a while so, let me know if it works: These are datagroups you will need:

 class cached_extensions { ".gif"
    ".js"
    ".bmp"
    ".png"
    ".css"
    ".jpg"
    ".JPG"
}
class no_cache_directives {
    "private"
    "no"
    "max-age"
}
class cached_content_types {
    "java"
    "image"
    "css"
    "plain"
}

Below is the iRule:

rule suppress_304 {
when RULE_INIT {
     0 - No, 1 - Yes.
    set static::obey_response_headers 0
    set static::cache_seconds 14400
}

when HTTP_REQUEST {

    set inject_maxage 0
    if { [class match [HTTP::uri] ends_with cached_extensions] } { 
        set inject_maxage 1
     }
}

when HTTP_RESPONSE {

    if {
        not (
            $static::obey_response_headers and 
            (
            [class match [HTTP::header "Cache-Control"] contains no_cache_directives] ||
            [HTTP::header exists "Expires" ]
                ) 
        )
        and 
        (
            $inject_maxage == 1 || 
            [HTTP::query] eq "" and
            [class match [HTTP::header "Content-type"] contains cached_content_types] 
        )
    } {
        HTTP::header replace Cache-Control "max-age=$static::cache_seconds"
    }
}