HTML MessagePort as mojo::MessagePipeHandle

content/browser/android/app_web_message_port.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/android/app_web_message_port.h"
+
+#include "base/android/jni_android.h"
+#include "base/android/jni_string.h"
+#include "base/bind.h"
+#include "content/browser/android/string_message_codec.h"
+#include "jni/AppWebMessagePort_jni.h"
+
+namespace content {
+
+// static
+void AppWebMessagePort::CreateAndBindToJavaObject(
+    JNIEnv* env,
+    mojo::ScopedMessagePipeHandle handle,
+    const base::android::JavaRef<jobject>& jobject) {
+  AppWebMessagePort* instance =
+      new AppWebMessagePort(env, std::move(handle), jobject);
+  Java_AppWebMessagePort_setNativeAppWebMessagePort(
+      env, jobject, reinterpret_cast<jlong>(instance));
+}
+
+// static
+std::vector<MessagePort> AppWebMessagePort::UnwrapJavaArray(
+    JNIEnv* env,
+    const base::android::JavaRef<jobjectArray>& jports) {
+  std::vector<MessagePort> ports;
+  if (!jports.is_null()) {
+    jsize num_ports = env->GetArrayLength(jports.obj());
+    for (jsize i = 0; i < num_ports; ++i) {
+      base::android::ScopedJavaLocalRef<jobject> jport(
+          env, env->GetObjectArrayElement(jports.obj(), i));
+      jlong native_port =
+          Java_AppWebMessagePort_releaseNativePortForTransfer(env, jport);
+      // Uninitialized ports should be trapper earlier at the Java layer.
+      DCHECK(native_port != -1);
+      AppWebMessagePort* instance =
+          reinterpret_cast<AppWebMessagePort*>(native_port);
+      ports.push_back(instance->port_);  // Transfers ownership.
+      delete instance;
+    }
+  }
+  return ports;
+}
+
+void AppWebMessagePort::CloseMessagePort(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& jcaller) {
+  // Explicitly reset the port here to ensure that OnMessagesAvailable has
+  // finished before we destroy this.
+  port_ = MessagePort();
+
+  delete this;
+}
+
+void AppWebMessagePort::PostMessage(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& jcaller,
+    const base::android::JavaParamRef<jstring>& jmessage,
+    const base::android::JavaParamRef<jobjectArray>& jports) {
+  port_.PostMessage(
+      EncodeStringMessage(base::android::ConvertJavaStringToUTF16(jmessage)),
+      UnwrapJavaArray(env, jports));
+}
+
+jboolean AppWebMessagePort::DispatchNextMessage(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& jcaller) {
+  base::android::ScopedJavaLocalRef<jobject> obj = java_ref_.get(env);
+  if (obj.is_null())
+    return false;
+
+  jmethodID app_web_message_port_constructor =
+      base::android::MethodID::Get<base::android::MethodID::TYPE_INSTANCE>(
+          env, AppWebMessagePort_clazz(env), "<init>", "()V");
+
+  base::string16 encoded_message;
+  std::vector<MessagePort> ports;
+  if (!port_.GetMessage(&encoded_message, &ports))

[sgurun-gerrit only, 2017/02/09 17:47:24]

It would be useful to document methods of MessagePort are thread safe I think.

[darin (slow to review), 2017/02/09 17:55:08]

Good idea, will do.

+    return false;
+
+  base::string16 message;
+  if (!DecodeStringMessage(encoded_message, &message))
+    return false;
+
+  base::android::ScopedJavaLocalRef<jstring> jmessage =
+      base::android::ConvertUTF16ToJavaString(env, message);
+
+  base::android::ScopedJavaLocalRef<jobjectArray> jports;
+  if (ports.size() > 0) {
+    jports = base::android::ScopedJavaLocalRef<jobjectArray>(
+        env,
+        env->NewObjectArray(ports.size(),
+                            AppWebMessagePort_clazz(env),
+                            nullptr));
+
+    // Instantiate the Java and C++ wrappers for the transferred ports.
+    for (size_t i = 0; i < ports.size(); ++i) {
+      base::android::ScopedJavaLocalRef<jobject> jport(
+          env,
+          env->NewObject(AppWebMessagePort_clazz(env),
+                         app_web_message_port_constructor));
+      CreateAndBindToJavaObject(env, ports[i].ReleaseHandle(), jport);
+
+      env->SetObjectArrayElement(jports.obj(), i, jport.obj());
+    }
+  }
+
+  Java_AppWebMessagePort_onReceivedMessage(env, obj, jmessage, jports);
+  return true;
+}
+
+void AppWebMessagePort::StartReceivingMessages(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& jcaller) {
+  port_.SetCallback(
+      base::Bind(&AppWebMessagePort::OnMessagesAvailable,
+                 base::Unretained(this)));
+}
+
+AppWebMessagePort::AppWebMessagePort(
+    JNIEnv* env,
+    mojo::ScopedMessagePipeHandle handle,
+    const base::android::JavaRef<jobject>& jobject)
+    : port_(std::move(handle)),
+      java_ref_(env, jobject) {
+}
+
+AppWebMessagePort::~AppWebMessagePort() {
+}
+
+void AppWebMessagePort::OnMessagesAvailable() {
+  // Called on a background thread.
+  JNIEnv* env = base::android::AttachCurrentThread();
+  base::android::ScopedJavaLocalRef<jobject> obj = java_ref_.get(env);

[sgurun-gerrit only, 2017/02/09 17:47:24]

the java_ref_ is not thread fully thread safe though. See notes in
JavaObjectWeakGlobalRef.

The get() and destructor are called from different threads, one from the UI
thread in close and the other from the onmessagesavailable in a background
thread. We need to make sure they are synchronized.

[darin (slow to review), 2017/02/09 17:55:08]

See the comment in ~AppWebMessagePort. Explicitly resetting port_ has
the result of ensuring that OnMessagesAvailable has finished running.
~MessagePort makes this so.

+  if (obj.is_null())
+    return;
+  Java_AppWebMessagePort_onMessagesAvailable(env, obj);
+}
+
+bool RegisterAppWebMessagePort(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+void InitializeAppWebMessagePortPair(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jclass>& jcaller,
+    const base::android::JavaParamRef<jobjectArray>& ports) {
+  DCHECK_EQ(2, env->GetArrayLength(ports.obj()));
+
+  mojo::MessagePipe pipe;
+
+  base::android::ScopedJavaLocalRef<jobject> jport0(
+      env, env->GetObjectArrayElement(ports.obj(), 0));
+  AppWebMessagePort::CreateAndBindToJavaObject(
+      env, std::move(pipe.handle0), jport0);
+
+  base::android::ScopedJavaLocalRef<jobject> jport1(
+      env, env->GetObjectArrayElement(ports.obj(), 1));
+  AppWebMessagePort::CreateAndBindToJavaObject(
+      env, std::move(pipe.handle1), jport1);
+}
+
+}  // namespace content