From e5ccdc4c2d354727482941867cbeadff28beb2d9 Mon Sep 17 00:00:00 2001
From: Marc Horowitz <mhorowitz@fb.com>
Date: Wed, 3 Aug 2016 18:03:42 -0700
Subject: [PATCH] add support for registering and calling sync methods in C++
 modules

Differential Revision: D3574800

fbshipit-source-id: 4c238fd96c8f83e9424c8e2bf2c8ebb1d39d397a
---
 ReactCommon/cxxreact/CxxModule.h         | 32 ++++++++++++++++++
 ReactCommon/cxxreact/CxxNativeModule.cpp | 43 ++++++++++++++++++++++--
 ReactCommon/cxxreact/ModuleRegistry.cpp  |  8 +++--
 3 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/ReactCommon/cxxreact/CxxModule.h b/ReactCommon/cxxreact/CxxModule.h
index 7c4b72ec1..55b79f10c 100644
--- a/ReactCommon/cxxreact/CxxModule.h
+++ b/ReactCommon/cxxreact/CxxModule.h
@@ -42,14 +42,23 @@ namespace facebook { namespace xplat { namespace module {
  */
 
 class CxxModule {
+  class AsyncTagType {};
+  class SyncTagType {};
+
 public:
   typedef std::function<void(std::vector<folly::dynamic>)> Callback;
 
+  constexpr static AsyncTagType AsyncTag = AsyncTagType();
+  constexpr static SyncTagType SyncTag = SyncTagType();
+
   struct Method {
     std::string name;
+
     size_t callbacks;
     std::function<void(folly::dynamic, Callback, Callback)> func;
 
+    std::function<folly::dynamic(folly::dynamic)> syncFunc;
+
     // std::function/lambda ctors
 
     Method(std::string aname,
@@ -101,6 +110,29 @@ public:
       : name(std::move(aname))
       , callbacks(2)
       , func(std::bind(method, t, _1, _2, _3)) {}
+
+    // sync std::function/lambda ctors
+
+    // Overloads for functions returning void give ambiguity errors.
+    // I am not sure if this is a runtime/compiler bug, or a
+    // limitation I do not understand.
+
+    Method(std::string aname,
+           std::function<folly::dynamic()>&& afunc,
+           SyncTagType)
+      : name(std::move(aname))
+      , callbacks(0)
+      , syncFunc([afunc=std::move(afunc)] (const folly::dynamic&)
+                 { return afunc(); })
+    {}
+
+    Method(std::string aname,
+           std::function<folly::dynamic(folly::dynamic)>&& afunc,
+           SyncTagType)
+      : name(std::move(aname))
+      , callbacks(0)
+      , syncFunc(std::move(afunc))
+      {}
   };
 
   /**
diff --git a/ReactCommon/cxxreact/CxxNativeModule.cpp b/ReactCommon/cxxreact/CxxNativeModule.cpp
index b18721394..8e3bb9b17 100644
--- a/ReactCommon/cxxreact/CxxNativeModule.cpp
+++ b/ReactCommon/cxxreact/CxxNativeModule.cpp
@@ -3,6 +3,8 @@
 #include "CxxNativeModule.h"
 #include "Instance.h"
 
+#include <folly/json.h>
+
 #include <cxxreact/JsArgumentHelpers.h>
 
 using facebook::xplat::module::CxxModule;
@@ -37,10 +39,12 @@ std::string CxxNativeModule::getName() {
 std::vector<MethodDescriptor> CxxNativeModule::getMethods() {
   // Same as MessageQueue.MethodTypes.remote
   static const auto kMethodTypeRemote = "remote";
+  static const auto kMethodTypeSyncHook = "syncHook";
 
   std::vector<MethodDescriptor> descs;
   for (auto& method : methods_) {
-    descs.emplace_back(method.name, kMethodTypeRemote);
+    assert(method.func || method.syncFunc);
+    descs.emplace_back(method.name, method.func ? kMethodTypeRemote : kMethodTypeSyncHook);
   }
   return descs;
 }
@@ -73,6 +77,12 @@ void CxxNativeModule::invoke(ExecutorToken token, unsigned int reactMethodId, fo
 
   const auto& method = methods_[reactMethodId];
 
+  if (!method.func) {
+    throw std::runtime_error(
+      folly::to<std::string>("Method ", method.name,
+                             " is synchronous but invoked asynchronously"));
+  }
+
   if (params.size() < method.callbacks) {
     throw std::invalid_argument(
       folly::to<std::string>("Expected ", method.callbacks, " callbacks, but only ",
@@ -119,8 +129,35 @@ void CxxNativeModule::invoke(ExecutorToken token, unsigned int reactMethodId, fo
   }
 }
 
-MethodCallResult CxxNativeModule::callSerializableNativeHook(ExecutorToken token, unsigned int hookId, folly::dynamic&& args) {
-  throw std::runtime_error("Not supported");
+MethodCallResult CxxNativeModule::callSerializableNativeHook(
+    ExecutorToken token, unsigned int hookId, folly::dynamic&& args) {
+  if (hookId >= methods_.size()) {
+    throw std::invalid_argument(
+      folly::to<std::string>("methodId ", hookId, " out of range [0..", methods_.size(), "]"));
+  }
+
+  const auto& method = methods_[hookId];
+
+  if (!method.syncFunc) {
+    throw std::runtime_error(
+      folly::to<std::string>("Method ", method.name,
+                             " is asynchronous but invoked synchronously"));
+  }
+
+  if (!args.isString()) {
+    throw std::invalid_argument(
+      folly::to<std::string>("method parameters should be string, but are ", args.typeName()));
+  }
+
+  folly::dynamic params = folly::parseJson(args.stringPiece());
+
+  if (!params.isArray()) {
+    throw std::invalid_argument(
+      folly::to<std::string>("parsed method parameters should be array, but are ",
+                             args.typeName()));
+  }
+
+  return { method.syncFunc(std::move(params)), false };
 }
 
 }
diff --git a/ReactCommon/cxxreact/ModuleRegistry.cpp b/ReactCommon/cxxreact/ModuleRegistry.cpp
index a7c09bca3..9f0058b60 100644
--- a/ReactCommon/cxxreact/ModuleRegistry.cpp
+++ b/ReactCommon/cxxreact/ModuleRegistry.cpp
@@ -65,18 +65,22 @@ folly::dynamic ModuleRegistry::getConfig(const std::string& name) {
 
     folly::dynamic methodNames = folly::dynamic::array;
     folly::dynamic asyncMethodIds = folly::dynamic::array;
+    folly::dynamic syncHookIds = folly::dynamic::array;
 
     for (auto& descriptor : methods) {
       methodNames.push_back(std::move(descriptor.name));
       if (descriptor.type == "remoteAsync") {
         asyncMethodIds.push_back(methodNames.size() - 1);
+      } else if (descriptor.type == "syncHook") {
+        syncHookIds.push_back(methodNames.size() - 1);
       }
     }
 
     if (!methodNames.empty()) {
       config.push_back(std::move(methodNames));
-      if (!asyncMethodIds.empty()) {
-        config.push_back(std::move(asyncMethodIds));
+      config.push_back(std::move(asyncMethodIds));
+      if (!syncHookIds.empty()) {
+        config.push_back(std::move(syncHookIds));
       }
     }
   }