ares_search.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.
 */
 
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "ares.h"
#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
      {
    free(squery->name);
        free(squery);
    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)
{
  size_t 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)
{
   size_t len = strlen(name);
   const char* hostaliases;
   FILE* fp;
   char* line = NULL;
   int linesize, status;
   const char* p, * q;
 
   /* 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_NOALIASES) && !strchr(name, '.'))
   {
      /* The name might be a host alias. */
#ifdef UNDER_CE
      hostaliases = NULL;
#elif defined(_MSC_VER)
      char hostaliasBuf[256] = { 0 };
      size_t requiredSize = 0;
      getenv_s(&requiredSize, hostaliasBuf, sizeof(hostaliasBuf), "HOSTALIASES");
      hostaliases = requiredSize > 0 ? hostaliasBuf : NULL;
#else
      hostaliases = getenv("HOSTALIASES");
#endif
      if (hostaliases)
      {
#ifdef WIN32
         fopen_s(&fp, hostaliases, "r");
#else
         fp = fopen(hostaliases, "r");
#endif
         if (fp)
         {
            while ((status = ares__read_line(fp, &line, &linesize))
               == ARES_SUCCESS)
            {
               if (strncasecmp(line, name, len) != 0 ||
                  !isspace((unsigned char)line[len]))
                  continue;
               p = line + len;
               while (isspace((unsigned char)*p))
                  p++;
               if (*p)
               {
                  q = p + 1;
                  while (*q && !isspace((unsigned char)*q))
                     q++;
                  *s = malloc(q - p + 1);
                  if (*s)
                  {
                     memcpy(*s, p, q - p);
                     (*s)[q - p] = 0;
                  }
                  free(line);
                  fclose(fp);
                  return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
               }
            }
            free(line);
            fclose(fp);
            if (status != ARES_SUCCESS)
               return status;
         }
      }
   }
 
   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;
}