fix: handle type 16 messages shorter than 96 bits

Author: M0r13n

examples/encode_msg.py

@@ -17,8 +17,9 @@
 For the following example, let's assume that we want to create a type 1 AIS message.
 """
 # Required imports
+from pyais.decode import decode
 from pyais.encode import encode_msg
-from pyais.messages import MessageType1
+from pyais.messages import MessageType1, MessageType16
 
 # You do not need to pass every attribute to the class.
 # All field other than `mmsi` do have default values.
@@ -36,3 +37,12 @@
 
 # You can also change the NMEA fields like the radio channel:
 print(encode_msg(msg, radio_channel="B"))
+
+msg_16_short = encode_msg(MessageType16.create(repeat=1, mmsi=123345, mmsi1=99999, increment1=23))[0]
+msg_16_long = encode_msg(MessageType16.create(repeat=1, mmsi=123345, mmsi1=99999, increment1=23, mmsi2=777777, increment2=45))[0]
+print(msg_16_short)
+print(msg_16_long)
+
+
+print(decode(msg_16_short))
+print(decode(msg_16_long))

pyais/messages.py

@@ -1341,9 +1341,26 @@ class MessageType15(Payload):
 
 
 @attr.s(slots=True)
-class MessageType16(Payload):
+class MessageType16DestinationA(Payload):
+    """
+    Assignment Mode Command (short)
+    Src: https://gpsd.gitlab.io/gpsd/AIVDM.html#_type_16_assignment_mode_command
+    """
+    msg_type = bit_field(6, int, default=16, signed=False)
+    repeat = bit_field(2, int, default=0, signed=False)
+    mmsi = bit_field(30, int, from_converter=from_mmsi)
+    spare_1 = bit_field(2, bytes, default=b'', is_spare=True)
+
+    mmsi1 = bit_field(30, int, default=0, from_converter=from_mmsi)
+    offset1 = bit_field(12, int, default=0, signed=False)
+    increment1 = bit_field(10, int, default=0, signed=False)
+    spare_2 = bit_field(4, bytes, default=b'', is_spare=True)
+
+
+@attr.s(slots=True)
+class MessageType16DestinationAB(Payload):
     """
-    Assignment Mode Command
+    Assignment Mode Command (long)
     Src: https://gpsd.gitlab.io/gpsd/AIVDM.html#_type_16_assignment_mode_command
     """
     msg_type = bit_field(6, int, default=16, signed=False)
@@ -1360,6 +1377,21 @@ class MessageType16(Payload):
     increment2 = bit_field(10, int, default=0, signed=False)
 
 
+@attr.s(slots=True)
+class MessageType16(Payload):
+    @classmethod
+    def create(cls, **kwargs: typing.Union[str, float, int, bool, bytes]) -> "ANY_MESSAGE":
+        if 'mmsi2' in kwargs:
+            return MessageType16DestinationAB.create(**kwargs)
+        return MessageType16DestinationA.create(**kwargs)
+
+    @classmethod
+    def from_bitarray(cls, bit_arr: bitarray) -> "ANY_MESSAGE":
+        if len(bit_arr) > 96:
+            return MessageType16DestinationAB.from_bitarray(bit_arr)
+        return MessageType16DestinationA.from_bitarray(bit_arr)
+
+
 @attr.s(slots=True)
 class MessageType17(Payload):
     """
@@ -1963,7 +1995,8 @@ class MessageType27(Payload):
     MessageType13,
     MessageType14,
     MessageType15,
-    MessageType16,
+    MessageType16DestinationA,
+    MessageType16DestinationAB,
     MessageType17,
     MessageType18,
     MessageType19,

tests/test_decode.py

@@ -461,7 +461,7 @@ def test_msg_type_15_b(self):
 
         ensure_type_for_msg_dict(msg)
 
-    def test_msg_type_16(self):
+    def test_msg_type_16_short(self):
         msg = decode(b"!AIVDM,1,1,,A,@01uEO@mMk7P<P00,0*18").asdict()
 
         assert msg["msg_type"] == 16
@@ -470,9 +470,24 @@ def test_msg_type_16(self):
         assert msg["mmsi1"] == 224251000
         assert msg["offset1"] == 200
         assert msg["increment1"] == 0
-        assert msg["mmsi2"] == 0
-        assert msg["offset2"] is None
-        assert msg["increment2"] is None
+        assert 'mmsi2' not in msg
+        assert 'offset2' not in msg
+        assert 'increment2' not in msg
+
+        ensure_type_for_msg_dict(msg)
+
+    def test_msg_type_16_long(self):
+        msg = decode(b"!AIVDO,1,1,,A,@@07Ql@01Qat005h0gN<@00e,0*46").asdict()
+
+        assert msg["msg_type"] == 16
+        assert msg["repeat"] == 1
+        assert msg["mmsi"] == 123345
+        assert msg["mmsi1"] == 99999
+        assert msg["offset1"] == 0
+        assert msg["increment1"] == 23
+        assert msg["mmsi2"] == 777777
+        assert msg["offset2"] == 0
+        assert msg["increment2"] == 45
 
         ensure_type_for_msg_dict(msg)
 
@@ -1813,3 +1828,7 @@ def test_decode_fragment_count_0(self):
         # IterMessages should just skip it
         decoded = list(IterMessages([msg]))
         self.assertEqual(decoded, [])
+
+
+if __name__ == '__main__':
+    unittest.main()

tests/test_encode.py

@@ -11,9 +11,9 @@
     MessageType26BroadcastStructured, MessageType26AddressedStructured, MessageType25BroadcastUnstructured, \
     MessageType25AddressedUnstructured, MessageType25BroadcastStructured, MessageType25AddressedStructured, \
     MessageType24PartB, MessageType24PartA, MessageType22Broadcast, MessageType22Addressed, MessageType27, \
-    MessageType23, MessageType21, MessageType20, MessageType19, MessageType18, MessageType17, MessageType16, \
+    MessageType23, MessageType21, MessageType20, MessageType19, MessageType18, MessageType17, MessageType16DestinationA, \
     MessageType15, MessageType4, MessageType5, MessageType6, MessageType7, MessageType8Default, MessageType2, MessageType3, \
-    MSG_CLASS
+    MSG_CLASS, MessageType16DestinationAB
 from pyais.util import decode_bin_as_ascii6, decode_into_bit_array, str_to_bin, int_to_bin, to_six_bit, encode_ascii_6, \
     int_to_bytes, bits2bytes
 
@@ -43,7 +43,10 @@ def test_widths():
     tot_width = sum(field.metadata['width'] for field in MessageType15.fields())
     assert tot_width == 160
 
-    tot_width = sum(field.metadata['width'] for field in MessageType16.fields())
+    tot_width = sum(field.metadata['width'] for field in MessageType16DestinationA.fields())
+    assert tot_width == 96
+
+    tot_width = sum(field.metadata['width'] for field in MessageType16DestinationAB.fields())
     assert tot_width == 144
 
     tot_width = sum(field.metadata['width'] for field in MessageType17.fields())
@@ -612,14 +615,27 @@ def test_encode_type_16():
         'increment2': 0,
         'mmsi': '002053501',
         'mmsi1': '224251000',
-        'mmsi2': '000000000',
+        'mmsi2': '123456',
         'offset1': 200,
         'offset2': 0,
         'repeat': 0,
         'type': 16
     }
     encoded = encode_dict(data)
-    assert encoded[0] == "!AIVDO,1,1,,A,@01uEO@mMk7P<P0000000000,0*1A"
+    assert encoded[0] == "!AIVDO,1,1,,A,@01uEO@mMk7P<P0007R@0000,0*0F"
+
+
+def test_encode_type_16_short():
+    data = {
+        'increment1': 0,
+        'mmsi': '002053501',
+        'mmsi1': '224251000',
+        'offset1': 200,
+        'repeat': 0,
+        'type': 16
+    }
+    encoded = encode_dict(data)
+    assert encoded[0] == "!AIVDO,1,1,,A,@01uEO@mMk7P<P00,0*1A"
 
 
 def test_encode_type_15_a():