Add HTTP header filter to pick headers for downloading request

Author: crazytonyli

SDWebImage/SDWebImageDownloader.h

@@ -58,6 +58,14 @@ typedef void(^SDWebImageDownloaderCompletedBlock)(UIImage *image, NSData *data,
 
 + (SDWebImageDownloader *)sharedDownloader;
 
+/**
+ * Set filter to pick headers for downloading image HTTP request.
+ *
+ * This block will be invoked for each downloading image request, returned
+ * NSDictionary will be used as headers in corresponding HTTP request.
+ */
+@property (nonatomic, strong) NSDictionary *(^headersFilter)(NSURL *url, NSDictionary *headers);
+
 /**
  * Set a value for a HTTP header to be appended to each download HTTP request.
  *

SDWebImage/SDWebImageDownloader.m

@@ -120,7 +120,14 @@ - (NSInteger)maxConcurrentDownloads
         NSMutableURLRequest *request = [NSMutableURLRequest.alloc initWithURL:url cachePolicy:(options & SDWebImageDownloaderUseNSURLCache ? NSURLRequestUseProtocolCachePolicy : NSURLRequestReloadIgnoringLocalCacheData) timeoutInterval:15];
         request.HTTPShouldHandleCookies = NO;
         request.HTTPShouldUsePipelining = YES;
-        request.allHTTPHeaderFields = wself.HTTPHeaders;
+        if (wself.headersFilter)
+        {
+            request.allHTTPHeaderFields = wself.headersFilter(url, [wself.HTTPHeaders copy]);
+        }
+        else
+        {
+            request.allHTTPHeaderFields = wself.HTTPHeaders;
+        }
         operation = [SDWebImageDownloaderOperation.alloc initWithRequest:request options:options progress:^(NSUInteger receivedSize, long long expectedSize)
         {
             if (!wself) return;