ClientServer.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>

#define MAX_MSG_SIZE 1024
#define DEFAULT_PORT 8080

void SendMsg(int sockfd, char *msg)
{
    int bytes_sent = send(sockfd, msg, strlen(msg), 0);
    if (bytes_sent < 0)
    {
        perror("Error sending message");
        exit(EXIT_FAILURE);
    }
}

void RecvMsg(int sockfd, char *buffer)
{
    memset(buffer, 0, MAX_MSG_SIZE); // clear the buffer before receiving data

    int bytes_received = recv(sockfd, buffer, MAX_MSG_SIZE, MSG_DONTWAIT);
    if (bytes_received < 0)
    {
        if (errno == EWOULDBLOCK || errno == EAGAIN)
        {
            // no data available, do nothing
            return;
        }
        else
        {
            perror("Error receiving message");
            exit(EXIT_FAILURE);
        }
    }
    else if (bytes_received == 0)
    {
        // connection closed
        printf("Connection closed by peer\n");
        exit(EXIT_SUCCESS);
    }
    else
    {
        buffer[bytes_received] = '\0';
        printf("Received message: %s\n", buffer);
    }
}

void TestInput(int sockfd)
{
    char buffer[MAX_MSG_SIZE];

    fd_set set;
    FD_ZERO(&set);
    FD_SET(STDIN_FILENO, &set);
    FD_SET(sockfd, &set);

    struct timeval timeout;
    timeout.tv_sec = 0;
    timeout.tv_usec = 10000; // 10 milliseconds

    int ready = select(sockfd + 1, &set, NULL, NULL, &timeout);

    if (ready == -1)
    {
        perror("select error");
        exit(EXIT_FAILURE);
    }
    else if (ready == 0)
    {
        // no data available to be read
        return;
    }
    else
    {
        // data available to be read
        if (FD_ISSET(STDIN_FILENO, &set))
        {
            fgets(buffer, MAX_MSG_SIZE, stdin);
            SendMsg(sockfd, buffer);
        }
        if (FD_ISSET(sockfd, &set))
        {
            RecvMsg(sockfd, buffer);
        }
    }
}

void RunClient(char *ip_addr, int port)
{
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_in server_addr = {
        .sin_family = AF_INET,
        .sin_port = htons(port),
        .sin_addr = {0}};
    if (inet_pton(AF_INET, ip_addr, &server_addr.sin_addr) < 0)
    {
        perror("Invalid IP address");
        exit(EXIT_FAILURE);
    }

    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
    {
        perror("Error connecting to server");
        exit(EXIT_FAILURE);
    }

    char buffer[MAX_MSG_SIZE];
    while (true)
    {
        TestInput(sockfd);

        RecvMsg(sockfd, buffer);
    }
}

void RunServer(int port)
{
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_in server_addr = {
        .sin_family = AF_INET,
        .sin_addr = {INADDR_ANY},
        .sin_port = htons(port)};

    if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
    {
        perror("Error binding socket");
        exit(EXIT_FAILURE);
    }

    if (listen(sockfd, 1) < 0)
    {
        perror("Error listening on socket");
        exit(EXIT_FAILURE);
    }

    printf("Waiting for client to connect...\n");

    int client_sockfd = accept(sockfd, NULL, NULL);
    if (client_sockfd < 0)
    {
        perror("Error accepting client connection");
        exit(EXIT_FAILURE);
    }

    printf("Client connected!\n");

    char buffer[MAX_MSG_SIZE];
    while (true)
    {
        TestInput(client_sockfd);

        RecvMsg(client_sockfd, buffer);
    }
}

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        printf("Usage: %s [server|client] [ip address (for client)] [port]\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    int port = DEFAULT_PORT;
    if (argc == 3)
    {
        port = atoi(argv[2]);
    }

    if (strcmp(argv[1], "server") == 0)
    {
        RunServer(port);
    }
    else if (strcmp(argv[1], "client") == 0)
    {
        if (argc < 3)
        {
            printf("Please specify IP address\n");
            exit(EXIT_FAILURE);
        }
        char *ip_addr = argv[2];
        RunClient(ip_addr, port);
    }
    else
    {
        printf("Invalid argument: %s\n", argv[1]);
        exit(EXIT_FAILURE);
    }

    return 0;
}