dns.c

/*
    mtr  --  a network diagnostic tool
    Copyright (C) 1997,1998  Matt Kimball

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 2 as 
    published by the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/*
    Non-blocking DNS portion --
    Copyright (C) 1998 by Simon Kirby <sim@neato.org>
    Released under GPL, as above.
*/

#include <config.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <sys/errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define BIND_8_COMPAT
#include <arpa/nameser.h>
#include <netdb.h>
#include <resolv.h>
#include <unistd.h>
#include <fcntl.h>
#include <ctype.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>

#include "mtr.h"
#include "dns.h"
#include "net.h"

/* OSX  Needs this. I don't know how to enable this for them automatically. 
 * Should be easy with autoconf. Please submit a patch if you know 
 * autoconf.... -- REW
 */
#if 0 
#include "nameser8_compat.h"
#endif


#ifdef NO_STRERROR
extern int sys_nerr;
extern char *sys_errlist[];
#define strerror(errno) (((errno) >= 0 && (errno) < sys_nerr) ? sys_errlist[errno] : "unlisted error")
#endif

#if !HAVE_DECL_ERRNO
/*  Hmm, it seems Irix requires this  */
extern int errno;
#endif

extern int af;

/* Defines */

#undef Debug

#undef CorruptCheck
#undef WipeFrees
#undef WipeMallocs

#define BashSize 8192			/* Size of hash tables */
#define BashModulo(x) ((x) & 8191)	/* Modulo for hash table size: */
#define HostnameLength 255		/* From RFC */
#define ResRetryDelay1 3
#define ResRetryDelay2 4
#define ResRetryDelay3 5

/* Macros */

#define nonull(s) (s) ? s : nullstring

/* Structures */

struct resolve {
   struct resolve *next;
   struct resolve *previous;
   struct resolve *nextid;
   struct resolve *previousid;
   struct resolve *nextip;
   struct resolve *previousip;
   struct resolve *nexthost;
   struct resolve *previoushost;
   float expiretime; /* Fucking HPUX has a problem with "double" here. */
   char *hostname;
   ip_t ip;
   word id;
   byte state;
};

/* Non-blocking nameserver interface routines */

#define MaxPacketsize (PACKETSZ)
#define DomainLength (MAXDNAME)

#define OpcodeCount 3
char *opcodes[OpcodeCount+1] = {
   "standard query",
   "inverse query",
   "server status request",
   "unknown",
};

#define ResponsecodeCount 6
char *responsecodes[ResponsecodeCount+1] = {
   "no error",
   "format error in query",
   "server failure",
   "queried domain name does not exist",
   "requested query type not implemented",
   "refused by name server",
   "unknown error",
};

#define ResourcetypeCount 17
char *resourcetypes[ResourcetypeCount+1] = {
   "unknown type",
   "A: host address",
   "NS: authoritative name server",
   "MD: mail destination (OBSOLETE)",
   "MF: mail forwarder (OBSOLETE)",
   "CNAME: name alias",
   "SOA: authority record",
   "MB: mailbox domain name (EXPERIMENTAL)",
   "MG: mail group member (EXPERIMENTAL)",
   "MR: mail rename domain name (EXPERIMENTAL)",
   "NULL: NULL RR (EXPERIMENTAL)",
   "WKS: well known service description",
   "PTR: domain name pointer",
   "HINFO: host information",
   "MINFO: mailbox or mail list information",
   "MX: mail exchange",
   "TXT: text string",
   "unknown type",
};

#define ClasstypeCount 5
char *classtypes[ClasstypeCount+1] = {
   "unknown class",
   "IN: the Internet",
   "CS: CSNET (OBSOLETE)",
   "CH: CHAOS",
   "HS: Hesoid [Dyer 87]",
   "unknown class"
};

char *rrtypes[] = {
   "Unknown",
   "Query",
   "Answer",
   "Authority reference",
   "Resource reference",
};


/* Please don't use a trailing comma in enumerations: It doesn't
   work on all compilers -- REW */
enum {
   RR_UNKNOWN,
   RR_QUERY,
   RR_ANSWER,
   RR_AUTHORITY,
   RR_RESOURCE
};

typedef struct {
   word id;             /* Packet id */
   byte databyte_a;
      /* rd:1           recursion desired
       * tc:1           truncated message
       * aa:1           authoritive answer
       * opcode:4       purpose of message
       * qr:1           response flag
       */
   byte databyte_b;
      /* rcode:4        response code
       * unassigned:2   unassigned bits
       * pr:1           primary server required (non standard)
       * ra:1           recursion available
       */
   word qdcount;        /* Query record count */
   word ancount;        /* Answer record count */
   word nscount;        /* Authority reference record count */
   word arcount;        /* Resource reference record count */
} packetheader;

#ifndef HFIXEDSZ
#define HFIXEDSZ (sizeof(packetheader))
#endif

/*
 * Byte order independent macros for packetheader
 */
#define getheader_rd(x) (x->databyte_a & 1)
#define getheader_tc(x) ((x->databyte_a >> 1) & 1)
#define getheader_aa(x) ((x->databyte_a >> 2) & 1)
#define getheader_opcode(x) ((x->databyte_a >> 3) & 15)
#define getheader_qr(x) (x->databyte_a >> 7)
#define getheader_rcode(x) (x->databyte_b & 15)
#define getheader_pr(x) ((x->databyte_b >> 6) & 1)
#define getheader_ra(x) (x->databyte_b >> 7)

#if 0

/* The execution order inside an expression is undefined! That means that
   this might work, but then again, it might not... Sun Lint pointed this 
   one out...*/

#define sucknetword(x) (((word)*(x) << 8) | (((x)+= 2)[-1]))
#define sucknetshort(x) (((short)*(x) << 8) | (((x)+= 2)[-1]))
#define sucknetdword(x) (((dword)*(x) << 24) | ((x)[1] << 16) | ((x)[2] << 8) | (((x)+= 4)[-1]))
#define sucknetlong(x) (((long)*(x) << 24) | ((x)[1] << 16) | ((x)[2] << 8) | (((x)+= 4)[-1]))
#else

#define sucknetword(x)  ((x)+=2,((word)  (((x)[-2] <<  8) | ((x)[-1] <<  0))))
#define sucknetshort(x) ((x)+=2,((short) (((x)[-2] <<  8) | ((x)[-1] <<  0))))
#define sucknetdword(x) ((x)+=4,((dword) (((x)[-4] << 24) | ((x)[-3] << 16) | \
                                          ((x)[-2] <<  8) | ((x)[-1] <<  0))))
#define sucknetlong(x)  ((x)+=4,((long)  (((x)[-4] << 24) | ((x)[-3] << 16) | \
                                          ((x)[-2] <<  8) | ((x)[-1] <<  0))))
#endif

enum {
   STATE_FINISHED,
   STATE_FAILED,
   STATE_PTRREQ1,
   STATE_PTRREQ2,
   STATE_PTRREQ3
};

#define Is_PTR(x) ((x->state == STATE_PTRREQ1) || (x->state == STATE_PTRREQ2) || (x->state == STATE_PTRREQ3))

dword resrecvbuf[(MaxPacketsize + 7) >> 2]; /* MUST BE DWORD ALIGNED */

struct resolve *idbash[BashSize];
struct resolve *ipbash[BashSize];
struct resolve *hostbash[BashSize];
struct resolve *expireresolves = NULL;
struct resolve *lastresolve = NULL;
struct logline *streamlog = NULL;
struct logline *lastlog = NULL;

ip_t alignedip;
ip_t localhost;

double sweeptime;

#ifdef Debug
int debug = 1;
#else
int debug = 0;
#endif

dword mem = 0;

dword res_iplookupsuccess = 0;
dword res_reversesuccess = 0;
dword res_nxdomain = 0;
dword res_nserror = 0;
dword res_hostipmismatch = 0;
dword res_unknownid = 0;
dword res_resend = 0;
dword res_timeout = 0;

dword resolvecount = 0;

long idseed = 0xdeadbeef;
long aseed;

#ifdef ENABLE_IPV6
struct sockaddr_storage from_sastruct;
struct sockaddr_in6 * from6 = (struct sockaddr_in6 *) &from_sastruct;
#else
struct sockaddr_in from_sastruct;
#endif

struct sockaddr_in * from4 = (struct sockaddr_in *) &from_sastruct;
struct sockaddr * from = (struct sockaddr *) &from_sastruct;

int resfd;
socklen_t fromlen = sizeof from_sastruct;

char tempstring[16384+1+1];
char sendstring[1024+1];
char namestring[1024+1];
char stackstring[1024+1];

char nullstring[] = "";

int use_dns = 1;

#ifdef res_ninit
#define MY_RES_INIT() res_ninit(&myres);
#define RES_MKQUERY(a, b, c, d, e, f, g, h, i) \
    res_nmkquery(&myres, a, b, c, d, e, f, g, h, i)
struct __res_state myres;
#else
#define MY_RES_INIT() res_init();
#define RES_MKQUERY(a, b, c, d, e, f, g, h, i) \
    res_mkquery(a, b, c, d, e, f, g, h, i)
#define myres _res
#endif

/* Code */
#ifdef CorruptCheck
#define TOT_SLACK 2
#define HEAD_SLACK 1
/* Need an entry for sparc systems here too. 
   Don't try this on Sparc for now. */
#else
#ifdef sparc
#define TOT_SLACK 2
#define HEAD_SLACK 2
#else
#define TOT_SLACK 1
#define HEAD_SLACK 1
#endif
#endif


void *statmalloc(size_t size)
{
  void *p;
  size_t mallocsize;

  mem+= size;
  mallocsize = size + TOT_SLACK * sizeof(dword);

  p = malloc(mallocsize);
  if (!p) {
    fprintf(stderr,"malloc() of %u bytes failed: %s\n", (unsigned int)size, strerror(errno));
    exit(-1);
  }
  *((dword *)p) = (dword)size;
#ifdef CorruptCheck
  *(byte *)((char *)p + size + sizeof(dword) + sizeof(byte) * 0) = 0xde;
  *(byte *)((char *)p + size + sizeof(dword) + sizeof(byte) * 1) = 0xad;
  *(byte *)((char *)p + size + sizeof(dword) + sizeof(byte) * 2) = 0xbe;
  *(byte *)((char *)p + size + sizeof(dword) + sizeof(byte) * 3) = 0xef;
#endif
  p = (void *)((dword *)p + HEAD_SLACK);
#ifdef WipeMallocs
  memset(p,0xf0,size);
#endif
  return p;
}


void statfree(void *p)
{
  if (p) {
    if (*((dword *)p - HEAD_SLACK) == 0) {
      fprintf(stderr,"ERROR: Attempt to free pointer twice.\n");
      *(int*)0=0;
      exit(-1);
    } else {
      if (*((dword *)p - HEAD_SLACK) > 8192) {
	fprintf (stderr,"ERROR: Corrupted free() buffer. (header)\n");
	*(int*)0=0;
	exit(-1);
      }
#ifdef CorruptCheck
      if ((*(byte *)((char *)p + (*((dword *)p - 1)) + sizeof(byte) * 0) != 0xde) ||
	  (*(byte *)((char *)p + (*((dword *)p - 1)) + sizeof(byte) * 1) != 0xad) ||
	  (*(byte *)((char *)p + (*((dword *)p - 1)) + sizeof(byte) * 2) != 0xbe) ||
	  (*(byte *)((char *)p + (*((dword *)p - 1)) + sizeof(byte) * 3) != 0xef)) {
	fprintf(stderr,"ERROR: Corrupted free() buffer. (footer)\n");
	*(int*)0=0;
	exit(-1);
      }
#endif
      mem-= *((dword *)p - HEAD_SLACK);
#ifdef WipeFrees
      memset(p,0xfe,*((dword *)p - HEAD_SLACK));
      *((dword *)p - 1) = 0;
#endif
      free((dword *)p - HEAD_SLACK);
    }
  }
}


char *strtdiff(char *d,long signeddiff)
{
  dword diff;
  dword seconds,minutes,hours;
  long days;

  if ((diff = labs(signeddiff))) {
    seconds = diff % 60; diff/= 60;
    minutes = diff % 60; diff/= 60;
    hours = diff % 24;
    days = signeddiff / (60 * 60 * 24);
    if (days)
      sprintf(d,"%lid",days);
    else
      *d = '\0';
    if (hours)
      sprintf(d + strlen(d),"%luh",hours);
    if (minutes)
      sprintf(d + strlen(d),"%lum",minutes);
    if (seconds)
      sprintf(d + strlen(d),"%lus",seconds);
  } else
    sprintf(d,"0s");
  return d;
}


int issetfd(fd_set *set,int fd)
{
  return (int)((FD_ISSET(fd,set)) && 1);
}


void setfd(fd_set *set,int fd)
{
  FD_SET(fd,set);
}


void clearfd(fd_set *set,int fd)
{
  FD_CLR(fd,set);
}


void clearset(fd_set *set)
{
  FD_ZERO(set);
}


char *strlongip(ip_t * ip)
{
#ifdef ENABLE_IPV6
  static char buf[INET6_ADDRSTRLEN];

  return (char *) inet_ntop( af, ip, buf, sizeof buf );
#else
  return inet_ntoa( *ip );
#endif
}


int longipstr( char *s, ip_t *dst, int af )
{
#ifdef ENABLE_IPV6
  return inet_pton( af, s, dst );
#else
  return inet_aton( s, dst );
#endif
}


struct hostent * dns_forward(const char *name)
{
  struct hostent *host;

  if ((host = gethostbyname(name)))
    return host;
  else
    return NULL;
}


int dns_waitfd(void)
{
  return resfd;
}


void dns_open(void)
{
  int option,i;

  if (!dns) return;
  MY_RES_INIT();
  if (!myres.nscount) {
    fprintf(stderr,"No nameservers defined.\n");
    exit(-1);
  }
  myres.options|= RES_RECURSE | RES_DEFNAMES | RES_DNSRCH;
  for (i = 0;i < myres.nscount;i++)
    myres.nsaddr_list[i].sin_family = AF_INET;
  resfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (resfd == -1) {
    fprintf(stderr,"Unable to allocate socket for nameserver communication: %s\n",
	    strerror(errno));
    exit(-1);
  }
  option = 1;
  if (setsockopt(resfd,SOL_SOCKET,SO_BROADCAST,(char *)&option,sizeof(option))) {
    fprintf(stderr,"Unable to setsockopt() on nameserver communication socket: %s\n",
	    strerror(errno));
    exit(-1);
  }
  longipstr( "127.0.0.1", &localhost, AF_INET );
  aseed = time(NULL) ^ (time(NULL) << 3) ^ (dword)getpid();
  for (i = 0;i < BashSize;i++) {
    idbash[i] = NULL;
    hostbash[i] = NULL;
  }
}


struct resolve *allocresolve(void)
{
  struct resolve *rp;

  rp = (struct resolve *)statmalloc(sizeof(struct resolve));
  if (!rp) {
    fprintf(stderr,"statmalloc() failed: %s\n",strerror(errno));
    exit(-1);
  }
  memset(rp,0, sizeof(struct resolve));
  return rp;
}


dword getidbash(word id)
{
  return (dword)BashModulo(id);
}


dword getipbash(ip_t * ip)
{
  char *p = (char *) ip;
  int i, len = 0;
  dword bashvalue = 0;

  switch ( af ) {
  case AF_INET:
    len = sizeof (struct in_addr);
    break;
#ifdef ENABLE_IPV6
  case AF_INET6:
    len = sizeof (struct in6_addr);
    break;
#endif
  }
  for (i = 0; i < len; i++, p++) {
    bashvalue^= *p;
    bashvalue+= (*p >> 1) + (bashvalue >> 1);
  }
  return BashModulo(bashvalue);
}


dword gethostbash(char *host)
{
  dword bashvalue = 0;

  for (;*host;host++) {
    bashvalue^= *host;
    bashvalue+= (*host >> 1) + (bashvalue >> 1);
  }
  return BashModulo(bashvalue);
}


void linkresolveid(struct resolve *addrp)
{
  struct resolve *rp;
  dword bashnum;

  bashnum = getidbash(addrp->id);
  rp = idbash[bashnum];
  if (rp) {
    while ((rp->nextid) && (addrp->id > rp->nextid->id))
      rp = rp->nextid;
    while ((rp->previousid) && (addrp->id < rp->previousid->id))
      rp = rp->previousid;
    if (rp->id < addrp->id) {
      addrp->previousid = rp;
      addrp->nextid = rp->nextid;
      if (rp->nextid)
	rp->nextid->previousid = addrp;
      rp->nextid = addrp;
    } else {
      addrp->previousid = rp->previousid;
      addrp->nextid = rp;
      if (rp->previousid)
	rp->previousid->nextid = addrp;
      rp->previousid = addrp;
    }
  } else
    addrp->nextid = addrp->previousid = NULL;
  idbash[bashnum] = addrp;
}


void unlinkresolveid(struct resolve *rp)
{
  dword bashnum;

  bashnum = getidbash(rp->id);
  if (idbash[bashnum] == rp) 
    idbash[bashnum] = (rp->previousid)? rp->previousid : rp->nextid;
  if (rp->nextid)
    rp->nextid->previousid = rp->previousid;
  if (rp->previousid)
    rp->previousid->nextid = rp->nextid;
}


void linkresolvehost(struct resolve *addrp)
{
  struct resolve *rp;
  dword bashnum;

  bashnum = gethostbash(addrp->hostname);
  rp = hostbash[bashnum];
  if (rp) {
    while ((rp->nexthost) && (strcasecmp(addrp->hostname,rp->nexthost->hostname) < 0))
      rp = rp->nexthost;
    while ((rp->previoushost) && (strcasecmp(addrp->hostname,rp->previoushost->hostname) > 0))
      rp = rp->previoushost;
    if (strcasecmp(addrp->hostname,rp->hostname) < 0) {
      addrp->previoushost = rp;
      addrp->nexthost = rp->nexthost;
      if (rp->nexthost)
	rp->nexthost->previoushost = addrp;
      rp->nexthost = addrp;
    } else {
      addrp->previoushost = rp->previoushost;
      addrp->nexthost = rp;
      if (rp->previoushost)
	rp->previoushost->nexthost = addrp;
      rp->previoushost = addrp;
    }
  } else
    addrp->nexthost = addrp->previoushost = NULL;
  hostbash[bashnum] = addrp;
}


void unlinkresolvehost(struct resolve *rp)
{
  dword bashnum;

  bashnum = gethostbash(rp->hostname);
  if (hostbash[bashnum] == rp)
    hostbash[bashnum] = (rp->previoushost)? rp->previoushost : rp->nexthost;
  if (rp->nexthost)
    rp->nexthost->previoushost = rp->previoushost;
  if (rp->previoushost)
    rp->previoushost->nexthost = rp->nexthost;
  statfree(rp->hostname);
}


void linkresolveip(struct resolve *addrp)
{
  struct resolve *rp;
  dword bashnum;

  bashnum = getipbash( &(addrp->ip) );
  rp = ipbash[bashnum];
  if (rp) {
    while ((rp->nextip) &&
	   ( addrcmp( (void *) &(addrp->ip),
		      (void *) &(rp->nextip->ip), af ) > 0 ))
      rp = rp->nextip;
    while ((rp->previousip) &&
	   ( addrcmp( (void *) &(addrp->ip),
		      (void *) &(rp->previousip->ip), af ) < 0 ))
      rp = rp->previousip;
    if ( addrcmp( (void *) &(rp->ip), (void *) &(addrp->ip), af ) < 0 ) {
      addrp->previousip = rp;
      addrp->nextip = rp->nextip;
      if (rp->nextip)
	rp->nextip->previousip = addrp;
      rp->nextip = addrp;
    } else {
      addrp->previousip = rp->previousip;
      addrp->nextip = rp;
      if (rp->previousip)
	rp->previousip->nextip = addrp;
      rp->previousip = addrp;
    }
  } else
    addrp->nextip = addrp->previousip = NULL;
  ipbash[bashnum] = addrp;
}


void unlinkresolveip(struct resolve *rp)
{
  dword bashnum;

  bashnum = getipbash( &(rp->ip) );
  if (ipbash[bashnum] == rp)
    ipbash[bashnum] = (rp->previousip)? rp->previousip : rp->nextip;
  if (rp->nextip)
    rp->nextip->previousip = rp->previousip;
  if (rp->previousip)
    rp->previousip->nextip = rp->nextip;
}


void linkresolve(struct resolve *rp)
{
  struct resolve *irp;

  if (expireresolves) {
    irp = expireresolves;
    while ((irp->next) && (rp->expiretime >= irp->expiretime)) irp = irp->next;
    if (rp->expiretime >= irp->expiretime) {
      rp->next = NULL;
      rp->previous = irp;
      irp->next = rp;
      lastresolve = rp;
    } else {
      rp->previous = irp->previous;
      rp->next = irp;
      if (irp->previous)
	irp->previous->next = rp;
      else
	expireresolves = rp;
      irp->previous = rp;
    }
  } else {
    rp->next = NULL;
    rp->previous = NULL;
    expireresolves = lastresolve = rp;
  }
  resolvecount++;
}


void lastlinkresolve(struct resolve *rp)
{
  struct resolve *irp;

  if (lastresolve) {
    irp = lastresolve;
    while ((irp->previous) && (rp->expiretime < irp->expiretime)) irp = irp->previous;
    while ((irp->next) && (rp->expiretime >= irp->expiretime)) irp = irp->next;
    if (rp->expiretime >= irp->expiretime) {
      rp->next = NULL;
      rp->previous = irp;
      irp->next = rp;
      lastresolve = rp;
    } else {
      rp->previous = irp->previous;
      rp->next = irp;
      if (irp->previous)
	irp->previous->next = rp;
      else
	expireresolves = rp;
      irp->previous = rp;
    }
  } else {
    rp->next = NULL;
    rp->previous = NULL;
    expireresolves = lastresolve = rp;
  }
  resolvecount++;
}


void untieresolve(struct resolve *rp)
{
  if (rp->previous)
    rp->previous->next = rp->next;
  else
    expireresolves = rp->next;
  if (rp->next)
    rp->next->previous = rp->previous;
  else
    lastresolve = rp->previous;
  resolvecount--;
}


void unlinkresolve(struct resolve *rp)
{
  untieresolve(rp);
  unlinkresolveid(rp);
  unlinkresolveip(rp);
  if (rp->hostname)
    unlinkresolvehost(rp);
}


struct resolve *findid(word id)
{
  struct resolve *rp;
  int bashnum;

  bashnum = getidbash(id);
  rp = idbash[bashnum];
  if (rp) {
    while ((rp->nextid) && (id >= rp->nextid->id))
      rp = rp->nextid;
    while ((rp->previousid) && (id <= rp->previousid->id))
      rp = rp->previousid;
    if (id == rp->id) {
      idbash[bashnum] = rp;
      return rp;
    } else
      return NULL;
  }
  return rp; /* NULL */
}


struct resolve *findhost(char *hostname)
{
  struct resolve *rp;
  int bashnum;

  bashnum = gethostbash(hostname);
  rp = hostbash[bashnum];
  if (rp) {
    while ((rp->nexthost) && (strcasecmp(hostname,rp->nexthost->hostname) >= 0))
      rp = rp->nexthost;
    while ((rp->previoushost) && (strcasecmp(hostname,rp->nexthost->hostname) <= 0))
      rp = rp->previoushost;
    if (strcasecmp(hostname,rp->hostname))
      return NULL;
    else {
      hostbash[bashnum] = rp;
      return rp;
    }
  }
  return rp; /* NULL */
}


struct resolve *findip(ip_t * ip)
{
  struct resolve *rp;
  dword bashnum;

  bashnum = getipbash(ip);
  rp = ipbash[bashnum];
  if (rp) {
    while ((rp->nextip) &&
	   ( addrcmp( (void *) ip, (void *) &(rp->nextip->ip), af ) >= 0 ))
      rp = rp->nextip;
    while ((rp->previousip) &&
           ( addrcmp( (void *) ip, (void *) &(rp->previousip->ip), af ) <= 0 ))
      rp = rp->previousip;
    if ( addrcmp( (void *) ip, (void *) &(rp->ip), af ) == 0 ) {
      ipbash[bashnum] = rp;
      return rp;
    } else
      return NULL;
  }
  return rp; /* NULL */
}


void restell(char *s)
{
  fputs(s,stderr);
  fputs("\r",stderr);
}


void dorequest(char *s,int type,word id)
{
  packetheader *hp;
  int r,i;
  unsigned char buf[MaxPacketsize];

  r = RES_MKQUERY(QUERY,s,C_IN,type,NULL,0,NULL,(unsigned char*)buf,MaxPacketsize);
  if (r == -1) {
    restell("Resolver error: Query too large.");
    return;
  }
  hp = (packetheader *)buf;
  hp->id = id;	/* htons() deliberately left out (redundant) */
  for (i = 0;i < myres.nscount;i++)
    (void)sendto(resfd,buf,r,0,(struct sockaddr *)&myres.nsaddr_list[i],
		 sizeof(struct sockaddr));
}

void resendrequest(struct resolve *rp,int type)
{
  if (type == T_A) {
    dorequest(rp->hostname,type,rp->id);
    if (debug) {
      snprintf(tempstring, sizeof(tempstring), "Resolver: Sent reverse authentication request for \"%s\".",
	      rp->hostname);
      restell(tempstring);
    }
  } else if (type == T_PTR) {
    switch ( af ) {
    case AF_INET:
    sprintf(tempstring,"%u.%u.%u.%u.in-addr.arpa",
	    ((byte *)&rp->ip)[3],
	    ((byte *)&rp->ip)[2],
	    ((byte *)&rp->ip)[1],
	    ((byte *)&rp->ip)[0]);
      break;
#ifdef ENABLE_IPV6
    case AF_INET6:
      addr2ip6arpa( &(rp->ip), tempstring );
      break;
#endif
    }
    dorequest(tempstring,type,rp->id);
    if (debug) {
      snprintf(tempstring, sizeof(tempstring), "Resolver: Sent domain lookup request for \"%s\".",
	      strlongip( &(rp->ip) ));
      restell(tempstring);
    }
  }
}

void sendrequest(struct resolve *rp,int type)
{
  do {
    idseed = (((idseed + idseed) | (long)time(NULL)) + idseed - 0x54bad4a) ^ aseed;
    aseed^= idseed;
    rp->id = (word)idseed;
  } while (findid(rp->id));
  linkresolveid(rp);
  resendrequest(rp,type);
}


void failrp(struct resolve *rp)
{
  if (rp->state == STATE_FINISHED)
    return;
  rp->state = STATE_FAILED;
  untieresolve(rp);
  if (debug)
    restell("Resolver: Lookup failed.\n");
}


void passrp(struct resolve *rp,long ttl)
{
  rp->state = STATE_FINISHED;
  rp->expiretime = sweeptime + (double)ttl;
  untieresolve(rp);
  if (debug) {
    snprintf(tempstring, sizeof(tempstring), "Resolver: Lookup successful: %s\n",rp->hostname);
    restell(tempstring);
  }
}


void parserespacket(byte *s, int l)
{
  struct resolve *rp;
  packetheader *hp;
  byte *eob;
  byte *c;
  long ttl;
  int r,usefulanswer;
  word rr,datatype,class,qdatatype,qclass;
  byte rdatalength;

  if (l < (int) sizeof(packetheader)) {
    restell("Resolver error: Packet smaller than standard header size.");
    return;
  }
  if (l == (int) sizeof(packetheader)) {
    restell("Resolver error: Packet has empty body.");
    return;
  }
  hp = (packetheader *)s;
  /* Convert data to host byte order */
  /* hp->id does not need to be redundantly byte-order flipped, it is only echoed by nameserver */
  rp = findid(hp->id);
  if (!rp) {
    res_unknownid++;
    return;
  }
  if ((rp->state == STATE_FINISHED) || (rp->state == STATE_FAILED))
    return;
  hp->qdcount = ntohs(hp->qdcount);
  hp->ancount = ntohs(hp->ancount);
  hp->nscount = ntohs(hp->nscount);
  hp->arcount = ntohs(hp->arcount);
  if (getheader_tc(hp)) { /* Packet truncated */
    restell("Resolver error: Nameserver packet truncated.");
    return;
  }
  if (!getheader_qr(hp)) { /* Not a reply */
    restell("Resolver error: Query packet received on nameserver communication socket.");
    return;
  }
  if (getheader_opcode(hp)) { /* Not opcode 0 (standard query) */
    restell("Resolver error: Invalid opcode in response packet.");
    return;
  }
  eob = s + l;
  c = s + HFIXEDSZ;
  switch (getheader_rcode(hp)) {
  case NOERROR:
    if (hp->ancount) {
      if (debug) {
	snprintf(tempstring, sizeof(tempstring), "Resolver: Received nameserver reply. (qd:%u an:%u ns:%u ar:%u)",
                hp->qdcount,hp->ancount,hp->nscount,hp->arcount);
	restell(tempstring);
      }
      if (hp->qdcount != 1) {
	restell("Resolver error: Reply does not contain one query.");
	return;
      }
      if (c > eob) {
	restell("Resolver error: Reply too short.");
	return;
      }
      switch (rp->state) { /* Construct expected query reply */
      case STATE_PTRREQ1:
      case STATE_PTRREQ2:
      case STATE_PTRREQ3:
        switch ( af ) {
        case AF_INET:
	sprintf(stackstring,"%u.%u.%u.%u.in-addr.arpa",
		((byte *)&rp->ip)[3],
		((byte *)&rp->ip)[2],
		((byte *)&rp->ip)[1],
		((byte *)&rp->ip)[0]);
	break;
#ifdef ENABLE_IPV6
        case AF_INET6:
          addr2ip6arpa( &(rp->ip), stackstring );
          break;
#endif
        }
      }
      *namestring = '\0';
      r = dn_expand(s,s + l,c,namestring,MAXDNAME);
      if (r == -1) {
	restell("Resolver error: dn_expand() failed while expanding query domain.");
	return;
      }
      namestring[strlen(stackstring)] = '\0';
      if (strcasecmp(stackstring,namestring)) {
	if (debug) {
	  snprintf(tempstring, sizeof(tempstring), "Resolver: Unknown query packet dropped. (\"%s\" does not match \"%s\")",
		  stackstring,namestring);
	  restell(tempstring);
	}
	return;
      }
      if (debug) {
	snprintf(tempstring, sizeof(tempstring), "Resolver: Queried domain name: \"%s\"",namestring);
	restell(tempstring);
      }
      c+= r;
      if (c + 4 > eob) {
	restell("Resolver error: Query resource record truncated.");
	return;
      }
      qdatatype = sucknetword(c);
      qclass = sucknetword(c);
      if (qclass != C_IN) {
	snprintf(tempstring, sizeof(tempstring), "Resolver error: Received unsupported query class: %u (%s)",
                qclass,qclass < ClasstypeCount ? classtypes[qclass] :
		classtypes[ClasstypeCount]);
	restell(tempstring);
      }
      switch (qdatatype) {
      case T_PTR:
	if (!Is_PTR(rp))
	  if (debug) {
	    restell("Resolver warning: Ignoring response with unexpected query type \"PTR\".");
	    return;
	  }
	break;
      default:
	snprintf(tempstring, sizeof(tempstring), "Resolver error: Received unimplemented query type: %u (%s)",
		qdatatype,qdatatype < ResourcetypeCount ?
		resourcetypes[qdatatype] : resourcetypes[ResourcetypeCount]);
	restell(tempstring);
      }
      for (rr = hp->ancount + hp->nscount + hp->arcount;rr;rr--) {
	if (c > eob) {
	  restell("Resolver error: Packet does not contain all specified resouce records.");
	  return;
	}
	*namestring = '\0';
	r = dn_expand(s,s + l,c,namestring,MAXDNAME);
	if (r == -1) {
	  restell("Resolver error: dn_expand() failed while expanding answer domain.");
	  return;
	}
	namestring[strlen(stackstring)] = '\0';
	if (strcasecmp(stackstring,namestring))
	  usefulanswer = 0;
	else
	  usefulanswer = 1;
	if (debug) {
	  snprintf(tempstring, sizeof(tempstring), "Resolver: answered domain query: \"%s\"",namestring);
	  restell(tempstring);
	}
	c+= r;
	if (c + 10 > eob) {
	  restell("Resolver error: Resource record truncated.");
	  return;
	}
	datatype = sucknetword(c);
	class = sucknetword(c);
	ttl = sucknetlong(c);
	rdatalength = sucknetword(c);
	if (class != qclass) {
	  snprintf(tempstring, sizeof(tempstring), "query class: %u (%s)",qclass,qclass < ClasstypeCount ?
		  classtypes[qclass] : classtypes[ClasstypeCount]);
	  restell(tempstring);
	  snprintf(tempstring, sizeof(tempstring), "rr class: %u (%s)",class,class < ClasstypeCount ?
		  classtypes[class] : classtypes[ClasstypeCount]);
	  restell(tempstring);
	  restell("Resolver error: Answered class does not match queried class.");
	  return;
	}
	if (!rdatalength) {
	  restell("Resolver error: Zero size rdata.");
	  return;
	}
	if (c + rdatalength > eob) {
	  restell("Resolver error: Specified rdata length exceeds packet size.");
	  return;
	}
	if (datatype == qdatatype || datatype == T_CNAME) {
	  if (debug) {
	    snprintf(tempstring, sizeof(tempstring), "Resolver: TTL: %s",strtdiff(sendstring,ttl));
	    restell(tempstring);
	  }
	  if (usefulanswer)
	    switch (datatype) {
	    case T_A:
	      if (rdatalength != 4) {
		snprintf(tempstring, sizeof(tempstring), "Resolver error: Unsupported rdata format for \"A\" type. (%u bytes)",
			rdatalength);
		restell(tempstring);
		return;
	      }
	      if ( addrcmp( (void *) &(rp->ip), (void *) c, af ) == 0 ) {
		snprintf(tempstring, sizeof(tempstring), "Resolver: Reverse authentication failed: %s != ",
			strlongip( &(rp->ip) ));
		addrcpy( (void *) &alignedip, (void *) c, af );
		strcat(tempstring,strlongip( &alignedip ));
		restell(tempstring);
		res_hostipmismatch++;
		failrp(rp);
	      } else {
		snprintf(tempstring, sizeof(tempstring), "Resolver: Reverse authentication complete: %s == \"%s\".",
			strlongip( &(rp->ip) ),nonull(rp->hostname));
		restell(tempstring);
		res_reversesuccess++;
		passrp(rp,ttl);
		return;
	      }
	      break;
	    case T_PTR:
	    case T_CNAME:
	      *namestring = '\0';
	      r = dn_expand(s,s + l,c,namestring,MAXDNAME);
	      if (r == -1) {
		restell("Resolver error: dn_expand() failed while expanding domain in rdata.");
		return;
	      }
	      if (debug) {
		snprintf(tempstring, sizeof(tempstring), "Resolver: Answered domain: \"%s\"",namestring);
		restell(tempstring);
	      }
	      if (r > HostnameLength) {
		restell("Resolver error: Domain name too long.");
		failrp(rp);
		return;
	      }
	      if (datatype == T_CNAME) {
		strcpy(stackstring,namestring);
		break;
	      }
	      if (!rp->hostname) {
		rp->hostname = (char *)statmalloc(strlen(namestring) + 1);
		if (!rp->hostname) {
		  fprintf(stderr,"statmalloc() error: %s\n",strerror(errno));
		  exit(-1);
		}
		strcpy(rp->hostname,namestring);
		linkresolvehost(rp);
		passrp(rp,ttl);
		res_iplookupsuccess++;
	      }
	      break;
	    default:
	      snprintf(tempstring, sizeof(tempstring), "Resolver error: Received unimplemented data type: %u (%s)",
		      datatype,datatype < ResourcetypeCount ?
		      resourcetypes[datatype] : resourcetypes[ResourcetypeCount]);
	      restell(tempstring);
	    }
	} else {
	  if (debug) {
	    snprintf(tempstring, sizeof(tempstring), "Resolver: Ignoring resource type %u. (%s)",
		    datatype,datatype < ResourcetypeCount ?
		    resourcetypes[datatype] : resourcetypes[ResourcetypeCount]);
	    restell(tempstring);
	  }
	}
	c+= rdatalength;
      }
    } else
      restell("Resolver error: No error returned but no answers given.");
    break;
  case NXDOMAIN:
    if (debug)
      restell("Resolver: Host not found.");
    res_nxdomain++;
    failrp(rp);
    break;
  default:
    snprintf(tempstring, sizeof(tempstring), "Resolver: Received error response %u. (%s)",
	    getheader_rcode(hp),getheader_rcode(hp) < ResponsecodeCount ?
	    responsecodes[getheader_rcode(hp)] : responsecodes[ResponsecodeCount]);
    restell(tempstring);
    res_nserror++;
  }
}


void dns_ack(void)
{
  int r,i;

  r = recvfrom(resfd,(byte *)resrecvbuf,MaxPacketsize,0,
               from, &fromlen);
  if (r > 0) {
    /* Check to see if this server is actually one we sent to */
    if ( addrcmp( (void *) &(from4->sin_addr), (void *) &localhost,
                  (int) AF_INET ) == 0 ) {
      for (i = 0;i < myres.nscount;i++)
	if ( addrcmp( (void *) &(myres.nsaddr_list[i].sin_addr),
		      (void *) &(from4->sin_addr), (int) AF_INET ) == 0 ||
	     addrcmp( (void *) &(myres.nsaddr_list[i].sin_addr),
		      (void *) &unspec_addr, (int) AF_INET ) == 0 )	/* 0.0.0.0 replies as 127.0.0.1 */
	  break;
    } else
      for (i = 0;i < myres.nscount;i++)
	if ( addrcmp( (void *) &(myres.nsaddr_list[i].sin_addr),
		      (void *) &(from4->sin_addr), AF_INET ) == 0 )
	  break;
    if (i == myres.nscount) {
      snprintf(tempstring, sizeof(tempstring), "Resolver error: Received reply from unknown source: %s",
	      inet_ntoa(from4->sin_addr ));
      restell(tempstring);
    } else
      parserespacket((byte *)resrecvbuf,r);
  } else {
    snprintf(tempstring, sizeof(tempstring), "Resolver: Socket error: %s",strerror(errno));
    restell(tempstring);
  }
}


int istime(double x,double *sinterval)
{
  if (x) {
    if (x > sweeptime) {
      if (*sinterval > x - sweeptime)
	*sinterval = x - sweeptime;
    } else
      return 1;
  }
  return 0;
}


void dns_events(double *sinterval)
{
  struct resolve *rp,*nextrp;

  for (rp = expireresolves;(rp) && (sweeptime >= rp->expiretime);rp = nextrp) {
    nextrp = rp->next;
    switch (rp->state) {
    case STATE_FINISHED:	/* TTL has expired */
    case STATE_FAILED:	/* Fake TTL has expired */
      if (debug) {
	snprintf(tempstring, sizeof(tempstring), "Resolver: Cache record for \"%s\" (%s) has expired. (state: %u)  Marked for expire at: %g, time: %g.",
                nonull(rp->hostname), strlongip( &(rp->ip) ), 
		rp->state, rp->expiretime, sweeptime);
	restell(tempstring);
      }
      unlinkresolve(rp);
      break;
    case STATE_PTRREQ1:	/* First T_PTR send timed out */
      resendrequest(rp,T_PTR);
      restell("Resolver: Send #2 for \"PTR\" query...");
      rp->state++;
      rp->expiretime = sweeptime + ResRetryDelay2;
      (void)istime(rp->expiretime,sinterval);
      res_resend++;
      break;
    case STATE_PTRREQ2:	/* Second T_PTR send timed out */
      resendrequest(rp,T_PTR);
      restell("Resolver: Send #3 for \"PTR\" query...");
      rp->state++;
      rp->expiretime = sweeptime + ResRetryDelay3;
      (void)istime(rp->expiretime,sinterval);
      res_resend++;
      break;
    case STATE_PTRREQ3:	/* Third T_PTR timed out */
      restell("Resolver: \"PTR\" query timed out.");
      failrp(rp);
      (void)istime(rp->expiretime,sinterval);
      res_timeout++;
      break;
    }
  }
  if (expireresolves)
    (void)istime(expireresolves->expiretime,sinterval);
}


char *dns_lookup2(ip_t * ip)
{
  struct resolve *rp;

  if ((rp = findip(ip))) {
    if ((rp->state == STATE_FINISHED) || (rp->state == STATE_FAILED)) {
      if ((rp->state == STATE_FINISHED) && (rp->hostname)) {
	if (debug) {
	  snprintf(tempstring, sizeof(tempstring), "Resolver: Used cached record: %s == \"%s\".\n",
		  strlongip(ip),rp->hostname);
	  restell(tempstring);
	}
	return rp->hostname;
      } else {
	if (debug) {
	  snprintf(tempstring, sizeof(tempstring), "Resolver: Used failed record: %s == ???\n",
		  strlongip(ip));
	  restell(tempstring);
	}
	return NULL;
      }
    }
    return NULL;
  }
  if (debug)
    fprintf(stderr,"Resolver: Added to new record.\n");
  rp = allocresolve();
  rp->state = STATE_PTRREQ1;
  rp->expiretime = sweeptime + ResRetryDelay1;
  addrcpy( (void *) &(rp->ip), (void *) ip, af );
  linkresolve(rp);
  addrcpy( (void *) &(rp->ip), (void *) ip, af );
  linkresolveip(rp);
  sendrequest(rp,T_PTR);
  return NULL;
}


char *dns_lookup(ip_t * ip)
{
  char *t;

  if (!dns) return strlongip (ip);
  t = dns_lookup2 (ip);
  return (t&&use_dns)?t:strlongip(ip);
}

#ifdef ENABLE_IPV6
/* Returns an ip6.arpa character string. */
void addr2ip6arpa( ip_t * ip, char * buf ) {
  unsigned char * p = (unsigned char *) ip;
  char * b = buf;
  int i;

  for ( i = sizeof (struct in6_addr) - 1; i >= 0; i-- ) {
        sprintf( b, "%x.%x.", p[i] % 16, p[i] >> 4 );
        b += 4;
  }
  sprintf( b, "ip6.arpa" );
  return;
}
#endif

/* Resolve an IP address to a hostname. */ 
struct hostent *addr2host( const char *addr, int af ) {
  int len = 0;
  switch ( af ) {
  case AF_INET:
    len = sizeof( struct in_addr );
    break;
#ifdef ENABLE_IPV6
  case AF_INET6:
    len = sizeof( struct in6_addr );
    break;
#endif
  }
  return gethostbyaddr( addr, len, af );
}