Fix the current transformer cache key generating rules, try to keep the image file extension as much as we can

SDWebImage/SDImageTransformer.m

@@ -18,7 +18,23 @@ NSString * _Nullable SDTransformedKeyForKey(NSString * _Nullable key, NSString *
     if (!key || !transformerKey) {
         return nil;
     }
-    return [[key stringByAppendingString:SDImageTransformerKeySeparator] stringByAppendingString:transformerKey];
+    // Find the file extension
+    NSURL *keyURL = [NSURL URLWithString:key];
+    NSString *ext = keyURL ? keyURL.pathExtension : key.pathExtension;
+    if (ext.length > 0) {
+        // For non-file URL
+        if (keyURL && !keyURL.isFileURL) {
+            // keep anything except path (like URL query)
+            NSURLComponents *component = [NSURLComponents componentsWithURL:keyURL resolvingAgainstBaseURL:NO];
+            component.path = [[[component.path.stringByDeletingPathExtension stringByAppendingString:SDImageTransformerKeySeparator] stringByAppendingString:transformerKey] stringByAppendingPathExtension:ext];
+            return component.URL.absoluteString;
+        } else {
+            // file URL
+            return [[[key.stringByDeletingPathExtension stringByAppendingString:SDImageTransformerKeySeparator] stringByAppendingString:transformerKey] stringByAppendingPathExtension:ext];
+        }
+    } else {
+        return [[key stringByAppendingString:SDImageTransformerKeySeparator] stringByAppendingString:transformerKey];
+    }
 }
 
 @interface UIColor (HexString)

Tests/Tests/SDImageTransformerTests.m

@@ -148,6 +148,42 @@
     expect(CGSizeEqualToSize(transformedImage.size, size)).beTruthy();
 }
 
+- (void)test10TransformerKeyForCacheKey {
+    NSString *transformerKey = @"SDImageFlippingTransformer(1,0)";
+    
+    // File path representation test cases
+    NSString *key = @"image.png";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"image-SDImageFlippingTransformer(1,0).png");
+    
+    key = @"image";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"image-SDImageFlippingTransformer(1,0)");
+    
+    key = @".image";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@".image-SDImageFlippingTransformer(1,0)");
+    
+    key = @"image.";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"image.-SDImageFlippingTransformer(1,0)");
+    
+    key = @"Test/image.png";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"Test/image-SDImageFlippingTransformer(1,0).png");
+    
+    // URL representation test cases
+    key = @"http://foo/image.png";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"http://foo/image-SDImageFlippingTransformer(1,0).png");
+    
+    key = @"http://foo/image";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"http://foo/image-SDImageFlippingTransformer(1,0)");
+    
+    key = @"http://foo/.image";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"http://foo/.image-SDImageFlippingTransformer(1,0)");
+    
+    key = @"http://foo/image.png?foo=bar#mark";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"http://foo/image-SDImageFlippingTransformer(1,0).png?foo=bar#mark");
+    
+    key = @"ftp://root:password@foo.com/image.png";
+    expect(SDTransformedKeyForKey(key, transformerKey)).equal(@"ftp://root:password@foo.com/image-SDImageFlippingTransformer(1,0).png");
+}
+
 #pragma mark - Helper
 
 - (UIImage *)testImage {