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mikey_webb's avatar
mikey_webb
Icon for Cirrus rankCirrus
Jan 07, 2015

Help with pattern match irule required

Need help with an irule to drop the request if pattern is not matched. The link and pattern is always as below whereby only the values will change....such as vid, height, quality values etc   htt...
Michael_Jenkins's avatar
Michael_Jenkins
Icon for Cirrostratus rankCirrostratus
Jan 07, 2015

Tested this with 

tclsh
through the CLI with success. You could use the tcl string match command to build your filter

 Good A: Proper pattern
set goodA "/getimage.aspx?vid=84687usehttp=0&cat=default&class=books&size=custom&resize=1&dpi=300&quality=90&type=jpg&width=&height=&id=470746"
 Bad A: Removed vid parameter
set badA "/getimage.aspx?usehttp=0&cat=default&class=books&size=custom&resize=1&dpi=300&quality=90&type=jpg&width=&height=&id=470746"

 Good B: Proper pattern
set goodB "/getimage.aspx?vid=8461&usehttp=0&cat=default&class=books&size=custom&resize=1&dpi=300&quality=100&type=jpg&width=&height=&id=470784"
 Bad B: Swapped parameter location (usehttp & vid)
set badB "/getimage.aspx?usehttp=0&vid=8461&cat=default&class=books&size=custom&resize=1&dpi=300&quality=100&type=jpg&width=&height=&id=470784"

 Match pattern
set pattern "/getimage.aspx\?vid=*usehttp=?&cat=*&class=*&size=*&resize=?&dpi=*&quality=*&type=*&width=*&height=*&id=*"

echo "A (Good): [string match $pattern $goodA]"
echo "A (Bad) : [string match $pattern $badA]"
echo "B (Good): [string match $pattern $goodB]"
echo "B (Bad) : [string match $pattern $badB]"

so an iRule might look like this

when HTTP_REQUEST {
     You don't have to set the pattern to a variable. you could just as easily paste it in the string match command, but this is a little clean (though not as performant)
    set pattern "/getimage.aspx\?vid=*usehttp=?&cat=*&class=*&size=*&resize=?&dpi=*&quality=*&type=*&width=*&height=*&id=*"

    if { not ([string match $pattern [string tolower [HTTP::uri]]]) } {
         Drop the request
        drop
    }
}