Add hybrid class to hold native delta client

Summary:
Adds hybrid JNI wrapper class that can hold a native delta client.

This class allows Java code in the `devsupport` package to hold onto a native delta client across reloads.
It also takes care of passing `okhttp` response objects to native code, where we build a `std::string` to hold JSON messages coming from Metro, and parse them with `folly::parseJson`.

In a follow-up, we will switch to a streaming-friendly binary format that will make allocating memory for the whole message unnecessary.

Reviewed By: fromcelticpark

Differential Revision: D7845138

fbshipit-source-id: 7a29b30645331addf843097dd0d05c03b3143991

ReactAndroid/src/main/java/com/facebook/react/bridge/NativeDeltaClient.java

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2018-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.bridge;
+
+import java.nio.channels.ReadableByteChannel;
+
+import com.facebook.jni.HybridData;
+
+public class NativeDeltaClient {
+  static {
+    ReactBridge.staticInit();
+  }
+
+  // C++ parts
+  private final HybridData mHybridData = initHybrid();
+  private native static HybridData initHybrid();
+
+  public native void reset();
+  public native void processDelta(ReadableByteChannel deltaMessage);
+}

ReactAndroid/src/main/jni/react/jni/Android.mk

@@ -18,6 +18,7 @@ LOCAL_SRC_FILES := \
   ModuleRegistryBuilder.cpp \
   NativeArray.cpp \
   NativeCommon.cpp \
+  NativeDeltaClient.cpp \
   NativeMap.cpp \
   OnLoad.cpp \
   ProxyExecutor.cpp \

ReactAndroid/src/main/jni/react/jni/NativeDeltaClient.cpp

@@ -0,0 +1,54 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+#include "NativeDeltaClient.h"
+
+#include <sstream>
+#include <fb/fbjni/ByteBuffer.h>
+#include <folly/json.h>
+
+namespace facebook {
+namespace react {
+
+jni::local_ref<NativeDeltaClient::jhybriddata> NativeDeltaClient::initHybrid(
+    jni::alias_ref<jclass>) {
+  return makeCxxInstance();
+}
+
+void NativeDeltaClient::registerNatives() {
+  registerHybrid({
+    makeNativeMethod("initHybrid", NativeDeltaClient::initHybrid),
+    makeNativeMethod("processDelta", NativeDeltaClient::jniProcessDelta),
+    makeNativeMethod("reset", NativeDeltaClient::jniReset),
+  });
+}
+
+void NativeDeltaClient::jniProcessDelta(
+    jni::alias_ref<jni::JReadableByteChannel> delta) {
+
+  std::ostringstream deltaMessage;
+  std::vector<uint8_t> buffer(8192);
+  auto byteBuffer = jni::JByteBuffer::wrapBytes(buffer.data(), buffer.size());
+
+  size_t pos = 0;
+  int read = 0;
+  do {
+    read = delta->read(byteBuffer);
+    if (read < 1) {
+      deltaMessage.write(reinterpret_cast<const char *>(buffer.data()), pos);
+      byteBuffer->rewind();
+      pos = 0;
+    } else {
+      pos += read;
+    }
+  } while (read != -1);
+
+
+  deltaClient_->patch(folly::parseJson(deltaMessage.str()));
+}
+
+void NativeDeltaClient::jniReset() {
+  deltaClient_->clear();
+}
+
+} // namespace react
+} // namespace facebook

ReactAndroid/src/main/jni/react/jni/NativeDeltaClient.h

@@ -0,0 +1,38 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+#pragma once
+
+#include <memory>
+
+#include <cxxreact/JSDeltaBundleClient.h>
+#include <fb/fbjni.h>
+#include <fb/fbjni/Hybrid.h>
+#include <fb/fbjni/ReadableByteChannel.h>
+
+namespace facebook {
+namespace react {
+
+class NativeDeltaClient : public jni::HybridClass<NativeDeltaClient> {
+
+public:
+  static constexpr auto kJavaDescriptor =
+    "Lcom/facebook/react/bridge/NativeDeltaClient;";
+  static jni::local_ref<jhybriddata> initHybrid(jni::alias_ref<jclass>);
+  static void registerNatives();
+
+  ~NativeDeltaClient() override = default;
+
+  std::shared_ptr<const JSDeltaBundleClient> getDeltaClient() {
+    return deltaClient_;
+  }
+
+private:
+  friend HybridBase;
+  void jniProcessDelta(jni::alias_ref<jni::JReadableByteChannel> delta);
+  void jniReset();
+  const std::shared_ptr<JSDeltaBundleClient> deltaClient_ =
+    std::make_shared<JSDeltaBundleClient>();
+};
+
+} // namespace react
+} // namespace facebook

ReactAndroid/src/main/jni/react/jni/OnLoad.cpp

@@ -16,6 +16,7 @@
 #include "CxxModuleWrapper.h"
 #include "JavaScriptExecutorHolder.h"
 #include "JCallback.h"
+#include "NativeDeltaClient.h"
 #include "ProxyExecutor.h"
 #include "WritableNativeArray.h"
 #include "WritableNativeMap.h"
@@ -91,6 +92,7 @@ extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
     CxxModuleWrapper::registerNatives();
     JCxxCallbackImpl::registerNatives();
     NativeArray::registerNatives();
+    NativeDeltaClient::registerNatives();
     ReadableNativeArray::registerNatives();
     WritableNativeArray::registerNatives();
     NativeMap::registerNatives();