ProtocolBuffer can't define data although it is received - c++

Question

I'm trying to use Google's ProtocolBuffer to send/receive data in a server/client architecture. I am able to connect the two with winsock and I am able to send and receive data from ProtocolBuffer with it but there seems to be a problem with deserializing the data on the server (I haven't done the opposite so I can't tell if that works yet)
Here's the code I use to create a sample packet of data to send to the server:
MessageID *message = new MessageID();
message->set_type(MessageID::Type::MessageID_Type_PLAYERDATA);
PlayerData::Vector2 *position = new PlayerData::Vector2();
position->set_x(10.0f);
position->set_y(25.0f);
PlayerData *data = new PlayerData();
data->set_health((UINT32)50);
data->set_allocated_position(position);
auto inventory = data->add_items();
inventory->set_itemid((INT32)1);
inventory->set_count((INT32)5);
message->set_allocated_playerdata(data);
m_pNetworkObject->Send(message);
This is the code that actually sends the data over a TCP connection:
// Serialize to string.
std::string sendData;
data->SerializeToString(&sendData);
// Convert data to const char*
const char* dataToSend = sendData.c_str();
int iResult;
iResult = send( ConnectSocket, dataToSend, data->ByteSize(), 0 );
if (iResult == SOCKET_ERROR)
{
printf("send failed with error: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
exit(1);
}
So, this was code that is run on the client. Now, when I receive this on the server I get the following errors from ProtocolBuffer:
Can't parse message of type "MessageID" because it is missing required fields: type
Can't parse message of type "PlayerData" because it is missing required fields: Position, Health
The code on the server that decompiles the winsock data is like this:
// decompile to a proto file and check ID
MessageID* receivedData = new MessageID();
receivedData->ParseFromArray(&recv, strlen(recv));
// check and redeserialize
switch (receivedData->type())
{
case MessageID::Type::MessageID_Type_PLAYERDATA:
{
PlayerData* playerData = new PlayerData();
playerData->ParseFromArray(&recv, strlen(recv));
UsePlayerData(sock, playerData);
break;
}
case MessageID::Type::MessageID_Type_WORLDDATA:
{
WorldData* worldData = new WorldData();
worldData->ParseFromArray(&recv, strlen(recv));
UseWorldData(sock, worldData);
break;
}
}
The weird thing is that, although the error says that the data doesn't contain the Type value it does set it to 1 and the switch statement works. After that when I try to take a look at the Position and Health data everything is 0.
I have no idea what I'm doing wrong. I read most of the ProtocolBuffer tutorials and help but it seems to no avail.
EDIT:
I tried serializing and then deserializing the data in the same application (without the networking involved) and with the following code it worked to do just that:
std::string sendData;
message->SerializeToString(&sendData);
MessageID* receivedData = new MessageID();
receivedData->ParseFromString(sendData);
If I check the data in receivedData it is exactly the same (so, the right values) as in the original object "message"

Answer 1

Your problem is that you are using strlen() to find the length of the message. strlen() just looks for the first zero-valued byte and assumes that's the end. This is the convention for text strings, but does not apply to binary messages like Protocol Buffers. In this case, strlen() is returning a size that is too short and so some fields are missing from the message, but the opposite can happen too -- strlen() can run off the end of the buffer and return a size that is too long, or even crash your program.
So, you need to make sure the actual exact size of the message is communicated from the sender to the receiver.