mirror of https://github.com/c-ares/c-ares.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
195 lines
6.3 KiB
195 lines
6.3 KiB
|
|
/* 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 "ares_setup.h" |
|
|
|
#ifdef HAVE_SYS_SOCKET_H |
|
# include <sys/socket.h> |
|
#endif |
|
#ifdef HAVE_NETINET_IN_H |
|
# include <netinet/in.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 |
|
|
|
#include <stdlib.h> |
|
#include <string.h> |
|
#include "ares.h" |
|
#include "ares_dns.h" |
|
#include "ares_private.h" |
|
|
|
/* Header format, from RFC 1035: |
|
* 1 1 1 1 1 1 |
|
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | ID | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* |QR| Opcode |AA|TC|RD|RA| Z | RCODE | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | QDCOUNT | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | ANCOUNT | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | NSCOUNT | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | ARCOUNT | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* |
|
* AA, TC, RA, and RCODE are only set in responses. Brief description |
|
* of the remaining fields: |
|
* ID Identifier to match responses with queries |
|
* QR Query (0) or response (1) |
|
* Opcode For our purposes, always QUERY |
|
* RD Recursion desired |
|
* Z Reserved (zero) |
|
* QDCOUNT Number of queries |
|
* ANCOUNT Number of answers |
|
* NSCOUNT Number of name server records |
|
* ARCOUNT Number of additional records |
|
* |
|
* Question format, from RFC 1035: |
|
* 1 1 1 1 1 1 |
|
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | | |
|
* / QNAME / |
|
* / / |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | QTYPE | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* | QCLASS | |
|
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|
* |
|
* The query name is encoded as a series of labels, each represented |
|
* as a one-byte length (maximum 63) followed by the text of the |
|
* label. The list is terminated by a label of length zero (which can |
|
* be thought of as the root domain). |
|
*/ |
|
|
|
int ares_mkquery(const char *name, int dnsclass, int type, unsigned short id, |
|
int rd, unsigned char **buf, int *buflen) |
|
{ |
|
int len; |
|
unsigned char *q; |
|
const char *p; |
|
|
|
/* Set our results early, in case we bail out early with an error. */ |
|
*buflen = 0; |
|
*buf = NULL; |
|
|
|
/* Compute the length of the encoded name so we can check buflen. |
|
* Start counting at 1 for the zero-length label at the end. */ |
|
len = 1; |
|
for (p = name; *p; p++) |
|
{ |
|
if (*p == '\\' && *(p + 1) != 0) |
|
p++; |
|
len++; |
|
} |
|
/* If there are n periods in the name, there are n + 1 labels, and |
|
* thus n + 1 length fields, unless the name is empty or ends with a |
|
* period. So add 1 unless name is empty or ends with a period. |
|
*/ |
|
if (*name && *(p - 1) != '.') |
|
len++; |
|
|
|
/* Immediately reject names that are longer than the maximum of 255 |
|
* bytes that's specified in RFC 1035 ("To simplify implementations, |
|
* the total length of a domain name (i.e., label octets and label |
|
* length octets) is restricted to 255 octets or less."). We aren't |
|
* doing this just to be a stickler about RFCs. For names that are |
|
* too long, 'dnscache' closes its TCP connection to us immediately |
|
* (when using TCP) and ignores the request when using UDP, and |
|
* BIND's named returns ServFail (TCP or UDP). Sending a request |
|
* that we know will cause 'dnscache' to close the TCP connection is |
|
* painful, since that makes any other outstanding requests on that |
|
* connection fail. And sending a UDP request that we know |
|
* 'dnscache' will ignore is bad because resources will be tied up |
|
* until we time-out the request. |
|
*/ |
|
if (len > MAXCDNAME) |
|
return ARES_EBADNAME; |
|
|
|
*buflen = len + HFIXEDSZ + QFIXEDSZ; |
|
*buf = malloc(*buflen); |
|
if (!*buf) |
|
return ARES_ENOMEM; |
|
|
|
/* Set up the header. */ |
|
q = *buf; |
|
memset(q, 0, HFIXEDSZ); |
|
DNS_HEADER_SET_QID(q, id); |
|
DNS_HEADER_SET_OPCODE(q, QUERY); |
|
if (rd) { |
|
DNS_HEADER_SET_RD(q, 1); |
|
} |
|
else { |
|
DNS_HEADER_SET_RD(q, 0); |
|
} |
|
DNS_HEADER_SET_QDCOUNT(q, 1); |
|
|
|
/* A name of "." is a screw case for the loop below, so adjust it. */ |
|
if (strcmp(name, ".") == 0) |
|
name++; |
|
|
|
/* Start writing out the name after the header. */ |
|
q += HFIXEDSZ; |
|
while (*name) |
|
{ |
|
if (*name == '.') |
|
return ARES_EBADNAME; |
|
|
|
/* Count the number of bytes in this label. */ |
|
len = 0; |
|
for (p = name; *p && *p != '.'; p++) |
|
{ |
|
if (*p == '\\' && *(p + 1) != 0) |
|
p++; |
|
len++; |
|
} |
|
if (len > MAXLABEL) |
|
return ARES_EBADNAME; |
|
|
|
/* Encode the length and copy the data. */ |
|
*q++ = (unsigned char)len; |
|
for (p = name; *p && *p != '.'; p++) |
|
{ |
|
if (*p == '\\' && *(p + 1) != 0) |
|
p++; |
|
*q++ = *p; |
|
} |
|
|
|
/* Go to the next label and repeat, unless we hit the end. */ |
|
if (!*p) |
|
break; |
|
name = p + 1; |
|
} |
|
|
|
/* Add the zero-length label at the end. */ |
|
*q++ = 0; |
|
|
|
/* Finish off the question with the type and class. */ |
|
DNS_QUESTION_SET_TYPE(q, type); |
|
DNS_QUESTION_SET_CLASS(q, dnsclass); |
|
|
|
return ARES_SUCCESS; |
|
}
|
|
|