hpopescu@ixiacom.com
13 years ago
committed by
Daniel Stenberg
parent
e447bc5c60
commit
90364defb0
12 changed files with 366 additions and 185 deletions
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.\" |
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.\" Copyright 1998, 2000 by the Massachusetts Institute of Technology. |
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.\" |
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.\" Permission to use, copy, modify, and distribute this |
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.\" software and its documentation for any purpose and without |
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.\" fee is hereby granted, provided that the above copyright |
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.\" notice appear in all copies and that both that copyright |
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.\" notice and this permission notice appear in supporting |
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.\" documentation, and that the name of M.I.T. not be used in |
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.\" advertising or publicity pertaining to distribution of the |
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.\" software without specific, written prior permission. |
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.\" M.I.T. makes no representations about the suitability of |
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.\" this software for any purpose. It is provided "as is" |
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.\" without express or implied warranty. |
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.\" |
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.TH ARES_CREATE_QUERY 3 "20 Nov 2009" |
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.SH NAME |
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ares_create_query \- Compose a single-question DNS query buffer |
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.SH SYNOPSIS |
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.nf |
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.B #include <ares.h> |
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.PP |
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.B int ares_create_query(const char *\fIname\fP, int \fIdnsclass\fP,\ |
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int \fItype\fP, |
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.B unsigned short \fIid\fP, int \fIrd\fP,\ |
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unsigned char **\fIbuf\fP, |
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.B int *\fIbuflen\fP, int \fImax_udp_size\fP) |
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.fi |
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.SH DESCRIPTION |
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The |
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.B ares_create_query |
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function composes a DNS query with a single question. |
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The parameter |
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.I name |
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gives the query name as a NUL-terminated C string of period-separated |
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labels optionally ending with a period; periods and backslashes within |
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a label must be escaped with a backlash. The parameters |
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.I dnsclass |
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and |
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.I type |
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give the class and type of the query using the values defined in |
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.BR <arpa/nameser.h> . |
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The parameter |
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.I id |
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gives a 16-bit identifier for the query. The parameter |
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.I rd |
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should be nonzero if recursion is desired, zero if not. The query |
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will be placed in an allocated buffer, a pointer to which will be |
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stored in the variable pointed to by |
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.IR buf , |
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and the length of which will be stored in the variable pointed to by |
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.IR buflen . |
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It is the caller's responsibility to free this buffer using |
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\fIares_free_string(3)\fP when it is no longer needed. |
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The parameter |
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.I max_udp_size |
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should be nonzero to activate EDNS. Usage of \fIares_create_query(3)\fP\ with |
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.I max_udp_size |
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set to zero is equivalent to \fIares_mkquery(3)\fP. |
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.SH RETURN VALUES |
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.B ares_create_query |
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can return any of the following values: |
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.TP 15 |
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.B ARES_SUCCESS |
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Construction of the DNS query succeeded. |
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.TP 15 |
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.B ARES_EBADNAME |
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The query name |
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.I name |
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could not be encoded as a domain name, either because it contained a |
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zero-length label or because it contained a label of more than 63 |
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characters. |
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.TP 15 |
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.B ARES_ENOMEM |
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Memory was exhausted. |
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.SH SEE ALSO |
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.BR ares_expand_name (3), |
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.BR ares_free_string (3) |
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.SH AUTHOR |
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@ -0,0 +1,209 @@ |
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|
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/* Copyright 1998 by the Massachusetts Institute of Technology.
|
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* |
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* Permission to use, copy, modify, and distribute this |
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* software and its documentation for any purpose and without |
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* fee is hereby granted, provided that the above copyright |
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* notice appear in all copies and that both that copyright |
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* notice and this permission notice appear in supporting |
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* documentation, and that the name of M.I.T. not be used in |
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* advertising or publicity pertaining to distribution of the |
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* software without specific, written prior permission. |
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* M.I.T. makes no representations about the suitability of |
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* this software for any purpose. It is provided "as is" |
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* without express or implied warranty. |
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*/ |
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|
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#include "ares_setup.h" |
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|
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#ifdef HAVE_SYS_SOCKET_H |
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# include <sys/socket.h> |
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#endif |
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#ifdef HAVE_NETINET_IN_H |
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# include <netinet/in.h> |
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#endif |
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#ifdef HAVE_ARPA_NAMESER_H |
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# include <arpa/nameser.h> |
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#else |
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# include "nameser.h" |
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#endif |
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#ifdef HAVE_ARPA_NAMESER_COMPAT_H |
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# include <arpa/nameser_compat.h> |
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#endif |
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|
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#include <stdlib.h> |
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#include <string.h> |
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#include "ares.h" |
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#include "ares_dns.h" |
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#include "ares_private.h" |
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|
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/* Header format, from RFC 1035:
|
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* 1 1 1 1 1 1 |
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ID | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |QR| Opcode |AA|TC|RD|RA| Z | RCODE | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QDCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ANCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | NSCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ARCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |
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* AA, TC, RA, and RCODE are only set in responses. Brief description |
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* of the remaining fields: |
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* ID Identifier to match responses with queries |
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* QR Query (0) or response (1) |
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* Opcode For our purposes, always QUERY |
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* RD Recursion desired |
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* Z Reserved (zero) |
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* QDCOUNT Number of queries |
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* ANCOUNT Number of answers |
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* NSCOUNT Number of name server records |
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* ARCOUNT Number of additional records |
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* |
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* Question format, from RFC 1035: |
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* 1 1 1 1 1 1 |
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | | |
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* / QNAME / |
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* / / |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QTYPE | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QCLASS | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |
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* The query name is encoded as a series of labels, each represented |
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* as a one-byte length (maximum 63) followed by the text of the |
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* label. The list is terminated by a label of length zero (which can |
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* be thought of as the root domain). |
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*/ |
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|
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int ares_create_query(const char *name, int dnsclass, int type, |
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unsigned short id, int rd, unsigned char **buf, |
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int *buflen, int max_udp_size) |
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{ |
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int len; |
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unsigned char *q; |
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const char *p; |
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|
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/* Set our results early, in case we bail out early with an error. */ |
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*buflen = 0; |
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*buf = NULL; |
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|
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/* Compute the length of the encoded name so we can check buflen.
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* Start counting at 1 for the zero-length label at the end. */ |
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len = 1; |
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for (p = name; *p; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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len++; |
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} |
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/* If there are n periods in the name, there are n + 1 labels, and
|
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* thus n + 1 length fields, unless the name is empty or ends with a |
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* period. So add 1 unless name is empty or ends with a period. |
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*/ |
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if (*name && *(p - 1) != '.') |
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len++; |
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|
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/* Immediately reject names that are longer than the maximum of 255
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* bytes that's specified in RFC 1035 ("To simplify implementations, |
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* the total length of a domain name (i.e., label octets and label |
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* length octets) is restricted to 255 octets or less."). We aren't |
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* doing this just to be a stickler about RFCs. For names that are |
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* too long, 'dnscache' closes its TCP connection to us immediately |
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* (when using TCP) and ignores the request when using UDP, and |
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* BIND's named returns ServFail (TCP or UDP). Sending a request |
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* that we know will cause 'dnscache' to close the TCP connection is |
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* painful, since that makes any other outstanding requests on that |
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* connection fail. And sending a UDP request that we know |
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* 'dnscache' will ignore is bad because resources will be tied up |
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* until we time-out the request. |
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*/ |
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if (len > MAXCDNAME) |
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return ARES_EBADNAME; |
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|
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*buflen = len + HFIXEDSZ + QFIXEDSZ + (max_udp_size ? EDNSFIXEDSZ : 0); |
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*buf = malloc(*buflen); |
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if (!*buf) |
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return ARES_ENOMEM; |
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|
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/* Set up the header. */ |
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q = *buf; |
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memset(q, 0, HFIXEDSZ); |
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DNS_HEADER_SET_QID(q, id); |
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DNS_HEADER_SET_OPCODE(q, QUERY); |
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if (rd) { |
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DNS_HEADER_SET_RD(q, 1); |
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} |
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else { |
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DNS_HEADER_SET_RD(q, 0); |
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} |
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DNS_HEADER_SET_QDCOUNT(q, 1); |
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|
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if (max_udp_size) { |
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DNS_HEADER_SET_ARCOUNT(q, 1); |
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} |
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|
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/* A name of "." is a screw case for the loop below, so adjust it. */ |
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if (strcmp(name, ".") == 0) |
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name++; |
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|
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/* Start writing out the name after the header. */ |
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q += HFIXEDSZ; |
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while (*name) |
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{ |
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if (*name == '.') |
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return ARES_EBADNAME; |
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|
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/* Count the number of bytes in this label. */ |
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len = 0; |
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for (p = name; *p && *p != '.'; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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len++; |
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} |
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if (len > MAXLABEL) |
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return ARES_EBADNAME; |
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|
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/* Encode the length and copy the data. */ |
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*q++ = (unsigned char)len; |
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for (p = name; *p && *p != '.'; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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*q++ = *p; |
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} |
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|
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/* Go to the next label and repeat, unless we hit the end. */ |
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if (!*p) |
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break; |
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name = p + 1; |
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} |
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|
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/* Add the zero-length label at the end. */ |
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*q++ = 0; |
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|
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/* Finish off the question with the type and class. */ |
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DNS_QUESTION_SET_TYPE(q, type); |
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DNS_QUESTION_SET_CLASS(q, dnsclass); |
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|
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if (max_udp_size) |
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{ |
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q += QFIXEDSZ; |
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memset(q, 0, EDNSFIXEDSZ); |
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q++; |
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DNS_RR_SET_TYPE(q, ns_t_opt); |
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DNS_RR_SET_CLASS(q, max_udp_size); |
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} |
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|
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return ARES_SUCCESS; |
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} |
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