feat: Reimplement the OMEMOMessage protobuf schema

lib/src/protobuf/omemo_message.dart

@@ -0,0 +1,72 @@
+import 'package:omemo_dart/src/helpers.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+
+class OmemoMessage {
+
+  const OmemoMessage(this.n, this.pn, this.dhPub, this.ciphertext);
+
+  factory OmemoMessage.fromBuffer(List<int> data) {
+    var i = 0;
+    
+    // required uint32 n          = 1;
+    if (data[0] != 8) {
+      throw Exception();
+    }
+    var decode = decodeVarint(data, 1);
+    final n = decode.n;
+    i += decode.length + 1;
+
+    // required uint32 pn         = 2;
+    if (data[i] != 16) {
+      throw Exception();
+    }
+    decode = decodeVarint(data, i + 1);
+    final pn = decode.n;
+    i += decode.length + 1;
+
+    // required bytes  dh_pub     = 3;
+    if (data[i] != ((3 << 3) | 2)) {
+      throw Exception();
+    }
+    final dhPub = data.sublist(i + 2, i + 2 + data[i + 1]);
+    i += 2 + data[i + 1];
+
+    // optional bytes  ciphertext = 4;
+    List<int>? ciphertext;
+    if (i < data.length) {
+      if (data[i] != ((4 << 3) | 2)) {
+        throw Exception();
+      }
+
+      ciphertext = data.sublist(i + 2, i + 2 + data[i + 1]);
+    }
+
+    return OmemoMessage(n, pn, dhPub, ciphertext);
+  }
+
+  final int n;
+  final int pn;
+  final List<int> dhPub;
+  final List<int>? ciphertext;
+
+  List<int> writeToBuffer() {
+    final data = concat([
+      [8],
+      encodeVarint(n),
+      [16],
+      encodeVarint(pn),
+      [((3 << 3) | 2), dhPub.length],
+      dhPub,
+    ]);
+
+    if (ciphertext != null) {
+      return concat([
+        data,
+        [((4 << 3) | 2), ciphertext!.length],
+        ciphertext!,
+      ]);
+    }
+
+    return data;
+  }
+}

lib/src/protobuf/protobuf.dart

@@ -0,0 +1,60 @@
+/// Masks the 7 LSB
+const lsb7Mask = 0x7F;
+
+/// Constant for setting the MSB
+const msb = 1 << 7;
+
+class VarintDecode {
+
+  const VarintDecode(this.n, this.length);
+  final int n;
+  final int length;
+}
+
+/// Decode a Varint that begins at [input]'s index [offset].
+VarintDecode decodeVarint(List<int> input, int offset) {
+  // The return value
+  var n = 0;
+  // The byte offset counter
+  var i = 0;
+
+  // Iterate until the MSB of the byte is 0
+  while (true) {
+    // Mask only the 7 LSB and "move" them accordingly
+    n += (input[offset + i] & lsb7Mask) << (7 * i);
+
+    // Break if we reached the end
+    if (input[offset + i] & 1 << 7 == 0) {
+      break;
+    }
+    i++;
+  }
+
+  return VarintDecode(n, i + 1);
+}
+
+// Encodes the integer [i] into a Varint.
+List<int> encodeVarint(int i) {
+  assert(i >= 0, "Two's complement is not implemented");
+  final ret = List<int>.empty(growable: true);
+
+  var j = 0;
+  while (true) {
+    // The 7 LSB of the byte we're creating
+    final x = (i & (lsb7Mask << j * 7)) >> j * 7;
+    // The next bits
+    final next = i & (lsb7Mask << (j + 1) * 7);
+
+    if (next == 0) {
+      // If we were to shift further, we only get zero, so we're at the end
+      ret.add(x);
+      break;
+    } else {
+      // We still have at least one bit more to go, so set the MSB to 1
+      ret.add(x + msb);
+      j++;
+    }
+  }
+
+  return ret;
+}

test/protobuf.dart

@@ -0,0 +1,110 @@
+import 'package:omemo_dart/protobuf/schema.pb.dart';
+import 'package:omemo_dart/src/protobuf/omemo_message.dart';
+import 'package:omemo_dart/src/protobuf/protobuf.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Base 128 Varints', () {
+    test('Test simple parsing of Varints', () {
+      expect(
+        decodeVarint(<int>[1], 0).n,
+        1,
+      );
+      expect(
+        decodeVarint(<int>[1], 0).length,
+        1,
+      );
+      expect(
+        decodeVarint(<int>[0x96, 0x01, 0x00], 0).n,
+        150,
+      );
+      expect(
+        decodeVarint(<int>[0x96, 0x01, 0x00], 0).length,
+        2,
+      );
+      expect(
+        decodeVarint(<int>[172, 2, 0x8], 0).n,
+        300,
+      );
+      expect(
+        decodeVarint(<int>[172, 2, 0x8], 0).length,
+        2,
+      );
+    });
+
+    test('Test encoding Varints', () {
+      expect(
+        encodeVarint(1),
+        <int>[1],
+      );
+      expect(
+        encodeVarint(150),
+        <int>[0x96, 0x01],
+      );
+      expect(
+        encodeVarint(300),
+        <int>[172, 2],
+      );
+    });
+  });
+
+  group('OMEMOMessage', () {
+    test('Decode a OMEMOMessage', () {
+      final pbMessage = OMEMOMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3]
+        ..ciphertext = <int>[4, 5, 6];
+      final serial = pbMessage.writeToBuffer();
+      final msg = OmemoMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[4, 5, 6]);
+    });
+    test('Decode a OMEMOMessage without ciphertext', () {
+      final pbMessage = OMEMOMessage()
+        ..n = 1
+        ..pn = 5
+        ..dhPub = <int>[1, 2, 3];
+      final serial = pbMessage.writeToBuffer();
+      final msg = OmemoMessage.fromBuffer(serial);
+      
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, null);
+    });
+    test('Encode a OMEMOMessage', () {
+      const m = OmemoMessage(
+        1,
+        5,
+        <int>[1, 2, 3],
+        <int>[4, 5, 6],
+      );
+      final serial = m.writeToBuffer();
+      final msg = OMEMOMessage.fromBuffer(serial);
+      
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[4, 5, 6]);
+    });
+    test('Encode a OMEMOMessage without ciphertext', () {
+      const m = OmemoMessage(
+        1,
+        5,
+        <int>[1, 2, 3],
+        null,
+      );
+      final serial = m.writeToBuffer();
+      final msg = OMEMOMessage.fromBuffer(serial);
+
+      expect(msg.n, 1);
+      expect(msg.pn, 5);
+      expect(msg.dhPub, <int>[1, 2, 3]);
+      expect(msg.ciphertext, <int>[]);
+    });
+  });
+}