How to strip all 4-byte chars in UTF8

How is it possible to strip all UTF8 chars with more than 3 bytes?

I only want to support UTF8mb3

>Solution :

You can iterate and copy only those runes that are smaller than 4-bytes:

out:=make([]rune, 0, len(str))
for i:=0;i<len(str); {
  r, n:=utf8.DecodeRune(str[i:])
  if n<4 {
    out=append(out,r)
  }
  i+=n
}
result:=string(out)