Revert "NSURLSession Reimplementation (#411)"

This reverts commit 07233534e6.

Source/GSMultiHandle.h

@@ -0,0 +1,89 @@
+#ifndef	INCLUDED_GSMULTIHANDLE_H
+#define	INCLUDED_GSMULTIHANDLE_H
+
+#import "common.h"
+#import <curl/curl.h>
+#import "GSDispatch.h"
+
+@class NSURLSessionConfiguration;
+@class GSEasyHandle;
+
+/*
+ * Minimal wrapper around curl multi interface
+ * (https://curl.haxx.se/libcurl/c/libcurl-multi.html).
+ *
+ * The the *multi handle* manages the sockets for easy handles
+ * (`GSEasyHandle`), and this implementation uses
+ * libdispatch to listen for sockets being read / write ready.
+ *
+ * Using `dispatch_source_t` allows this implementation to be
+ * non-blocking and all code to run on the same thread 
+ * thus keeping is simple.
+ *
+ * - SeeAlso: GSEasyHandle
+ */
+@interface GSMultiHandle : NSObject
+{
+  CURLM  *_rawHandle;
+}
+
+- (CURLM*) rawHandle;
+- (instancetype) initWithConfiguration: (NSURLSessionConfiguration*)configuration 
+                             workQueue: (dispatch_queue_t)workQueque;
+- (void) addHandle: (GSEasyHandle*)easyHandle;
+- (void) removeHandle: (GSEasyHandle*)easyHandle;
+- (void) updateTimeoutTimerToValue: (NSInteger)value;
+
+@end
+
+// What read / write ready event to register / unregister.
+typedef NS_ENUM(NSUInteger, GSSocketRegisterActionType) {
+    GSSocketRegisterActionTypeNone = 0,
+    GSSocketRegisterActionTypeRegisterRead,
+    GSSocketRegisterActionTypeRegisterWrite,
+    GSSocketRegisterActionTypeRegisterReadAndWrite,
+    GSSocketRegisterActionTypeUnregister,
+};
+
+@interface GSSocketRegisterAction : NSObject
+{
+  GSSocketRegisterActionType  _type;
+}
+
+- (instancetype) initWithRawValue: (int)rawValue;
+- (GSSocketRegisterActionType) type;
+- (BOOL) needsReadSource;
+- (BOOL) needsWriteSource;
+- (BOOL) needsSource;
+
+@end
+
+/*
+ * Read and write libdispatch sources for a specific socket.
+ *
+ * A simple helper that combines two sources -- both being optional.
+ *
+ * This info is stored into the socket using `curl_multi_assign()`.
+ *
+ * - SeeAlso: GSSocketRegisterAction
+ */
+@interface GSSocketSources : NSObject
+{
+  dispatch_source_t _readSource;
+  dispatch_source_t _writeSource;
+}
+
+- (void) createSourcesWithAction: (GSSocketRegisterAction *)action
+                          socket: (curl_socket_t)socket
+                           queue: (dispatch_queue_t)queue
+                         handler: (dispatch_block_t)handler;
+- (dispatch_source_t) createSourceWithType: (dispatch_source_type_t)type
+                                    socket: (curl_socket_t)socket
+                                     queue: (dispatch_queue_t)queue
+                                   handler: (dispatch_block_t)handler;
+
++ (instancetype) from: (void*)socketSourcePtr;
+
+@end
+
+#endif