client.c

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

pid_t server_pid;
int index = 0, bit_index = 0, checksum = 0;
char* str;

void resend(int sig) {
    index = 0;
    bit_index = 0;
    checksum = 0;
    printf("Resending...\n");
}

int main(int argc, char **argv) {
    if (argc != 3) {
        printf("Usage: %s <server_pid> <message>\n", argv[0]);
        exit(1);
    }

    server_pid = atoi(argv[1]);
    str = argv[2];

    signal(SIGUSR1, resend);

    kill(server_pid, SIGUSR1);
    usleep(100);

    while (1) {
        if (str[index] == '\0') {
            kill(server_pid, SIGUSR1);
            usleep(100);
            kill(server_pid, SIGUSR1);
            index++;
            continue;
        }
        if ((str[index] >> (7 - bit_index)) & 1) {
            kill(server_pid, SIGUSR2);
            checksum++;
        }
        else {
            kill(server_pid, SIGUSR1);
        }
        usleep(100);
        bit_index++;
        if (bit_index == 8) {
            bit_index = 0;
            index++;
        }
    }

    // Send checksum
    for (int i = 0; i < 8; i++) {
        if ((checksum >> (7 - i)) & 1) {
            kill(server_pid, SIGUSR2);
        } else {
            kill(server_pid, SIGUSR1);
        }
        usleep(100);
    }

    // Wait for server response
    pause();

    free(str);
    return 0;
}


      

server.c

#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

volatile sig_atomic_t received = 0;
char* str;
int index = 0, bit_index = 0, checksum = 0, calculated_checksum = 0;
pid_t client_pid;

void handler(int sig, siginfo_t *info, void *context) {
    if (received == 0) {
        client_pid = info->si_pid;
        received = 1;
        return;
    }
    if (sig == SIGUSR1) {
        str[index] = str[index] << 1;
    }
    else {
        str[index] = (str[index] << 1) | 1;
        calculated_checksum++;
    }
    bit_index++;
    if (bit_index == 8) {
        index++;
        bit_index = 0;
    }
    if (str[index] == '\0') {
        if (checksum == calculated_checksum) {
            printf("Received: %s\n", str);
            kill(client_pid, SIGUSR1);
        } else {
            printf("Error in transmission\n");
            kill(client_pid, SIGUSR2);
        }
        received = 0;
    }
}

int main() {
    struct sigaction sa;
    sigemptyset(&sa.sa_mask);
    sa.sa_sigaction = handler;
    sa.sa_flags = SA_SIGINFO;

    sigaction(SIGUSR1, &sa, NULL);
    sigaction(SIGUSR2, &sa, NULL);

    str = (char*) malloc(100);
    pause();

    while (1) {
        pause();
    }

    free(str);
    return 0;
}