Revert "NSURLSession Reimplementation (#411)"

This reverts commit 07233534e6.

Source/GSURLSessionTaskBodySource.h

@@ -0,0 +1,52 @@
+#ifndef	INCLUDED_GSURLSESSIONTASKBODYSOURCE_H
+#define	INCLUDED_GSURLSESSIONTASKBODYSOURCE_H
+
+#import "common.h"
+#import "GSDispatch.h"
+
+@class	NSFileHandle;
+@class	NSInputStream;
+
+typedef NS_ENUM(NSUInteger, GSBodySourceDataChunk) {
+    GSBodySourceDataChunkData,
+    // The source is depleted.
+    GSBodySourceDataChunkDone,
+    // Retry later to get more data.
+    GSBodySourceDataChunkRetryLater,
+    GSBodySourceDataChunkError
+};
+
+/*
+ * A (non-blocking) source for body data.
+ */
+@protocol GSURLSessionTaskBodySource <NSObject>
+
+/*
+ * Get the next chunck of data.
+ */
+- (void) getNextChunkWithLength: (NSInteger)length
+              completionHandler: (void (^)(GSBodySourceDataChunk chunk, NSData *data))completionHandler;
+
+@end
+
+@interface GSBodyStreamSource : NSObject <GSURLSessionTaskBodySource>
+
+- (instancetype) initWithInputStream: (NSInputStream*)inputStream;
+
+@end
+
+@interface GSBodyDataSource : NSObject <GSURLSessionTaskBodySource>
+
+- (instancetype)initWithData:(NSData *)data;
+
+@end
+
+@interface GSBodyFileSource : NSObject <GSURLSessionTaskBodySource>
+
+- (instancetype) initWithFileURL: (NSURL*)fileURL
+                       workQueue: (dispatch_queue_t)workQueue
+            dataAvailableHandler: (void (^)(void))dataAvailableHandler;
+
+@end
+
+#endif