Adds support for custom sentences

CHANGELOG.md

@@ -1,6 +1,11 @@
 Changelog
 =========
 
+Version 2.1.0
+-------------
+
+* Adds support for custom sentence types
+
 Version 2.0.0
 -------------
 
@@ -41,4 +46,4 @@ Version 1.0.0+1
 Initial release.
 
 * Added `NmeaSentence`, `NmeaSentenceType`, `ChecksumSentence`, `TalkerSentence`, `QuerySentence`,
-  `ProprietarySentence`, `NmeaUtils` and `NmeaDecoder` classes.
+  `ProprietarySentence`, `NmeaUtils` and `NmeaDecoder` classes.

lib/nmea.dart

@@ -12,6 +12,7 @@ export 'src/nmea_sentence.dart'
     show NmeaSentence, nmeaPrefix, nmeaSuffix, nmeaFieldSeparator;
 export 'src/proprietary_sentence.dart'
     show ProprietarySentence, nmeaProprietaryDenominator, nmeaProprietaryPrefix;
+export 'src/custom_sentence.dart' show CustomSentence;
 export 'src/talker_sentence.dart' show TalkerSentence;
 export 'src/multipart_sentence.dart' show MultipartSentence;
 export 'src/query_sentence.dart' show QuerySentence, nmeaQueryDenominator;
@@ -20,6 +21,7 @@ export 'src/checksum_sentence.dart'
 export 'src/nmea_decoder.dart'
     show
         NmeaDecoder,
+        CustomSentenceFactory,
         ProprietarySentenceFactory,
         TalkerSentenceFactory,
         OptionalProprietarySentenceFactory,

lib/src/checksum_sentence.dart

@@ -56,11 +56,9 @@ class ChecksumSentence extends NmeaSentence {
   /// This is the actual sentence, without any fixtures, which is used to
   /// calculate the checksum.
   @override
-  String get rawWithoutFixtures =>
-      _rawWithoutFixtures ??= super.rawWithoutFixtures.substring(
-          0,
-          super.raw.length -
-              4); // -4 to remove the checksum + separator character
+  String get rawWithoutFixtures => _rawWithoutFixtures ??= (hasChecksum
+      ? super.rawWithoutFixtures.split(nmeaChecksumSeparator).first
+      : super.rawWithoutFixtures); // remove the checksum + separator character
 
   /// The [ChecksumSentence] constructor has the same parameters as the parent
   /// [NmeaSentence] does.

lib/src/custom_sentence.dart

@@ -0,0 +1,24 @@
+import 'package:nmea/src/checksum_sentence.dart';
+import 'package:nmea/src/nmea_sentence.dart';
+import 'package:nmea/src/nmea_sentence_type.dart';
+
+/// The data format is completely customizable, as long as it fits in the general
+/// envelope of an NMEA0183 sentence (begins with '$' and ends with windows-
+/// style newline characters).
+class CustomSentence extends ChecksumSentence {
+  /// Returns the identifier used to identify this sentence type
+  final String identifier;
+  final bool validateChecksums;
+
+  CustomSentence(
+      {required this.identifier,
+      required super.raw,
+      this.validateChecksums = true})
+      : super(
+          type: NmeaSentenceType.unknown,
+          prefix: nmeaPrefix,
+        );
+
+  @override
+  bool get hasValidChecksum => super.hasValidChecksum || !validateChecksums;
+}

lib/src/nmea_decoder.dart

@@ -1,12 +1,17 @@
 import 'dart:async';
 import 'dart:convert';
 
+import 'package:nmea/src/custom_sentence.dart';
 import 'package:nmea/src/multipart_sentence.dart';
 import 'package:nmea/src/nmea_sentence.dart';
 import 'package:nmea/src/proprietary_sentence.dart';
 import 'package:nmea/src/query_sentence.dart';
 import 'package:nmea/src/talker_sentence.dart';
 
+/// A function to create a [CustomSentence] from a raw string and an
+/// identifier.
+typedef CustomSentenceFactory = CustomSentence Function(String line);
+
 /// A function to create a [ProprietarySentence] from a raw string and a
 /// manufacturer id.
 typedef ProprietarySentenceFactory = ProprietarySentence Function(String line);
@@ -34,6 +39,7 @@ typedef OptionalNmeaSentenceFactory = NmeaSentence? Function(String line);
 /// this transformer doesn't buffer the input and tries to parse every piece of
 /// data it receives as a complete NMEA sentence.
 class NmeaDecoder extends StreamTransformerBase<String, NmeaSentence> {
+  final Map<String, CustomSentenceFactory> _customGenerators = {};
   final Map<String, ProprietarySentenceFactory> _proprietaryGenerators = {};
   final Map<String, TalkerSentenceFactory> _talkerGenerators = {};
   final List<MultipartSentence<dynamic>> _incompleteSentences = [];
@@ -68,6 +74,14 @@ class NmeaDecoder extends StreamTransformerBase<String, NmeaSentence> {
     this.onlyAllowValid = false,
   });
 
+  /// Registers a [CustomSentenceFactory] for a given identifier.
+  void registerCustomSentence(
+    String identifier,
+    CustomSentenceFactory factory,
+  ) {
+    _customGenerators[identifier] = factory;
+  }
+
   /// Registers a [ProprietarySentenceFactory] for a given manufacturer id.
   void registerProprietarySentence(
     String manufacturer,
@@ -143,7 +157,21 @@ class NmeaDecoder extends StreamTransformerBase<String, NmeaSentence> {
       return decodeQuery(line);
     }
 
-    return decodeTalker(line);
+    return decodeTalker(line) ?? decodeCustom(line);
+  }
+
+  /// Tries to decode the given line as a custom sentence.
+  /// The identifier is extracted from the line and the corresponding
+  /// [CustomSentenceFactory] is used to create the sentence.
+  /// If none is found `null` is returned.
+  CustomSentence? decodeCustom(String line) {
+    for (final identifier in _customGenerators.keys) {
+      if (line.startsWith(nmeaPrefix + identifier)) {
+        return _customGenerators[identifier]!(line);
+      }
+    }
+
+    return null;
   }
 
   /// Tries to decode the given line as a proprietary sentence.
@@ -175,7 +203,7 @@ class NmeaDecoder extends StreamTransformerBase<String, NmeaSentence> {
   /// If no fallback is registered, `null` is returned.
   TalkerSentence? decodeTalker(String line) {
     final separatorIndex = line.indexOf(nmeaFieldSeparator);
-    if (separatorIndex < 0 || line.length < 6) {
+    if (separatorIndex < 3 || line.length < 6) {
       return null;
     }
 

pubspec.yaml

@@ -4,7 +4,7 @@ homepage: https://github.com/ricardoboss/dart_nmea
 repository: https://github.com/ricardoboss/dart_nmea
 issue_tracker: https://github.com/ricardoboss/dart_nmea/issues
 
-version: 2.0.0
+version: 2.1.0
 
 environment:
   sdk: ">=2.17.1 <3.0.0"
@@ -16,4 +16,4 @@ dev_dependencies:
   lints: ^2.0.0
 
 # For information on the generic Dart part of this file, see the
-# following page: https://dart.dev/tools/pub/pubspec
+# following page: https://dart.dev/tools/pub/pubspec

test/nmea_decoder_test.dart

@@ -20,6 +20,54 @@ void main() {
     expect(decoded.raw, equals("\$--TES,123,345*56"));
   });
 
+  test("decodes custom sentences with invalid checksums", () {
+    final decoder = NmeaDecoder()
+      ..registerCustomSentence(
+          TestCustomSentence.id, (line) => TestCustomSentence(raw: line));
+    final decoded = decoder.decodeCustom("\$CST,123,345*56");
+
+    expect(decoded, isNotNull);
+    expect(decoded!.fields, equals(["CST", "123", "345"]));
+    expect(decoded.rawWithoutFixtures, "CST,123,345");
+    expect(decoded.hasChecksum, isTrue);
+    expect(decoded.checksum, equals("56"));
+    expect(decoded.actualChecksum, equals("46"));
+    expect(decoded.valid, isFalse);
+    expect(decoded.raw, equals("\$CST,123,345*56"));
+  });
+
+  test("decodes custom sentences with valid checksums", () {
+    final decoder = NmeaDecoder()
+      ..registerCustomSentence(
+          TestCustomSentence.id, (line) => TestCustomSentence(raw: line));
+    final decoded = decoder.decodeCustom("\$CST,123,345*46");
+
+    expect(decoded, isNotNull);
+    expect(decoded!.fields, equals(["CST", "123", "345"]));
+    expect(decoded.rawWithoutFixtures, "CST,123,345");
+    expect(decoded.hasChecksum, isTrue);
+    expect(decoded.checksum, equals("46"));
+    expect(decoded.actualChecksum, equals("46"));
+    expect(decoded.valid, isTrue);
+    expect(decoded.raw, equals("\$CST,123,345*46"));
+  });
+
+  test("decodes custom sentences with skipped checksums", () {
+    final decoder = NmeaDecoder()
+      ..registerCustomSentence(TestCustomSentence.id,
+          (line) => TestCustomSentence(raw: line, validateChecksums: false));
+    final decoded = decoder.decodeCustom("\$CST,123,345*56");
+
+    expect(decoded, isNotNull);
+    expect(decoded!.fields, equals(["CST", "123", "345"]));
+    expect(decoded.rawWithoutFixtures, "CST,123,345");
+    expect(decoded.hasChecksum, isTrue);
+    expect(decoded.checksum, equals("56"));
+    expect(decoded.actualChecksum, equals("46"));
+    expect(decoded.valid, isTrue);
+    expect(decoded.raw, equals("\$CST,123,345*56"));
+  });
+
   test("decodes query sentences", () {
     final decoder = NmeaDecoder();
     final decoded = decoder.decodeQuery("\$GPECQ,RMC");
@@ -45,3 +93,9 @@ class TestTalkerSentence extends TalkerSentence {
 
   TestTalkerSentence({required super.raw});
 }
+
+class TestCustomSentence extends CustomSentence {
+  static const String id = "CST";
+  TestCustomSentence({required super.raw, super.validateChecksums = true})
+      : super(identifier: id);
+}