HTML MessagePort as mojo::MessagePipeHandle

content/browser/android/app_web_message_port.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.

[jam, 2017/01/23 18:08:56]

I don't remember who worked on the initial implementation of this feature on
Android. +tedchoc to review the content/browser/android and
content/public/android files as I don't feel qualified.

+// 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 "base/logging.h"
+#include "base/strings/utf_string_conversions.h"
+#include "jni/AppWebMessagePort_jni.h"
+
+namespace content {
+namespace {
+
+// To avoid setting up a V8 context here, we just hard code the format for
+// string type messages. /me ducks!
+
+const uint32_t kVarIntShift = 7;
+const uint32_t kVarIntMask = (1 << kVarIntShift) - 1;
+
+const uint8_t kVersionTag = 0xFF;
+const uint8_t kStringTag = 'S';
+const uint8_t kStringUCharTag = 'c';
+
+const uint32_t kVersion = 9;
+
+void WriteUint8(uint8_t value, std::vector<uint8_t>* buffer) {
+  buffer->push_back(value);
+}
+
+void WriteUint32(uint32_t value, std::vector<uint8_t>* buffer) {
+  for (;;) {
+    uint8_t b = (value & kVarIntMask);
+    value >>= kVarIntShift;
+    if (!value) {
+      WriteUint8(b, buffer);
+      break;
+    }
+    WriteUint8(b | (1 << kVarIntShift), buffer);
+  }
+}
+
+void WriteBytes(const char* bytes, size_t num_bytes,
+                std::vector<uint8_t>* buffer) {
+  buffer->insert(buffer->end(), bytes, bytes + num_bytes);
+}
+
+base::string16 EncodeStringMessage(const base::string16& data) {
+  std::string data_utf8(base::UTF16ToUTF8(data));
+
+  std::vector<uint8_t> buffer;
+  WriteUint8(kVersionTag, &buffer);
+  WriteUint32(kVersion, &buffer);
+
+  WriteUint8(kStringTag, &buffer);
+  WriteUint32(static_cast<uint32_t>(data_utf8.size()), &buffer);
+  WriteBytes(data_utf8.data(), data_utf8.size(), &buffer);
+
+  base::string16 result;
+  size_t result_num_bytes = (buffer.size() + 1) & ~1;
+  result.resize(result_num_bytes / 2);
+  uint8_t* destination = reinterpret_cast<uint8_t*>(&result[0]);
+  memcpy(destination, &buffer[0], buffer.size());
+  if (result_num_bytes > buffer.size())

[jbroman, 2017/01/24 22:41:51]

nit: std::basic_string::resize promises to zero-initialize characters (well,
technically initialize to CharT()), so this isn't necessary.

[darin (slow to review), 2017/02/04 01:43:02]

Thanks

+    destination[result_num_bytes - 1] = '\0';
+
+  return result;
+}
+
+bool ReadUint8(const uint8_t** ptr, const uint8_t* end, uint8_t* value) {
+  if (*ptr >= end)
+    return false;
+  *value = *(*ptr)++;
+  return true;
+}
+
+bool ReadUint32(const uint8_t** ptr, const uint8_t* end, uint32_t* value) {
+  *value = 0;
+  uint8_t current_byte;
+  int shift = 0;
+  do {
+    if (*ptr >= end)
+      return false;
+    current_byte = *(*ptr)++;
+    *value |= (static_cast<uint32_t>(current_byte & kVarIntMask) << shift);

[jbroman, 2017/01/24 22:41:51]

nit: shifts of >=32 bits are undefined behavior.

Especially if these messages can come from out of process, probably safer to
check for that and not invoke undefined behavior? (I did add this check to the
V8 implementation, even though the legacy Blink one doesn't have it. Not
necessarily a big deal, because I have a hard time imagining a compiler doing
anything terrible with this particular bit of UB.)

https://chromium.googlesource.com/v8/v8/+/e56437b6/src/value-serializer.cc#951

+    shift += kVarIntShift;
+  } while (current_byte & (1 << kVarIntShift));
+  return true;
+}
+
+bool DecodeStringMessage(const base::string16& encoded_data,
+                         base::string16* result) {
+  size_t num_bytes = encoded_data.size() * 2;
+
+  const uint8_t* ptr = reinterpret_cast<const uint8_t*>(&encoded_data[0]);
+  const uint8_t* end = ptr + num_bytes;
+
+  uint8_t tag;
+  if (!ReadUint8(&ptr, end, &tag) || tag != kVersionTag)
+    return false;
+
+  uint32_t version;
+  if (!ReadUint32(&ptr, end, &version))
+    return false;
+
+  if (!ReadUint8(&ptr, end, &tag))
+    return false;
+
+  switch (tag) {

[jbroman, 2017/01/24 22:41:51]

You also need to be able to handle the padding tag, '\0' (for legacy reasons --
I may simplify this in the future). This can occur for two-byte strings,
depending on the length of the string. If the beginning of the character array
would not be two-byte-aligned, a padding tag is added before kStringUCharTag.

For messages where the string is the entire message (as here), this will occur
if the byte length of the string takes an even number of bytes to encode (e.g.,
from 128 to 16384 bytes, or 64 to 8192 two-byte chars).

Here it's probably sufficient to essentially add this before the switch:

// Discard a leading padding tag if one is present.
if (tag == kPaddingTag && !ReadUint8Tag(&ptr, end, &tag))
  return false;

That should be sufficient to handle the current output of the serializer. A unit
test with 200 smilies or similar would catch this.

Apologies for this weird corner case. :)

+    case kStringTag: {
+      uint32_t num_utf8_bytes;
+      if (!ReadUint32(&ptr, end, &num_utf8_bytes))
+        return false;
+      const char* utf8_start = reinterpret_cast<const char*>(ptr);
+      return base::UTF8ToUTF16(utf8_start, num_utf8_bytes, result);
+    }
+    case kStringUCharTag: {
+      uint32_t num_uchar_bytes;
+      if (!ReadUint32(&ptr, end, &num_uchar_bytes))
+        return false;
+      const base::char16* uchar_start =
+          reinterpret_cast<const base::char16*>(ptr);
+      result->assign(uchar_start, num_uchar_bytes / 2);
+      return true;
+    }
+  }
+
+  LOG(WARNING) << "Unexpected tag: " << tag;
+  return false;
+}
+
+} // namespace
+
+// 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 (!env->IsSameObject(jports.obj(), nullptr)) {
+    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_);
+    }
+  }
+  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));
+}
+
+void AppWebMessagePort::DispatchReceivedMessages(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& jcaller) {
+  jmethodID app_web_message_port_constructor =
+      base::android::MethodID::Get<base::android::MethodID::TYPE_INSTANCE>(
+          env, AppWebMessagePort_clazz(env), "<init>", "()V");
+
+  // Consume all of the available messages.
+  // TODO(darin): Consider breaking this up across multiple PostTask calls.
+  for (;;) {
+    base::string16 encoded_message;
+    std::vector<MessagePort> ports;
+    if (!port_.GetMessage(&encoded_message, &ports))
+      return;
+
+    base::string16 message;
+    if (!DecodeStringMessage(encoded_message, &message))
+      return;
+
+    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, java_ref_.get(env), jmessage, jports);
+  }
+}
+
+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 the IO thread.
+  JNIEnv* env = base::android::AttachCurrentThread();
+  Java_AppWebMessagePort_onMessagesAvailable(env, java_ref_.get(env));
+}
+
+bool RegisterAppWebMessagePort(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace content