a sample code

最新推荐文章于 2020-03-31 17:58:09 发布

原创最新推荐文章于 2020-03-31 17:58:09 发布 · 191 阅读

CC 4.0 BY-SA版权

本文介绍了一个使用C语言实现的UDP套接字编程示例，展示了如何设置和接收TTL值。程序首先创建一个UDP套接字，然后绑定到指定端口，并通过setsockopt设置IP_RECVTTL选项以接收TTL信息。接着，程序通过recvmsg函数接收来自客户端的消息及TTL值。

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#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <netinet/in.h>
#include <sys/param.h> /* ALIGN macro for CMSG_NXTHDR() macro */

#define UDP_RCV_PORT 20001
#define MAXLINE 1500

int main(int argc, char **argv)
{
    int sockfd;
    ssize_t n;
    int yes=1;
    int ttl = -1;
    socklen_t msg_namelen;
    char mesg[MAXLINE];
    struct iovec    iov[1];
    char control[CMSG_SPACE(sizeof(char))];
    struct msghdr   msg;
    struct sockaddr_in cliaddr, servaddr;
    struct cmsghdr * cmsg;

sockfd = socket(AF_INET, SOCK_DGRAM, 0);
setsockopt(sockfd, IPPROTO_IP, IP_RECVTTL, &yes, sizeof(yes));

    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port        = htons(UDP_RCV_PORT);

    if (bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
        printf("bind socket error!");
        return -1;
    }

    msg.msg_name = (struct sockaddr *) &cliaddr;
    msg.msg_namelen = msg_namelen;
    iov[0].iov_base = mesg;
    iov[0].iov_len = sizeof(mesg);
    msg.msg_iov = iov;
    msg.msg_iovlen = 1;
    msg.msg_control = control;
    msg.msg_controllen = sizeof(control);
    msg.msg_flags = 0;

    printf("start recv mesg\n");
    n = recvmsg(sockfd, &msg, 0);
    printf("n = %lu\n", n);
    cmsg = CMSG_FIRSTHDR(&msg);
    for (; cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
        if (cmsg->cmsg_level == IPPROTO_IP && cmsg->cmsg_type == IP_RECVTTL) {
            char *ttlPtr = CMSG_DATA(cmsg);
            ttl = *ttlPtr;
            break;
        }
    }
    printf("rcv ttl = %d\n", ttl);

}