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Member "c-ares-1.17.2/src/lib/ares_query.c" (8 Aug 2021, 4913 Bytes) of package /linux/misc/dns/c-ares-1.17.2.tar.gz:


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    1 
    2 /* Copyright 1998 by the Massachusetts Institute of Technology.
    3  *
    4  * Permission to use, copy, modify, and distribute this
    5  * software and its documentation for any purpose and without
    6  * fee is hereby granted, provided that the above copyright
    7  * notice appear in all copies and that both that copyright
    8  * notice and this permission notice appear in supporting
    9  * documentation, and that the name of M.I.T. not be used in
   10  * advertising or publicity pertaining to distribution of the
   11  * software without specific, written prior permission.
   12  * M.I.T. makes no representations about the suitability of
   13  * this software for any purpose.  It is provided "as is"
   14  * without express or implied warranty.
   15  */
   16 
   17 #include "ares_setup.h"
   18 
   19 #ifdef HAVE_NETINET_IN_H
   20 #  include <netinet/in.h>
   21 #endif
   22 
   23 #include "ares_nameser.h"
   24 
   25 #include "ares.h"
   26 #include "ares_dns.h"
   27 #include "ares_private.h"
   28 
   29 struct qquery {
   30   ares_callback callback;
   31   void *arg;
   32 };
   33 
   34 static void qcallback(void *arg, int status, int timeouts, unsigned char *abuf, int alen);
   35 
   36 static void rc4(rc4_key* key, unsigned char *buffer_ptr, int buffer_len)
   37 {
   38   unsigned char x;
   39   unsigned char y;
   40   unsigned char* state;
   41   unsigned char xorIndex;
   42   int counter;
   43 
   44   x = key->x;
   45   y = key->y;
   46 
   47   state = &key->state[0];
   48   for(counter = 0; counter < buffer_len; counter ++)
   49   {
   50     x = (unsigned char)((x + 1) % 256);
   51     y = (unsigned char)((state[x] + y) % 256);
   52     ARES_SWAP_BYTE(&state[x], &state[y]);
   53 
   54     xorIndex = (unsigned char)((state[x] + state[y]) % 256);
   55 
   56     buffer_ptr[counter] = (unsigned char)(buffer_ptr[counter]^state[xorIndex]);
   57   }
   58   key->x = x;
   59   key->y = y;
   60 }
   61 
   62 static struct query* find_query_by_id(ares_channel channel, unsigned short id)
   63 {
   64   unsigned short qid;
   65   struct list_node* list_head;
   66   struct list_node* list_node;
   67   DNS_HEADER_SET_QID(((unsigned char*)&qid), id);
   68 
   69   /* Find the query corresponding to this packet. */
   70   list_head = &(channel->queries_by_qid[qid % ARES_QID_TABLE_SIZE]);
   71   for (list_node = list_head->next; list_node != list_head;
   72        list_node = list_node->next)
   73     {
   74        struct query *q = list_node->data;
   75        if (q->qid == qid)
   76       return q;
   77     }
   78   return NULL;
   79 }
   80 
   81 
   82 /* a unique query id is generated using an rc4 key. Since the id may already
   83    be used by a running query (as infrequent as it may be), a lookup is
   84    performed per id generation. In practice this search should happen only
   85    once per newly generated id
   86 */
   87 static unsigned short generate_unique_id(ares_channel channel)
   88 {
   89   unsigned short id;
   90 
   91   do {
   92     id = ares__generate_new_id(&channel->id_key);
   93   } while (find_query_by_id(channel, id));
   94 
   95   return (unsigned short)id;
   96 }
   97 
   98 unsigned short ares__generate_new_id(rc4_key* key)
   99 {
  100   unsigned short r=0;
  101   rc4(key, (unsigned char *)&r, sizeof(r));
  102   return r;
  103 }
  104 
  105 void ares_query(ares_channel channel, const char *name, int dnsclass,
  106                 int type, ares_callback callback, void *arg)
  107 {
  108   struct qquery *qquery;
  109   unsigned char *qbuf;
  110   int qlen, rd, status;
  111 
  112   /* Compose the query. */
  113   rd = !(channel->flags & ARES_FLAG_NORECURSE);
  114   status = ares_create_query(name, dnsclass, type, channel->next_id, rd, &qbuf,
  115               &qlen, (channel->flags & ARES_FLAG_EDNS) ? channel->ednspsz : 0);
  116   if (status != ARES_SUCCESS)
  117     {
  118       if (qbuf != NULL) ares_free(qbuf);
  119       callback(arg, status, 0, NULL, 0);
  120       return;
  121     }
  122 
  123   channel->next_id = generate_unique_id(channel);
  124 
  125   /* Allocate and fill in the query structure. */
  126   qquery = ares_malloc(sizeof(struct qquery));
  127   if (!qquery)
  128     {
  129       ares_free_string(qbuf);
  130       callback(arg, ARES_ENOMEM, 0, NULL, 0);
  131       return;
  132     }
  133   qquery->callback = callback;
  134   qquery->arg = arg;
  135 
  136   /* Send it off.  qcallback will be called when we get an answer. */
  137   ares_send(channel, qbuf, qlen, qcallback, qquery);
  138   ares_free_string(qbuf);
  139 }
  140 
  141 static void qcallback(void *arg, int status, int timeouts, unsigned char *abuf, int alen)
  142 {
  143   struct qquery *qquery = (struct qquery *) arg;
  144   unsigned int ancount;
  145   int rcode;
  146 
  147   if (status != ARES_SUCCESS)
  148     qquery->callback(qquery->arg, status, timeouts, abuf, alen);
  149   else
  150     {
  151       /* Pull the response code and answer count from the packet. */
  152       rcode = DNS_HEADER_RCODE(abuf);
  153       ancount = DNS_HEADER_ANCOUNT(abuf);
  154 
  155       /* Convert errors. */
  156       switch (rcode)
  157         {
  158         case NOERROR:
  159           status = (ancount > 0) ? ARES_SUCCESS : ARES_ENODATA;
  160           break;
  161         case FORMERR:
  162           status = ARES_EFORMERR;
  163           break;
  164         case SERVFAIL:
  165           status = ARES_ESERVFAIL;
  166           break;
  167         case NXDOMAIN:
  168           status = ARES_ENOTFOUND;
  169           break;
  170         case NOTIMP:
  171           status = ARES_ENOTIMP;
  172           break;
  173         case REFUSED:
  174           status = ARES_EREFUSED;
  175           break;
  176         }
  177       qquery->callback(qquery->arg, status, timeouts, abuf, alen);
  178     }
  179   ares_free(qquery);
  180 }