Cancel network requests from the correct queue

Summary: Fix suggested by sooth-sayer (facebook#10280)

Reviewed By: mmmulani

Differential Revision: D4001618

fbshipit-source-id: cc28d19d02a29b62d2bdbddcd30f94b1c1bcfd76

Libraries/Image/RCTImageLoader.m

@@ -440,7 +440,9 @@ - (RCTImageLoaderCancellationBlock)_loadURLRequest:(NSURLRequest *)request
 
   // Download image
   __weak __typeof(self) weakSelf = self;
-  RCTNetworkTask *task = [networking networkTaskWithRequest:request completionBlock:^(NSURLResponse *response, NSData *data, NSError *error) {
+  __block RCTNetworkTask *task =
+  [networking networkTaskWithRequest:request
+                     completionBlock:^(NSURLResponse *response, NSData *data, NSError *error) {
     __typeof(self) strongSelf = weakSelf;
     if (!strongSelf) {
       return;
@@ -480,8 +482,15 @@ - (RCTImageLoaderCancellationBlock)_loadURLRequest:(NSURLRequest *)request
   }
 
   return ^{
-    [task cancel];
-    [weakSelf dequeueTasks];
+    __typeof(self) strongSelf = weakSelf;
+    if (!strongSelf || !task) {
+      return;
+    }
+    dispatch_async(strongSelf->_URLRequestQueue, ^{
+      [task cancel];
+      task = nil;
+    });
+    [strongSelf dequeueTasks];
   };
 }
 
@@ -496,7 +505,7 @@ - (RCTImageLoaderCancellationBlock)loadImageWithURLRequest:(NSURLRequest *)image
   __block volatile uint32_t cancelled = 0;
   __block dispatch_block_t cancelLoad = nil;
   dispatch_block_t cancellationBlock = ^{
-    if (cancelLoad) {
+    if (cancelLoad && !cancelled) {
       cancelLoad();
     }
     OSAtomicOr32Barrier(1, &cancelled);

Libraries/Network/RCTNetworkTask.m

@@ -53,6 +53,7 @@ - (void)invalidate
   _incrementalDataBlock = nil;
   _responseBlock = nil;
   _uploadProgressBlock = nil;
+  _requestToken = nil;
 }
 
 - (void)dispatchCallback:(dispatch_block_t)callback
@@ -66,6 +67,11 @@ - (void)dispatchCallback:(dispatch_block_t)callback
 
 - (void)start
 {
+  if (_status != RCTNetworkTaskPending) {
+    RCTLogError(@"RCTNetworkTask was already started or completed");
+    return;
+  }
+
   if (_requestToken == nil) {
     id token = [_handler sendRequest:_request withDelegate:self];
     if ([self validateRequestToken:token]) {
@@ -77,6 +83,10 @@ - (void)start
 
 - (void)cancel
 {
+  if (_status == RCTNetworkTaskFinished) {
+    return;
+  }
+
   _status = RCTNetworkTaskFinished;
   id token = _requestToken;
   if (token && [_handler respondsToSelector:@selector(cancelRequest:)]) {