source: azure_iot_hub/trunk/musl-1.1.18/src/network/res_msend.c@ 389

#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <stdint.h>
#include <string.h>
#include <poll.h>
#include <time.h>
#include <ctype.h>
#include <unistd.h>
#include <errno.h>
#include <pthread.h>
#include "stdio_impl.h"
#include "syscall.h"
#include "lookup.h"

static void cleanup(void *p)
{
        __syscall(SYS_close, (intptr_t)p);
}

static unsigned long mtime()
{
        struct timespec ts;
        clock_gettime(CLOCK_REALTIME, &ts);
        return (unsigned long)ts.tv_sec * 1000
                + ts.tv_nsec / 1000000;
}

int __res_msend_rc(int nqueries, const unsigned char *const *queries,
        const int *qlens, unsigned char *const *answers, int *alens, int asize,
        const struct resolvconf *conf)
{
        int fd;
        int timeout, attempts, retry_interval, servfail_retry;
        union {
                struct sockaddr_in sin;
                struct sockaddr_in6 sin6;
        } sa = {0}, ns[MAXNS] = {{0}};
        socklen_t sl = sizeof sa.sin;
        int nns = 0;
        int family = AF_INET;
        int rlen;
        int next;
        int i, j;
        int cs;
        struct pollfd pfd;
        unsigned long t0, t1, t2;

        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

        timeout = 1000*conf->timeout;
        attempts = conf->attempts;

        for (nns=0; nns<conf->nns; nns++) {
                const struct address *iplit = &conf->ns[nns];
                if (iplit->family == AF_INET) {
                        memcpy(&ns[nns].sin.sin_addr, iplit->addr, 4);
                        ns[nns].sin.sin_port = htons(53);
                        ns[nns].sin.sin_family = AF_INET;
                } else {
                        sl = sizeof sa.sin6;
                        memcpy(&ns[nns].sin6.sin6_addr, iplit->addr, 16);
                        ns[nns].sin6.sin6_port = htons(53);
                        ns[nns].sin6.sin6_scope_id = iplit->scopeid;
                        ns[nns].sin6.sin6_family = family = AF_INET6;
                }
        }

        /* Get local address and open/bind a socket */
        sa.sin.sin_family = family;
        fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);

        /* Handle case where system lacks IPv6 support */
        if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
                fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
                family = AF_INET;
        }
        if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) {
                if (fd >= 0) close(fd);
                pthread_setcancelstate(cs, 0);
                return -1;
        }

        /* Past this point, there are no errors. Each individual query will
         * yield either no reply (indicated by zero length) or an answer
         * packet which is up to the caller to interpret. */

        pthread_cleanup_push(cleanup, (void *)(intptr_t)fd);
        pthread_setcancelstate(cs, 0);

        /* Convert any IPv4 addresses in a mixed environment to v4-mapped */
        if (family == AF_INET6) {
                setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
                for (i=0; i<nns; i++) {
                        if (ns[i].sin.sin_family != AF_INET) continue;
                        memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
                                &ns[i].sin.sin_addr, 4);
                        memcpy(ns[i].sin6.sin6_addr.s6_addr,
                                "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
                        ns[i].sin6.sin6_family = AF_INET6;
                        ns[i].sin6.sin6_flowinfo = 0;
                        ns[i].sin6.sin6_scope_id = 0;
                }
        }

        memset(alens, 0, sizeof *alens * nqueries);

        pfd.fd = fd;
        pfd.events = POLLIN;
        retry_interval = timeout / attempts;
        next = 0;
        t0 = t2 = mtime();
        t1 = t2 - retry_interval;

        for (; t2-t0 < timeout; t2=mtime()) {
                if (t2-t1 >= retry_interval) {
                        /* Query all configured namservers in parallel */
                        for (i=0; i<nqueries; i++)
                                if (!alens[i])
                                        for (j=0; j<nns; j++)
                                                sendto(fd, queries[i],
                                                        qlens[i], MSG_NOSIGNAL,
                                                        (void *)&ns[j], sl);
                        t1 = t2;
                        servfail_retry = 2 * nqueries;
                }

                /* Wait for a response, or until time to retry */
                if (poll(&pfd, 1, t1+retry_interval-t2) <= 0) continue;

                while ((rlen = recvfrom(fd, answers[next], asize, 0,
                  (void *)&sa, (socklen_t[1]){sl})) >= 0) {

                        /* Ignore non-identifiable packets */
                        if (rlen < 4) continue;

                        /* Ignore replies from addresses we didn't send to */
                        for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
                        if (j==nns) continue;

                        /* Find which query this answer goes with, if any */
                        for (i=next; i<nqueries && (
                                answers[next][0] != queries[i][0] ||
                                answers[next][1] != queries[i][1] ); i++);
                        if (i==nqueries) continue;
                        if (alens[i]) continue;

                        /* Only accept positive or negative responses;
                         * retry immediately on server failure, and ignore
                         * all other codes such as refusal. */
                        switch (answers[next][3] & 15) {
                        case 0:
                        case 3:
                                break;
                        case 2:
                                if (servfail_retry && servfail_retry--)
                                        sendto(fd, queries[i],
                                                qlens[i], MSG_NOSIGNAL,
                                                (void *)&ns[j], sl);
                        default:
                                continue;
                        }

                        /* Store answer in the right slot, or update next
                         * available temp slot if it's already in place. */
                        alens[i] = rlen;
                        if (i == next)
                                for (; next<nqueries && alens[next]; next++);
                        else
                                memcpy(answers[i], answers[next], rlen);

                        if (next == nqueries) goto out;
                }
        }
out:
        pthread_cleanup_pop(1);

        return 0;
}

int __res_msend(int nqueries, const unsigned char *const *queries,
        const int *qlens, unsigned char *const *answers, int *alens, int asize)
{
        struct resolvconf conf;
        if (__get_resolv_conf(&conf, 0, 0) < 0) return -1;
        return __res_msend_rc(nqueries, queries, qlens, answers, alens, asize, &conf);
}