how to send classes defined in .proto (protocol-buffers) over a socket

Question

Hi,

I am trying to send a proto over a socket, but i am getting segmentation error. Could someone please help and tell me what is wrong with this example?

file.proto

message data{  
    required string x1 = 1;
    required uint32 x2 = 2;
    required float x3 = 3;
}

xxx.cpp

    ...
    data data_snd, data_rec;

    //sending data to the server
    if (send(socket, &data_snd, sizeof(data_snd), 0) < 0) {
       cerr << "send() failed" ;
       exit(1);
     }  

     //receiving data from the client
     if (recv(socket, &data_rec, sizeof(data_rec), 0) < 0) {
        cerr << "recv() failed";
        exit(1);
     }  

Thanks for help and replies-

Answer 1

For one thing, you're assuming that a single call to recv will retrieve all the data. More importantly though, you're not going through the serialization / deserialization code - you're just reading from the network and putting the bytes directly into the object. You should be using the stream-based APIs in Protocol Buffers to write and read the data.

See the Protocol Buffers C++ tutorial for more details - that gives an example of saving to disk, but I expect that the network version would be similar, just with a different stream.

Answer 2

Give more details about where it segfaults and how you manage the connection between server and client.

Use a debugger and print the backtrace, it will help ...

Answer 3

See this article How to send objects from Java to .Net that shows how to serialize complex structures over the wire. You can use the same techniques to serialize using C/C++.

Use htons() and htonl() to serialize integers/shorts on the wire. Then you can use ntohs() and ntohl() to deserialize from the wire onto the C/C++ structure.

Answer 4

You're not supposed to write the protobuf object itself to the socket. Use the SerializeXXX family of methods to get a sequence of bytes which you can write to the socket.

std::string buf;
data.SerializeToString(&buf);
// now you can write buf.data() to the socket