设定IP协议的OPTIONS内容

client.c

// Client side C/C++ program to demonstrate Socket programming
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#define PORT 8080

#define MAXLINE 4096
#define MAXSIZE 40

#define IPOPT_TAG 0x21 //IP选项标志字段
#define IPOPT_LEN 8    //IP选项长度字段

int main(int argc, char const *argv[])
{
    int sock = 0, valread;
    struct sockaddr_in serv_addr;
    char *hello = "Hello from client";
    char buffer[1024] = {0};
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Socket creation error \n");
        return -1;
    }

    //构造自定义的TCP选项
    unsigned char opt[MAXSIZE];
    opt[0] = IPOPT_TAG;
    opt[1] = IPOPT_LEN;

    //设置套接字发送该选项
    if (setsockopt(sock, IPPROTO_IP, IP_OPTIONS, (void *)opt, IPOPT_LEN) < 0)
    {
        perror("setsockopt error ");
        exit(1);
    }
    printf("socket ip options: 0x%02x, 0x%02x, options len: %d\n", opt[0], opt[1], IPOPT_LEN);

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);

    // Convert IPv4 and IPv6 addresses from text to binary form
    if (inet_pton(AF_INET, "172.17.0.2", &serv_addr.sin_addr) <= 0)
    {
        printf("\nInvalid address/ Address not supported \n");
        return -1;
    }

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        printf("\nConnection Failed \n");
        return -1;
    }

    send(sock, hello, strlen(hello), 0);
    printf("Hello message sent\n");
    valread = read(sock, buffer, 1024);
    printf("%s\n", buffer);
    return 0;
}

server.c

// Server side C/C++ program to demonstrate Socket programming
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#define PORT 8080
#define MAXOPTLEN 44
int main(int argc, char const *argv[])
{
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char *hello = "Hello from server";

    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // Forcefully attaching socket to the port 8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
                   &opt, sizeof(opt)))
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Forcefully attaching socket to the port 8080
    if (bind(server_fd, (struct sockaddr *)&address,
             sizeof(address)) < 0)
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address,
                             (socklen_t *)&addrlen)) < 0)
    {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    unsigned char ip_opt[MAXOPTLEN];
    int ip_opt_len = 0;
    // TODO 获取套接字发送该选项
    if (getsockopt(new_socket, IPPROTO_IP, IP_OPTIONS, ip_opt, &ip_opt_len) < 0)
    {
        perror("getsockopt error ");
        exit(1);
    }
    printf("socket ip options: 0x%02x, 0x%02x, options len: %d\n", ip_opt[0], ip_opt[1], ip_opt_len);

    valread = read(new_socket, buffer, 1024);
    printf("%s\n", buffer);
    send(new_socket, hello, strlen(hello), 0);
    printf("Hello message sent\n");
    return 0;
}

error occured while running client: setsockopt error : Invalid argument

These code can only work on ancient kernels like the one in Centos7(3.10), recent kernel seems to forbid unsupported ipv4 options.