Question

我想在同一个套接字上发送和接收数据包，是否可能或者我必须创建两个套接字，一个发送一个接收？如果是的话，你能举个例子吗？

另一个问题：如何从收到的数据包中获取源IP？

编辑（代码示例）：

int main(void) {
    struct sockaddr_in si_me, si_other;
    int s, i, slen=sizeof(si_other);
    char buf[BUFLEN];

    if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
        die("socket");

    memset((char *) &si_me, 0, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(1234);
    si_me.sin_addr.s_addr = htonl(192.168.1.1);

    if (bind(s, &si_me, sizeof(si_me))==-1)
        die("bind");

    if (recvfrom(s, buf, BUFLEN, 0, &si_other, &slen)==-1)
       diep("recvfrom()");
    printf("Data: %s \nReceived from %s:%d\n\n", buf, inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));

    //now I want the server to answer back to the client

    close(s);
    return 0;
}

Answer 1

是的，您可以使用相同的套接字进行发送和接收。 recvfrom()告诉您发件人的IP /端口。简单sendto()该IP /端口使用与recvfrom()相同的套接字，例如：

int main(void) {
    struct sockaddr_in si_me, si_other;
    int s, i, blen, slen = sizeof(si_other);
    char buf[BUFLEN];

    s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (s == -1)
        die("socket");

    memset((char *) &si_me, 0, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(1234);
    si_me.sin_addr.s_addr = htonl(192.168.1.1);

    if (bind(s, (struct sockaddr*) &si_me, sizeof(si_me))==-1)
        die("bind");

    int blen = recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr*) &si_other, &slen);
    if (blen == -1)
       diep("recvfrom()");

    printf("Data: %.*s \nReceived from %s:%d\n\n", blen, buf, inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));

    //send answer back to the client
    if (sendto(s, buf, blen, 0, (struct sockaddr*) &si_other, slen) == -1)
        diep("sendto()");

    close(s);
    return 0;
}

c - udp在同一个套接字上发送和接收

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