ares_process.c

最新rtlinux内核源码

/* 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.
 *
 * CHANGELOG: this file has been modified by Sergio Perez Alca駃z <[e-mail]> 
 *            Departamento de Inform醫ica de Sistemas y Computadores          
 *            Universidad Polit閏nica de Valencia                             
 *            Valencia (Spain)    
 *            Date: April 2003                                          
 *
 */

#include "ares_private.h"
#include "ares_dns.h"

static void write_tcp_data(ares_channel channel, fd_set *write_fds,
			   time_t now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds, time_t now);
static void read_udp_packets(ares_channel channel, 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, int 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 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);

/* 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, read_fds, now);
  read_udp_packets(channel, read_fds, now);
  process_timeouts(channel, now);
}

/* If any TCP sockets select true for writing, write out queued data
 * we have for them.
 */
static void write_tcp_data(ares_channel channel, fd_set *write_fds, time_t now)
{
  struct server_state *server;
  struct send_request *sendreq;
#ifdef HAVE_WRITEV
  struct iovec *vec;
#endif
  int i, n, count;

  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
	  || !FD_ISSET(server->tcp_socket, write_fds))
	continue;

      /* Count the number of send queue items. */
      n = 0;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
	n++;

#ifdef HAVE_WRITEV
      /* Allocate iovecs so we can send all our data at once. */
      vec = malloc(n * sizeof(struct iovec));
      if (vec)
	{
	  /* 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);
	  if (count < 0)
	    {
	      handle_error(channel, i, now);
	      continue;
	    }

	  /* 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;
		  if (server->qhead == NULL)
		    server->qtail = NULL;
		  free(sendreq);
		}
	      else
		{
		  sendreq->data += count;
		  sendreq->len -= count;
		  break;
		}
	    }
	}
      else
#endif /* HAVE_WRITEV */
	{
	  /* Can't allocate iovecs; just send the first request. */
	  sendreq = server->qhead;
	  count = write(server->tcp_socket, (void *) sendreq->data, sendreq->len);
	  if (count < 0)
	    {
	      handle_error(channel, i, now);
	      continue;
	    }

	  /* 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 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, 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. */
      server = &channel->servers[i];
      if (server->tcp_socket == -1 || !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).
	   */
	  count = read(server->tcp_socket,
		       server->tcp_lenbuf + server->tcp_lenbuf_pos,
		       2 - server->tcp_lenbuf_pos);
	  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);
	      server->tcp_buffer_pos = 0;
	    }
	}
      else
	{
	  /* Read data into the allocated buffer. */
	  count = read(server->tcp_socket,
		       server->tcp_buffer + server->tcp_buffer_pos,
		       server->tcp_length - server->tcp_buffer_pos);
	  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, 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++)
    {
      /* Make sure the server has a socket and is selected in read_fds. */
      server = &channel->servers[i];
      if (server->udp_socket == -1 || !FD_ISSET(server->udp_socket, read_fds))
	continue;

      count = recv(server->udp_socket, buf, sizeof(buf), 0);
      if (count <= 0)
	handle_error(channel, i, now);

      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)
	{
	  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, int 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