Regex "before text matching" in GoLang

I have a piece of JavaScript code that I'm trying to replace with GoLang. The logic requires me to split the following string on ";" only when followed by "I" or "D":

I.E.viewability:-2;D.ua:Mozilla/5.0 (Linux; Android 7.0; SM-G920W8 Build/NRD90M) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.125 Mobile Safari/537.36;D.G.city:Burnaby;D.G.zip:V5C;D.G.region:BC;D.G.E.country_code2:CA;

In JavaScript I accomplish this using:

/;(?=[ID]|$)/

My understanding is that GoLang uses this regex lib

https://github.com/google/re2/wiki/Syntax

which clearly shows the above syntax (called before text matching re) as not supported.

What would be the correct way of achieving the same result in GoLang?

You may "reverse" the regex to match the strings you need. You want to match any 1+ chars other than ; followed with ; that are not followed with I or D.

Use

[^;]+(?:;[^ID;][^;]*)*

See the regex demo

Details:

• [^;]+ - 1 or more chars other than ;
• (?:;[^ID;][^;]*)* - zero or more sequences of:
  • ; - a ;
  • [^ID;] - a char other than I, D or ; (that is in order not to match empty values)
  • [^;]* - zero or more chars other than ;

See a Go demo.

package main

import (
    "regexp"
    "fmt"
)

func main() {
    var re = regexp.MustCompile(`[^;]+(?:;[^ID;][^;]*)*`)
    var str = `I.E.viewability:-2;D.ua:Mozilla/5.0 (Linux; Android 7.0; SM-G920W8 Build/NRD90M) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.125 Mobile Safari/537.36;D.G.city:Burnaby;D.G.zip:V5C;D.G.region:BC;D.G.E.country_code2:CA;`
    
    for _, match := range re.FindAllString(str, -1) {
        fmt.Println(match)
    }
}

Output:

I.E.viewability:-2
D.ua:Mozilla/5.0 (Linux; Android 7.0; SM-G920W8 Build/NRD90M) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.125 Mobile Safari/537.36
D.G.city:Burnaby
D.G.zip:V5C
D.G.region:BC
D.G.E.country_code2:CA