recv_v4.lc

unix网络编程卷1：套接口API的全书源码

#include    "trace.h"##  1 ##src/traceroute/recv_v4.c##

/*##  2 ##src/traceroute/recv_v4.c##
 * Return: -3 on timeout##  3 ##src/traceroute/recv_v4.c##
 *         -2 on ICMP time exceeded in transit (caller keeps going)##  4 ##src/traceroute/recv_v4.c##
 *         -1 on ICMP port unreachable (caller is done)##  5 ##src/traceroute/recv_v4.c##
 *       >= 0 return value is some other ICMP unreachable code##  6 ##src/traceroute/recv_v4.c##
 */##  7 ##src/traceroute/recv_v4.c##

int##  8 ##src/traceroute/recv_v4.c##
recv_v4(int seq, struct timeval *tv)##  9 ##src/traceroute/recv_v4.c##
{## 10 ##src/traceroute/recv_v4.c##
    int     hlen1, hlen2, icmplen;## 11 ##src/traceroute/recv_v4.c##
    socklen_t len;## 12 ##src/traceroute/recv_v4.c##
    ssize_t n;## 13 ##src/traceroute/recv_v4.c##
    struct ip *ip, *hip;## 14 ##src/traceroute/recv_v4.c##
    struct icmp *icmp;## 15 ##src/traceroute/recv_v4.c##
    struct udphdr *udp;## 16 ##src/traceroute/recv_v4.c##

    alarm(3);## 17 ##src/traceroute/recv_v4.c##
    for (;;) {## 18 ##src/traceroute/recv_v4.c##
        len = pr->salen;## 19 ##src/traceroute/recv_v4.c##
        n = recvfrom(recvfd, recvbuf, sizeof(recvbuf), 0, pr->sarecv, &len);## 20 ##src/traceroute/recv_v4.c##
        if (n < 0) {## 21 ##src/traceroute/recv_v4.c##
            if (errno == EINTR)## 22 ##src/traceroute/recv_v4.c##
                return (-3);    /* alarm expired */## 23 ##src/traceroute/recv_v4.c##
            else## 24 ##src/traceroute/recv_v4.c##
                err_sys("recvfrom error");## 25 ##src/traceroute/recv_v4.c##
        }## 26 ##src/traceroute/recv_v4.c##
        Gettimeofday(tv, NULL); /* get time of packet arrival */## 27 ##src/traceroute/recv_v4.c##

        ip = (struct ip *) recvbuf; /* start of IP header */## 28 ##src/traceroute/recv_v4.c##
        hlen1 = ip->ip_hl << 2; /* length of IP header */## 29 ##src/traceroute/recv_v4.c##

        icmp = (struct icmp *) (recvbuf + hlen1);   /* start of ICMP header */## 30 ##src/traceroute/recv_v4.c##
        if ((icmplen = n - hlen1) < 8)## 31 ##src/traceroute/recv_v4.c##
            err_quit("icmplen (%d) < 8", icmplen);## 32 ##src/traceroute/recv_v4.c##

        if (icmp->icmp_type == ICMP_TIMXCEED &&## 33 ##src/traceroute/recv_v4.c##
            icmp->icmp_code == ICMP_TIMXCEED_INTRANS) {## 34 ##src/traceroute/recv_v4.c##
            if (icmplen < 8 + 20 + 8)## 35 ##src/traceroute/recv_v4.c##
                err_quit("icmplen (%d) < 8 + 20 + 8", icmplen);## 36 ##src/traceroute/recv_v4.c##

            hip = (struct ip *) (recvbuf + hlen1 + 8);## 37 ##src/traceroute/recv_v4.c##
            hlen2 = hip->ip_hl << 2;## 38 ##src/traceroute/recv_v4.c##
            udp = (struct udphdr *) (recvbuf + hlen1 + 8 + hlen2);## 39 ##src/traceroute/recv_v4.c##
            if (hip->ip_p == IPPROTO_UDP &&## 40 ##src/traceroute/recv_v4.c##
                udp->uh_sport == htons(sport) &&## 41 ##src/traceroute/recv_v4.c##
                udp->uh_dport == htons(dport + seq))## 42 ##src/traceroute/recv_v4.c##
                return (-2);    /* we hit an intermediate router */## 43 ##src/traceroute/recv_v4.c##

        } else if (icmp->icmp_type == ICMP_UNREACH) {## 44 ##src/traceroute/recv_v4.c##
            if (icmplen < 8 + 20 + 8)## 45 ##src/traceroute/recv_v4.c##
                err_quit("icmplen (%d) < 8 + 20 + 8", icmplen);## 46 ##src/traceroute/recv_v4.c##

            hip = (struct ip *) (recvbuf + hlen1 + 8);## 47 ##src/traceroute/recv_v4.c##
            hlen2 = hip->ip_hl << 2;## 48 ##src/traceroute/recv_v4.c##
            udp = (struct udphdr *) (recvbuf + hlen1 + 8 + hlen2);## 49 ##src/traceroute/recv_v4.c##
            if (hip->ip_p == IPPROTO_UDP &&## 50 ##src/traceroute/recv_v4.c##
                udp->uh_sport == htons(sport) &&## 51 ##src/traceroute/recv_v4.c##
                udp->uh_dport == htons(dport + seq)) {## 52 ##src/traceroute/recv_v4.c##
                if (icmp->icmp_code == ICMP_UNREACH_PORT)## 53 ##src/traceroute/recv_v4.c##
                    return (-1);    /* have reached destination */## 54 ##src/traceroute/recv_v4.c##
                else## 55 ##src/traceroute/recv_v4.c##
                    return (icmp->icmp_code);   /* 0, 1, 2, ... */## 56 ##src/traceroute/recv_v4.c##
            }## 57 ##src/traceroute/recv_v4.c##
        } else if (verbose) {## 58 ##src/traceroute/recv_v4.c##
            printf(" (from %s: type = %d, code = %d)\n",## 59 ##src/traceroute/recv_v4.c##
                   Sock_ntop_host(pr->sarecv, pr->salen),## 60 ##src/traceroute/recv_v4.c##
                   icmp->icmp_type, icmp->icmp_code);## 61 ##src/traceroute/recv_v4.c##
        }## 62 ##src/traceroute/recv_v4.c##
        /* Some other ICMP error, recvfrom() again */## 63 ##src/traceroute/recv_v4.c##
    }## 64 ##src/traceroute/recv_v4.c##
}## 65 ##src/traceroute/recv_v4.c##