feat: NIP21

README.md

@@ -24,6 +24,7 @@ flutter pub add nostr
 - [x] [NIP 15 End of Stored Events Notice](https://github.com/nostr-protocol/nips/blob/master/15.md)
 - [x] [NIP 19 bech32-encoded entities](https://github.com/nostr-protocol/nips/blob/master/19.md)
 - [x] [NIP 20 Command Results](https://github.com/nostr-protocol/nips/blob/master/20.md)
+- [x] [NIP 21 nostr: URI scheme](https://github.com/nostr-protocol/nips/blob/master/21.md)
 - [x] [NIP 28 Public Chat](https://github.com/nostr-protocol/nips/blob/master/28.md)
 - [x] [NIP 50 Search Capability](https://github.com/nostr-protocol/nips/blob/master/50.md)
 - [x] [NIP 51 Lists](https://github.com/nostr-protocol/nips/blob/master/51.md)

lib/nostr.dart

@@ -20,5 +20,6 @@ export 'src/nips/nip_010.dart';
 export 'src/nips/nip_013.dart';
 export 'src/nips/nip_019.dart';
 export 'src/nips/nip_020.dart';
+export 'src/nips/nip_021.dart';
 export 'src/nips/nip_028.dart';
 export 'src/nips/nip_051.dart';

lib/src/nips/nip_021.dart

@@ -0,0 +1,19 @@
+/// A utility class to handle Nostr URIs according to NIP-21 specification.
+/// Provides encode, decode functionalities for Nostr URIs.
+class NIP21 {
+  static const String _prefix = 'nostr:';
+
+  /// Parses a `nostr:` URI and extracts the identifier.
+  ///
+  /// Throws an [Exception] if the prefix `nostr:` is missing
+  static String decode(String uri) {
+    if (!uri.startsWith(_prefix)) {
+      throw Exception('Invalid Nostr URI: must start with "nostr:"');
+    }
+
+    return uri.substring(_prefix.length);
+  }
+
+  /// Generates a `nostr:` URI from a given content
+  static String encode(String content) => _prefix + content;
+}

test/nips/nip_021_test.dart

@@ -0,0 +1,34 @@
+import 'package:nostr/nostr.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('NIP21 URI Tests', () {
+    test('Parse valid npub URI', () {
+      expect(
+          NIP21.decode(
+              'nostr:npub1sn0wdenkukak0d9dfczzeacvhkrgz92ak56egt7vdgzn8pv2wfqqhrjdv9'),
+          equals(
+              'npub1sn0wdenkukak0d9dfczzeacvhkrgz92ak56egt7vdgzn8pv2wfqqhrjdv9'));
+    });
+
+    test('Parse valid nprofile URI', () {
+      expect(
+          NIP21.decode(
+              'nostr:nprofile1qqsrhuxx8l9ex335q7he0f09aej04zpazpl0ne2cgukyawd24mayt8gpp4mhxue69uhhytnc9e3k7mgpz4mhxue69uhkg6nzv9ejuumpv34kytnrdaksjlyr9p'),
+          equals(
+              'nprofile1qqsrhuxx8l9ex335q7he0f09aej04zpazpl0ne2cgukyawd24mayt8gpp4mhxue69uhhytnc9e3k7mgpz4mhxue69uhkg6nzv9ejuumpv34kytnrdaksjlyr9p'));
+    });
+
+    test('Generate npub URI', () {
+      expect(
+          NIP21.encode(
+              'npub1sn0wdenkukak0d9dfczzeacvhkrgz92ak56egt7vdgzn8pv2wfqqhrjdv9'),
+          equals(
+              'nostr:npub1sn0wdenkukak0d9dfczzeacvhkrgz92ak56egt7vdgzn8pv2wfqqhrjdv9'));
+    });
+
+    test('Invalid Nostr URI parsing', () {
+      expect(() => NIP21.decode('noprefix'), throwsA(isA<Exception>()));
+    });
+  });
+}