程式語言 - GNU - C/C++ - TCP Server、Client

參考資訊：
https://www.geeksforgeeks.org/socket-programming-cc/

server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char const* argv[])
{
    ssize_t r = 0;
    int opt = 1;
    int fd = -1;
    int new_socket = 0;
    char buf[1024] = {0};
    struct sockaddr_in addr = {0};
    const char *hello = "hello from server !";

    if (argc != 3) {
        printf("usage: %s ip port\n", argv[0]);
        return 0;
    }

    socklen_t addrlen = sizeof(addr);
    fd = socket(AF_INET, SOCK_STREAM, 0);
    if (fd < 0) {
        perror("socket");
        return -1;
    }

    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        return -1;
    }

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(argv[1]); // INADDR_ANY;
    addr.sin_port = htons(atoi(argv[2])); 
    if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("bind");
        return -1;
    }

    if (listen(fd, 3) < 0) {
        perror("listen");
        return -1;
    }

    new_socket = accept(fd, (struct sockaddr *)&addr, &addrlen);
    if (new_socket < 0) {
        perror("accept");
        return -1;
    }

    r = read(new_socket, buf, sizeof(buf));
    printf("%s\n", buf);
    send(new_socket, hello, strlen(hello), 0);
    close(new_socket);
    close(fd);
    return 0;
}

client.c

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

int main(int argc, char const* argv[])
{
    int r = 0;
    int fd = -1;
    struct sockaddr_in addr = {0};
    const char *hello = "hello from client !";
    char buf[1024] = {0};

    if (argc != 3) {
        printf("usage: %s ip port\n", argv[0]);
        return 0;
    }

    fd = socket(AF_INET, SOCK_STREAM, 0);
    if (fd < 0) {
        perror("socket");
        return -1;
    }

    addr.sin_family = AF_INET;
    addr.sin_port = htons(atoi(argv[2])); 
    if (inet_pton(AF_INET, argv[1], &addr.sin_addr) <= 0) {
        perror("inet_pton");
        return -1;
    }

    if (connect(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("connect");
        return -1;
    }

    send(fd, hello, strlen(hello), 0);
    r = read(fd, buf, sizeof(buf));
    printf("%s\n", buf);
    close(fd);
    return 0;
}

編譯、執行

$ gcc server.c -o server
$ gcc client.c -o client

$ ./server 127.0.0.1 9999 &
$ ./client 127.0.0.1 9999
hello from client !
hello from server !