library/DNS_Helpers: add f_enc_IPv4

Used by upcoming D-GSM test, to pass the IP of the emulated GSUP server.
The code is based on f_enc_dns_hostname() in the same file.

Related: OS#4380
Change-Id: I8a5450988711680c93cfd657a34db759a56bc41e

library/DNS_Helpers.ttcn

@@ -70,4 +70,27 @@ function f_dec_dns_hostname(octetstring inp) return charstring {
 }
 
 
+function f_enc_IPv4(charstring str) return octetstring {
+	var octetstring ret := ''O;
+
+	while (lengthof(str) > 0) {
+		var integer dot_idx;
+		var charstring num;
+
+		dot_idx := f_strchr(str, ".");
+		if (dot_idx >= 0) {
+			/* there is another dot */
+			num := substr(str, 0, dot_idx);
+			str := substr(str, dot_idx+1, lengthof(str)-dot_idx-1);
+		} else {
+			/* no more dot */
+			num := str;
+			str := "";
+		}
+		ret := ret & int2oct(str2int(num), 1);
+	}
+
+	return ret;
+}
+
 }