make window update assert catch more

Author: apolcyn

transport/control.go

@@ -220,13 +220,13 @@ func (f *inFlow) onRead(n uint32) uint32 {
 func (f *inFlow) preConsumeWindowSpace(n uint32) uint32 {
 	f.mu.Lock()
 	defer f.mu.Unlock()
-	if n > http2MaxWindowUpdate {
-		grpclog.Fatalf("potential window update too large. n is %v; max n is %v", f.pendingUpdate, http2MaxWindowUpdate)
-	}
 	if f.preConsumedWindowSpace > 0 {
 		grpclog.Fatalf("pre-consuming window space while there is pre-consumed window space stil  outstanding")
 	}
 	f.preConsumedWindowSpace = n
+	if f.preConsumedWindowSpace+f.pendingData > http2MaxWindowUpdate {
+		grpclog.Fatalf("potential window of %v update too large. http2 max window update is %v", f.preConsumedWindowSpace+f.pendingData, http2MaxWindowUpdate)
+	}
 	if f.preConsumedWindowSpace+f.pendingUpdate >= f.limit/4 {
 		wu := f.pendingUpdate + f.preConsumedWindowSpace
 		f.pendingUpdate = 0