Preparing to remove the need for the `recalculateFromImage` param for store in cache. Only if the data provided is nil and we have an image, we will recaculate. Moved the NSData calculation in the UIImage MultiFormat categ, plus instead of another variant to check for PNG, relly on `sd_imageFormatForImageData`

SDWebImage/SDImageCache.m

@@ -39,22 +39,6 @@
 @end
 
 static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
-// PNG signature bytes and data (below)
-static unsigned char kPNGSignatureBytes[8] = {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A};
-static NSData *kPNGSignatureData = nil;
-
-BOOL ImageDataHasPNGPreffix(NSData *data);
-
-BOOL ImageDataHasPNGPreffix(NSData *data) {
-    NSUInteger pngSignatureLength = kPNGSignatureData.length;
-    if (data.length >= pngSignatureLength) {
-        if ([[data subdataWithRange:NSMakeRange(0, pngSignatureLength)] isEqualToData:kPNGSignatureData]) {
-            return YES;
-        }
-    }
-
-    return NO;
-}
 
 FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
 #if SD_MAC
@@ -100,10 +84,7 @@ FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
                        diskCacheDirectory:(nonnull NSString *)directory {
     if ((self = [super init])) {
         NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
-
-        // initialise PNG signature data
-        kPNGSignatureData = [NSData dataWithBytes:kPNGSignatureBytes length:8];
-
+        
         // Create IO serial queue
         _ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
 
@@ -218,46 +199,10 @@ FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
     if (toDisk) {
         dispatch_async(self.ioQueue, ^{
             NSData *data = imageData;
-
-            if (image && (recalculate || !data)) {
-#if SD_UIKIT || SD_WATCH
-                // We need to determine if the image is a PNG or a JPEG
-                // PNGs are easier to detect because they have a unique signature (http://www.w3.org/TR/PNG-Structure.html)
-                // The first eight bytes of a PNG file always contain the following (decimal) values:
-                // 137 80 78 71 13 10 26 10
-
-                // If the imageData is nil (i.e. if trying to save a UIImage directly or the image was transformed on download)
-                // and the image has an alpha channel, we will consider it PNG to avoid losing the transparency
-                int alphaInfo = CGImageGetAlphaInfo(image.CGImage);
-                BOOL hasAlpha = !(alphaInfo == kCGImageAlphaNone ||
-                                  alphaInfo == kCGImageAlphaNoneSkipFirst ||
-                                  alphaInfo == kCGImageAlphaNoneSkipLast);
-                BOOL imageIsPng = hasAlpha;
-
-                // But if we have an image data, we will look at the preffix
-                if (imageData.length >= kPNGSignatureData.length) {
-                    imageIsPng = ImageDataHasPNGPreffix(imageData);
-                }
-
-                if (imageIsPng) {
-                    data = UIImagePNGRepresentation(image);
-                }
-                else {
-                    data = UIImageJPEGRepresentation(image, (CGFloat)1.0);
-                }
-#else
-                NSString *contentType = [NSData sd_contentTypeForImageData:data];
-                NSBitmapImageFileType imageFileType = NSJPEGFileType;
-                if ([contentType isEqualToString:@"image/gif"]) {
-                    imageFileType = NSGIFFileType;
-                } else if ([contentType isEqualToString:@"image/png"]) {
-                    imageFileType = NSPNGFileType;
-                }
-                
-                data = [NSBitmapImageRep representationOfImageRepsInArray:image.representations
-                                                                usingType:imageFileType
-                                                               properties:@{}];
-#endif
+            
+            if (!data && image) {
+                SDImageFormat imageFormatFromData = [NSData sd_imageFormatForImageData:data];
+                data = [image sd_imageDataAsFormat:imageFormatFromData];
             }
 
             [self storeImageDataToDisk:data forKey:key];

SDWebImage/UIImage+MultiFormat.h

@@ -7,9 +7,12 @@
  */
 
 #import "SDWebImageCompat.h"
+#import "NSData+ImageContentType.h"
 
 @interface UIImage (MultiFormat)
 
 + (nullable UIImage *)sd_imageWithData:(nullable NSData *)data;
+- (nullable NSData *)sd_imageData;
+- (nullable NSData *)sd_imageDataAsFormat:(SDImageFormat)imageFormat;
 
 @end

SDWebImage/UIImage+MultiFormat.m

@@ -116,5 +116,46 @@
 }
 #endif
 
+- (nullable NSData *)sd_imageData {
+    return [self sd_imageDataAsFormat:SDImageFormatUndefined];
+}
+
+- (nullable NSData *)sd_imageDataAsFormat:(SDImageFormat)imageFormat {
+    NSData *imageData = nil;
+    if (self) {
+#if SD_UIKIT || SD_WATCH
+        int alphaInfo = CGImageGetAlphaInfo(self.CGImage);
+        BOOL hasAlpha = !(alphaInfo == kCGImageAlphaNone ||
+                          alphaInfo == kCGImageAlphaNoneSkipFirst ||
+                          alphaInfo == kCGImageAlphaNoneSkipLast);
+        
+        BOOL usePNG = hasAlpha;
+        
+        // the imageFormat param has priority here. But if the format is undefined, we relly on the alpha channel
+        if (imageFormat != SDImageFormatUndefined) {
+            usePNG = (imageFormat == SDImageFormatPNG);
+        }
+        
+        if (usePNG) {
+            imageData = UIImagePNGRepresentation(self);
+        } else {
+            imageData = UIImageJPEGRepresentation(self, (CGFloat)1.0);
+        }
+#else
+        NSBitmapImageFileType imageFileType = NSJPEGFileType;
+        if (imageFormat == SDImageFormatGIF) {
+            imageFileType = NSGIFFileType;
+        } else if (imageFormat == SDImageFormatPNG) {
+            imageFileType = NSPNGFileType;
+        }
+        
+        imageData = [NSBitmapImageRep representationOfImageRepsInArray:self.representations
+                                                             usingType:imageFileType
+                                                            properties:@{}];
+#endif
+    }
+    return imageData;
+}
+
 
 @end