ares_process.c

Go to the documentation of this file.

/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include <sys/types.h>
#include "rutil/ResipAssert.h"
 
#ifndef WIN32
#include <sys/socket.h>
#include <sys/uio.h>
#include <netinet/in.h>
#ifndef __CYGWIN__
#  include "ares_nameser.h"
#endif
#include <unistd.h>
#endif
 
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include <errno.h>
#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"
#include "ares_local.h"
 
#ifdef WIN32
static int getErrno() { return WSAGetLastError(); }
#else
static int getErrno() { return errno; }
#endif
 
/* A read that would block is not a server error.  When handle_error() moves
 * a query on, the new server's socket can reuse the descriptor number of the
 * one just closed, and so look ready to a select() or poll that ran before. */
static int would_block(void)
{
#ifdef WIN32
   return getErrno() == WSAEWOULDBLOCK;
#else
   return getErrno() == EAGAIN || getErrno() == EWOULDBLOCK || getErrno() == EINTR;
#endif
}
 
static void write_tcp_data_core(ares_channel channel, int server_idx,
               time_t now);
static void write_tcp_data(ares_channel channel,
               fd_set *write_fds, time_t now);
static void read_tcp_data(ares_channel channel, int server_idx,
             fd_set *read_fds, time_t now);
static void read_udp_packets(ares_channel channel, int server_idx,
            fd_set *read_fds,
                 time_t now);
static void process_timeouts(ares_channel channel, time_t now);
static void process_answer(ares_channel channel, unsigned char *abuf,
               int alen, int whichserver, int tcp, time_t now);
static void handle_error(ares_channel channel, int whichserver, time_t now);
static void next_server(ares_channel channel, struct query *query, time_t now);
static int next_server_new_network(ares_channel channel, struct query *query, time_t now);
static int open_tcp_socket(ares_channel channel, struct server_state *server);
static int open_udp_socket(ares_channel channel, struct server_state *server);
static int same_questions(const unsigned char *qbuf, int qlen,
              const unsigned char *abuf, int alen);
static void end_query(ares_channel channel, struct query *query, int status,
              unsigned char *abuf, int alen);
static int make_socket_non_blocking(int s);
 
/* Something interesting happened on the wire, or there was a timeout.
 * See what's up and respond accordingly.
 */
void ares_process(ares_channel channel, fd_set* read_fds, fd_set* write_fds)
{
   time_t now;
 
   time(&now);
   write_tcp_data(channel, write_fds, now);
   read_tcp_data(channel, -1, read_fds, now);
   read_udp_packets(channel, -1, read_fds, now);
   process_timeouts(channel, now);
 
   /* See if our local pseudo-db has any results. */
   /* Querying this only on timeouts is OK (is not high-performance) */
   ares_local_process_requests();
}
 
/* Something happened on wire or there was a timeout. This interface
 * is called for poll()-like systems.
 */
void ares_process_poll(ares_channel channel, int server_idx,
   int rdFd, int wrFd, time_t now) 
{
   if (server_idx != -1) {
      resip_assert(rdFd != -1 || wrFd != -1);   // at least one active
      if (wrFd != -1 && channel->servers[server_idx].tcp_socket == wrFd) 
      {
         write_tcp_data_core(channel, server_idx, now);
      }
      // writes can only be for TCP (we don't ask for UDP writable events)
      if (rdFd != -1 && channel->servers[server_idx].tcp_socket == rdFd)
         read_tcp_data(channel, server_idx, NULL, now);
      if (rdFd != -1 && channel->servers[server_idx].udp_socket == rdFd)
         read_udp_packets(channel, server_idx, NULL, now);
   }
   else 
   {
      process_timeouts(channel, now);
      ares_local_process_requests();
   }
}
 
/* If any TCP sockets select true for writing, write out queued data
 * we have for them.
 */
static void write_tcp_data_core(ares_channel channel, int server_idx,
   time_t now)
{
   struct server_state* server;
   struct send_request* sendreq;
#ifdef WIN32
   WSABUF* vec;
#else
   struct iovec* vec;
#endif
   int n, count;
 
   server = &channel->servers[server_idx];
   if (!server->qhead || server->tcp_socket == -1)
      return;
 
   /* Count the number of send queue items. */
   n = 0;
   for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
      n++;
 
#ifdef WIN32
   /* Allocate iovecs so we can send all our data at once. */
   vec = malloc(n * sizeof(WSABUF));
   if (vec)
   {
      int err;
      /* Fill in the iovecs and send. */
      n = 0;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
      {
         vec[n].buf = (char*)sendreq->data;
         vec[n].len = sendreq->len;
         n++;
      }
      err = WSASend(server->tcp_socket, vec, n, &count, 0, 0, 0);
      if (err == SOCKET_ERROR)
      {
         count = -1;
      }
      free(vec);
#else
   /* Allocate iovecs so we can send all our data at once. */
   vec = malloc(n * sizeof(struct iovec));
   if (vec)
   {
      // int err;
  /* Fill in the iovecs and send. */
      n = 0;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
      {
         vec[n].iov_base = (char*)sendreq->data;
         vec[n].iov_len = sendreq->len;
         n++;
      }
      count = writev(server->tcp_socket, vec, n);
      free(vec);
#endif
 
      if (count < 0)
      {
         handle_error(channel, server_idx, now);
         return;
      }
 
      /* Advance the send queue by as many bytes as we sent. */
      while (count)
      {
         sendreq = server->qhead;
         if (count >= sendreq->len)
         {
            count -= sendreq->len;
            server->qhead = sendreq->next;
            free(sendreq);
            if (server->qhead == NULL)
            {
               server->qtail = NULL;
               resip_assert(count == 0);
               break;
            }
         }
         else
         {
            sendreq->data += count;
            sendreq->len -= count;
            break;
         }
      }
   }
   else
   {
      /* Can't allocate iovecs; just send the first request. */
      sendreq = server->qhead;
#ifndef UNDER_CE
      count = write(server->tcp_socket, sendreq->data, sendreq->len);
#else
      count = send(server->tcp_socket, sendreq->data, sendreq->len, 0);
#endif
      if (count < 0)
      {
         handle_error(channel, server_idx, now);
         return;
      }
 
      /* Advance the send queue by as many bytes as we sent. */
      if (count == sendreq->len)
      {
         server->qhead = sendreq->next;
         if (server->qhead == NULL)
            server->qtail = NULL;
         free(sendreq);
      }
      else
      {
         sendreq->data += count;
         sendreq->len -= count;
      }
   }
   if (server->qhead == NULL && channel->poll_cb_func) 
   {
      (*(channel->poll_cb_func))(channel->poll_cb_data, channel, server_idx,
         server->tcp_socket, 1, ARES_POLLACTION_WRITEOFF);
   }
}
 
static void write_tcp_data(ares_channel channel, fd_set* write_fds, time_t now)
{
   struct server_state* server;
   int i;
 
   for (i = 0; i < channel->nservers; i++)
   {
      /* Make sure server has data to send and is selected in write_fds. */
      server = &channel->servers[i];
      if (!server->qhead || server->tcp_socket == -1)
         continue;
      if (write_fds && !FD_ISSET(server->tcp_socket, write_fds))
         continue;
 
      write_tcp_data_core(channel, i, now);
   }
}
 
/* If any TCP socket selects true for reading, read some data,
 * allocate a buffer if we finish reading the length word, and process
 * a packet if we finish reading one.
 */
static void read_tcp_data(ares_channel channel, int server_idx, fd_set* read_fds, time_t now)
{
   struct server_state* server;
   int i, count;
 
   for (i = 0; i < channel->nservers; i++)
   {
      /* Make sure the server has a socket and is selected in read_fds. */
      if (server_idx >= 0 && i != server_idx)
         continue;
      server = &channel->servers[i];
      if (server->tcp_socket == -1)
         continue;
      if (read_fds && !FD_ISSET(server->tcp_socket, read_fds))
         continue;
 
      if (server->tcp_lenbuf_pos != 2)
      {
         /* We haven't yet read a length word, so read that (or
          * what's left to read of it).
          */
#if defined UNDER_CE || defined WIN32
         count = recv(server->tcp_socket,
            server->tcp_lenbuf + server->tcp_lenbuf_pos,
            2 - server->tcp_lenbuf_pos, 0);
#else
         count = read(server->tcp_socket,
            server->tcp_lenbuf + server->tcp_lenbuf_pos,
            2 - server->tcp_lenbuf_pos);
#endif
         if (count < 0 && would_block())
            continue;
         if (count <= 0)
         {
            handle_error(channel, i, now);
            continue;
         }
 
         server->tcp_lenbuf_pos += count;
         if (server->tcp_lenbuf_pos == 2)
         {
            /* We finished reading the length word.  Decode the
                  * length and allocate a buffer for the data.
             */
            server->tcp_length = server->tcp_lenbuf[0] << 8
               | server->tcp_lenbuf[1];
            server->tcp_buffer = malloc(server->tcp_length);
            if (!server->tcp_buffer)
            {
               handle_error(channel, i, now);
               return; /* bail out on malloc failure. TODO: make this function return error codes */
            }
            server->tcp_buffer_pos = 0;
         }
      }
      else
      {
         /* Read data into the allocated buffer. */
#if defined UNDER_CE || defined WIN32
         count = recv(server->tcp_socket,
            server->tcp_buffer + server->tcp_buffer_pos,
            server->tcp_length - server->tcp_buffer_pos, 0);
#else
         count = read(server->tcp_socket,
            server->tcp_buffer + server->tcp_buffer_pos,
            server->tcp_length - server->tcp_buffer_pos);
#endif
 
         if (count < 0 && would_block())
            continue;
         if (count <= 0)
         {
            handle_error(channel, i, now);
            continue;
         }
 
         server->tcp_buffer_pos += count;
         if (server->tcp_buffer_pos == server->tcp_length)
         {
            /* We finished reading this answer; process it and
                  * prepare to read another length word.
             */
            process_answer(channel, server->tcp_buffer, server->tcp_length,
               i, 1, now);
            free(server->tcp_buffer);
            server->tcp_buffer = NULL;
            server->tcp_lenbuf_pos = 0;
         }
      }
   }
}
 
/* If any UDP sockets select true for reading, process them. */
static void read_udp_packets(ares_channel channel, int server_idx,
   fd_set* read_fds, time_t now)
{
   struct server_state* server;
   int i, count;
   unsigned char buf[PACKETSZ + 1];
 
   for (i = 0; i < channel->nservers; i++)
   {
      if (server_idx >= 0 && i != server_idx)
         continue;
      /* Make sure the server has a socket and is selected in read_fds. */
      server = &channel->servers[i];
      if (server->udp_socket == -1)
         continue;
      if (read_fds && !FD_ISSET(server->udp_socket, read_fds))
         continue;
 
      resip_assert(server->udp_socket != -1);
 
      count = recv(server->udp_socket, buf, sizeof(buf), 0);
      if (count <= 0)
      {
#if defined(WIN32)
         //int err;
         //err = WSAGetLastError();
         //err = errno;
         switch (getErrno())
         {
         case WSAEWOULDBLOCK:
            if (read_fds) {
               // read_fds is only null when using epoll
               // which shouldn't happen under windows
               // don't know why CLR is here anyways
               FD_CLR(server->udp_socket, read_fds);
            }
            continue;
         case WSAECONNABORTED:
            break;
         case WSAECONNRESET: // got an ICMP error on a previous send
            break;
         }
#else
         if (count < 0 && would_block())
            continue;
#endif
         handle_error(channel, i, now);
      }
      else
      {
         process_answer(channel, buf, count, i, 0, now);
      }
   }
}
 
/* If any queries have timed out, note the timeout and move them on. */
static void process_timeouts(ares_channel channel, time_t now)
{
   struct query* query, * next;
 
   for (query = channel->queries; query; query = next)
   {
      next = query->next;
      if (query->timeout != 0 && now >= query->timeout)
      {
         //fprintf(stderr, "kennard:ares:process_timeouts: got timeout\n");
         query->error_status = ARES_ETIMEOUT;
         next_server(channel, query, now);
      }
   }
}
 
/* Handle an answer from a server. */
static void process_answer(ares_channel channel, unsigned char* abuf,
   int alen, int whichserver, int tcp, time_t now)
{
   int id, tc, rcode;
   struct query* query;
 
   /* If there's no room in the answer for a header, we can't do much
    * with it. */
   if (alen < HFIXEDSZ)
      return;
 
   /* Grab the query ID, truncate bit, and response code from the packet. */
   id = DNS_HEADER_QID(abuf);
   tc = DNS_HEADER_TC(abuf);
   rcode = DNS_HEADER_RCODE(abuf);
 
   /* Find the query corresponding to this packet. */
   for (query = channel->queries; query; query = query->next)
   {
      if (query->qid == id)
         break;
   }
   if (!query)
      return;
 
   /* If we got a truncated UDP packet and are not ignoring truncation,
    * don't accept the packet, and switch the query to TCP if we hadn't
    * done so already.
    */
   if ((tc || alen > PACKETSZ) && !tcp && !(channel->flags & ARES_FLAG_IGNTC))
   {
      if (!query->using_tcp)
      {
         query->using_tcp = 1;
         ares__send_query(channel, query, now);
      }
      return;
   }
 
   /* Limit alen to PACKETSZ if we aren't using TCP (only relevant if we
    * are ignoring truncation.
    */
   if (alen > PACKETSZ && !tcp)
      alen = PACKETSZ;
 
   /* If we aren't passing through all error packets, discard packets
    * with SERVFAIL, NOTIMP, or REFUSED response codes.
    */
   if (!(channel->flags & ARES_FLAG_NOCHECKRESP))
   {
      if (rcode == SERVFAIL || rcode == NOTIMP || rcode == REFUSED)
      {
         query->skip_server[whichserver] = 1;
         if (query->server == whichserver)
            next_server(channel, query, now);
         return;
      }
      if (!same_questions((unsigned char*)query->qbuf, query->qlen, abuf, alen))
      {
         if (query->server == whichserver)
            next_server(channel, query, now);
         return;
      }
 
      /* 'No such name' */
      if ((channel->flags & ARES_FLAG_TRY_NEXT_SERVER_ON_RCODE3) && rcode == NXDOMAIN)
      {
         if (query->server == whichserver)
         {
            if (next_server_new_network(channel, query, now))
               return;
         }
      }
   }
 
   end_query(channel, query, ARES_SUCCESS, abuf, alen);
}
 
static void handle_error(ares_channel channel, int whichserver, time_t now)
{
   struct query* query, * next;
 
   /* Reset communications with this server. */
   //fprintf(stderr,"kennard:ares:handle_error: ...\n");
   ares__close_poll(channel, whichserver);
   ares__close_sockets(&channel->servers[whichserver]);
 
   /* Tell all queries talking to this server to move on and not try
    * this server again.
    */
   for (query = channel->queries; query != 0; query = next)
   {
      /* next_server() can end the query and free it.  Queries it adds
       * through the callback go on the head of the list, so next stays
       * valid. */
      next = query->next;
      if (query->server == whichserver)
      {
         query->skip_server[whichserver] = 1;
         next_server(channel, query, now);
      }
   }
}
 
static void next_server(ares_channel channel, struct query* query, time_t now)
{
   /* Advance to the next server or try. */
   query->server++;
   for (; query->itry < channel->tries; query->itry++)
   {
      for (; query->server < channel->nservers; query->server++)
      {
         if (!query->skip_server[query->server])
         {
            ares__send_query(channel, query, now);
            return;
         }
      }
      query->server = 0;
 
      /* Only one try if we're using TCP. */
      if (query->using_tcp)
         break;
   }
   //fprintf(stderr, "kennard:ares:next_server: ran out of servers: code %d\n", query->error_status);
   end_query(channel, query, query->error_status, NULL, 0);
}
 
/*
 * Same as next_server, but only attempt the next one if it's in a different network
 * (subnet, designated by the NIC's physical address). We don't loop around to the
 * beginning of the servers list since server responded with reply-code of 3
 * 'No such name'
 * returns:
 *  1 - query sent
 *  0 - nothing happened
 */
static int next_server_new_network(ares_channel channel, struct query* query, time_t now)
{
   if (query->itry >= channel->tries)
      return 0;
 
   query->server++;
   for (; query->server < channel->nservers; query->server++)
   {
      int i = 0;
      struct server_state* nextToTry = &channel->servers[query->server];
      if (query->skip_server[query->server])
         continue;
      if (nextToTry->physical_addr_len == 0)
         continue;
 
      // only try the next DNS server, nextToTry, if it hasn't been tried UP TO THIS POINT: query->server.
      for (i = 0; i < query->server; i++)
      {
         if ((channel->servers[i].physical_addr_len == nextToTry->physical_addr_len)
            && (memcmp(nextToTry->physical_addr, channel->servers[i].physical_addr, nextToTry->physical_addr_len) == 0))
         {
            // we've tried this network already, try next one (query->server++).
            break;
         }
      }
      if (i == query->server)
      {
         ares__send_query(channel, query, now);
         return 1;
      }
   }
   return 0;
}
 
void ares__send_query(ares_channel channel, struct query* query, time_t now)
{
   struct send_request* sendreq;
   struct server_state* server;
 
   server = &channel->servers[query->server];
   if (query->using_tcp)
   {
      int tryWrite = 0;
      /* Make sure the TCP socket for this server is set up and queue
       * a send request.
       */
      if (server->tcp_socket == -1)
      {
         if (open_tcp_socket(channel, server) == -1)
         {
            query->skip_server[query->server] = 1;
            next_server(channel, query, now);
            return;
         }
         if (channel->poll_cb_func) 
         {
            // printf("ares_send_q: pollopen tcp fd=%d\n", server->tcp_socket);
            (*(channel->poll_cb_func))(channel->poll_cb_data, channel,
               query->server, server->tcp_socket, 1, ARES_POLLACTION_OPEN);
         }
      }
      sendreq = malloc(sizeof(struct send_request));
      if (!sendreq)
      {
         end_query(channel, query, ARES_ENOMEM, NULL, 0);
         return;
      }
      sendreq->data = query->tcpbuf;
      sendreq->len = query->tcplen;
      sendreq->next = NULL;
      if (server->qtail) 
      {
         server->qtail->next = sendreq;
      }
      else 
      {
         server->qhead = sendreq;
         tryWrite = 1;
      }
      server->qtail = sendreq;
      query->timeout = 0;
      if (tryWrite)
      {
#if 0
         time_t now;
         time(&now);
         write_tcp_data(channel, query->server, now);
         /* XXX: the write code doesn't seem to handle EAGAIN properly! */
#else
         if (channel->poll_cb_func)
            (*(channel->poll_cb_func))(channel->poll_cb_data,
               channel, query->server,
               server->tcp_socket, 1, ARES_POLLACTION_WRITEON);
#endif
      }
   }
   else
   {
      if (server->udp_socket == -1)
      {
         if (open_udp_socket(channel, server) == -1)
         {
            //fprintf(stderr,"kennard:ares:send_query:open_udp failed\n");
            query->skip_server[query->server] = 1;
            next_server(channel, query, now);
            return;
         }
         if (channel->poll_cb_func) 
         {
            // printf("ares_send_q: pollopen udp fd=%d\n", server->udp_socket);
            (*(channel->poll_cb_func))(channel->poll_cb_data, channel,
               query->server, server->udp_socket, 0, ARES_POLLACTION_OPEN);
         }
      }
      if (send(server->udp_socket, query->qbuf, query->qlen, 0) == -1)
      {
         //fprintf(stderr,"kennard:ares:send_query:send_udp failed\n");
         query->skip_server[query->server] = 1;
         next_server(channel, query, now);
         return;
      }
   }
   // Start timeout for either UDP or TCP
   query->timeout = now
      + ((query->itry == 0) ? channel->timeout
         : channel->timeout << query->itry / channel->nservers);
}
 
static int open_tcp_socket(ares_channel channel, struct server_state* server)
{
   int s;
   struct sockaddr_in sin;
#ifdef USE_IPV6
   struct sockaddr_in6 sin6;
#endif
 
   /* Acquire a socket. */
#ifdef USE_IPV6
   resip_assert(server->family == AF_INET || server->family == AF_INET6);
   s = (int)socket(server->family, SOCK_STREAM, 0);
#else
   s = (int)socket(AF_INET, SOCK_STREAM, 0);
#endif
   if (s == -1)
      return -1;
 
   if (make_socket_non_blocking(s))
   {
      ares__kill_socket(s);
      return -1;
   }
 
#ifdef WIN32
#define PORTABLE_INPROGRESS_ERR WSAEWOULDBLOCK
#else
#define PORTABLE_INPROGRESS_ERR EINPROGRESS
#endif
 
   /* Connect to the server. */
#ifdef USE_IPV6
   if (server->family == AF_INET6)
   {
      memset(&sin6, 0, sizeof(sin6));
      sin6.sin6_family = AF_INET6;
      sin6.sin6_addr = server->addr6;
      sin6.sin6_port = channel->tcp_port;
      sin6.sin6_flowinfo = 0;
      sin6.sin6_scope_id = 0;
      // do i need to explicitly set the length?
 
      if (connect(s, (const struct sockaddr*)&sin6, sizeof(sin6)) == -1
         && getErrno() != PORTABLE_INPROGRESS_ERR)
      {
         ares__kill_socket(s);
         return -1;
      }
   }
   else // IPv4 DNS server
#endif
   {
      memset(&sin, 0, sizeof(sin));
      sin.sin_family = AF_INET;
      sin.sin_addr = server->addr;
      sin.sin_port = channel->tcp_port;
 
      if (connect(s, (struct sockaddr*)&sin, sizeof(sin)) == -1 && 
          getErrno() != PORTABLE_INPROGRESS_ERR)
      {
         ares__kill_socket(s);
         return -1;
      }
   }
 
   if (channel->socket_function)
   {
      channel->socket_function(s, 0, __FILE__, __LINE__);
   }
 
   server->tcp_socket = s;
   return 0;
}
 
static int connect_udp_ipv4(int s, ares_channel channel, struct server_state* server) {
   struct sockaddr_in sin;
 
   /* Connect to the server. */
   memset(&sin, 0, sizeof(sin));
   sin.sin_family = AF_INET;
   sin.sin_addr = server->addr;
   sin.sin_port = channel->udp_port;
 
   if (connect(s, (struct sockaddr*)&sin, sizeof(sin)) == -1)
   {
      //fprintf(stderr,"kennard:ares:open_udp:ipv4: connect error %d: %s\n", errno, strerror(errno));
      ares__kill_socket(s);
      return -1;
   }
   return 0;
}
 
static int open_udp_socket(ares_channel channel, struct server_state* server)
{
   u_int8_t family;
   int s;
 
#ifdef USE_IPV6
   family = server->family;
   resip_assert(family == AF_INET || family == AF_INET6);
#else
   family = AF_INET;
#endif
 
   /* Acquire a socket. */
   s = (int)socket(family, SOCK_DGRAM, 0);
 
   if (s == -1) {
      //fprintf(stderr,"kennard:ares:open_udp: no socket %d: %s\n", errno, strerror(errno));
      return -1;
   }
 
   if (make_socket_non_blocking(s))
   {
      //fprintf(stderr,"kennard:ares:open_udp: nonblocking failed %d: %s\n", errno, strerror(errno));
      ares__kill_socket(s);
      return -1;
   }
 
#ifdef USE_IPV6
   // added by Rohan 7-Sept-2004
   // should really replace sockaddr_in6 with sockaddr_storage
 
 
   /* Connect to the server. */
   if (server->family == AF_INET6)
   {
      struct sockaddr_in6 sin6;
      memset(&sin6, 0, sizeof(sin6));
      sin6.sin6_family = AF_INET6;
      sin6.sin6_addr = server->addr6;
      sin6.sin6_port = channel->udp_port;
      sin6.sin6_flowinfo = 0;
      sin6.sin6_scope_id = 0;
      // do i need to explicitly set the length?
 
      if (connect(s, (const struct sockaddr*)&sin6, sizeof(sin6)) == -1)
      {
         ares__kill_socket(s);
         return -1;
      }
   }
   else // IPv4 DNS server
   {
      if (connect_udp_ipv4(s, channel, server) == -1)
         return -1;
   }
 
#else
 
   if (connect_udp_ipv4(s, channel, server) == -1)
      return -1;
 
#endif
   if (channel->socket_function)
   {
      channel->socket_function(s, 0, __FILE__, __LINE__);
   }
 
   server->udp_socket = s;
   return 0;
}
 
static int same_questions(const unsigned char* qbuf, int qlen,
   const unsigned char* abuf, int alen)
{
   struct {
      const unsigned char* p;
      int qdcount;
      char* name;
      long int namelen;
      int type;
      int dnsclass;
   } q, a;
   int i, j;
 
   if (qlen < HFIXEDSZ || alen < HFIXEDSZ)
      return 0;
 
   /* Extract qdcount from the request and reply buffers and compare them. */
   q.qdcount = DNS_HEADER_QDCOUNT(qbuf);
   a.qdcount = DNS_HEADER_QDCOUNT(abuf);
   if (q.qdcount != a.qdcount)
      return 0;
 
   /* For each question in qbuf, find it in abuf. */
   q.p = qbuf + HFIXEDSZ;
   for (i = 0; i < q.qdcount; i++)
   {
      /* Decode the question in the query. */
      if (ares_expand_name(q.p, qbuf, qlen, &q.name, &q.namelen)
         != ARES_SUCCESS)
         return 0;
      q.p += q.namelen;
      if (q.p + QFIXEDSZ > qbuf + qlen)
      {
         free(q.name);
         return 0;
      }
      q.type = DNS_QUESTION_TYPE(q.p);
      q.dnsclass = DNS_QUESTION_CLASS(q.p);
      q.p += QFIXEDSZ;
 
      /* Search for this question in the answer. */
      a.p = abuf + HFIXEDSZ;
      for (j = 0; j < a.qdcount; j++)
      {
         /* Decode the question in the answer. */
         if (ares_expand_name(a.p, abuf, alen, &a.name, &a.namelen)
            != ARES_SUCCESS)
         {
            free(q.name);
            return 0;
         }
         a.p += a.namelen;
         if (a.p + QFIXEDSZ > abuf + alen)
         {
            free(q.name);
            free(a.name);
            return 0;
         }
         a.type = DNS_QUESTION_TYPE(a.p);
         a.dnsclass = DNS_QUESTION_CLASS(a.p);
         a.p += QFIXEDSZ;
 
         /* Compare the decoded questions. */
         if (strcasecmp(q.name, a.name) == 0 && q.type == a.type
            && q.dnsclass == a.dnsclass)
         {
            free(a.name);
            break;
         }
         free(a.name);
      }
 
      free(q.name);
      if (j == a.qdcount)
         return 0;
   }
   return 1;
}
 
static void end_query(ares_channel channel, struct query* query, int status,
   unsigned char* abuf, int alen)
{
   struct query** q;
   int i;
 
   query->callback(query->arg, status, abuf, alen);
   for (q = &channel->queries; *q; q = &(*q)->next)
   {
      if (*q == query)
         break;
   }
   *q = query->next;
   free(query->tcpbuf);
   free(query->skip_server);
   free(query);
 
   /* Simple cleanup policy: if no queries are remaining, close all
    * network sockets unless STAYOPEN is set.
    */
   if (!channel->queries && !(channel->flags & ARES_FLAG_STAYOPEN))
   {
      for (i = 0; i < channel->nservers; i++)
      {
         //printf("end_query: closing...\n");
         ares__close_poll(channel, i);
         ares__close_sockets(&channel->servers[i]);
      }
   }
}
 
void ares__kill_socket(int s)
{
#ifdef WIN32
   closesocket(s);
#else
   close(s);
#endif
}
 
int make_socket_non_blocking(int s)
{
#ifdef WIN32
   unsigned long noBlock = 1;
   int errNoBlock = ioctlsocket(s, FIONBIO, &noBlock);
   if (errNoBlock != 0)
   {
      return -1;
   }
#else
   int flags;
   // WATCHOUT: F_GETTL returns the flags, it doesn't use the argument!
   if ((flags = fcntl(s, F_GETFL, 0)) == -1)
   {
      return -1;
   }
   flags |= O_NONBLOCK; // Fixed evil but here - used to be &=
   if (fcntl(s, F_SETFL, flags) == -1)
   {
      return -1;
   }
#endif
   return 0;
}
 
void ares_process_set_poll_cb(ares_channel channel, ares_poll_cb_func* cbf, void* cbd)
{
   channel->poll_cb_func = cbf;
   channel->poll_cb_data = cbd;
}