Commit 4524618b authored by William Ahern's avatar William Ahern
Browse files

Handle EAGAIN/EWOULDBLOCK readiness errors, which can occur for both TCP and 

UDP even when a poll(2) or select(2) suggest otherwise.
parent 55d22ba1

ares/CHANGES

+8 −0
Original line number Diff line number Diff line 
  Changelog for the c-ares project



* June 18, 2006



- William Ahern handles EAGAIN/EWOULDBLOCK errors in most of the I/O calls

  from area_process.c.



  TODO: Handle one last EAGAIN for a UDP socket send(2) in

  ares__send_query().



* May 10, 2006



- Bram Matthys brought my attention to a libtool peculiarity where detecting

ares/ares_process.c

+38 −5
Original line number Diff line number Diff line
@@ -63,6 +63,7 @@ 
#define GET_ERRNO()  errno

#endif



static int try_again(int errnum);

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);
@@ -94,6 +95,31 @@ void ares_process(ares_channel channel, fd_set *read_fds, fd_set *write_fds) 
  process_timeouts(channel, now);

}



/* Return 1 if the specified errno describes a readiness error, or 0

 * otherwise. This is mostly for HP-UX, which could return EAGAIN or

 * EWOULDBLOCK. See this man page

 *

 * 	http://devrsrc1.external.hp.com/STKS/cgi-bin/man2html?manpage=/usr/share/man/man2.Z/send.2

 */

static int try_again(int errnum)

{

#if !defined EWOULDBLOCK && !defined EAGAIN

#error "Neither EWOULDBLOCK nor EAGAIN defined"

#endif

  switch (errnum)

    {

#ifdef EWOULDBLOCK

    case EWOULDBLOCK:

      return 1;

#endif

#if defined EAGAIN && EAGAIN != EWOULDBLOCK

    case EAGAIN:

      return 1;

#endif

    }

  return 0;

}



/* If any TCP sockets select true for writing, write out queued data

 * we have for them.

 */
@@ -136,6 +162,7 @@ static void write_tcp_data(ares_channel channel, fd_set *write_fds, time_t now) 
          free(vec);

          if (wcount < 0)

            {

              if (!try_again(GET_ERRNO()))

                  handle_error(channel, i, now);

              continue;

            }
@@ -173,6 +200,7 @@ static void write_tcp_data(ares_channel channel, fd_set *write_fds, time_t now) 


          if (scount < 0)

            {

              if (!try_again(GET_ERRNO()))

                  handle_error(channel, i, now);

              continue;

            }
@@ -224,6 +252,7 @@ static void read_tcp_data(ares_channel channel, fd_set *read_fds, time_t now) 
                       2 - server->tcp_lenbuf_pos, 0);

          if (count <= 0)

            {

              if (!(count == -1 && try_again(GET_ERRNO())))

                  handle_error(channel, i, now);

              continue;

            }
@@ -250,6 +279,7 @@ static void read_tcp_data(ares_channel channel, fd_set *read_fds, time_t now) 
                       server->tcp_length - server->tcp_buffer_pos, 0);

          if (count <= 0)

            {

              if (!(count == -1 && try_again(GET_ERRNO())))

                  handle_error(channel, i, now);

              continue;

            }
@@ -289,7 +319,9 @@ static void read_udp_packets(ares_channel channel, fd_set *read_fds, 
        continue;



      count = recv(server->udp_socket, (void *)buf, sizeof(buf), 0);

      if (count <= 0)

      if (count == -1 && try_again(GET_ERRNO()))

        continue;

      else if (count <= 0)

        handle_error(channel, i, now);



      process_answer(channel, buf, count, i, 0, now);
@@ -479,6 +511,7 @@ void ares__send_query(ares_channel channel, struct query *query, time_t now) 
      if (send(server->udp_socket, (void *)query->qbuf,

               query->qlen, 0) == -1)

        {

          /* FIXME: Handle EAGAIN here since it likely can happen. */

          query->skip_server[query->server] = 1;

          next_server(channel, query, now);

          return;