dns.c

linux下qmail的源码 本人加了一些注释

#include <stdio.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <errno.h>
extern int res_query();
extern int res_search();
extern int errno;
extern int h_errno;
#include "ip.h"
#include "ipalloc.h"
#include "fmt.h"
#include "alloc.h"
#include "str.h"
#include "stralloc.h"
#include "dns.h"
#include "case.h"

static unsigned short getshort(c) unsigned char *c;
{ unsigned short u; u = c[0]; return (u << 8) + c[1]; }

static union { HEADER hdr; unsigned char buf[PACKETSZ]; } response;
static int responselen;
static unsigned char *responseend;
static unsigned char *responsepos;

static int numanswers;
static char name[MAXDNAME];
static struct ip_address ip;
unsigned short pref;

static stralloc glue = {0};

static int (*lookup)() = res_query;

static int resolve(domain,type)
stralloc *domain;
int type;
{
 int n;
 int i;

 errno = 0;
 if (!stralloc_copy(&glue,domain)) return DNS_MEM;
 if (!stralloc_0(&glue)) return DNS_MEM;
 responselen = lookup(glue.s,C_IN,type,response.buf,sizeof(response));
 if (responselen <= 0)
  {
   if (errno == ECONNREFUSED) return DNS_SOFT;
   if (h_errno == TRY_AGAIN) return DNS_SOFT;
   return DNS_HARD;
  }
 if (responselen >= sizeof(response))
   responselen = sizeof(response);
 responseend = response.buf + responselen;
 responsepos = response.buf + sizeof(HEADER);
 n = ntohs(response.hdr.qdcount);
 while (n-- > 0)
  {
   i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
   if (i < 0) return DNS_SOFT;
   responsepos += i;
   i = responseend - responsepos;
   if (i < QFIXEDSZ) return DNS_SOFT;
   responsepos += QFIXEDSZ;
  }
 numanswers = ntohs(response.hdr.ancount);
 return 0;
}

static int findname(wanttype)
int wanttype;
{
 unsigned short rrtype;
 unsigned short rrdlen;
 int i;

 if (numanswers <= 0) return 2;
 --numanswers;
 if (responsepos == responseend) return DNS_SOFT;

 i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
 if (i < 0) return DNS_SOFT;
 responsepos += i;

 i = responseend - responsepos;
 if (i < 4 + 3 * 2) return DNS_SOFT;
   
 rrtype = getshort(responsepos);
 rrdlen = getshort(responsepos + 8);
 responsepos += 10;

 if (rrtype == wanttype)
  {
   if (dn_expand(response.buf,responseend,responsepos,name,MAXDNAME) < 0)
     return DNS_SOFT;
   responsepos += rrdlen;
   return 1;
  }
   
 responsepos += rrdlen;
 return 0;
}

static int findip(wanttype)
int wanttype;
{
 unsigned short rrtype;
 unsigned short rrdlen;
 int i;

 if (numanswers <= 0) return 2;
 --numanswers;
 if (responsepos == responseend) return DNS_SOFT;

 i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
 if (i < 0) return DNS_SOFT;
 responsepos += i;

 i = responseend - responsepos;
 if (i < 4 + 3 * 2) return DNS_SOFT;
   
 rrtype = getshort(responsepos);
 rrdlen = getshort(responsepos + 8);
 responsepos += 10;

 if (rrtype == wanttype)
  {
   if (rrdlen < 4)
     return DNS_SOFT;
   ip.d[0] = responsepos[0];
   ip.d[1] = responsepos[1];
   ip.d[2] = responsepos[2];
   ip.d[3] = responsepos[3];
   responsepos += rrdlen;
   return 1;
  }
   
 responsepos += rrdlen;
 return 0;
}

static int findmx(wanttype)
int wanttype;
{
 unsigned short rrtype;
 unsigned short rrdlen;
 int i;

 if (numanswers <= 0) return 2;
 --numanswers;
 if (responsepos == responseend) return DNS_SOFT;

 i = dn_expand(response.buf,responseend,responsepos,name,MAXDNAME);
 if (i < 0) return DNS_SOFT;
 responsepos += i;

 i = responseend - responsepos;
 if (i < 4 + 3 * 2) return DNS_SOFT;
   
 rrtype = getshort(responsepos);
 rrdlen = getshort(responsepos + 8);
 responsepos += 10;

 if (rrtype == wanttype)
  {
   if (rrdlen < 3)
     return DNS_SOFT;
   pref = (responsepos[0] << 8) + responsepos[1];
   if (dn_expand(response.buf,responseend,responsepos + 2,name,MAXDNAME) < 0)
     return DNS_SOFT;
   responsepos += rrdlen;
   return 1;
  }
   
 responsepos += rrdlen;
 return 0;
}

void dns_init(flagsearch)
int flagsearch;
{
 res_init();
 if (flagsearch) lookup = res_search;
}

int dns_cname(sa)
stralloc *sa;
{
 int r;
 int loop;
 for (loop = 0;loop < 10;++loop)
  {
   if (!sa->len) return loop;
   if (sa->s[sa->len - 1] == ']') return loop;
   if (sa->s[sa->len - 1] == '.') { --sa->len; continue; }
   switch(resolve(sa,T_ANY))
    {
     case DNS_MEM: return DNS_MEM;
     case DNS_SOFT: return DNS_SOFT;
     case DNS_HARD: return loop;
     default:
       while ((r = findname(T_CNAME)) != 2)
	{
	 if (r == DNS_SOFT) return DNS_SOFT;
	 if (r == 1)
	  {
	   if (!stralloc_copys(sa,name)) return DNS_MEM;
	   break;
	  }
	}
       if (r == 2) return loop;
    }
  }
 return DNS_HARD; /* alias loop */
}

#define FMT_IAA 40

static int iaafmt(s,ip)
char *s;
struct ip_address *ip;
{
 unsigned int i;
 unsigned int len;
 len = 0;
 i = fmt_ulong(s,(unsigned long) ip->d[3]); len += i; if (s) s += i;
 i = fmt_str(s,"."); len += i; if (s) s += i;
 i = fmt_ulong(s,(unsigned long) ip->d[2]); len += i; if (s) s += i;
 i = fmt_str(s,"."); len += i; if (s) s += i;
 i = fmt_ulong(s,(unsigned long) ip->d[1]); len += i; if (s) s += i;
 i = fmt_str(s,"."); len += i; if (s) s += i;
 i = fmt_ulong(s,(unsigned long) ip->d[0]); len += i; if (s) s += i;
 i = fmt_str(s,".in-addr.arpa."); len += i; if (s) s += i;
 return len;
}

int dns_ptr(sa,ip)
stralloc *sa;
struct ip_address *ip;
{
 int r;

 if (!stralloc_ready(sa,iaafmt((char *) 0,ip))) return DNS_MEM;
 sa->len = iaafmt(sa->s,ip);
 switch(resolve(sa,T_PTR))
  {
   case DNS_MEM: return DNS_MEM;
   case DNS_SOFT: return DNS_SOFT;
   case DNS_HARD: return DNS_HARD;
  }
 while ((r = findname(T_PTR)) != 2)
  {
   if (r == DNS_SOFT) return DNS_SOFT;
   if (r == 1)
    {
     if (!stralloc_copys(sa,name)) return DNS_MEM;
     return 0;
    }
  }
 return DNS_HARD;
}

static int dns_ipplus(ia,sa,pref)
ipalloc *ia;
stralloc *sa;
int pref;
{
 int r;
 struct ip_mx ix;

 if (!stralloc_copy(&glue,sa)) return DNS_MEM;
 if (!stralloc_0(&glue)) return DNS_MEM;
 if (glue.s[0]) {
   ix.pref = 0;
   if (!glue.s[ip_scan(glue.s,&ix.ip)] || !glue.s[ip_scanbracket(glue.s,&ix.ip)])
    {
     if (!ipalloc_append(ia,&ix)) return DNS_MEM;
     return 0;
    }
 }

 switch(resolve(sa,T_A))
  {
   case DNS_MEM: return DNS_MEM;
   case DNS_SOFT: return DNS_SOFT;
   case DNS_HARD: return DNS_HARD;
  }
 while ((r = findip(T_A)) != 2)
  {
   ix.ip = ip;
   ix.pref = pref;
   if (r == DNS_SOFT) return DNS_SOFT;
   if (r == 1)
     if (!ipalloc_append(ia,&ix)) return DNS_MEM;
  }
 return 0;
}

int dns_ip(ia,sa)
ipalloc *ia;
stralloc *sa;
{
 if (!ipalloc_readyplus(ia,0)) return DNS_MEM;
 ia->len = 0;
 return dns_ipplus(ia,sa,0);
}

int dns_mxip(ia,sa,random)
ipalloc *ia;
stralloc *sa;
unsigned long random;
{
 int r;
 struct mx { stralloc sa; unsigned short p; } *mx;
 struct ip_mx ix;
 int nummx;
 int i;
 int j;
 int flagsoft;

 if (!ipalloc_readyplus(ia,0)) return DNS_MEM;
 ia->len = 0;

 if (!stralloc_copy(&glue,sa)) return DNS_MEM;
 if (!stralloc_0(&glue)) return DNS_MEM;
 if (glue.s[0]) {
   ix.pref = 0;
   if (!glue.s[ip_scan(glue.s,&ix.ip)] || !glue.s[ip_scanbracket(glue.s,&ix.ip)])
    {
     if (!ipalloc_append(ia,&ix)) return DNS_MEM;
     return 0;
    }
 }

 switch(resolve(sa,T_MX))
  {
   case DNS_MEM: return DNS_MEM;
   case DNS_SOFT: return DNS_SOFT;
   case DNS_HARD: return dns_ip(ia,sa);
  }

 mx = (struct mx *) alloc(numanswers * sizeof(struct mx));
 if (!mx) return DNS_MEM;
 nummx = 0;

 while ((r = findmx(T_MX)) != 2)
  {
   if (r == DNS_SOFT) { alloc_free(mx); return DNS_SOFT; }
   if (r == 1)
    {
     mx[nummx].p = pref;
     mx[nummx].sa.s = 0;
     if (!stralloc_copys(&mx[nummx].sa,name))
      {
       while (nummx > 0) alloc_free(mx[--nummx].sa.s);
       alloc_free(mx); return DNS_MEM;
      }
     ++nummx;
    }
  }

 if (!nummx) return dns_ip(ia,sa); /* e.g., CNAME -> A */

 flagsoft = 0;
 while (nummx > 0)
  {
   unsigned long numsame;

   i = 0;
   numsame = 1;
   for (j = 1;j < nummx;++j)
     if (mx[j].p < mx[i].p)
      {
       i = j;
       numsame = 1;
      }
     else if (mx[j].p == mx[i].p)
      {
       ++numsame;
       random = random * 69069 + 1;
       if ((random / 2) < (2147483647 / numsame))
         i = j;
      }

   switch(dns_ipplus(ia,&mx[i].sa,mx[i].p))
    {
     case DNS_MEM: case DNS_SOFT:
       flagsoft = 1; break;
    }

   alloc_free(mx[i].sa.s);
   mx[i] = mx[--nummx];
  }

 alloc_free(mx);
 return flagsoft;
}