fusl/src/network/res_msend.c

#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;

  nns = conf->nns;
  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)
    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);
}