feat(extension): add custom URL handler support for extensions

- Add URLHandlerConfig to extension manifest (Go)
- Add HandleURL method to extension providers (Go)
- Add export functions for URL handling (Go)
- Add URLHandler class to extension_provider.dart (Flutter)
- Add platform bridge methods for URL handling (Flutter)
- Update fetchFromUrl to check extension URL handlers first
- Add Android/iOS native handlers for extension URL routing
- Update CHANGELOG with new feature

CHANGELOG.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## [3.0.0-alpha.4] - Upcoming
+
+### Added
+
+- **Custom URL Handler for Extensions**: Extensions can now register custom URL patterns
+  - Handle URLs from YouTube Music, SoundCloud, Bandcamp, etc.
+  - Manifest config: `urlHandler: { enabled: true, patterns: ["music.youtube.com"] }`
+  - Implement `handleURL(url)` function in extension to parse and return track metadata
+  - SpotiFLAC automatically routes matching URLs to the appropriate extension
+  - Supports share intents and paste from clipboard
+
+### Documentation
+
+- Updated `docs/EXTENSION_DEVELOPMENT.md`:
+  - Added Custom URL Handler section with examples
+  - Added `handleURL` function documentation
+  - Added URL pattern examples for YouTube, SoundCloud, Bandcamp
+
+---
+
 ## [3.0.0-alpha.3] - 2026-01-12
 
 ### Added

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -551,6 +551,27 @@ class MainActivity: FlutterActivity() {
                             }
                             result.success(response)
                         }
+                        // Extension URL Handler API
+                        "handleURLWithExtension" -> {
+                            val url = call.argument<String>("url") ?: ""
+                            val response = withContext(Dispatchers.IO) {
+                                Gobackend.handleURLWithExtensionJSON(url)
+                            }
+                            result.success(response)
+                        }
+                        "findURLHandler" -> {
+                            val url = call.argument<String>("url") ?: ""
+                            val response = withContext(Dispatchers.IO) {
+                                Gobackend.findURLHandlerJSON(url)
+                            }
+                            result.success(response)
+                        }
+                        "getURLHandlers" -> {
+                            val response = withContext(Dispatchers.IO) {
+                                Gobackend.getURLHandlersJSON()
+                            }
+                            result.success(response)
+                        }
                         // Extension Post-Processing API
                         "runPostProcessing" -> {
                             val filePath = call.argument<String>("file_path") ?: ""

go_backend/exports.go

@@ -1506,6 +1506,127 @@ func GetSearchProvidersJSON() (string, error) {
 	return string(jsonBytes), nil
 }
 
+// ==================== EXTENSION URL HANDLER ====================
+
+// HandleURLWithExtensionJSON tries to handle a URL with any matching extension
+// Returns JSON with type, tracks, album info, etc.
+func HandleURLWithExtensionJSON(url string) (string, error) {
+	manager := GetExtensionManager()
+	result, extensionID, err := manager.HandleURLWithExtension(url)
+	if err != nil {
+		return "", err
+	}
+
+	// Build response
+	response := map[string]interface{}{
+		"type":         result.Type,
+		"extension_id": extensionID,
+		"name":         result.Name,
+		"cover_url":    result.CoverURL,
+	}
+
+	// Add track if single track
+	if result.Track != nil {
+		response["track"] = map[string]interface{}{
+			"id":           result.Track.ID,
+			"name":         result.Track.Name,
+			"artists":      result.Track.Artists,
+			"album_name":   result.Track.AlbumName,
+			"album_artist": result.Track.AlbumArtist,
+			"duration_ms":  result.Track.DurationMS,
+			"images":       result.Track.ResolvedCoverURL(),
+			"release_date": result.Track.ReleaseDate,
+			"track_number": result.Track.TrackNumber,
+			"disc_number":  result.Track.DiscNumber,
+			"isrc":         result.Track.ISRC,
+			"provider_id":  result.Track.ProviderID,
+		}
+	}
+
+	// Add tracks if multiple
+	if len(result.Tracks) > 0 {
+		tracks := make([]map[string]interface{}, len(result.Tracks))
+		for i, track := range result.Tracks {
+			tracks[i] = map[string]interface{}{
+				"id":           track.ID,
+				"name":         track.Name,
+				"artists":      track.Artists,
+				"album_name":   track.AlbumName,
+				"album_artist": track.AlbumArtist,
+				"duration_ms":  track.DurationMS,
+				"images":       track.ResolvedCoverURL(),
+				"release_date": track.ReleaseDate,
+				"track_number": track.TrackNumber,
+				"disc_number":  track.DiscNumber,
+				"isrc":         track.ISRC,
+				"provider_id":  track.ProviderID,
+			}
+		}
+		response["tracks"] = tracks
+	}
+
+	// Add album info if present
+	if result.Album != nil {
+		response["album"] = map[string]interface{}{
+			"id":           result.Album.ID,
+			"name":         result.Album.Name,
+			"artists":      result.Album.Artists,
+			"cover_url":    result.Album.CoverURL,
+			"release_date": result.Album.ReleaseDate,
+			"total_tracks": result.Album.TotalTracks,
+		}
+	}
+
+	// Add artist info if present
+	if result.Artist != nil {
+		response["artist"] = map[string]interface{}{
+			"id":        result.Artist.ID,
+			"name":      result.Artist.Name,
+			"image_url": result.Artist.ImageURL,
+		}
+	}
+
+	jsonBytes, err := json.Marshal(response)
+	if err != nil {
+		return "", err
+	}
+
+	return string(jsonBytes), nil
+}
+
+// FindURLHandlerJSON finds an extension that can handle the given URL
+// Returns extension ID or empty string if none found
+func FindURLHandlerJSON(url string) string {
+	manager := GetExtensionManager()
+	handler := manager.FindURLHandler(url)
+	if handler == nil {
+		return ""
+	}
+	return handler.extension.ID
+}
+
+// GetURLHandlersJSON returns all extensions that handle custom URLs
+func GetURLHandlersJSON() (string, error) {
+	manager := GetExtensionManager()
+	handlers := manager.GetURLHandlers()
+
+	result := make([]map[string]interface{}, 0, len(handlers))
+	for _, h := range handlers {
+		result = append(result, map[string]interface{}{
+			"id":           h.extension.ID,
+			"display_name": h.extension.Manifest.DisplayName,
+			"patterns":     h.extension.Manifest.URLHandler.Patterns,
+		})
+	}
+
+	jsonBytes, err := json.Marshal(result)
+	if err != nil {
+		return "", err
+	}
+
+	return string(jsonBytes), nil
+}
+
 // ==================== EXTENSION POST-PROCESSING ====================
 
 // RunPostProcessingJSON runs post-processing hooks on a file

go_backend/extension_manifest.go

@@ -74,6 +74,12 @@ type SearchBehaviorConfig struct {
 	ThumbnailHeight int    `json:"thumbnailHeight,omitempty"` // Custom thumbnail height in pixels
 }
 
+// URLHandlerConfig defines custom URL handling for an extension
+type URLHandlerConfig struct {
+	Enabled  bool     `json:"enabled"`            // Whether extension handles URLs
+	Patterns []string `json:"patterns,omitempty"` // URL patterns to match (e.g., "music.youtube.com", "soundcloud.com")
+}
+
 // TrackMatchingConfig defines custom track matching behavior
 type TrackMatchingConfig struct {
 	CustomMatching    bool   `json:"customMatching"`              // Whether extension handles matching
@@ -113,6 +119,7 @@ type ExtensionManifest struct {
 	SkipMetadataEnrichment bool                  `json:"skipMetadataEnrichment,omitempty"` // If true, don't enrich metadata from Deezer/Spotify
 	SkipBuiltInFallback    bool                  `json:"skipBuiltInFallback,omitempty"`    // If true, don't fallback to built-in providers (tidal/qobuz/amazon)
 	SearchBehavior         *SearchBehaviorConfig `json:"searchBehavior,omitempty"`         // Custom search behavior
+	URLHandler             *URLHandlerConfig     `json:"urlHandler,omitempty"`             // Custom URL handling
 	TrackMatching          *TrackMatchingConfig  `json:"trackMatching,omitempty"`          // Custom track matching
 	PostProcessing         *PostProcessingConfig `json:"postProcessing,omitempty"`         // Post-processing hooks
 }
@@ -270,6 +277,29 @@ func (m *ExtensionManifest) HasPostProcessing() bool {
 	return m.PostProcessing != nil && m.PostProcessing.Enabled
 }
 
+// HasURLHandler returns true if extension handles custom URLs
+func (m *ExtensionManifest) HasURLHandler() bool {
+	return m.URLHandler != nil && m.URLHandler.Enabled && len(m.URLHandler.Patterns) > 0
+}
+
+// MatchesURL checks if a URL matches any of the extension's URL patterns
+func (m *ExtensionManifest) MatchesURL(urlStr string) bool {
+	if !m.HasURLHandler() {
+		return false
+	}
+
+	// Parse URL to get host
+	urlStr = strings.ToLower(strings.TrimSpace(urlStr))
+	for _, pattern := range m.URLHandler.Patterns {
+		pattern = strings.ToLower(strings.TrimSpace(pattern))
+		// Check if URL contains the pattern (host match)
+		if strings.Contains(urlStr, pattern) {
+			return true
+		}
+	}
+	return false
+}
+
 // GetPostProcessingHooks returns all post-processing hooks
 func (m *ExtensionManifest) GetPostProcessingHooks() []PostProcessingHook {
 	if m.PostProcessing == nil {

go_backend/extension_providers.go

@@ -981,6 +981,69 @@ func (p *ExtensionProviderWrapper) CustomSearch(query string, options map[string
 	return tracks, nil
 }
 
+// ==================== Custom URL Handler ====================
+
+// ExtURLHandleResult represents the result of URL handling
+type ExtURLHandleResult struct {
+	Type     string             `json:"type"`                // "track", "album", "playlist", "artist"
+	Track    *ExtTrackMetadata  `json:"track,omitempty"`     // For single track
+	Tracks   []ExtTrackMetadata `json:"tracks,omitempty"`    // For album/playlist
+	Album    *ExtAlbumMetadata  `json:"album,omitempty"`     // Album info
+	Artist   *ExtArtistMetadata `json:"artist,omitempty"`    // Artist info
+	Name     string             `json:"name,omitempty"`      // Playlist/album name
+	CoverURL string             `json:"cover_url,omitempty"` // Cover image
+}
+
+// HandleURL processes a URL using the extension's URL handler
+func (p *ExtensionProviderWrapper) HandleURL(url string) (*ExtURLHandleResult, error) {
+	if !p.extension.Manifest.HasURLHandler() {
+		return nil, fmt.Errorf("extension '%s' does not support URL handling", p.extension.ID)
+	}
+
+	if !p.extension.Enabled {
+		return nil, fmt.Errorf("extension '%s' is disabled", p.extension.ID)
+	}
+
+	script := fmt.Sprintf(`
+		(function() {
+			if (typeof extension !== 'undefined' && typeof extension.handleUrl === 'function') {
+				return extension.handleUrl(%q);
+			}
+			return null;
+		})()
+	`, url)
+
+	result, err := p.vm.RunString(script)
+	if err != nil {
+		return nil, fmt.Errorf("handleUrl failed: %w", err)
+	}
+
+	if result == nil || goja.IsUndefined(result) || goja.IsNull(result) {
+		return nil, fmt.Errorf("handleUrl returned null - URL not recognized")
+	}
+
+	exported := result.Export()
+	jsonBytes, err := json.Marshal(exported)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal result: %w", err)
+	}
+
+	var handleResult ExtURLHandleResult
+	if err := json.Unmarshal(jsonBytes, &handleResult); err != nil {
+		return nil, fmt.Errorf("failed to parse URL handle result: %w", err)
+	}
+
+	// Set provider ID on tracks
+	if handleResult.Track != nil {
+		handleResult.Track.ProviderID = p.extension.ID
+	}
+	for i := range handleResult.Tracks {
+		handleResult.Tracks[i].ProviderID = p.extension.ID
+	}
+
+	return &handleResult, nil
+}
+
 // ==================== Custom Track Matching ====================
 
 // MatchTrackResult represents the result of custom track matching
@@ -1120,6 +1183,48 @@ func (m *ExtensionManager) GetSearchProviders() []*ExtensionProviderWrapper {
 	return providers
 }
 
+// GetURLHandlers returns all extensions that handle custom URLs
+func (m *ExtensionManager) GetURLHandlers() []*ExtensionProviderWrapper {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	var providers []*ExtensionProviderWrapper
+	for _, ext := range m.extensions {
+		if ext.Enabled && ext.Manifest.HasURLHandler() && ext.Error == "" {
+			providers = append(providers, NewExtensionProviderWrapper(ext))
+		}
+	}
+	return providers
+}
+
+// FindURLHandler finds an extension that can handle the given URL
+func (m *ExtensionManager) FindURLHandler(url string) *ExtensionProviderWrapper {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	for _, ext := range m.extensions {
+		if ext.Enabled && ext.Manifest.MatchesURL(url) && ext.Error == "" {
+			return NewExtensionProviderWrapper(ext)
+		}
+	}
+	return nil
+}
+
+// HandleURLWithExtension tries to handle a URL with any matching extension
+func (m *ExtensionManager) HandleURLWithExtension(url string) (*ExtURLHandleResult, string, error) {
+	handler := m.FindURLHandler(url)
+	if handler == nil {
+		return nil, "", fmt.Errorf("no extension found to handle URL: %s", url)
+	}
+
+	result, err := handler.HandleURL(url)
+	if err != nil {
+		return nil, handler.extension.ID, err
+	}
+
+	return result, handler.extension.ID, nil
+}
+
 // GetPostProcessingProviders returns all extensions that provide post-processing
 func (m *ExtensionManager) GetPostProcessingProviders() []*ExtensionProviderWrapper {
 	m.mu.RLock()

ios/Runner/AppDelegate.swift

@@ -484,6 +484,25 @@ import Gobackend  // Import Go framework
             if let error = error { throw error }
             return response
             
+        // Extension URL Handler API
+        case "handleURLWithExtension":
+            let args = call.arguments as! [String: Any]
+            let url = args["url"] as! String
+            let response = GobackendHandleURLWithExtensionJSON(url, &error)
+            if let error = error { throw error }
+            return response
+            
+        case "findURLHandler":
+            let args = call.arguments as! [String: Any]
+            let url = args["url"] as! String
+            let response = GobackendFindURLHandlerJSON(url)
+            return response
+            
+        case "getURLHandlers":
+            let response = GobackendGetURLHandlersJSON(&error)
+            if let error = error { throw error }
+            return response
+            
         // Extension Post-Processing API
         case "runPostProcessing":
             let args = call.arguments as! [String: Any]

lib/providers/extension_provider.dart

@@ -24,6 +24,7 @@ class Extension {
   final bool hasDownloadProvider;
   final bool skipMetadataEnrichment; // If true, use metadata from extension instead of enriching
   final SearchBehavior? searchBehavior; // Custom search behavior
+  final URLHandler? urlHandler; // Custom URL handling
   final TrackMatching? trackMatching; // Custom track matching
   final PostProcessing? postProcessing; // Post-processing hooks
 
@@ -45,6 +46,7 @@ class Extension {
     this.hasDownloadProvider = false,
     this.skipMetadataEnrichment = false,
     this.searchBehavior,
+    this.urlHandler,
     this.trackMatching,
     this.postProcessing,
   });
@@ -74,6 +76,9 @@ class Extension {
       searchBehavior: json['search_behavior'] != null 
           ? SearchBehavior.fromJson(json['search_behavior'] as Map<String, dynamic>)
           : null,
+      urlHandler: json['url_handler'] != null
+          ? URLHandler.fromJson(json['url_handler'] as Map<String, dynamic>)
+          : null,
       trackMatching: json['track_matching'] != null
           ? TrackMatching.fromJson(json['track_matching'] as Map<String, dynamic>)
           : null,
@@ -101,6 +106,7 @@ class Extension {
     bool? hasDownloadProvider,
     bool? skipMetadataEnrichment,
     SearchBehavior? searchBehavior,
+    URLHandler? urlHandler,
     TrackMatching? trackMatching,
     PostProcessing? postProcessing,
   }) {
@@ -122,12 +128,14 @@ class Extension {
       hasDownloadProvider: hasDownloadProvider ?? this.hasDownloadProvider,
       skipMetadataEnrichment: skipMetadataEnrichment ?? this.skipMetadataEnrichment,
       searchBehavior: searchBehavior ?? this.searchBehavior,
+      urlHandler: urlHandler ?? this.urlHandler,
       trackMatching: trackMatching ?? this.trackMatching,
       postProcessing: postProcessing ?? this.postProcessing,
     );
   }
 
   bool get hasCustomSearch => searchBehavior?.enabled ?? false;
+  bool get hasURLHandler => urlHandler?.enabled ?? false;
   bool get hasCustomMatching => trackMatching?.customMatching ?? false;
   bool get hasPostProcessing => postProcessing?.enabled ?? false;
 }
@@ -226,6 +234,36 @@ class PostProcessing {
   }
 }
 
+/// URL handler configuration for custom URL patterns
+class URLHandler {
+  final bool enabled;
+  final List<String> patterns;
+
+  const URLHandler({
+    required this.enabled,
+    this.patterns = const [],
+  });
+
+  factory URLHandler.fromJson(Map<String, dynamic> json) {
+    return URLHandler(
+      enabled: json['enabled'] as bool? ?? false,
+      patterns: (json['patterns'] as List<dynamic>?)?.cast<String>() ?? [],
+    );
+  }
+
+  /// Check if a URL matches any of the patterns
+  bool matchesURL(String url) {
+    if (!enabled || patterns.isEmpty) return false;
+    final lowerUrl = url.toLowerCase();
+    for (final pattern in patterns) {
+      if (lowerUrl.contains(pattern.toLowerCase())) {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+
 /// A post-processing hook
 class PostProcessingHook {
   final String id;

lib/providers/track_provider.dart

@@ -131,6 +131,45 @@ class TrackNotifier extends Notifier<TrackState> {
     state = TrackState(isLoading: true, hasSearchText: state.hasSearchText);
 
     try {
+      // First, check if any extension can handle this URL
+      final extensionHandler = await PlatformBridge.findURLHandler(url);
+      if (extensionHandler != null) {
+        _log.i('Found extension URL handler: $extensionHandler for URL: $url');
+        final result = await PlatformBridge.handleURLWithExtension(url);
+        if (!_isRequestValid(requestId)) return;
+        
+        if (result != null) {
+          final type = result['type'] as String?;
+          final extensionId = result['extension_id'] as String?;
+          
+          if (type == 'track' && result['track'] != null) {
+            final trackData = result['track'] as Map<String, dynamic>;
+            final track = _parseSearchTrack(trackData, source: extensionId);
+            state = TrackState(
+              tracks: [track],
+              isLoading: false,
+              coverUrl: track.coverUrl,
+              searchExtensionId: extensionId,
+            );
+            return;
+          } else if ((type == 'album' || type == 'playlist') && result['tracks'] != null) {
+            final trackList = result['tracks'] as List<dynamic>;
+            final tracks = trackList.map((t) => _parseSearchTrack(t as Map<String, dynamic>, source: extensionId)).toList();
+            state = TrackState(
+              tracks: tracks,
+              isLoading: false,
+              albumId: result['album']?['id'] as String?,
+              albumName: result['name'] as String? ?? result['album']?['name'] as String?,
+              playlistName: type == 'playlist' ? result['name'] as String? : null,
+              coverUrl: result['cover_url'] as String?,
+              searchExtensionId: extensionId,
+            );
+            return;
+          }
+        }
+      }
+      
+      // No extension handler found, try Spotify URL parsing
       final parsed = await PlatformBridge.parseSpotifyUrl(url);
       if (!_isRequestValid(requestId)) return; // Request cancelled
       

lib/services/platform_bridge.dart

@@ -753,6 +753,40 @@ class PlatformBridge {
     return list.map((e) => e as Map<String, dynamic>).toList();
   }
 
+  // ==================== EXTENSION URL HANDLER ====================
+
+  /// Handle a URL with any matching extension
+  /// Returns null if no extension can handle the URL
+  static Future<Map<String, dynamic>?> handleURLWithExtension(String url) async {
+    try {
+      final result = await _channel.invokeMethod('handleURLWithExtension', {
+        'url': url,
+      });
+      if (result == null || result == '') return null;
+      return jsonDecode(result as String) as Map<String, dynamic>;
+    } catch (e) {
+      // No extension found or error handling URL
+      return null;
+    }
+  }
+
+  /// Find an extension that can handle the given URL
+  /// Returns extension ID or null if none found
+  static Future<String?> findURLHandler(String url) async {
+    final result = await _channel.invokeMethod('findURLHandler', {
+      'url': url,
+    });
+    if (result == null || result == '') return null;
+    return result as String;
+  }
+
+  /// Get all extensions that handle custom URLs
+  static Future<List<Map<String, dynamic>>> getURLHandlers() async {
+    final result = await _channel.invokeMethod('getURLHandlers');
+    final list = jsonDecode(result as String) as List<dynamic>;
+    return list.map((e) => e as Map<String, dynamic>).toList();
+  }
+
   // ==================== EXTENSION POST-PROCESSING ====================
 
   /// Run post-processing hooks on a file