Release stream callback, once the stream has finished

Author: fabianfett

Sources/GRPC/ClientCalls/ResponseContainers.swift

@@ -98,7 +98,9 @@ internal class StreamingResponseParts<Response> {
   private let eventLoop: EventLoop
 
   /// A callback for response messages.
-  private let responseCallback: (Response) -> Void
+  private var responseCallback: (Response) -> Void
+
+  private static let noopCallback: (Response) -> Void = { _ in }
 
   /// Lazy promises for the status, initial-, and trailing-metadata.
   private var initialMetadataPromise: LazyEventLoopPromise<HPACKHeaders>
@@ -142,13 +144,23 @@ internal class StreamingResponseParts<Response> {
       self.responseCallback(response)
 
     case let .end(status, trailers):
+      // Once the stream has finished, we must release the callback, to make sure don't
+      // break potential retain cycles (the callback may reference other object's that in
+      // turn reference `StreamingResponseParts`).
+      self.responseCallback = Self.noopCallback
       self.initialMetadataPromise.fail(status)
       self.trailingMetadataPromise.succeed(trailers)
       self.statusPromise.succeed(status)
     }
   }
 
   internal func handleError(_ error: Error) {
+    self.eventLoop.assertInEventLoop()
+
+    // Once the stream has finished, we must release the callback, to make sure don't
+    // break potential retain cycles (the callback may reference other object's that in
+    // turn reference `StreamingResponseParts`).
+    self.responseCallback = Self.noopCallback
     let withoutContext = error.removingContext()
     let status = withoutContext.makeGRPCStatus()
     self.initialMetadataPromise.fail(withoutContext)