Change the method of get file extension.

flutter_cache_manager/example/android/build.gradle

@@ -15,4 +15,4 @@ subprojects {
 
 tasks.register("clean", Delete) {
     delete rootProject.buildDir
-}
+}

flutter_cache_manager/example/android/settings.gradle

@@ -19,7 +19,7 @@ pluginManagement {
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "7.3.0" apply false
-    id "org.jetbrains.kotlin.android" version "1.7.10" apply false
+    id "org.jetbrains.kotlin.android" version "1.8.22" apply false
 }
 
 include ":app"

flutter_cache_manager/lib/src/cache_managers/image_cache_manager.dart

@@ -61,6 +61,31 @@ mixin ImageCacheManager on BaseCacheManager {
     _runningResizes.remove(resizedKey);
   }
 
+  Future<bool> _isImage(File file) async {
+    if (!await file.exists()) {
+      debugPrint('file is not found: ${file.path}');
+      return false;
+    }
+    final raf = await file.open();
+    final header = await raf.read(8);
+    await raf.close();
+    final hexString =
+        header.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join('');
+    if (hexString.startsWith('ffd8')) {
+      return true; // JPEG
+    } else if (hexString.startsWith('89504e47')) {
+      return true; // PNG
+    } else if (hexString.startsWith('00000200')) {
+      return true; // TGA
+    } else if (hexString.startsWith('00000100')) {
+      return true; // CUR
+    } else if (hexString.startsWith('00000000')) {
+      return true; // ICO
+    }
+
+    return false;
+  }
+
   final Map<String, Stream<FileResponse>> _runningResizes = {};
 
   Future<FileInfo> _resizeImageFile(
@@ -69,9 +94,10 @@ mixin ImageCacheManager on BaseCacheManager {
     int? maxWidth,
     int? maxHeight,
   ) async {
+    bool isImage = await _isImage(originalFile.file);
     final originalFileName = originalFile.file.path;
     final fileExtension = originalFileName.split('.').last;
-    if (!supportedFileNames.contains(fileExtension)) {
+    if (!isImage) {
       return originalFile;
     }
 

flutter_cache_manager/pubspec.yaml

@@ -22,7 +22,7 @@ dependencies:
   uuid: ^4.4.2
 
 dev_dependencies:
-  build_runner: ^2.4.12
+  build_runner: ^2.4.9
   flutter_lints: ^4.0.0
   flutter_test:
     sdk: flutter