Merge pull request #2973 from dreampiggy/behavior_uttype_from_unkown_format

Change the behavior to return the abstract type for unknown image format, this  can solve the accident issue for custom coder who provide a new format

SDWebImage/Core/NSData+ImageContentType.h

@@ -45,6 +45,7 @@ static const SDImageFormat SDImageFormatSVG       = 8;
  *
  *  @param format Format as SDImageFormat
  *  @return The UTType as CFStringRef
+ *  @note For unknown format, `kUTTypeImage` abstract type will return
  */
 + (nonnull CFStringRef)sd_UTTypeFromImageFormat:(SDImageFormat)format CF_RETURNS_NOT_RETAINED NS_SWIFT_NAME(sd_UTType(from:));
 
@@ -53,6 +54,7 @@ static const SDImageFormat SDImageFormatSVG       = 8;
  *
  *  @param uttype The UTType as CFStringRef
  *  @return The Format as SDImageFormat
+ *  @note For unknown type, `SDImageFormatUndefined` will return
  */
 + (SDImageFormat)sd_imageFormatFromUTType:(nonnull CFStringRef)uttype;
 

SDWebImage/Core/NSData+ImageContentType.m

@@ -119,8 +119,8 @@
             UTType = kUTTypeScalableVectorGraphics;
             break;
         default:
-            // default is kUTTypePNG
-            UTType = kUTTypePNG;
+            // default is kUTTypeImage abstract type
+            UTType = kUTTypeImage;
             break;
     }
     return UTType;

Tests/Tests/SDCategoriesTests.m

@@ -25,7 +25,7 @@
     
     // Test invalid format
     CFStringRef type = [NSData sd_UTTypeFromImageFormat:SDImageFormatUndefined];
-    expect(CFStringCompare(kUTTypePNG, type, 0)).equal(kCFCompareEqualTo);
+    expect(CFStringCompare(kUTTypeImage, type, 0)).equal(kCFCompareEqualTo);
     expect([NSData sd_imageFormatFromUTType:kUTTypeImage]).equal(SDImageFormatUndefined);
 }