Basic echo between Python client and C server via socket using Python ctypes

.python-c-echo

Basic echo between Python client and C server via socket using Python ctypes

client.py

#!/usr/bin/env python

""" client.py - Echo client for sending/receiving C-like structs via socket

References:
- Ctypes fundamental data types: https://docs.python.org/2/library/ctypes.html#ctypes-fundamental-data-types-2
- Ctypes structures: https://docs.python.org/2/library/ctypes.html#structures-and-unions
- Sockets: https://docs.python.org/2/howto/sockets.html
"""

import socket
import sys
import random
from ctypes import *


""" This class defines a C-like struct """
class Payload(Structure):
    _fields_ = [("id", c_uint32),
                ("counter", c_uint32),
                ("temp", c_float)]


def main():
    server_addr = ('localhost', 2300)
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    if s < 0:
        print "Error creating socket"

    try:
        s.connect(server_addr)
        print "Connected to %s" % repr(server_addr)
    except:
        print "ERROR: Connection to %s refused" % repr(server_addr)
        sys.exit(1)

    try:
        for i in range(5):
            print ""
            payload_out = Payload(1, i, random.uniform(-10, 30))
            print "Sending id=%d, counter=%d, temp=%f" % (payload_out.id,
                                                        payload_out.counter,
                                                        payload_out.temp)
            nsent = s.send(payload_out)
            # Alternative: s.sendall(...): coontinues to send data until either
            # all data has been sent or an error occurs. No return value.
            print "Sent %d bytes" % nsent

            buff = s.recv(sizeof(Payload))
            payload_in = Payload.from_buffer_copy(buff)
            print "Received id=%d, counter=%d, temp=%f" % (payload_in.id,
                                                        payload_in.counter,
                                                        payload_in.temp)
    finally:
        print "Closing socket"
        s.close()


if __name__ == "__main__":
    main()

server.c

#include <sys/socket.h>
#include <arpa/inet.h> //inet_addr
#include <unistd.h>    //write

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#pragma pack(1)

typedef struct payload_t {
    uint32_t id;
    uint32_t counter;
    float temp;
} payload;

#pragma pack()


int createSocket(int port)
{
    int sock, err;
    struct sockaddr_in server;

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("ERROR: Socket creation failed\n");
        exit(1);
    }
    printf("Socket created\n");

    bzero((char *) &server, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons(port);
    if (bind(sock, (struct sockaddr *)&server , sizeof(server)) < 0)
    {
        printf("ERROR: Bind failed\n");
        exit(1);
    }
    printf("Bind done\n");

    listen(sock , 3);

    return sock;
}

void closeSocket(int sock)
{
    close(sock);
    return;
}

void sendMsg(int sock, void* msg, uint32_t msgsize)
{
    if (write(sock, msg, msgsize) < 0)
    {
        printf("Can't send message.\n");
        closeSocket(sock);
        exit(1);
    }
    printf("Message sent (%d bytes).\n", msgsize);
    return;
}

int main()
{
    int PORT = 2300;
    int BUFFSIZE = 512;
    char buff[BUFFSIZE];
    int ssock, csock;
    int nread;
    struct sockaddr_in client;
    int clilen = sizeof(client);

    ssock = createSocket(PORT);
    printf("Server listening on port %d\n", PORT);

    while (1)
    {
        csock = accept(ssock, (struct sockaddr *)&client, &clilen);
        if (csock < 0)
        {
            printf("Error: accept() failed\n");
            continue;
        }

        printf("Accepted connection from %s\n", inet_ntoa(client.sin_addr));
        bzero(buff, BUFFSIZE);
        while ((nread=read(csock, buff, BUFFSIZE)) > 0)
        {
            printf("\nReceived %d bytes\n", nread);
            payload *p = (payload*) buff;
            printf("Received contents: id=%d, counter=%d, temp=%f\n",
                    p->id, p->counter, p->temp);

            printf("Sending it back.. ");
            sendMsg(csock, p, sizeof(payload));
        }
        printf("Closing connection to client\n");
        printf("----------------------------\n");
        closeSocket(csock);
    }

    closeSocket(ssock);
    printf("bye");
    return 0;
}