请问怎样编程访问DNS服务器，来解析IP地址，特别是邮件服务器的IP地址，谢谢

先去看看DNS的查询报文格式吧

struct hostent FAR *gethostbyname(
const char FAR *name
);返回的结构里面有关于这个服务器的详细信息

关注啊楼主是要做SMTP服务器吗？

nslookuptype = mx应该可以的

#ifndef DNS_H
#define DNS_H#define DNS_SOFT -1
#define DNS_HARD -2
#define DNS_MEM -3void dns_init();
int dns_cname();
int dns_mxip();
int dns_ip();
int dns_ptr();#endif
以上代码来自qmail, 你可以到qmail.org去找,dns.c文件

sigh,你最好还是不要看Dan Bernstein的代码了,那太神奇了,不看也罢.
还是下载一份Bind的源码罢,http://www.isc.org/products/BIND/bind9.html网上太多太多这种代码了,找找吧.

#include "stdafx.h"
#include <winsock2.h>
#include <stdio.h>#define ASCII_NULL              '\0'
#define MAXHOSTNAME             256
#define BUFSIZE                 2048
#define QUERYTIMEOUT            30 //secondtypedef 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#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) */
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 */
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
#define DNS_RRTYPE_TXT   16/* DNS Resource Record 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 */
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 20typedef 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(const char FAR *pQName );
int  PutQName(const char FAR *pszHostName, char FAR *pQName );
int  dn_expand(char *msg,char  *eomorig,char *comp_dn,char *exp_dn,int length);
int  dn_expand_new(char *msg,char  *eomorig,char *comp_dn,char *exp_dn,int length, bool stop=false);
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);
checked += 2;
/*
* Check for loops in the compressed name;
* if we've looked at the whole message,
* there must be a loop.
*/
if (checked >= eomorig - msg)
return (-1);
break; default:
return (-1); /* flag error */
}
}
*dn = '\0';
if (len < 0)
len = cp - comp_dn;
return (len);
}

void GetQName( char FAR *pszHostName, char FAR *pQName )
{    int i, j, k;    for ( i = 0; i < BUFSIZE; i++ )
    {
            j = *pQName;            if ( j == 0 )
                    break;            for ( k = 1; k <= j; k++ )
            {
                    *pszHostName++ = *( pQName + i + k );
            } // end for loop
    } // end for loop    *pszHostName++ = ASCII_NULL;
} /* end GetQName() */
void PrintQName( char FAR *pQName )
{
    int i, j, k;    for ( i = 0; i < BUFSIZE; i++ )
    {
            j = *pQName;            if ( j == 0 )
                    break;            for ( k = 1; k <= j; k++ )
            {
                    //printf( "%c", *( pQName + i + k ) );
            } // end for loop
    } // end for loop
} /* end PrintQName() */
int PutQName(const char FAR *pszHostName, char FAR *pQName )
{
    int     i;
    int     j = 0;
    int     k = 0;    for ( i = 0; *( pszHostName + i ); i++ )
    {
            char c = *( pszHostName + i );   /* get next character */            if ( c == '.' )
            {
                    /* dot encountered, fill in previous length */
                    *( pQName + j ) = k;                    k = 0;      /* reset segment length */
                    j = i + 1;    /* set index to next counter */
            }
            else
            {
                    *( pQName + i + 1 ) = c;  /* assign to QName */
                    k++;                /* inc count of seg chars */
            } // end if
    } // end for loop    *(pQName + j )                  = k;   /* count for final segment */
    *(pQName + i + 1 )      = 0;   /* count for trailing NULL segment is 0 */    return ( i + 1 );        /* return total length of QName */
} /* end PutQName() *//*
* Skip over a compressed domain name. Return the size or -1.
*/
int dn_skipname(u_char *comp_dn,  u_char *eom)

{
register u_char *cp;
register int n; cp = comp_dn;
while (cp < eom && (n = *cp++)) {
/*
* check for indirection
*/
switch (n & INDIR_MASK) {
case 0: /* normal case, n == len */
cp += n;
continue;
default: /* illegal type */
return (-1);
case INDIR_MASK: /* indirection */
cp++;
}
break;
}
return (cp - comp_dn);
}

调试易

请问怎样编程访问DNS服务器，来解析IP地址，特别是邮件服务器的IP地址，谢谢

解决方案 »