Sending data from C++ to Python using UDP and protobuf
So here is one example how to use Googles `protobuf` to send a data structure from a `C++` script to a `Python` script via `UDP`. This is tested on Mac OS X Mavericks but should work fine on other Unix systems too.
The first step is of course installing the `protobuf` library. I used homebrew for the main library and `pip` to install the `Python` modules:
brew install protobuf
pip install protobuf
Then I defined a very simple data structure using the proto-syntax:
package prototest;
message Foo {
  required int32 id = 1;
  required string bar = 2;
  optional string baz = 3;
}
This proto-file can now be translated into C++ and Python classes via:
protoc foo.proto --cpp_out=. --python_out=.
The folder should now contain the C++ header and source files and the Python code:
âââ foo.pb.cc
âââ foo.pb.h
âââ foo.proto
âââ foo_pb2.py
Let's have a look at the very basic `C++` code, which is meant to send an instance of `foo` over the network, using UDP (to localhost on port 5555):
#include <sys/socket.h>
#include <arpa/inet.h>
// this is our proto of foo
#include "foo.pb.h"
int main(int argc, char **argv)
{
struct sockaddr_in addr;
addr.sin_family = AF_INET;
inet_aton("127.0.0.1", &addr.sin_addr);
addr.sin_port = htons(5555);
// initialise a foo and set some properties
GOOGLE_PROTOBUF_VERIFY_VERSION;
prototest::Foo foo;
foo.set_id(4);
foo.set_bar("narf");
// serialise to string, this one is obvious ; )
std::string buf;
foo.SerializeToString(&buf);
int sock = socket(PF_INET, SOCK_DGRAM, 0);
sendto(sock, buf.data(), strlen(buf.c_str()), 0, (struct sockaddr *)&addr, sizeof(addr));
return 0;
}
I compiled it via `clang++`:
clang++ -o send send.cc foo.pb.cc -lprotobuf
And finally, this is the `Python` code, which waits for UDP packets and deserialise them into `foo`. Again: no error checking whatsoever, this is only to demonstrate the functionality:
import socket
from foo_pb2 import Foo
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(("127.0.0.1", 5555))
foo = Foo()
while True:
  data, addr = sock.recvfrom(1024)
  foo.ParseFromString(data)
  print("Got foo with id={0} and bar={1}".format(foo.id, foo.bar))
Now we're done and this is the final directory structure:
âââ foo.pb.cc
âââ foo.pb.h
âââ foo.proto
âââ foo_pb2.py
âââ receive.py
âââ send
âââ send.cc
To test the script, simply run `receive.py` to listen to UDP packets via
and keep your eyes on the output when you execute the C++ generated `send` script:
romaincrisis
turnnoffyourmind
areudirty
