ensure that the NMEA sentence length does not exceed 82 characters (#84)

CHANGELOG.txt

@@ -1,6 +1,18 @@
 ====================
  pyais CHANGELOG
 ====================
+-------------------------------------------------------------------------------
+ Version 2.2.1 03 Oct 2022
+-------------------------------------------------------------------------------
+* Closes https://github.com/M0r13n/pyais/issues/81  
+  * ensure that the NMEA sentence length does not exceed 82 characters
+-------------------------------------------------------------------------------
+ Version 2.2.0 02 Oct 2022
+-------------------------------------------------------------------------------
+* Closes https://github.com/M0r13n/pyais/issues/82
+  * introduces optional error_if_checksum_invalid keyword (default=False)
+  * adds the possibility to raise an exception if the checksum is invalid
+
 -------------------------------------------------------------------------------
  Version 2.1.2 14 May 2022
 -------------------------------------------------------------------------------

pyais/__init__.py

@@ -4,7 +4,7 @@
 from pyais.decode import decode
 
 __license__ = 'MIT'
-__version__ = '2.2.0'
+__version__ = '2.2.1'
 __author__ = 'Leon Morten Richter'
 
 __all__ = (

pyais/encode.py

@@ -36,7 +36,8 @@ def data_to_payload(ais_type: int, data: DATA_DICT) -> Payload:
 def ais_to_nmea_0183(payload: str, ais_talker_id: str, radio_channel: str, fill_bits: int) -> AIS_SENTENCES:
     """
     Splits the AIS payload into sentences, ASCII encodes the payload, creates
-    and sends the relevant NMEA 0183 sentences.
+    and sends the relevant NMEA 0183 sentences. Messages have a maximum length
+    of 82 characters, including the $ or ! starting character and the ending <LF>.
 
     HINT:
         This method takes care of splitting large payloads (larger than 60 characters)
@@ -51,7 +52,7 @@ def ais_to_nmea_0183(payload: str, ais_talker_id: str, radio_channel: str, fill_
     @return:                A list of relevant AIS sentences.
     """
     messages = []
-    max_len = 61
+    max_len = 60
     frag_cnt = math.ceil(len(payload) / max_len)
     seq_id = '0' if frag_cnt > 1 else ''
 

tests/test_encode.py

@@ -654,10 +654,14 @@ def test_encode_type_15():
 
 def test_encode_type_14():
     data = {'mmsi': '351809000', 'repeat': 0, 'text': 'RCVD YR TEST MSG', 'type': 14}
-    encoded = encode_dict(data)
-    assert encoded[0] == "!AIVDO,3,1,0,A,>5?Per18=HB1U:1@E=B0m<L00000000000000000000000000000000000000,0*63"
-    assert encoded[1] == "!AIVDO,3,2,0,A,0000000000000000000000000000000000000000000000000000000000000,0*25"
-    assert encoded[2] == "!AIVDO,3,3,0,A,0000000000000000000000000000000000000000000000,2*16"
+    actual = encode_dict(data)
+    expected = [
+        '!AIVDO,3,1,0,A,>5?Per18=HB1U:1@E=B0m<L0000000000000000000000000000000000000,0*53',
+        '!AIVDO,3,2,0,A,000000000000000000000000000000000000000000000000000000000000,0*15',
+        '!AIVDO,3,3,0,A,000000000000000000000000000000000000000000000000,2*16'
+    ]
+
+    assert expected == actual
 
 
 def test_encode_type_13():
@@ -688,10 +692,14 @@ def test_encode_type_12():
         'text': 'MSG FROM 271002099',
         'type': 12
     }
-    encoded = encode_dict(data)
-    assert encoded[0] == "!AIVDO,3,1,0,A,<42Lati0W:Ov=C7P6B?=Pjoihhjhqq0000000000000000000000000000000,0*19"
-    assert encoded[1] == "!AIVDO,3,2,0,A,0000000000000000000000000000000000000000000000000000000000000,0*25"
-    assert encoded[2] == "!AIVDO,3,3,0,A,0000000000000000000000000000000000000000000000,0*14"
+    actual = encode_dict(data)
+    expected = [
+        '!AIVDO,3,1,0,A,<42Lati0W:Ov=C7P6B?=Pjoihhjhqq000000000000000000000000000000,0*29',
+        '!AIVDO,3,2,0,A,000000000000000000000000000000000000000000000000000000000000,0*15',
+        '!AIVDO,3,3,0,A,000000000000000000000000000000000000000000000000,0*14'
+    ]
+
+    assert expected == actual
 
 
 def test_encode_type_11():
@@ -869,10 +877,12 @@ def test_encode_type_5_issue_59():
         'type': 5
     }
 
-    encoded_part_1 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[0]
-    encoded_part_2 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[1]
-    assert encoded_part_1 == "!AIVDM,2,1,0,B,55?MbV02;H;s<HtKP00EHE:0@T4@Dl0000000000L961O5Gf0P3QEp6ClRh00,0*45"
-    assert encoded_part_2 == "!AIVDM,2,2,0,B,0000000000,2*17"
+    actual = encode_dict(data, radio_channel="B", talker_id="AIVDM")
+    expected = [
+        '!AIVDM,2,1,0,B,55?MbV02;H;s<HtKP00EHE:0@T4@Dl0000000000L961O5Gf0P3QEp6ClRh0,0*75',
+        '!AIVDM,2,2,0,B,00000000000,2*27'
+    ]
+    assert actual == expected
 
 
 def test_encode_type_5():
@@ -902,21 +912,27 @@ def test_encode_type_5():
         'type': 5
     }
 
-    encoded_part_1 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[0]
-    encoded_part_2 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[1]  #
-    assert encoded_part_1 == "!AIVDM,2,1,0,B,55?MbV02;H;s<HtKP00EHE:0@T4@Dl0000000000L961O5Gf0NSQEp6ClRh00,0*3B"
-    assert encoded_part_2 == "!AIVDM,2,2,0,B,0000000000,2*17"
+    actual = encode_dict(data, radio_channel="B", talker_id="AIVDM")
+    expected = [
+        '!AIVDM,2,1,0,B,55?MbV02;H;s<HtKP00EHE:0@T4@Dl0000000000L961O5Gf0NSQEp6ClRh0,0*0B',
+        '!AIVDM,2,2,0,B,00000000000,2*27'
+    ]
+
+    assert actual == expected
 
 
 def test_encode_type_5_default():
     """
     Verified using http://ais.tbsalling.dk/.
     """
     data = {'mmsi': 123456789, 'type': 5}
-    encoded_part_1 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[0]
-    encoded_part_2 = encode_dict(data, radio_channel="B", talker_id="AIVDM")[1]
-    assert encoded_part_1 == "!AIVDM,2,1,0,B,51mg=5@000000000000000000000000000000000000000000000000000000,0*50"
-    assert encoded_part_2 == "!AIVDM,2,2,0,B,0000000000,2*17"
+    actual = encode_dict(data, radio_channel="B", talker_id="AIVDM")
+    expected = [
+        '!AIVDM,2,1,0,B,51mg=5@00000000000000000000000000000000000000000000000000000,0*60',
+        '!AIVDM,2,2,0,B,00000000000,2*27'
+    ]
+
+    assert actual == expected
 
 
 def test_encode_msg_type2():
@@ -1013,9 +1029,14 @@ def test_lon_too_large():
 
 def test_ship_name_too_lon():
     msg = MessageType5.create(mmsi="123", shipname="Titanic Titanic Titanic")
-    encoded = encode_msg(msg)
-    assert encoded[0] == "!AIVDO,2,1,0,A,50000Nh000000000001@U@4pT>1@U@4pT>1@U@40000000000000000000000,0*64"
-    assert encoded[1] == "!AIVDO,2,2,0,A,0000000000,2*16"
+    actual = encode_msg(msg)
+
+    expected = [
+        '!AIVDO,2,1,0,A,50000Nh000000000001@U@4pT>1@U@4pT>1@U@4000000000000000000000,0*54',
+        '!AIVDO,2,2,0,A,00000000000,2*26'
+    ]
+
+    assert actual == expected
 
 
 def test_int_to_bytes():
@@ -1054,3 +1075,20 @@ def test_encode_ascii_6_bit():
     bit_arr = decode_into_bit_array(ascii6.encode())
     assert bit_arr.to01() == input_val
     assert decode_bin_as_ascii6(bit_arr) == "HELLO WORLD!"
+
+
+def test_encode_does_not_exceed_nmea_sentence_length_limit():
+    data = {
+        'type': 5, 'repeat': 0, 'mmsi': '259725000', 'ais_version': 1,
+        'imo': 9103128, 'callsign': 'LAXP4', 'shipname': 'STAR HANSA',
+        'shiptype': 70, 'to_bow': 177, 'to_stern': 22, 'to_port': 17,
+        'to_starboard': 14, 'epfd': 1, 'month': 5, 'day': 20, 'hour': 6,
+        'minute': 0, 'draught': 7.4, 'destination': 'US BAL', 'dte': 0
+    }
+
+    encoded = encode_dict(data)
+    encoded = [e + '\r\n' for e in encoded]
+
+    assert len(encoded) == 2
+    assert len(encoded[0]) == 82
+    assert len(encoded[1]) == 33