src/apn_encdec.erl

-module(apn_encdec).

% decode APN Name Encoded Format
% TS 23.003 APN
-export([decode_apn/1, encode_apn/1]).

decode_apn(ApnEnc) ->
	decode_apn("", ApnEnc, 0).

decode_apn(Result, [], 0) ->
	Result;

decode_apn(Result, << >>, 0) ->
	Result;

decode_apn("", ApnEnc, 0) ->
	<< NewElemLen:8, RemainEnc/bytes >> = ApnEnc,
	case NewElemLen of
		0 -> "";
		_ -> decode_apn("", RemainEnc, NewElemLen)
	end;

decode_apn(Result, ApnEnc, 0) ->
	<< NewElemLen:8, RemainEnc/bytes >> = ApnEnc,
	case NewElemLen of
		0 -> Result;
		_ -> decode_apn(Result ++ ".", RemainEnc, NewElemLen)
	end;

decode_apn(Result, ApnEnc, RemainLen) when RemainLen > 0 ->
	<< Char:8, RemainEnc/bytes >> = ApnEnc,
	decode_apn(Result ++ [Char], RemainEnc, RemainLen - 1).

encode_apn(ApnStr) ->
	encode_apn(<<>>, ApnStr, "", 0).

encode_apn(ApnEnc, "", "", 0) ->
	ApnEnc;

encode_apn(ApnEnc, "", CurStr, Len) ->
	CurBin = binary:list_to_bin(CurStr),
	Result = << ApnEnc/binary, Len, CurBin/binary >>,
	Result;

encode_apn(ApnEnc, [ Char | RemainStr ], CurStr, Len) ->
	case Char of
		46 -> CurBin = binary:list_to_bin(CurStr),
		       encode_apn(<<ApnEnc/binary, Len,  CurBin/binary >>, RemainStr, "", 0);
		_ -> encode_apn(ApnEnc, RemainStr, CurStr ++ [Char], Len + 1)
	end.