URL/URI rewrite without changing in Client browser

I've tried to modify my syntax, haven't had the chance to test it in a lab so please be careful with this and don't run it in prod without testing. 

Code below is supposed to replace anything that matches /aaa/ /bbb/ or /ccc/ at depth1 in your path (this is driven by "starts_with" condition)  with static /mnp/ 

so /aaa/path/to/index.jsp will change into /mnp/path/to/index.jsp/

and i believe /bbb/bbb/file.txt should change to /mnp/bbb/file.txt 

Please also integrate knowledge shared by Kevin_Stewart in his comments which is very detailed and much more reliable than my attempt 🙂 

Lastly, I don't think you will need to change anything in HTTP response. 

when HTTP_REQUEST {
  set uri [HTTP::uri]; set path [HTTP::path]; set query [HTTP::query]
  HTTP::header replace Host "pqr.com"
  
  if {[class match $path starts_with datagroup_rewriteURL]} {
		
		set dgValue [class match -value $path eq datagroup_rewriteURL] ; #i believe this should return /xyz/ if you've set as a string entry in the data group  
		log local0. "replacing $dgValue with /mnp/"
		
        set newpath [string map -nocase { $dgValue "/mnp/"} $path]
        HTTP::uri "$newpath$query"
    }
}

ltm object will be something like 

ltm data-group internal datagroup_rewriteURL {
    records {
        /aaa/ {}
        /bbb/ {}
        /ccc/ {}
    }
    type string
}

Okay, so let's say you have a string datagroup that looks like this:

ltm data-group internal url_datagroup {
    records {
        www.blah.com:/blah {
            data www.test.com:/test
        }
        www.foo.com:/foo {
            data www.bar.com:/bar
        }
    }
    type string
}

I've intentionally added a colon ":" between the host and uri to make it easier to separate them later. So then you're matching on "[HTTP::host]:[HTTP::uri]" in the following iRule. If you have a match, you'll split the corresponding value into host and uri (split on the ":" to make a list object). You'll then, on separate lines, update the HTTP Host header and replace the HTTP URI.

when HTTP_REQUEST {
    if { [set match [class match -value -- "[HTTP::host]:[HTTP::uri]" equals url_datagroup]] ne "" } {
        log local0. "match = $match"
        set matchlist [split $match ":"]
        log local0. "match host = [lindex $matchlist 0]"
        log local0. "match uri = [lindex $matchlist 1]"
        
        HTTP::host [lindex $matchlist 0]
        HTTP::uri [lindex $matchlist 1]
    }
}

You can now just add all of these HOST:URI patterns to a single datagroup. Now as I was mentioning earlier, it also depends on how static or dynamic the URLs are. For example, if the URI is statically "/foo", then the above works fine. But if /foo is just the start of the URI (ex. /foo/blah?this=that...), then the above won't completely address the problem. It'll change the HTTP Host, but then you need to do a string map to replace the portion of the URI while (presumably) keeping the rest. Example:

/foo/blah?this=that

would be changed to:

/bar/blah?this=that

You're doing all of this in the HTTP request. There's no URI, path or URI values in an HTTP response.

Point is, if you need to keep the user's browser on http://abc.com, you need to keep that traffic on the abc.com VIP. You can change the HTTP Host and URI on the abc VIP and forward the traffic to the pqr VIP, but there's no scenario where the abc VIP would change these values if the user was able to go directly to the pqr VIP directly.