From 1a064fa6aece492352271ae164b29262d66f6b6d Mon Sep 17 00:00:00 2001
From: Pau Espin Pedrol <pespin@sysmocom.de>
Date: Mon, 22 Jan 2024 17:41:30 +0100
Subject: [PATCH] Decode/Encode Apn as string

Change-Id: I1206e31272f03853aa8447fb263fff7757282b83
---
 include/gsup_protocol.hrl        |  2 +-
 src/apn_encdec.erl               | 51 ++++++++++++++++++++++++++++++++
 src/gsup_protocol.erl            |  7 +++--
 test/gsup_encode_decode_test.erl |  5 ++--
 4 files changed, 58 insertions(+), 7 deletions(-)
 create mode 100644 src/apn_encdec.erl

diff --git a/include/gsup_protocol.hrl b/include/gsup_protocol.hrl
index 3082521..1c755ac 100644
--- a/include/gsup_protocol.hrl
+++ b/include/gsup_protocol.hrl
@@ -81,7 +81,7 @@
 -type 'GSUPPdpInfo'() :: #{
   pdp_context_id => integer(),
   pdp_address => 'GSUPPdpAddress'(),
-  access_point_name => binary(),
+  access_point_name => string(),
   quality_of_service => binary(),
   pdp_charging => integer()
 }.
diff --git a/src/apn_encdec.erl b/src/apn_encdec.erl
new file mode 100644
index 0000000..60a5ede
--- /dev/null
+++ b/src/apn_encdec.erl
@@ -0,0 +1,51 @@
+
+-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.
diff --git a/src/gsup_protocol.erl b/src/gsup_protocol.erl
index 1dcc628..1aea289 100644
--- a/src/gsup_protocol.erl
+++ b/src/gsup_protocol.erl
@@ -267,7 +267,7 @@ decode_pdp_info(<<?PDP_ADDRESS, Len, PDPAddress:Len/binary, Tail/binary>>, Map)
 
 decode_pdp_info(<<?ACCESS_POINT_NAME, Len, APN:Len/binary, Tail/binary>>, Map) ->
   ?CHECK_LEN(access_point_name, Len, 1, 100),
-  decode_pdp_info(Tail, Map#{access_point_name => APN});
+  decode_pdp_info(Tail, Map#{access_point_name => apn_encdec:decode_apn(APN)});
 
 decode_pdp_info(<<?QUALITY_OF_SERVICE, Len, QOS:Len/binary, Tail/binary>>, Map) ->
   ?CHECK_LEN(quality_of_service, Len, 1, 20),
@@ -620,9 +620,10 @@ encode_pdp_info(#{pdp_address := Value} = Map, Head) ->
   encode_pdp_info(maps:without([pdp_address], Map), <<Head/binary, ?PDP_ADDRESS, Len, PDPTypeOrg, PDPTypeNr, Addr/binary>>);
 
 encode_pdp_info(#{access_point_name := Value} = Map, Head) ->
-  Len = size(Value),
+  ApnBin = apn_encdec:encode_apn(Value),
+  Len = size(ApnBin),
   ?CHECK_LEN(access_point_name, Len, 1, 100),
-  encode_pdp_info(maps:without([access_point_name], Map), <<Head/binary, ?ACCESS_POINT_NAME, Len, Value/binary>>);
+  encode_pdp_info(maps:without([access_point_name], Map), <<Head/binary, ?ACCESS_POINT_NAME, Len, ApnBin/binary>>);
 
 encode_pdp_info(#{quality_of_service := Value} = Map, Head) ->
   Len = size(Value),
diff --git a/test/gsup_encode_decode_test.erl b/test/gsup_encode_decode_test.erl
index c80abdc..0637160 100644
--- a/test/gsup_encode_decode_test.erl
+++ b/test/gsup_encode_decode_test.erl
@@ -217,14 +217,13 @@ lu_res_test() ->
                    msisdn => <<145,148,97,70,50,36,67>>,
                    pdp_charging => 44799,pdp_info_complete => true,
                    pdp_info_list =>
-                       [#{access_point_name =>
-                              <<4,116,101,115,116,3,97,112,110>>,
+                       [#{access_point_name => "test.apn",
                           pdp_charging => 65315,pdp_context_id => 1,
                           pdp_address => #{address => #{},
                                            pdp_type_org => 241,
                                            pdp_type_nr => 33},
                           quality_of_service => <<2>>},
-                        #{access_point_name => <<3,102,111,111,3,97,112,110>>,
+                        #{access_point_name => "foo.apn",
                           pdp_context_id => 2,
                           pdp_address => #{address => #{},
                                            pdp_type_org => 241,