C++中protobuf消息的长度前缀

Question

我正在使用protobuf序列化我通过C++中的套接字连接发送的消息.对于通信,我想在消息标记中添加标题,指示消息的长度.您对此实施有何看法？我做了一些研究,这就是我放在一起的东西.

有没有更好的方法来做到这一点？这种实施能否造成任何麻烦？我知道Java有API支持,但遗憾的是不支持C++.

bool send_message(int socket, my_protobuf::Message message)
{
  google::protobuf::uint32 message_length = message.ByteSize();
  int prefix_length = sizeof(message_length);
  int buffer_length = prefix_length + message_length;
  google::protobuf::uint8 buffer[buffer_length];

  google::protobuf::io::ArrayOutputStream array_output(buffer, buffer_length);
  google::protobuf::io::CodedOutputStream coded_output(&array_output);

  coded_output.WriteLittleEndian32(message_length);
  message.SerializeToCodedStream(&coded_output);

  int sent_bytes = write(socket, buffer, buffer_length);
  if (sent_bytes != buffer_length) {
    return false;
  }

  return true;
}

bool recv_message(int socket, my_protobuf::Message *message)
{
  google::protobuf::uint32 message_length;
  int prefix_length = sizeof(message_length);
  google::protobuf::uint8 prefix[prefix_length];

  if (prefix_length != read(socket, prefix, prefix_length)) {
    return false;
  }
  google::protobuf::io::CodedInputStream::ReadLittleEndian32FromArray(prefix,
      &message_length);

  google::protobuf::uint8 buffer[message_length];
  if (message_length != read(socket, buffer, message_length)) {
    return false;
  }
  google::protobuf::io::ArrayInputStream array_input(buffer, message_length);
  google::protobuf::io::CodedInputStream coded_input(&array_input);

  if (!message->ParseFromCodedStream(&coded_input)) {
    return false;
  }

  return true;
}

Answer 1

使用varint(例如WriteVarint32)而不是fixed32(你所拥有的WriteLittleEndian32)更常见,但是通过前缀长度来划分protobuf流的做法是合理的.