Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1445 insertions, 0 deletions

diff --git a/src/c-ares/ares_process.c b/src/c-ares/ares_process.c
new file mode 100644
index 000000000..e96489651
--- /dev/null
+++ b/src/c-ares/ares_process.c
@@ -0,0 +1,1445 @@
+
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ * Copyright (C) 2004-2017 by Daniel Stenberg
+ *
+ * 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.
+ */
+
+#include "ares_setup.h"
+
+#ifdef HAVE_SYS_UIO_H
+#  include <sys/uio.h>
+#endif
+#ifdef HAVE_NETINET_IN_H
+#  include <netinet/in.h>
+#endif
+#ifdef HAVE_NETINET_TCP_H
+#  include <netinet/tcp.h>
+#endif
+#ifdef HAVE_NETDB_H
+#  include <netdb.h>
+#endif
+#ifdef HAVE_ARPA_NAMESER_H
+#  include <arpa/nameser.h>
+#else
+#  include "nameser.h"
+#endif
+#ifdef HAVE_ARPA_NAMESER_COMPAT_H
+#  include <arpa/nameser_compat.h>
+#endif
+
+#ifdef HAVE_STRINGS_H
+#  include <strings.h>
+#endif
+#ifdef HAVE_SYS_IOCTL_H
+#  include <sys/ioctl.h>
+#endif
+#ifdef NETWARE
+#  include <sys/filio.h>
+#endif
+
+#include <assert.h>
+#include <fcntl.h>
+
+#include "ares.h"
+#include "ares_dns.h"
+#include "ares_nowarn.h"
+#include "ares_private.h"
+
+
+static int try_again(int errnum);
+static void write_tcp_data(ares_channel channel, fd_set *write_fds,
+                           ares_socket_t write_fd, struct timeval *now);
+static void read_tcp_data(ares_channel channel, fd_set *read_fds,
+                          ares_socket_t read_fd, struct timeval *now);
+static void read_udp_packets(ares_channel channel, fd_set *read_fds,
+                             ares_socket_t read_fd, struct timeval *now);
+static void advance_tcp_send_queue(ares_channel channel, int whichserver,
+                                   ssize_t num_bytes);
+static void process_timeouts(ares_channel channel, struct timeval *now);
+static void process_broken_connections(ares_channel channel,
+                                       struct timeval *now);
+static void process_answer(ares_channel channel, unsigned char *abuf,
+                           int alen, int whichserver, int tcp,
+                           struct timeval *now);
+static void handle_error(ares_channel channel, int whichserver,
+                         struct timeval *now);
+static void skip_server(ares_channel channel, struct query *query,
+                        int whichserver);
+static void next_server(ares_channel channel, struct query *query,
+                        struct timeval *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 int same_address(struct sockaddr *sa, struct ares_addr *aa);
+static void end_query(ares_channel channel, struct query *query, int status,
+                      unsigned char *abuf, int alen);
+
+/* return true if now is exactly check time or later */
+int ares__timedout(struct timeval *now,
+                   struct timeval *check)
+{
+  long secs = (now->tv_sec - check->tv_sec);
+
+  if(secs > 0)
+    return 1; /* yes, timed out */
+  if(secs < 0)
+    return 0; /* nope, not timed out */
+
+  /* if the full seconds were identical, check the sub second parts */
+  return (now->tv_usec - check->tv_usec >= 0);
+}
+
+/* add the specific number of milliseconds to the time in the first argument */
+static void timeadd(struct timeval *now, int millisecs)
+{
+  now->tv_sec += millisecs/1000;
+  now->tv_usec += (millisecs%1000)*1000;
+
+  if(now->tv_usec >= 1000000) {
+    ++(now->tv_sec);
+    now->tv_usec -= 1000000;
+  }
+}
+
+/*
+ * generic process function
+ */
+static void processfds(ares_channel channel,
+                       fd_set *read_fds, ares_socket_t read_fd,
+                       fd_set *write_fds, ares_socket_t write_fd)
+{
+  struct timeval now = ares__tvnow();
+
+  write_tcp_data(channel, write_fds, write_fd, &now);
+  read_tcp_data(channel, read_fds, read_fd, &now);
+  read_udp_packets(channel, read_fds, read_fd, &now);
+  process_timeouts(channel, &now);
+  process_broken_connections(channel, &now);
+}
+
+/* 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)
+{
+  processfds(channel, read_fds, ARES_SOCKET_BAD, write_fds, ARES_SOCKET_BAD);
+}
+
+/* Something interesting happened on the wire, or there was a timeout.
+ * See what's up and respond accordingly.
+ */
+void ares_process_fd(ares_channel channel,
+                     ares_socket_t read_fd, /* use ARES_SOCKET_BAD or valid
+                                               file descriptors */
+                     ares_socket_t write_fd)
+{
+  processfds(channel, NULL, read_fd, NULL, write_fd);
+}
+
+
+/* Return 1 if the specified error number 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;
+}
+
+static ssize_t socket_writev(ares_channel channel, ares_socket_t s, const struct iovec * vec, int len)
+{
+  if (channel->sock_funcs)
+    return channel->sock_funcs->asendv(s, vec, len, channel->sock_func_cb_data);
+
+  return writev(s, vec, len);
+}
+
+static ssize_t socket_write(ares_channel channel, ares_socket_t s, const void * data, size_t len)
+{
+  if (channel->sock_funcs)
+    {
+      struct iovec vec;
+      vec.iov_base = (void*)data;
+      vec.iov_len = len;
+      return channel->sock_funcs->asendv(s, &vec, 1, channel->sock_func_cb_data);
+    }
+  return swrite(s, data, len);
+}
+
+/* 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,
+                           ares_socket_t write_fd,
+                           struct timeval *now)
+{
+  struct server_state *server;
+  struct send_request *sendreq;
+  struct iovec *vec;
+  int i;
+  ssize_t scount;
+  ssize_t wcount;
+  size_t n;
+
+  if(!write_fds && (write_fd == ARES_SOCKET_BAD))
+    /* no possible action */
+    return;
+
+  for (i = 0; i < channel->nservers; i++)
+    {
+      /* Make sure server has data to send and is selected in write_fds or
+         write_fd. */
+      server = &channel->servers[i];
+      if (!server->qhead || server->tcp_socket == ARES_SOCKET_BAD ||
+          server->is_broken)
+        continue;
+
+      if(write_fds) {
+        if(!FD_ISSET(server->tcp_socket, write_fds))
+          continue;
+      }
+      else {
+        if(server->tcp_socket != write_fd)
+          continue;
+      }
+
+      if(write_fds)
+        /* If there's an error and we close this socket, then open
+         * another with the same fd to talk to another server, then we
+         * don't want to think that it was the new socket that was
+         * ready. This is not disastrous, but is likely to result in
+         * extra system calls and confusion. */
+        FD_CLR(server->tcp_socket, write_fds);
+
+      /* Count the number of send queue items. */
+      n = 0;
+      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
+        n++;
+
+      /* Allocate iovecs so we can send all our data at once. */
+      vec = ares_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++;
+            }
+          wcount = socket_writev(channel, server->tcp_socket, vec, (int)n);
+          ares_free(vec);
+          if (wcount < 0)
+            {
+              if (!try_again(SOCKERRNO))
+                handle_error(channel, i, now);
+              continue;
+            }
+
+          /* Advance the send queue by as many bytes as we sent. */
+          advance_tcp_send_queue(channel, i, wcount);
+        }
+      else
+        {
+          /* Can't allocate iovecs; just send the first request. */
+          sendreq = server->qhead;
+
+          scount = socket_write(channel, server->tcp_socket, sendreq->data, sendreq->len);
+          if (scount < 0)
+            {
+              if (!try_again(SOCKERRNO))
+                handle_error(channel, i, now);
+              continue;
+            }
+
+          /* Advance the send queue by as many bytes as we sent. */
+          advance_tcp_send_queue(channel, i, scount);
+        }
+    }
+}
+
+/* Consume the given number of bytes from the head of the TCP send queue. */
+static void advance_tcp_send_queue(ares_channel channel, int whichserver,
+                                   ssize_t num_bytes)
+{
+  struct send_request *sendreq;
+  struct server_state *server = &channel->servers[whichserver];
+  while (num_bytes > 0) {
+    sendreq = server->qhead;
+    if ((size_t)num_bytes >= sendreq->len) {
+      num_bytes -= sendreq->len;
+      server->qhead = sendreq->next;
+      if (sendreq->data_storage)
+        ares_free(sendreq->data_storage);
+      ares_free(sendreq);
+      if (server->qhead == NULL) {
+        SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
+        server->qtail = NULL;
+
+        /* qhead is NULL so we cannot continue this loop */
+        break;
+      }
+    }
+    else {
+      sendreq->data += num_bytes;
+      sendreq->len -= num_bytes;
+      num_bytes = 0;
+    }
+  }
+}
+
+static ssize_t socket_recvfrom(ares_channel channel,
+   ares_socket_t s,
+   void * data,
+   size_t data_len,
+   int flags,
+   struct sockaddr *from,
+   socklen_t *from_len)
+{
+   if (channel->sock_funcs)
+      return channel->sock_funcs->arecvfrom(s, data, data_len,
+	 flags, from, from_len,
+	 channel->sock_func_cb_data);
+
+#ifdef HAVE_RECVFROM
+   return recvfrom(s, data, data_len, flags, from, from_len);
+#else
+   return sread(s, data, data_len);
+#endif
+}
+
+static ssize_t socket_recv(ares_channel channel,
+   ares_socket_t s,
+   void * data,
+   size_t data_len)
+{
+   if (channel->sock_funcs)
+      return channel->sock_funcs->arecvfrom(s, data, data_len, 0, 0, 0,
+	 channel->sock_func_cb_data);
+
+   return sread(s, data, data_len);
+}
+
+/* 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,
+                          ares_socket_t read_fd, struct timeval *now)
+{
+  struct server_state *server;
+  int i;
+  ssize_t count;
+
+  if(!read_fds && (read_fd == ARES_SOCKET_BAD))
+    /* no possible action */
+    return;
+
+  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 == ARES_SOCKET_BAD || server->is_broken)
+        continue;
+
+      if(read_fds) {
+        if(!FD_ISSET(server->tcp_socket, read_fds))
+          continue;
+      }
+      else {
+        if(server->tcp_socket != read_fd)
+          continue;
+      }
+
+      if(read_fds)
+        /* If there's an error and we close this socket, then open another
+         * with the same fd to talk to another server, then we don't want to
+         * think that it was the new socket that was ready. This is not
+         * disastrous, but is likely to result in extra system calls and
+         * confusion. */
+        FD_CLR(server->tcp_socket, read_fds);
+
+      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 = socket_recv(channel, server->tcp_socket,
+			      server->tcp_lenbuf + server->tcp_lenbuf_pos,
+			      2 - server->tcp_lenbuf_pos);
+          if (count <= 0)
+            {
+              if (!(count == -1 && try_again(SOCKERRNO)))
+                handle_error(channel, i, now);
+              continue;
+            }
+
+          server->tcp_lenbuf_pos += (int)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 = ares_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. */
+          count = socket_recv(channel, server->tcp_socket,
+			      server->tcp_buffer + server->tcp_buffer_pos,
+			      server->tcp_length - server->tcp_buffer_pos);
+          if (count <= 0)
+            {
+              if (!(count == -1 && try_again(SOCKERRNO)))
+                handle_error(channel, i, now);
+              continue;
+            }
+
+          server->tcp_buffer_pos += (int)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);
+              ares_free(server->tcp_buffer);
+              server->tcp_buffer = NULL;
+              server->tcp_lenbuf_pos = 0;
+              server->tcp_buffer_pos = 0;
+            }
+        }
+    }
+}
+
+/* If any UDP sockets select true for reading, process them. */
+static void read_udp_packets(ares_channel channel, fd_set *read_fds,
+                             ares_socket_t read_fd, struct timeval *now)
+{
+  struct server_state *server;
+  int i;
+  ssize_t count;
+  unsigned char buf[MAXENDSSZ + 1];
+#ifdef HAVE_RECVFROM
+  ares_socklen_t fromlen;
+  union {
+    struct sockaddr     sa;
+    struct sockaddr_in  sa4;
+    struct sockaddr_in6 sa6;
+  } from;
+#endif
+
+  if(!read_fds && (read_fd == ARES_SOCKET_BAD))
+    /* no possible action */
+    return;
+
+  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 == ARES_SOCKET_BAD || server->is_broken)
+        continue;
+
+      if(read_fds) {
+        if(!FD_ISSET(server->udp_socket, read_fds))
+          continue;
+      }
+      else {
+        if(server->udp_socket != read_fd)
+          continue;
+      }
+
+      if(read_fds)
+        /* If there's an error and we close this socket, then open
+         * another with the same fd to talk to another server, then we
+         * don't want to think that it was the new socket that was
+         * ready. This is not disastrous, but is likely to result in
+         * extra system calls and confusion. */
+        FD_CLR(server->udp_socket, read_fds);
+
+      /* To reduce event loop overhead, read and process as many
+       * packets as we can. */
+      do {
+        if (server->udp_socket == ARES_SOCKET_BAD)
+          count = 0;
+
+        else {
+          if (server->addr.family == AF_INET)
+            fromlen = sizeof(from.sa4);
+          else
+            fromlen = sizeof(from.sa6);
+          count = socket_recvfrom(channel, server->udp_socket, (void *)buf,
+                                  sizeof(buf), 0, &from.sa, &fromlen);
+        }
+
+        if (count == -1 && try_again(SOCKERRNO))
+          continue;
+        else if (count <= 0)
+          handle_error(channel, i, now);
+#ifdef HAVE_RECVFROM
+        else if (!same_address(&from.sa, &server->addr))
+          /* The address the response comes from does not match the address we
+           * sent the request to. Someone may be attempting to perform a cache
+           * poisoning attack. */
+          break;
+#endif
+        else
+          process_answer(channel, buf, (int)count, i, 0, now);
+       } while (count > 0);
+    }
+}
+
+/* If any queries have timed out, note the timeout and move them on. */
+static void process_timeouts(ares_channel channel, struct timeval *now)
+{
+  time_t t;  /* the time of the timeouts we're processing */
+  struct query *query;
+  struct list_node* list_head;
+  struct list_node* list_node;
+
+  /* Process all the timeouts that have fired since the last time we processed
+   * timeouts. If things are going well, then we'll have hundreds/thousands of
+   * queries that fall into future buckets, and only a handful of requests
+   * that fall into the "now" bucket, so this should be quite quick.
+   */
+  for (t = channel->last_timeout_processed; t <= now->tv_sec; t++)
+    {
+      list_head = &(channel->queries_by_timeout[t % ARES_TIMEOUT_TABLE_SIZE]);
+      for (list_node = list_head->next; list_node != list_head; )
+        {
+          query = list_node->data;
+          list_node = list_node->next;  /* in case the query gets deleted */
+          if (query->timeout.tv_sec && ares__timedout(now, &query->timeout))
+            {
+              query->error_status = ARES_ETIMEOUT;
+              ++query->timeouts;
+              next_server(channel, query, now);
+            }
+        }
+     }
+  channel->last_timeout_processed = now->tv_sec;
+}
+
+/* Handle an answer from a server. */
+static void process_answer(ares_channel channel, unsigned char *abuf,
+                           int alen, int whichserver, int tcp,
+                           struct timeval *now)
+{
+  int tc, rcode, packetsz;
+  unsigned short id;
+  struct query *query;
+  struct list_node* list_head;
+  struct list_node* list_node;
+
+  /* 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. The queries are
+   * hashed/bucketed by query id, so this lookup should be quick.  Note that
+   * both the query id and the questions must be the same; when the query id
+   * wraps around we can have multiple outstanding queries with the same query
+   * id, so we need to check both the id and question.
+   */
+  query = NULL;
+  list_head = &(channel->queries_by_qid[id % ARES_QID_TABLE_SIZE]);
+  for (list_node = list_head->next; list_node != list_head;
+       list_node = list_node->next)
+    {
+      struct query *q = list_node->data;
+      if ((q->qid == id) && same_questions(q->qbuf, q->qlen, abuf, alen))
+        {
+          query = q;
+          break;
+        }
+    }
+  if (!query)
+    return;
+
+  packetsz = PACKETSZ;
+  /* If we use EDNS and server answers with one of these RCODES, the protocol
+   * extension is not understood by the responder. We must retry the query
+   * without EDNS enabled.
+   */
+  if (channel->flags & ARES_FLAG_EDNS)
+  {
+      packetsz = channel->ednspsz;
+      if (rcode == NOTIMP || rcode == FORMERR || rcode == SERVFAIL)
+      {
+          int qlen = (query->tcplen - 2) - EDNSFIXEDSZ;
+          channel->flags ^= ARES_FLAG_EDNS;
+          query->tcplen -= EDNSFIXEDSZ;
+          query->qlen -= EDNSFIXEDSZ;
+          query->tcpbuf[0] = (unsigned char)((qlen >> 8) & 0xff);
+          query->tcpbuf[1] = (unsigned char)(qlen & 0xff);
+          DNS_HEADER_SET_ARCOUNT(query->tcpbuf + 2, 0);
+          query->tcpbuf = ares_realloc(query->tcpbuf, query->tcplen);
+          query->qbuf = query->tcpbuf + 2;
+          ares__send_query(channel, query, now);
+          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)
+        {
+          skip_server(channel, query, whichserver);
+          if (query->server == whichserver)
+            next_server(channel, query, now);
+          return;
+        }
+    }
+
+  end_query(channel, query, ARES_SUCCESS, abuf, alen);
+}
+
+/* Close all the connections that are no longer usable. */
+static void process_broken_connections(ares_channel channel,
+                                       struct timeval *now)
+{
+  int i;
+  for (i = 0; i < channel->nservers; i++)
+    {
+      struct server_state *server = &channel->servers[i];
+      if (server->is_broken)
+        {
+          handle_error(channel, i, now);
+        }
+    }
+}
+
+/* Swap the contents of two lists */
+static void swap_lists(struct list_node* head_a,
+                       struct list_node* head_b)
+{
+  int is_a_empty = ares__is_list_empty(head_a);
+  int is_b_empty = ares__is_list_empty(head_b);
+  struct list_node old_a = *head_a;
+  struct list_node old_b = *head_b;
+
+  if (is_a_empty) {
+    ares__init_list_head(head_b);
+  } else {
+    *head_b = old_a;
+    old_a.next->prev = head_b;
+    old_a.prev->next = head_b;
+  }
+  if (is_b_empty) {
+    ares__init_list_head(head_a);
+  } else {
+    *head_a = old_b;
+    old_b.next->prev = head_a;
+    old_b.prev->next = head_a;
+  }
+}
+
+static void handle_error(ares_channel channel, int whichserver,
+                         struct timeval *now)
+{
+  struct server_state *server;
+  struct query *query;
+  struct list_node list_head;
+  struct list_node* list_node;
+
+  server = &channel->servers[whichserver];
+
+  /* Reset communications with this server. */
+  ares__close_sockets(channel, server);
+
+  /* Tell all queries talking to this server to move on and not try this
+   * server again. We steal the current list of queries that were in-flight to
+   * this server, since when we call next_server this can cause the queries to
+   * be re-sent to this server, which will re-insert these queries in that
+   * same server->queries_to_server list.
+   */
+  ares__init_list_head(&list_head);
+  swap_lists(&list_head, &(server->queries_to_server));
+  for (list_node = list_head.next; list_node != &list_head; )
+    {
+      query = list_node->data;
+      list_node = list_node->next;  /* in case the query gets deleted */
+      assert(query->server == whichserver);
+      skip_server(channel, query, whichserver);
+      next_server(channel, query, now);
+    }
+  /* Each query should have removed itself from our temporary list as
+   * it re-sent itself or finished up...
+   */
+  assert(ares__is_list_empty(&list_head));
+}
+
+static void skip_server(ares_channel channel, struct query *query,
+                        int whichserver)
+{
+  /* The given server gave us problems with this query, so if we have the
+   * luxury of using other servers, then let's skip the potentially broken
+   * server and just use the others. If we only have one server and we need to
+   * retry then we should just go ahead and re-use that server, since it's our
+   * only hope; perhaps we just got unlucky, and retrying will work (eg, the
+   * server timed out our TCP connection just as we were sending another
+   * request).
+   */
+  if (channel->nservers > 1)
+    {
+      query->server_info[whichserver].skip_server = 1;
+    }
+}
+
+static void next_server(ares_channel channel, struct query *query,
+                        struct timeval *now)
+{
+  /* We need to try each server channel->tries times. We have channel->nservers
+   * servers to try. In total, we need to do channel->nservers * channel->tries
+   * attempts. Use query->try to remember how many times we already attempted
+   * this query. Use modular arithmetic to find the next server to try. */
+  while (++(query->try_count) < (channel->nservers * channel->tries))
+    {
+      struct server_state *server;
+
+      /* Move on to the next server. */
+      query->server = (query->server + 1) % channel->nservers;
+      server = &channel->servers[query->server];
+
+      /* We don't want to use this server if (1) we decided this connection is
+       * broken, and thus about to be closed, (2) we've decided to skip this
+       * server because of earlier errors we encountered, or (3) we already
+       * sent this query over this exact connection.
+       */
+      if (!server->is_broken &&
+           !query->server_info[query->server].skip_server &&
+           !(query->using_tcp &&
+             (query->server_info[query->server].tcp_connection_generation ==
+              server->tcp_connection_generation)))
+        {
+           ares__send_query(channel, query, now);
+           return;
+        }
+
+      /* You might think that with TCP we only need one try. However, even
+       * when using TCP, servers can time-out our connection just as we're
+       * sending a request, or close our connection because they die, or never
+       * send us a reply because they get wedged or tickle a bug that drops
+       * our request.
+       */
+    }
+
+  /* If we are here, all attempts to perform query failed. */
+  end_query(channel, query, query->error_status, NULL, 0);
+}
+
+void ares__send_query(ares_channel channel, struct query *query,
+                      struct timeval *now)
+{
+  struct send_request *sendreq;
+  struct server_state *server;
+  int timeplus;
+
+  server = &channel->servers[query->server];
+  if (query->using_tcp)
+    {
+      /* Make sure the TCP socket for this server is set up and queue
+       * a send request.
+       */
+      if (server->tcp_socket == ARES_SOCKET_BAD)
+        {
+          if (open_tcp_socket(channel, server) == -1)
+            {
+              skip_server(channel, query, query->server);
+              next_server(channel, query, now);
+              return;
+            }
+        }
+      sendreq = ares_malloc(sizeof(struct send_request));
+      if (!sendreq)
+        {
+        end_query(channel, query, ARES_ENOMEM, NULL, 0);
+          return;
+        }
+      memset(sendreq, 0, sizeof(struct send_request));
+      /* To make the common case fast, we avoid copies by using the query's
+       * tcpbuf for as long as the query is alive. In the rare case where the
+       * query ends while it's queued for transmission, then we give the
+       * sendreq its own copy of the request packet and put it in
+       * sendreq->data_storage.
+       */
+      sendreq->data_storage = NULL;
+      sendreq->data = query->tcpbuf;
+      sendreq->len = query->tcplen;
+      sendreq->owner_query = query;
+      sendreq->next = NULL;
+      if (server->qtail)
+        server->qtail->next = sendreq;
+      else
+        {
+          SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 1);
+          server->qhead = sendreq;
+        }
+      server->qtail = sendreq;
+      query->server_info[query->server].tcp_connection_generation =
+        server->tcp_connection_generation;
+    }
+  else
+    {
+      if (server->udp_socket == ARES_SOCKET_BAD)
+        {
+          if (open_udp_socket(channel, server) == -1)
+            {
+              skip_server(channel, query, query->server);
+              next_server(channel, query, now);
+              return;
+            }
+        }
+      if (socket_write(channel, server->udp_socket, query->qbuf, query->qlen) == -1)
+        {
+          /* FIXME: Handle EAGAIN here since it likely can happen. */
+          skip_server(channel, query, query->server);
+          next_server(channel, query, now);
+          return;
+        }
+    }
+    timeplus = channel->timeout << (query->try_count / channel->nservers);
+    timeplus = (timeplus * (9 + (rand () & 7))) / 16;
+    query->timeout = *now;
+    timeadd(&query->timeout, timeplus);
+    /* Keep track of queries bucketed by timeout, so we can process
+     * timeout events quickly.
+     */
+    ares__remove_from_list(&(query->queries_by_timeout));
+    ares__insert_in_list(
+        &(query->queries_by_timeout),
+        &(channel->queries_by_timeout[query->timeout.tv_sec %
+                                      ARES_TIMEOUT_TABLE_SIZE]));
+
+    /* Keep track of queries bucketed by server, so we can process server
+     * errors quickly.
+     */
+    ares__remove_from_list(&(query->queries_to_server));
+    ares__insert_in_list(&(query->queries_to_server),
+                         &(server->queries_to_server));
+}
+
+/*
+ * setsocknonblock sets the given socket to either blocking or non-blocking
+ * mode based on the 'nonblock' boolean argument. This function is highly
+ * portable.
+ */
+static int setsocknonblock(ares_socket_t sockfd,    /* operate on this */
+                           int nonblock   /* TRUE or FALSE */)
+{
+#if defined(USE_BLOCKING_SOCKETS)
+
+  return 0; /* returns success */
+
+#elif defined(HAVE_FCNTL_O_NONBLOCK)
+
+  /* most recent unix versions */
+  int flags;
+  flags = fcntl(sockfd, F_GETFL, 0);
+  if (FALSE != nonblock)
+    return fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
+  else
+    return fcntl(sockfd, F_SETFL, flags & (~O_NONBLOCK));  /* LCOV_EXCL_LINE */
+
+#elif defined(HAVE_IOCTL_FIONBIO)
+
+  /* older unix versions */
+  int flags = nonblock ? 1 : 0;
+  return ioctl(sockfd, FIONBIO, &flags);
+
+#elif defined(HAVE_IOCTLSOCKET_FIONBIO)
+
+#ifdef WATT32
+  char flags = nonblock ? 1 : 0;
+#else
+  /* Windows */
+  unsigned long flags = nonblock ? 1UL : 0UL;
+#endif
+  return ioctlsocket(sockfd, FIONBIO, &flags);
+
+#elif defined(HAVE_IOCTLSOCKET_CAMEL_FIONBIO)
+
+  /* Amiga */
+  long flags = nonblock ? 1L : 0L;
+  return IoctlSocket(sockfd, FIONBIO, flags);
+
+#elif defined(HAVE_SETSOCKOPT_SO_NONBLOCK)
+
+  /* BeOS */
+  long b = nonblock ? 1L : 0L;
+  return setsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b));
+
+#else
+#  error "no non-blocking method was found/used/set"
+#endif
+}
+
+static int configure_socket(ares_socket_t s, int family, ares_channel channel)
+{
+  union {
+    struct sockaddr     sa;
+    struct sockaddr_in  sa4;
+    struct sockaddr_in6 sa6;
+  } local;
+
+  /* do not set options for user-managed sockets */
+  if (channel->sock_funcs)
+    return 0;
+
+  (void)setsocknonblock(s, TRUE);
+
+#if defined(FD_CLOEXEC) && !defined(MSDOS)
+  /* Configure the socket fd as close-on-exec. */
+  if (fcntl(s, F_SETFD, FD_CLOEXEC) == -1)
+    return -1;  /* LCOV_EXCL_LINE */
+#endif
+
+  /* Set the socket's send and receive buffer sizes. */
+  if ((channel->socket_send_buffer_size > 0) &&
+      setsockopt(s, SOL_SOCKET, SO_SNDBUF,
+                 (void *)&channel->socket_send_buffer_size,
+                 sizeof(channel->socket_send_buffer_size)) == -1)
+    return -1;
+
+  if ((channel->socket_receive_buffer_size > 0) &&
+      setsockopt(s, SOL_SOCKET, SO_RCVBUF,
+                 (void *)&channel->socket_receive_buffer_size,
+                 sizeof(channel->socket_receive_buffer_size)) == -1)
+    return -1;
+
+#ifdef SO_BINDTODEVICE
+  if (channel->local_dev_name[0]) {
+    if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE,
+                   channel->local_dev_name, sizeof(channel->local_dev_name))) {
+      /* Only root can do this, and usually not fatal if it doesn't work, so */
+      /* just continue on. */
+    }
+  }
+#endif
+
+  if (family == AF_INET) {
+    if (channel->local_ip4) {
+      memset(&local.sa4, 0, sizeof(local.sa4));
+      local.sa4.sin_family = AF_INET;
+      local.sa4.sin_addr.s_addr = htonl(channel->local_ip4);
+      if (bind(s, &local.sa, sizeof(local.sa4)) < 0)
+        return -1;
+    }
+  }
+  else if (family == AF_INET6) {
+    if (memcmp(channel->local_ip6, &ares_in6addr_any,
+               sizeof(channel->local_ip6)) != 0) {
+      memset(&local.sa6, 0, sizeof(local.sa6));
+      local.sa6.sin6_family = AF_INET6;
+      memcpy(&local.sa6.sin6_addr, channel->local_ip6,
+             sizeof(channel->local_ip6));
+      if (bind(s, &local.sa, sizeof(local.sa6)) < 0)
+        return -1;
+    }
+  }
+
+  return 0;
+}
+
+static int open_socket(ares_channel channel, int af, int type, int protocol)
+{
+  if (channel->sock_funcs != 0)
+    return channel->sock_funcs->asocket(af,
+                                        type,
+                                        protocol,
+                                        channel->sock_func_cb_data);
+
+  return socket(af, type, protocol);
+}
+
+static int connect_socket(ares_channel channel, ares_socket_t sockfd,
+			  const struct sockaddr * addr,
+	                  socklen_t addrlen)
+{
+   if (channel->sock_funcs != 0)
+      return channel->sock_funcs->aconnect(sockfd,
+	                                   addr,
+	                                   addrlen,
+	                                   channel->sock_func_cb_data);
+
+   return connect(sockfd, addr, addrlen);
+}
+
+static int open_tcp_socket(ares_channel channel, struct server_state *server)
+{
+  ares_socket_t s;
+  int opt;
+  ares_socklen_t salen;
+  union {
+    struct sockaddr_in  sa4;
+    struct sockaddr_in6 sa6;
+  } saddr;
+  struct sockaddr *sa;
+
+  switch (server->addr.family)
+    {
+      case AF_INET:
+        sa = (void *)&saddr.sa4;
+        salen = sizeof(saddr.sa4);
+        memset(sa, 0, salen);
+        saddr.sa4.sin_family = AF_INET;
+        if (server->addr.tcp_port) {
+          saddr.sa4.sin_port = aresx_sitous(server->addr.tcp_port);
+        } else {
+          saddr.sa4.sin_port = aresx_sitous(channel->tcp_port);
+        }
+        memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
+               sizeof(server->addr.addrV4));
+        break;
+      case AF_INET6:
+        sa = (void *)&saddr.sa6;
+        salen = sizeof(saddr.sa6);
+        memset(sa, 0, salen);
+        saddr.sa6.sin6_family = AF_INET6;
+        if (server->addr.tcp_port) {
+          saddr.sa6.sin6_port = aresx_sitous(server->addr.tcp_port);
+        } else {
+          saddr.sa6.sin6_port = aresx_sitous(channel->tcp_port);
+        }
+        memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
+               sizeof(server->addr.addrV6));
+        break;
+      default:
+        return -1;  /* LCOV_EXCL_LINE */
+    }
+
+  /* Acquire a socket. */
+  s = open_socket(channel, server->addr.family, SOCK_STREAM, 0);
+  if (s == ARES_SOCKET_BAD)
+    return -1;
+
+  /* Configure it. */
+  if (configure_socket(s, server->addr.family, channel) < 0)
+    {
+       ares__socket_close(channel, s);
+       return -1;
+    }
+
+#ifdef TCP_NODELAY
+  /*
+   * Disable the Nagle algorithm (only relevant for TCP sockets, and thus not
+   * in configure_socket). In general, in DNS lookups we're pretty much
+   * interested in firing off a single request and then waiting for a reply,
+   * so batching isn't very interesting.
+   */
+  opt = 1;
+  if (channel->sock_funcs == 0
+     &&
+     setsockopt(s, IPPROTO_TCP, TCP_NODELAY,
+                (void *)&opt, sizeof(opt)) == -1)
+    {
+       ares__socket_close(channel, s);
+       return -1;
+    }
+#endif
+
+  if (channel->sock_config_cb)
+    {
+      int err = channel->sock_config_cb(s, SOCK_STREAM,
+                                        channel->sock_config_cb_data);
+      if (err < 0)
+        {
+          ares__socket_close(channel, s);
+          return err;
+        }
+    }
+
+  /* Connect to the server. */
+  if (connect_socket(channel, s, sa, salen) == -1)
+    {
+      int err = SOCKERRNO;
+
+      if (err != EINPROGRESS && err != EWOULDBLOCK)
+        {
+          ares__socket_close(channel, s);
+          return -1;
+        }
+    }
+
+  if (channel->sock_create_cb)
+    {
+      int err = channel->sock_create_cb(s, SOCK_STREAM,
+                                        channel->sock_create_cb_data);
+      if (err < 0)
+        {
+          ares__socket_close(channel, s);
+          return err;
+        }
+    }
+
+  SOCK_STATE_CALLBACK(channel, s, 1, 0);
+  server->tcp_buffer_pos = 0;
+  server->tcp_socket = s;
+  server->tcp_connection_generation = ++channel->tcp_connection_generation;
+  return 0;
+}
+
+static int open_udp_socket(ares_channel channel, struct server_state *server)
+{
+  ares_socket_t s;
+  ares_socklen_t salen;
+  union {
+    struct sockaddr_in  sa4;
+    struct sockaddr_in6 sa6;
+  } saddr;
+  struct sockaddr *sa;
+
+  switch (server->addr.family)
+    {
+      case AF_INET:
+        sa = (void *)&saddr.sa4;
+        salen = sizeof(saddr.sa4);
+        memset(sa, 0, salen);
+        saddr.sa4.sin_family = AF_INET;
+        if (server->addr.udp_port) {
+          saddr.sa4.sin_port = aresx_sitous(server->addr.udp_port);
+        } else {
+          saddr.sa4.sin_port = aresx_sitous(channel->udp_port);
+        }
+        memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
+               sizeof(server->addr.addrV4));
+        break;
+      case AF_INET6:
+        sa = (void *)&saddr.sa6;
+        salen = sizeof(saddr.sa6);
+        memset(sa, 0, salen);
+        saddr.sa6.sin6_family = AF_INET6;
+        if (server->addr.udp_port) {
+          saddr.sa6.sin6_port = aresx_sitous(server->addr.udp_port);
+        } else {
+          saddr.sa6.sin6_port = aresx_sitous(channel->udp_port);
+        }
+        memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
+               sizeof(server->addr.addrV6));
+        break;
+      default:
+        return -1;  /* LCOV_EXCL_LINE */
+    }
+
+  /* Acquire a socket. */
+  s = open_socket(channel, server->addr.family, SOCK_DGRAM, 0);
+  if (s == ARES_SOCKET_BAD)
+    return -1;
+
+  /* Set the socket non-blocking. */
+  if (configure_socket(s, server->addr.family, channel) < 0)
+    {
+       ares__socket_close(channel, s);
+       return -1;
+    }
+
+  if (channel->sock_config_cb)
+    {
+      int err = channel->sock_config_cb(s, SOCK_DGRAM,
+                                        channel->sock_config_cb_data);
+      if (err < 0)
+        {
+          ares__socket_close(channel, s);
+          return err;
+        }
+    }
+
+  /* Connect to the server. */
+  if (connect_socket(channel, s, sa, salen) == -1)
+    {
+      int err = SOCKERRNO;
+
+      if (err != EINPROGRESS && err != EWOULDBLOCK)
+        {
+          ares__socket_close(channel, s);
+          return -1;
+        }
+    }
+
+  if (channel->sock_create_cb)
+    {
+      int err = channel->sock_create_cb(s, SOCK_DGRAM,
+                                        channel->sock_create_cb_data);
+      if (err < 0)
+        {
+          ares__socket_close(channel, s);
+          return err;
+        }
+    }
+
+  SOCK_STATE_CALLBACK(channel, s, 1, 0);
+
+  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 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)
+        {
+          ares_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)
+            {
+              ares_free(q.name);
+              return 0;
+            }
+          a.p += a.namelen;
+          if (a.p + QFIXEDSZ > abuf + alen)
+            {
+              ares_free(q.name);
+              ares_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)
+            {
+              ares_free(a.name);
+              break;
+            }
+          ares_free(a.name);
+        }
+
+      ares_free(q.name);
+      if (j == a.qdcount)
+        return 0;
+    }
+  return 1;
+}
+
+static int same_address(struct sockaddr *sa, struct ares_addr *aa)
+{
+  void *addr1;
+  void *addr2;
+
+  if (sa->sa_family == aa->family)
+    {
+      switch (aa->family)
+        {
+          case AF_INET:
+            addr1 = &aa->addrV4;
+            addr2 = &((struct sockaddr_in *)sa)->sin_addr;
+            if (memcmp(addr1, addr2, sizeof(aa->addrV4)) == 0)
+              return 1; /* match */
+            break;
+          case AF_INET6:
+            addr1 = &aa->addrV6;
+            addr2 = &((struct sockaddr_in6 *)sa)->sin6_addr;
+            if (memcmp(addr1, addr2, sizeof(aa->addrV6)) == 0)
+              return 1; /* match */
+            break;
+          default:
+            break;  /* LCOV_EXCL_LINE */
+        }
+    }
+  return 0; /* different */
+}
+
+static void end_query (ares_channel channel, struct query *query, int status,
+                       unsigned char *abuf, int alen)
+{
+  int i;
+
+  /* First we check to see if this query ended while one of our send
+   * queues still has pointers to it.
+   */
+  for (i = 0; i < channel->nservers; i++)
+    {
+      struct server_state *server = &channel->servers[i];
+      struct send_request *sendreq;
+      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
+        if (sendreq->owner_query == query)
+          {
+            sendreq->owner_query = NULL;
+            assert(sendreq->data_storage == NULL);
+            if (status == ARES_SUCCESS)
+              {
+                /* We got a reply for this query, but this queued sendreq
+                 * points into this soon-to-be-gone query's tcpbuf. Probably
+                 * this means we timed out and queued the query for
+                 * retransmission, then received a response before actually
+                 * retransmitting. This is perfectly fine, so we want to keep
+                 * the connection running smoothly if we can. But in the worst
+                 * case we may have sent only some prefix of the query, with
+                 * some suffix of the query left to send. Also, the buffer may
+                 * be queued on multiple queues. To prevent dangling pointers
+                 * to the query's tcpbuf and handle these cases, we just give
+                 * such sendreqs their own copy of the query packet.
+                 */
+               sendreq->data_storage = ares_malloc(sendreq->len);
+               if (sendreq->data_storage != NULL)
+                 {
+                   memcpy(sendreq->data_storage, sendreq->data, sendreq->len);
+                   sendreq->data = sendreq->data_storage;
+                 }
+              }
+            if ((status != ARES_SUCCESS) || (sendreq->data_storage == NULL))
+              {
+                /* We encountered an error (probably a timeout, suggesting the
+                 * DNS server we're talking to is probably unreachable,
+                 * wedged, or severely overloaded) or we couldn't copy the
+                 * request, so mark the connection as broken. When we get to
+                 * process_broken_connections() we'll close the connection and
+                 * try to re-send requests to another server.
+                 */
+               server->is_broken = 1;
+               /* Just to be paranoid, zero out this sendreq... */
+               sendreq->data = NULL;
+               sendreq->len = 0;
+             }
+          }
+    }
+
+  /* Invoke the callback */
+  query->callback(query->arg, status, query->timeouts, abuf, alen);
+  ares__free_query(query);
+
+  /* Simple cleanup policy: if no queries are remaining, close all network
+   * sockets unless STAYOPEN is set.
+   */
+  if (!(channel->flags & ARES_FLAG_STAYOPEN) &&
+      ares__is_list_empty(&(channel->all_queries)))
+    {
+      for (i = 0; i < channel->nservers; i++)
+        ares__close_sockets(channel, &channel->servers[i]);
+    }
+}
+
+void ares__free_query(struct query *query)
+{
+  /* Remove the query from all the lists in which it is linked */
+  ares__remove_from_list(&(query->queries_by_qid));
+  ares__remove_from_list(&(query->queries_by_timeout));
+  ares__remove_from_list(&(query->queries_to_server));
+  ares__remove_from_list(&(query->all_queries));
+  /* Zero out some important stuff, to help catch bugs */
+  query->callback = NULL;
+  query->arg = NULL;
+  /* Deallocate the memory associated with the query */
+  ares_free(query->tcpbuf);
+  ares_free(query->server_info);
+  ares_free(query);
+}
+
+void ares__socket_close(ares_channel channel, ares_socket_t s)
+{
+  if (channel->sock_funcs)
+    channel->sock_funcs->aclose(s, channel->sock_func_cb_data);
+  else
+    sclose(s);
+}