dnsmx.cpp

一个SMTP邮件发送的源代码

/*
 *  The code I found by Bob Quinn was not complete - I hacked it to
 *  completion just to see what the issues were with getting MX entries.
 *
 *  Part of the hacking involved extracting code from Unix BIND which 
 *  does the low level packet parsing.  (The dn_ routines)
 *
 *  It needs to determine the DNS server's IP address - right now it is
 *  hard coded into this program.  NSLOOKUP probably looks in the 
 *  registry for that value.
 *
 * - David
 */

/*---------------------------------------------------------------------
 *
 * Program: DNS_QRY.EXE  Query DNS Server, and parse response
 *
 * filename: DNS_QRY.c
 *
 *  Copyright by Bob Quinn, 1997          http://www.sockets.com
 *
 * Description:
 *  Not a test application, per se, but designed to allow custom
 *  queries of DNS records by actually sending and receiving DNS
 *  messages, rather than relying on the hostname resolution APIs
 *  to do it for me.  The big advantage is that I can ask for any
 *  DNS record types that I want.  The downside is that I have to
 *  hard-code the DNS server myself, or peak at the implementation's
 *  configuration (e.g. MSTCP) for the config'd server(s).
 *
 *  I started creating this in response to a Frequently Asked Question
 *  on one of the WinSock mailing lists for a way to use WinSock to
 *  retrieve an MX record.
 *
 *  NOTE: Eventually, I'd like to provide the same command-line
 *   capabilities as available from BSD Unix NSLOOKUP utility.
 *
 * Editing History:
 *  8/17/97  rcq  started work  -- STOPPED BEFORE GOT IT WORKING
 *                 (serious byte order problems and buffer/format
 *                 management problems in general, causing Format Err).
 *  2/15/98  mjd  got query and reply working, working on decoding reply
 *
 *
 *
 ---------------------------------------------------------------------*/
#include "stdafx.h"
#include "tools.h"
#include <stdio.h>


#define ASCII_NULL              '\0'
#define MAXHOSTNAME             256
#define BUFSIZE                 2048
//#define BUFSIZE                 4096





/* DNS Header Format
 *
 * All DNS Message Formats have basically the same structure
 *   (note that an RR (DNS Resource Record) is described in
 *   the other structures that follow this header description):
 *
 *        +--------------------------------+
 *        | DNS Header: <defined below>    |
 *        +--------------------------------+
 *        | Question:   type of query      |
 *        |   QNAME:    <see below>        |
 *        |   QTYPE:    2-octet RR type    |
 *        |   QCLASS:   2-octet RR class   |
 *        +--------------------------------+
 *        | Answer:     RR answer to query |
 *        +--------------------------------+
 *        | Authority:  RR for name server |
 *        +--------------------------------+
 *        | Additional: RR(s) other info   |
 *        +--------------------------------+
 *
 *  QNAME is a variable length field where each portion of the
 *   "dotted-notation" domain name is replaced by the number of
 *   octets to follow.  So, for example, the domain name
 *   "www.sockets.com" is represented by:
 *
 *         0                   1
 *   octet 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
 *        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *        |3|w|w|w|7|s|o|c|k|e|t|s|3|c|o|m|0|
 *        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * NOTE: The last section, "Additional," often contains records
 *  for queries the server anticipates will be sent (to reduce
 *  traffic).  For example, a response to an MX query, would
 *  usually have the A record in additional information.
 */
typedef struct dns_hdr
{
        u_short dns_id;          /* client query ID number */
        u_short dns_flags;       /* qualify contents <see below> */
        u_short dns_q_count;     /* number of questions */
        u_short dns_rr_count;    /* number of answer RRs */
        u_short dns_auth_count;  /* number of authority RRs */
        u_short dns_add_count;   /* number of additional RRs */
} DNS_HDR, *PDNS_HDR, FAR *LPDNS_HDR;

#define DNS_HDR_LEN 12

/* DNS Flags field values
 *
 *  bits:  0     1-4     5    6    7    8     9-11    12-15
 *       +----+--------+----+----+----+----+--------+-------+
 *       | QR | opcode | AA | TC | RD | RA | <zero> | rcode |
 *       +----+--------+----+----+----+----+--------+-------+
 *
 *  QR:     0 for query, and 1 for response
 *  opcode: type of query (0: standard, and 1: inverse query)
 *  AA:     set if answer from domain authority
 *  TC:     set if message had to be truncated
 *  RD:     set if recursive query desired
 *  RA:     set if recursion is available from server
 *  <zero>: reserved field
 *  rcode:  resulting error non-zero value from authoritative
 *           server (0: no error, 3: name does not exist)
 */
#define DNS_FLAG_QR 0x8000
#define DNS_FLAG_AA 0x0400
#define DNS_FLAG_TC 0x0200
#define DNS_FLAG_RD 0x0100
#define DNS_FLAG_RA 0x0080
#define DNS_RCODE_MASK  0x000F
#define DNS_OPCODE_MASK 0x7800

/* DNS Opcode (type of query) */
char *DNS_Opcode[] =
{
        "Standard Query",         /* 0: QUERY  */
        "Inverse Query",          /* 1: IQUERY */
        "Server Status Request",  /* 2: STATUS */
};

/* DNS Response Codes (error descriptions) */
char *DNS_RCode[] =
{
        "No Error",        /* 0: ok */
        "Format Error",    /* 1: bad query */
        "Server Failure",  /* 2: server is hosed */
        "Name Error",      /* 3: name doesn't exist (authoritative) */
        "Not Implemented", /* 4: server doesn't support query */
        "Refused"          /* 5: server refused request */
};

/* DNS Generic Resource Record format (from RFC 1034 and 1035)
 *
 *  NOTE: The first field in the DNS RR Record header is always
 *   the domain name in QNAME format (see earlier description)
 */
typedef struct dns_rr_hdr
{
        u_short rr_type;                /* RR type code (e.g. A, MX, NS, etc.) */
        u_short rr_class;               /* RR class code (IN for Internet) */
        u_long  rr_ttl;         /* Time-to-live for resource */
        u_short rr_rdlength;    /* length of RDATA field (in octets) */
        u_short rr_rdata;               /* (fieldname used as a ptr) */
} DNS_RR_HDR, *PDNS_RR_HDR, FAR *LPDNS_RR_HDR;

#define DNS_RR_HDR_LEN 12

/* DNS Resource Record RDATA Field Descriptions
 *
 *  The RDATA field contains resource record data associated
 *  with the specified domain name
 *
 *  Type Value Description
 *  -------------------------------------------------------------
 *   A     1   IP Address (32-bit IP version 4)
 *   NS    2   Name server QNAME (for referrals & recursive queries)
 *   CNAME 5   Canonical name of an alias (in QNAME format)
 *   SOA   6   Start of Zone Transfer (see definition below)
 *   WKS   11  Well-known services (see definition below)
 *   PTR   12  QNAME pointing to other nodes (e.g. in inverse lookups)
 *   HINFO 13  Host Information (CPU string, then OS string)
 *   MX    15  Mail server preference and QNAME (see below)
 */
char *DNS_RR_Type [] =
{
        "<invalid>",
        "A",     // 1:  Host Address
        "NS",    // 2:  Authoritative Name Server
        "MD",    // 3:  <obsolete>
        "MF",    // 4:  <obsolete>
        "CNAME", // 5:  The true, canonical name for an alias
        "SOA",   // 6:  Start-of-Zone of authority record
        "MB",    // 7:  Mailbox   <experimental>
        "MG",    // 8:  Mailgroup <experimental>
        "MR",    // 9:  Mail Rename Domain Name <experimental>
        "NULL",  // 10: NULL Resource Record    <experimental>
        "WKS",   // 11: Well-known service description
        "PTR",   // 12: Domain Name Pointer
        "HINFO", // 13: Host Information
        "MINFO", // 14: Mailbox or Mail List information
        "MX",    // 15: Mail Exchange (from RFC 974)
        "TXT"    // 16: Text String
};

#define DNS_RRTYPE_A     1
#define DNS_RRTYPE_NS    2
#define DNS_RRTYPE_CNAME 5
#define DNS_RRTYPE_SOA   6
#define DNS_RRTYPE_WKS   11
#define DNS_RRTYPE_PTR   12
#define DNS_RRTYPE_HINFO 13
#define DNS_RRTYPE_MX    15

/* DNS Resource Record Classes:
 *
 * One almost always uses Internet RR Class (also note: the
 *  class value 255 denotes a wildcard, all classes)
 */
char *DNS_RR_Class [] =
{
        "<invalid>",
        "IN",    // 1: Internet - used for most queries!
        "CS",    // 2: CSNET <obsolete>
        "CH",    // 3: CHAOS Net
        "HS"     // 4: Hesiod
};

#define DNS_RRCLASS_IN  1
#define DNS_RRCLASS_CS  2
#define DNS_RRCLASS_CH  3
#define DNS_RRCLASS_HS  4

/* DNS SOA Resource Data Field
 *
 *  NOTE: First two fields not shown here.  They are:
 *    MNAME: QNAME of primary server for this zone
 *    RNAME: QNAME of mailbox of admin for this zone
 */
typedef struct dns_rdata_soa
{
        u_long soa_serial;  /* data version for this zone */
        u_long soa_refresh; /* time-to-live for data (in seconds) */
        u_long soa_retry;   /* time between retrieds (in seconds) */
        u_long soa_expire;  /* time until zone not auth (in seconds) */
        u_long soa_minimum; /* default TTL for RRs (in seconds) */
} DNS_RDATA_SOA, PDNS_RDATA_SOA, FAR *LPDNS_RDATA_SOA;

#define DNS_SOA_LEN 20

/* DNS WKS Resource Data Field (RFC 1035)
 *
 *  NOTE: The bitmap field is variable length, with as many
 *   octets necessary to indicate the bit field for the port
 *   number.
 */
typedef struct dns_rdata_wks
{
        u_long wks_addr;      /* IPv4 address */
        u_char wks_protocol;  /* Protocol (e.g. 6=TCP, 17=UDP) */
        u_char wks_bitmap;    /* e.g. bit 26 = SMTP (port 25) */
} DNS_RDATA_WKS, *PDNS_RDATA_WKS, FAR *LPDNS_RDATA_WKS;

#define DNS_WKX_LEN 6

/* DNS MX Resource Data Field
 */
typedef struct dns_rdata_mx
{
        u_short mx_pref;     /* Preference value */
        u_short mx_xchange;  /* QNAME (field used as ptr) */
} DNS_RDATA_MX, *PDNS_RDATA_MX, FAR *LPDNS_RDATA_MX;

#define DNS_MX_LEN 4

/* Variables used for DNS Header construction & parsing */
PDNS_HDR       pDNShdr;
PDNS_RR_HDR    pDNS_RR;
PDNS_RDATA_SOA pDNS_SOA;
PDNS_RDATA_WKS pDNS_WKS;
PDNS_RDATA_MX  pDNS_MX;

    /* For Parsing Names in a Reply */
#define INDIR_MASK	0xc0

	/* Number of bytes of fixed size data in query structure */
#define QFIXEDSZ	4
	/* number of bytes of fixed size data in resource record */
#define RRFIXEDSZ	10

/* Processor Types */
char *aszProcessor[] =
{
        "",
        "",
        "",
        "Intel 386",
        "Intel 486",
        "Intel Pentium"
};


void GetQName( char FAR *pszHostName, char FAR *pQName );
void PrintQName( char FAR *pQName );
int  PutQName( char FAR *pszHostName, char FAR *pQName );




u_short
_getshort(char *msgp)
{
	register u_char *p = (u_char *) msgp;
	register u_short u;

	u = *p++ << 8;
	return ((u_short)(u | *p));
}

u_long
_getlong(char *msgp)
{
	register u_char *p = (u_char *) msgp;
	register u_long u;

	u = *p++; u <<= 8;
	u |= *p++; u <<= 8;
	u |= *p++; u <<= 8;
	return (u | *p);
}


/*
 * Expand compressed domain name 'comp_dn' to full domain name.
 * 'msg' is a pointer to the begining of the message,
 * 'eomorig' points to the first location after the message,
 * 'exp_dn' is a pointer to a buffer of size 'length' for the result.
 * Return size of compressed name or -1 if there was an error.
 */
int dn_expand(char *msg,char  *eomorig,char *comp_dn,char *exp_dn,int length)
	
	
{
	register char *cp, *dn;
	register int n, c;
	char *eom;
	int len = -1, checked = 0;

	dn = exp_dn;
	cp = comp_dn;
	eom = exp_dn + length - 1;
	/*
	 * fetch next label in domain name
	 */
	while (n = *cp++) {
		/*
		 * Check for indirection
		 */
		switch (n & INDIR_MASK) {
		case 0:
			if (dn != exp_dn) {
				if (dn >= eom)
					return (-1);
				*dn++ = '.';
			}
			if (dn+n >= eom)
				return (-1);
			checked += n + 1;
			while (--n >= 0) {
				if ((c = *cp++) == '.') {
					if (dn+n+1 >= eom)
						return (-1);
					*dn++ = '\\';
				}
				*dn++ = c;
				if (cp >= eomorig)	/* out of range */
					return(-1);
			}
			break;

		case INDIR_MASK:
			if (len < 0)
				len = cp - comp_dn + 1;
			cp = msg + (((n & 0x3f) << 8) | (*cp & 0xff));
			if (cp < msg || cp >= eomorig)	/* out of range */
				return(-1);