IRULE Template for URL Masking (Request and Response)

Hello Experts

I am in the process of doing URL masking (changing host name, hard code links in header and payload). The front end user URL is webportal.abc.com and backend server URL is server1. User to F5 is https and backend is http. Below is the irule I got from internet, can any body explain the below irule

when RULE_INIT
{
    ==============================
     REQUEST REWRITES
    ==============================
    set static::webportal_request_uri
    {

    }
    set static::webportal_request_host
    {
                "http://====https://"
        "http://server1====https://webportal.abc.com"
    } 
    set static::webportal_request_referer
    {
                "http://====https://"   
        "http://server1====https://webportal.abc.com"
    }
    set static::webportal_request_cookie
    {

    }

    ==============================
     RESPONSE REWRITES
    ==============================
    set static::webportal_response_setCookie
    {


    }
    set static::webportal_response_location
    {
                "http://====https://"
        "http://server1====https://webportal.abc.com"

    }
    set static::webportal_response_contentLocation
    {
                "http://====https://"
        "http://server1====https://webportal.abc.com"

    }
    set static::webportal_response_body
    {
                "http://====https://"
        "http://server1====https://webportal.abc.com"

    }
}

when HTTP_REQUEST
{
    STREAM::disable
    -----------------
    URI
    -----------------
    HTTP::header remove Accept-Encoding
    if {[llength $static::webportal_request_uri] > 0}
    {
    set request_val [HTTP::uri]
    foreach request_rewriteRecord $static::webportal_request_uri
    {
        set request_find [getfield $request_rewriteRecord "====" 1]
        set request_replace [getfield $request_rewriteRecord "====" 2]
        if {$request_replace == "nothing"}
        {
            set request_replace ""
        }

        regsub -all $request_find $request_val $request_replace request_val
    }
    HTTP::uri $request_val
    }
    -----------------
    Host
    -----------------
    if {[llength $static::webportal_request_host] > 0}
    {
    if {[HTTP::header exists Host]}
    {
        set request_val [HTTP::host]
        foreach request_rewriteRecord $static::webportal_request_host
        {
            set request_find [getfield $request_rewriteRecord "====" 1]
            set request_replace [getfield $request_rewriteRecord "====" 2]

            if {$request_replace == "nothing"}
            {
                set request_replace ""
            }
            regsub -all $request_find $request_val $request_replace request_val
        }

        HTTP::header replace Host $request_val
    }
    }
    -----------------
    Referer
    -----------------
    if {[llength $static::webportal_request_referer] > 0}
    {
    if {[HTTP::header exists Referer]}
    {
        set request_val [HTTP::header value Referer]
        foreach request_rewriteRecord $static::webportal_request_referer
        {
            set request_find [getfield $request_rewriteRecord "====" 1]
            set request_replace [getfield $request_rewriteRecord "====" 2]

            if {$request_replace == "nothing"}
            {
                set request_replace ""
            }

            regsub -all $request_find $request_val $request_replace request_val
        }
        HTTP::header replace Referer $request_val
    }
    }
    -----------------
    cookies
    -----------------
    if {[llength $static::webportal_request_cookie] > 0}
    {
    if {[HTTP::header exists Cookie]}
    {
        set request_val [HTTP::header value Cookie]
        foreach request_rewriteRecord $static::webportal_request_cookie
        {
            set request_find [getfield $request_rewriteRecord "====" 1]
            set request_replace [getfield $request_rewriteRecord "====" 2]

            if {$request_replace == "nothing"}
            {
                set request_replace ""
            }

            regsub -all $request_find $request_val $request_replace request_val
        }
        HTTP::header replace Cookie $request_val
    }
    }
}

when HTTP_RESPONSE
{
    STREAM::disable
    -------------------------
     rewrite set-cookies
    -------------------------
    if {[llength $static::webportal_response_setCookie] > 0}
    {
    if {[HTTP::header exists Set-Cookie]}
    {
        set request_val_list [HTTP::header values Set-Cookie]
        HTTP::header remove Set-Cookie

        foreach request_val $request_val_list
        {
            foreach request_rewriteRecord $static::webportal_response_setCookie
            {
                set request_find [getfield $request_rewriteRecord "====" 1]
                set request_replace [getfield $request_rewriteRecord "====" 2]

                if {$request_replace == "nothing"}
                {
                    set request_replace ""
                }
                regsub -all $request_find $request_val $request_replace request_val
            }
            HTTP::header insert Set-Cookie $request_val
        }
    }
    }
    -------------------------
     rewrite Location
    -------------------------
    if {[llength $static::webportal_response_location] > 0}
    {
    if {[HTTP::is_redirect]}
    {
        set request_val [HTTP::header value Location]

        foreach request_rewriteRecord $static::webportal_response_location
        {
            set request_find [getfield $request_rewriteRecord "====" 1]
            set request_replace [getfield $request_rewriteRecord "====" 2]
            if {$request_replace == "nothing"}
            {
                set request_replace ""
            }

            regsub -all $request_find $request_val $request_replace request_val
        }
        HTTP::header replace Location $request_val
    }
    }
    -------------------------
     rewrite Content-Location
    -------------------------
    if {[llength $static::webportal_response_contentLocation] > 0}
    {
    if {[HTTP::header exists Content-Location]}
    {
        set request_val [HTTP::header value Content-Location]

        foreach request_rewriteRecord $static::webportal_response_contentLocation
        {
            set request_find [getfield $request_rewriteRecord "====" 1]
            set request_replace [getfield $request_rewriteRecord "====" 2]
            if {$request_replace == "nothing"}
            {
                set request_replace ""
            }

            regsub -all $request_find $request_val $request_replace request_val
        }
        HTTP::header replace Content-Location $request_val
    }
    }

    ----------------------------
     Body
    ----------------------------
    if {[llength $static::webportal_response_body] > 0}
    {
    set expression ""
    foreach request_rewriteRecord $static::webportal_response_body
    {
        set request_find [getfield $request_rewriteRecord "====" 1]
        set request_replace [getfield $request_rewriteRecord "====" 2]
        if {$request_replace == "nothing"}
        {
            set request_replace ""
        }

        set expression "$expression@$request_find@$request_replace@"
    }
    if {[HTTP::header Content-Type] contains "text" or [HTTP::header Content-Type] contains "xml" or [HTTP::header Content-Type] contains "java"}
    {
        STREAM::expression $expression
        STREAM::enable
    }
    }
}