ares_search.c

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/* 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 Alcañiz <serpeal@disca.upv.es> 
 *            Departamento de Informática de Sistemas y Computadores          
 *            Universidad Politécnica de Valencia                             
 *            Valencia (Spain)    
 *            Date: April 2003                                          
 *
 */

#include "ares_private.h"

struct search_query {
  /* Arguments passed to ares_search */
  ares_channel channel;
  char *name;                   /* copied into an allocated buffer */
  int dnsclass;
  int type;
  ares_callback callback;
  void *arg;

  int status_as_is;             /* error status from trying as-is */
  int next_domain;              /* next search domain to try */
  int trying_as_is;             /* current query is for name as-is */
};

static void search_callback(void *arg, int status, unsigned char *abuf,
                            int alen);
static void end_squery(struct search_query *squery, int status,
                       unsigned char *abuf, int alen);
static int cat_domain(const char *name, const char *domain, char **s);
static int single_domain(ares_channel channel, const char *name, char **s);

void ares_search(ares_channel channel, const char *name, int dnsclass,
                 int type, ares_callback callback, void *arg)
{
  struct search_query *squery;
  char *s;
  const char *p;
  int status, ndots;
  
  /* If name only yields one domain to search, then we don't have
   * to keep extra state, so just do an ares_query().
   */
  status = single_domain(channel, name, &s);
  if (status != ARES_SUCCESS)
    {
      callback(arg, status, NULL, 0);
      return;
    }
  if (s)
    {
      ares_query(channel, s, dnsclass, type, callback, arg);
      free(s);
      return;
    }
  
  /* Allocate a search_query structure to hold the state necessary for
   * doing multiple lookups.
   */
  squery = malloc(sizeof(struct search_query));
  if (!squery)
    {
      callback(arg, ARES_ENOMEM, NULL, 0);
      return;
    }
  squery->channel = channel;
  squery->name = strdup(name);
  if(!squery->name)
    {
      free(squery);
      callback(arg, ARES_ENOMEM, NULL, 0);
      return;
    }
  squery->dnsclass = dnsclass;
  squery->type = type;
  squery->status_as_is = -1;
  squery->callback = callback;
  squery->arg = arg;
  
  /* Count the number of dots in name. */
  ndots = 0;
  for (p = name; *p; p++)
    {
      if (*p == '.')
        ndots++;
    }
  
  /* If ndots is at least the channel ndots threshold (usually 1),
   * then we try the name as-is first.  Otherwise, we try the name
   * as-is last.
   */
  if (ndots >= channel->ndots)
    {
      /* Try the name as-is first. */
      squery->next_domain = 0;
      squery->trying_as_is = 1;
      ares_query(channel, name, dnsclass, type, search_callback, squery);
    }
  else
    {
      /* Try the name as-is last; start with the first search domain. */
      squery->next_domain = 1;
      squery->trying_as_is = 0;
      status = cat_domain(name, channel->domains[0], &s);
      if (status == ARES_SUCCESS)
        {
          ares_query(channel, s, dnsclass, type, search_callback, squery);
          free(s);
        }
      else
        callback(arg, status, NULL, 0);
    }
}

static void search_callback(void *arg, int status, unsigned char *abuf,
                            int alen)
{
  struct search_query *squery = (struct search_query *) arg;
  ares_channel channel = squery->channel;
  char *s;
  
  /* Stop searching unless we got a non-fatal error. */
  if (status != ARES_ENODATA && status != ARES_ESERVFAIL
      && status != ARES_ENOTFOUND)
    end_squery(squery, status, abuf, alen);
  else
    {
      /* Save the status if we were trying as-is. */
      if (squery->trying_as_is)
        squery->status_as_is = status;
      if (squery->next_domain < channel->ndomains)
        {
          /* Try the next domain. */
          status = cat_domain(squery->name,
                              channel->domains[squery->next_domain], &s);
          if (status != ARES_SUCCESS)
            end_squery(squery, status, NULL, 0);
          else
            {
              squery->trying_as_is = 0;
              squery->next_domain++;
              ares_query(channel, s, squery->dnsclass, squery->type,
                         search_callback, squery);
              free(s);
            }
        }
      else if (squery->status_as_is == -1)
        {
          /* Try the name as-is at the end. */
          squery->trying_as_is = 1;
          ares_query(channel, squery->name, squery->dnsclass, squery->type,
                     search_callback, squery);
        }
      else
        end_squery(squery, squery->status_as_is, NULL, 0);
    }
}

static void end_squery(struct search_query *squery, int status,
                       unsigned char *abuf, int alen)
{
  squery->callback(squery->arg, status, abuf, alen);
  free(squery->name);
  free(squery);
}

/* Concatenate two domains. */
static int cat_domain(const char *name, const char *domain, char **s)
{
  int nlen = strlen(name), dlen = strlen(domain);
  
  *s = malloc(nlen + 1 + dlen + 1);
  if (!*s)
    return ARES_ENOMEM;
  memcpy(*s, name, nlen);
  (*s)[nlen] = '.';
  memcpy(*s + nlen + 1, domain, dlen);
  (*s)[nlen + 1 + dlen] = 0;
  return ARES_SUCCESS;
}

/* Determine if this name only yields one query.  If it does, set *s to
 * the string we should query, in an allocated buffer.  If not, set *s
 * to NULL.
 */
static int single_domain(ares_channel channel, const char *name, char **s)
{
  int len = strlen(name);
  
  /* If the name contains a trailing dot, then the single query is the name
   * sans the trailing dot.
   */
  if (name[len - 1] == '.')
    {
      *s = strdup(name);
      return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
    }
  
  if (channel->flags & ARES_FLAG_NOSEARCH || channel->ndomains == 0)
    {
      /* No domain search to do; just try the name as-is. */
      *s = strdup(name);
      return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
    }
  
  *s = NULL;
  return ARES_SUCCESS;
}

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