Add requestResponse handler for incoming calls

Summary:
Flipper exposes a call() api to plugins which lets them call their sdk component, and it returns a promise with the response.
Currently this is done by sending a fireAndForget request, noting the id of the request, and then receiving fireAndForget requests and matching up the ids to give the result back to the right plugin promise.

Instead, it will be simpler to use rsocket requestResponse, instead of fireAndForget, which is for this exact use case. This diff adds a requestResponse handler to the SDK, so that it can deal with such requests and respond accordingly, while preserving the current functionality if it receives a fireAndForget.

So this part is backwards compatible and should be safe to land in isolation.

A later diff will change the desktop app to use requestResponse, which may not be backwards compatible, so that will have to be deployed more carefully.

Reviewed By: passy

Differential Revision: D13974049

fbshipit-source-id: b371d94a86b1f186375161ed8f2242a462ce418f

xplat/Flipper/FireAndForgetBasedFlipperResponder.h

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
+#pragma once
+
+#include "FlipperResponder.h"
+#include "FlipperConnectionManager.h"
+#include <folly/json.h>
+
+namespace facebook {
+namespace flipper {
+
+/* Responder for responding to legacy flipper applications.
+   Originally, flipper desktop used fireAndForget for all messages, so calling
+   the SDK would send a fire and forget message, to which the SDK would respond
+   with another one, with an id field that flipper uses to map it to the
+   original request. This Responder should be used when such requests are
+   received.
+ */
+class FireAndForgetBasedFlipperResponder : public FlipperResponder {
+ public:
+  FireAndForgetBasedFlipperResponder(
+      FlipperConnectionManager* socket,
+      int64_t responseID)
+      : socket_(socket), responseID_(responseID) {}
+
+  void success(const folly::dynamic& response) const override {
+    const folly::dynamic message =
+        folly::dynamic::object("id", responseID_)("success", response);
+    socket_->sendMessage(message);
+  }
+
+  void error(const folly::dynamic& response) const override {
+    const folly::dynamic message =
+        folly::dynamic::object("id", responseID_)("error", response);
+    socket_->sendMessage(message);
+  }
+
+ private:
+  FlipperConnectionManager* socket_;
+  int64_t responseID_;
+};
+
+} // namespace flipper
+} // namespace facebook