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当未连接到网络(AF_路由)时,没有此类过程(3)

bsd routes networking c

TekuConcept · 技术社区 · 7 年前

当我连接到网络时,我可以发送 struct rt_msghdr* send() errno = ESRCH (3) No such process

通用代码:(在MacOS上测试)

int sd = create_socket(AF_ROUTE, IPPROTO_RAW, AF_UNSPEC);

memset(&buffer[0], 0, buffer.size());
struct rt_msghdr* rmh = (struct rt_msghdr*)(&buffer[0]);
rmh->rtm_msglen       = sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in);
rmh->rtm_version      = RTM_VERSION;
rmh->rtm_type         = RTM_GET;
rmh->rtm_addrs        = RTA_DST;
rmh->rtm_pid          = getpid();
rmh->rtm_seq          = 1;
struct sockaddr_in* sa_in = (struct sockaddr_in*)(rmh + 1);
sa_in->sin_len            = sizeof(struct sockaddr_in);
sa_in->sin_family         = AF_INET;

int status;
if ((status = send(sd, rmh, rmh->rtm_msglen, 0) < 0) {
    rmh->rtm_msglen =
        sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in6);
    struct sockaddr_in6* sa_in6 = (struct sockaddr_in6*)(rmh + 1);
    memset(sa_in6, 0, sizeof(struct sockaddr_in6));
    sa_in6->sin6_len    = sizeof(struct sockaddr_in6);
    sa_in6->sin6_family = AF_INET6;
    if ((status = send(sd, rmh, rmh->rtm_msglen, 0) < 0) {
        // process errno
        // * issue happens here when not connected to a network
    }
}

// receive kernel response(s)
// process responses

close(sd);

我验证了进程ID(pid)在标头中的设置是否正确。当未连接到网络时,netstat-nr返回默认路由而不出现问题。我很难理解为什么此代码依赖于网络连接。

netstat -nr :

# with a network connection (Internet)
Destination        Gateway     Flags          Refs      Use   Netif Expire
default            X.X.X.X     UGSc           58        0     en1

# without a network connection (Internet6)
Destination        Gateway            Flags         Netif Expire
default            fe80::%utun0       UGcI          utun0