wraith-ircbot/src/mod/dns.mod/coredns.c

/*
 * dnscore.c -- part of dns.mod
 *   This file contains all core functions needed for the eggdrop dns module.
 *   Many of them are only minimaly modified from the original source.
 *
 * Modified/written by Fabian Knittel <fknittel@gmx.de>
 *
 */

/*
 * Borrowed from mtr  --  a network diagnostic tool
 * Copyright (C) 1997,1998  Matt Kimball <mkimball@xmission.com>
 * Released under the GPL, as above.
 *
 * Non-blocking DNS portion --
 * Copyright (C) 1998  Simon Kirby <sim@neato.org>
 * Released under the GPL, as above.
 */

#include "src/net.h"
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <errno.h>


/* Defines */

#define BASH_SIZE	 8192		/* Size of hash tables */
#define HOSTNAMELEN 	  255		/* From RFC */
#define RES_RETRYDELAY      3
#define RES_MAXSENDS        4
#define RES_FAILEDDELAY   600		/* TTL for failed records (in
					   seconds). */
#define RES_MAX_TTL     86400		/* Maximum TTL (in seconds). */

#define RES_ERR "DNS Resolver error: "
#define RES_MSG "DNS Resolver: "
#define RES_WRN "DNS Resolver warning: "

#define MAX_PACKETSIZE (PACKETSZ)
#define MAX_DOMAINLEN (MAXDNAME)

/* Macros */

#define nonull(s) (s) ? s : nullstring
#define BASH_MODULO(x) ((x) & 8191)	/* Modulo for hash table size */

/* Non-blocking nameserver interface routines */

#ifdef DEBUG_DNS
#  define RESPONSECODES_COUNT 6
static char *responsecodes[RESPONSECODES_COUNT + 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",
};
#endif /* DEBUG_DNS */

#ifdef DEBUG_DNS
#  define RESOURCETYPES_COUNT 18
static const char *resourcetypes[RESOURCETYPES_COUNT + 1] = {
    "unknown type",
    "A: host address",
    "AAAA: host address v6",
    "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",
};
#endif /* DEBUG_DNS */

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

typedef struct {
    u_16bit_t	id;			/* Packet id */
    u_8bit_t	databyte_a;
    /* rd:1				recursion desired
     * tc:1				truncated message
     * aa:1				authoritive answer
     * opcode:4				purpose of message
     * qr:1				response flag
     */
    u_8bit_t	databyte_b;
    /* rcode:4				response code
     * unassigned:2			unassigned bits
     * pr:1				primary server required (non standard)
     * ra:1				recursion available
     */
    u_16bit_t	qdcount;		/* Query record count */
    u_16bit_t	ancount;		/* Answer record count */
    u_16bit_t	nscount;		/* Authority reference record count */
    u_16bit_t	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)

#define sucknetword(x)  ((x)+=2,((u_16bit_t)  (((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))))


static u_32bit_t resrecvbuf[(MAX_PACKETSIZE + 7) >> 2];	/* MUST BE DWORD ALIGNED */

static struct resolve *idbash[BASH_SIZE];
static struct resolve *ipbash[BASH_SIZE];
static struct resolve *hostbash[BASH_SIZE];
static struct resolve *expireresolves = NULL;

static IP localhost;

static long idseed = 0xdeadbeef;
static long aseed;

static int resfd;

static char tempstring[512] = "";
static char namestring[1024 + 1] = "";
static char stackstring[1024 + 1] = "";

#ifdef DEBUG_DNS
static char sendstring[1024 + 1] = "";
#endif /* DEBUG_DNS */

static const char nullstring[] = "";


/*
 *    Miscellaneous helper functions
 */

#ifdef DEBUG_DNS
/* Displays the time difference passed in signeddiff.
 */
static char *strtdiff(char *d, long signeddiff)
{
    u_32bit_t diff;
    u_32bit_t seconds, minutes, hours;
    long day;

    if ((diff = labs(signeddiff))) {
	seconds = diff % 60;
	diff /= 60;
	minutes = diff % 60;
	diff /= 60;
	hours = diff % 24;
	day = signeddiff / 86400;
	if (day)
	    sprintf(d, "%lid", day);
	else
	    *d = '\0';
	if (hours)
	    sprintf(d + strlen(d), "%uh", hours);
	if (minutes)
	    sprintf(d + strlen(d), "%um", minutes);
	if (seconds)
	    sprintf(d + strlen(d), "%us", seconds);
    } else
	sprintf(d, "0s");
    return d;
}
#endif /* DEBUG_DNS */

/* Allocate memory to hold one resolve request structure.
 */
static struct resolve *allocresolve()
{
    struct resolve *rp = NULL;

    rp = (struct resolve *) calloc(1, sizeof(struct resolve));
    return rp;
}

/*
 *    Hash and linked-list related functions
 */

/* Return the hash bucket number for id.
 */
inline static u_32bit_t getidbash(u_16bit_t id)
{
    return (u_32bit_t) BASH_MODULO(id);
}

/* Return the hash bucket number for ip.
 */
inline static u_32bit_t getipbash(IP ip)
{
    return (u_32bit_t) BASH_MODULO(ip);
}

/* Return the hash bucket number for host.
 */
static u_32bit_t gethostbash(char *host)
{
    u_32bit_t bashvalue = 0;

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

/* Insert request structure addrp into the id hash table.
 */
static void linkresolveid(struct resolve *addrp)
{
    struct resolve *rp = NULL;
    u_32bit_t 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 if (rp->id > addrp->id) {
	    addrp->previousid = rp->previousid;
	    addrp->nextid = rp;
	    if (rp->previousid)
		rp->previousid->nextid = addrp;
	    rp->previousid = addrp;
	} else		/* Trying to add the same id! */
	    return;
    } else
	addrp->nextid = addrp->previousid = NULL;
    idbash[bashnum] = addrp;
}

/* Remove request structure rp from the id hash table.
 */
static void unlinkresolveid(struct resolve *rp)
{
    u_32bit_t bashnum;

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

/* Insert request structure addrp into the host hash table.
 */
static void linkresolvehost(struct resolve *addrp)
{
    struct resolve *rp = NULL;
    u_32bit_t bashnum;
    int ret;

    bashnum = gethostbash(addrp->hostn);
    rp = hostbash[bashnum];
    if (rp) {
	while ((rp->nexthost) &&
	       (egg_strcasecmp(addrp->hostn, rp->nexthost->hostn) < 0))
	    rp = rp->nexthost;
	while ((rp->previoushost) &&
	       (egg_strcasecmp(addrp->hostn, rp->previoushost->hostn) > 0))
	    rp = rp->previoushost;
	ret = egg_strcasecmp(addrp->hostn, rp->hostn);
	if (ret < 0) {
	    addrp->previoushost = rp;
	    addrp->nexthost = rp->nexthost;
	    if (rp->nexthost)
		rp->nexthost->previoushost = addrp;
	    rp->nexthost = addrp;
	} else if (ret > 0) {
	    addrp->previoushost = rp->previoushost;
	    addrp->nexthost = rp;
	    if (rp->previoushost)
		rp->previoushost->nexthost = addrp;
	    rp->previoushost = addrp;
	} else		/* Trying to add the same host! */
	    return;
    } else
	addrp->nexthost = addrp->previoushost = NULL;
    hostbash[bashnum] = addrp;
}

/* Remove request structure rp from the host hash table.
 */
static void unlinkresolvehost(struct resolve *rp)
{
    u_32bit_t bashnum;

    bashnum = gethostbash(rp->hostn);
    if (hostbash[bashnum] == rp) {
	if (rp->previoushost)
	    hostbash[bashnum] = rp->previoushost;
	else
	    hostbash[bashnum] = rp->nexthost;
    }
    if (rp->nexthost)
	rp->nexthost->previoushost = rp->previoushost;
    if (rp->previoushost)
	rp->previoushost->nexthost = rp->nexthost;
    free(rp->hostn);
}

/* Insert request structure addrp into the ip hash table.
 */
static void linkresolveip(struct resolve *addrp)
{
    struct resolve *rp = NULL;
    u_32bit_t bashnum;

    bashnum = getipbash(addrp->ip);
    rp = ipbash[bashnum];
    if (rp) {
	while ((rp->nextip) && (addrp->ip > rp->nextip->ip))
	    rp = rp->nextip;
	while ((rp->previousip) && (addrp->ip < rp->previousip->ip))
	    rp = rp->previousip;
	if (rp->ip < addrp->ip) {
	    addrp->previousip = rp;
	    addrp->nextip = rp->nextip;
	    if (rp->nextip)
		rp->nextip->previousip = addrp;
	    rp->nextip = addrp;
	} else if (rp->ip > addrp->ip) {
	    addrp->previousip = rp->previousip;
	    addrp->nextip = rp;
	    if (rp->previousip)
		rp->previousip->nextip = addrp;
	    rp->previousip = addrp;
	} else		/* Trying to add the same ip! */
	    return;
    } else
	addrp->nextip = addrp->previousip = NULL;
    ipbash[bashnum] = addrp;
}

/* Remove request structure rp from the ip hash table.
 */
static void unlinkresolveip(struct resolve *rp)
{
    u_32bit_t bashnum;

    bashnum = getipbash(rp->ip);
    if (ipbash[bashnum] == rp) {
	if (rp->previousip)
	    ipbash[bashnum] = rp->previousip;
	else
	    ipbash[bashnum] = rp->nextip;
    }
    if (rp->nextip)
	rp->nextip->previousip = rp->previousip;
    if (rp->previousip)
	rp->previousip->nextip = rp->nextip;
}

/* Add request structure rp to the expireresolves list. Entries are sorted
 * by expire time.
 */
static void linkresolve(struct resolve *rp)
{
    struct resolve *irp = NULL;

    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;
	} 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 = rp;
    }
}

/* Remove reqeust structure rp from the expireresolves list.
 */
static 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;
}

/* Remove request structure rp from all lists and hash tables and
 * then delete and free the structure
 */
static void unlinkresolve(struct resolve *rp)
{

    untieresolve(rp);		/* Not really needed. Left in to be on the
				   safe side. */
    unlinkresolveid(rp);
    unlinkresolveip(rp);
    if (rp->hostn)
	unlinkresolvehost(rp);
    free(rp);
}

/* Find request structure using the id.
 */
static struct resolve *findid(u_16bit_t id)
{
    struct resolve *rp = NULL;
    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 */
}

/* Find request structure using the host.
 */
static struct resolve *findhost(char *hostn)
{
    struct resolve *rp = NULL;
    int bashnum;

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

/* Find request structure using the ip.
 */
static struct resolve *findip(IP ip)
{
    struct resolve *rp = NULL;
    u_32bit_t bashnum;

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


/*
 *    Network and resolver related functions
 */

/* Create packet for the request and send it to all available nameservers.
 */
static void dorequest(char *s, int type, u_16bit_t id)
{
    packetheader *hp = NULL;
    int r, i;
    u_8bit_t buf[(MAX_PACKETSIZE / sizeof(char)) + 1];

    r = res_mkquery(QUERY, s, C_IN, type, NULL, 0, NULL, buf,
		    MAX_PACKETSIZE);
    if (r == -1) {
	ddebug0(RES_ERR "Query too large.");
	return;
    }
    hp = (packetheader *) buf;
    hp->id = id;	/* htons() deliberately left out (redundant) */
    for (i = 0; i < _res.nscount; i++)
	(void) sendto(resfd, buf, r, 0,
		      (struct sockaddr *) &_res.nsaddr_list[i],
		      sizeof(struct sockaddr));
}

/* (Re-)send request with existing id.
 */
static void resendrequest(struct resolve *rp, int type)
{
    rp->sends++;
    /* Update expire time */
    rp->expiretime = now + (RES_RETRYDELAY * rp->sends);
    /* Add (back) to expire list */
    linkresolve(rp);

    if (type == T_A) {
	dorequest(rp->hostn, type, rp->id);
	ddebug1(RES_MSG "Sent domain lookup request for \"%s\".",
		rp->hostn);
    } else if (type == T_PTR) {
	sprintf(tempstring, "%u.%u.%u.%u.in-addr.arpa",
		((u_8bit_t *) & rp->ip)[3],
		((u_8bit_t *) & rp->ip)[2],
		((u_8bit_t *) & rp->ip)[1], ((u_8bit_t *) & rp->ip)[0]);
	dorequest(tempstring, type, rp->id);
	ddebug1(RES_MSG "Sent domain lookup request for \"%s\".",
		iptostr(rp->ip));
    }
}

/* Send request for the first time.
 */
static void sendrequest(struct resolve *rp, int type)
{
    /* Create unique id */
    do {
	idseed = (((idseed + idseed) | (long) now)
		  + idseed - 0x54bad4a) ^ aseed;
	aseed ^= idseed;
	rp->id = (u_16bit_t) idseed;
    } while (findid(rp->id));
    linkresolveid(rp);		/* Add id to id hash table */
    resendrequest(rp, type);	/* Send request */
}

/* Gets called as soon as the request turns out to have failed. Calls
 * the eggdrop hook.
 */
static void failrp(struct resolve *rp, int type)
{
    if (rp->state == STATE_FINISHED)
	return;
    rp->expiretime = now + RES_FAILEDDELAY;
    rp->state = STATE_FAILED;

    /* Expire time was changed, reinsert entry to maintain order */
    untieresolve(rp);
    linkresolve(rp);

    ddebug0(RES_MSG "Lookup failed.");
    dns_event_failure(rp, type);
}

/* Gets called as soon as the request turns out to be successful. Calls
 * the eggdrop hook.
 */
static void passrp(struct resolve *rp, long ttl, int type)
{
    rp->state = STATE_FINISHED;

    /* Do not cache entries for too long. */
    if (ttl < RES_MAX_TTL)
	rp->expiretime = now + (time_t) ttl;
    else
	rp->expiretime = now + RES_MAX_TTL;

    /* Expire time was changed, reinsert entry to maintain order */
    untieresolve(rp);
    linkresolve(rp);

    ddebug1(RES_MSG "Lookup successful: %s", rp->hostn);
    dns_event_success(rp, type);
}

/* Parses the response packets received.
 */
static void parserespacket(u_8bit_t *s, size_t l)
{
    struct resolve *rp = NULL;
    packetheader *hp = NULL;
    u_8bit_t *eob = NULL;
    u_8bit_t *c = NULL;
    long ttl;
    int r, usefulanswer;
    u_16bit_t rr, datatype, myclass, qdatatype, qclass;
    u_8bit_t rdatalength;

    if (l < sizeof(packetheader)) {
	debug0(RES_ERR "Packet smaller than standard header size.");
	return;
    }
    if (l == sizeof(packetheader)) {
	debug0(RES_ERR "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)
	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 */
	ddebug0(RES_ERR "Nameserver packet truncated.");
	return;
    }
    if (!getheader_qr(hp)) {	/* Not a reply */
	ddebug0(RES_ERR "Query packet received on nameserver communication socket.");
	return;
    }
    if (getheader_opcode(hp)) {	/* Not opcode 0 (standard query) */
	ddebug0(RES_ERR "Invalid opcode in response packet.");
	return;
    }
    eob = s + l;
    c = s + HFIXEDSZ;
    switch (getheader_rcode(hp)) {
    case NOERROR:
	if (hp->ancount) {
	    ddebug4(RES_MSG
		    "Received nameserver reply. (qd:%u an:%u ns:%u ar:%u)",
		    hp->qdcount, hp->ancount, hp->nscount, hp->arcount);
	    if (hp->qdcount != 1) {
		ddebug0(RES_ERR "Reply does not contain one query.");
		return;
	    }
	    if (c > eob) {
		ddebug0(RES_ERR "Reply too short.");
		return;
	    }
	    switch (rp->state) {	/* Construct expected query reply */
	    case STATE_PTRREQ:
		sprintf(stackstring,
			"%u.%u.%u.%u.in-addr.arpa",
			((u_8bit_t *) & rp->ip)[3],
			((u_8bit_t *) & rp->ip)[2],
			((u_8bit_t *) & rp->ip)[1], ((u_8bit_t *) & rp->ip)[0]);
		break;
	    case STATE_AREQ:
		strncpy(stackstring, rp->hostn, 1024);
	    }
	    *namestring = '\0';
	    r = dn_expand(s, s + l, c, namestring, MAXDNAME);
	    if (r == -1) {
		ddebug0(RES_ERR "dn_expand() failed while expanding query domain.");
		return;
	    }
	    namestring[strlen(stackstring)] = '\0';
	    if (egg_strcasecmp(stackstring, namestring)) {
		ddebug2(RES_MSG "Unknown query packet dropped. (\"%s\" does not match \"%s\")", stackstring, namestring);
		return;
	    }
	    ddebug1(RES_MSG "Queried domain name: \"%s\"", namestring);
	    c += r;
	    if (c + 4 > eob) {
		ddebug0(RES_ERR "Query resource record truncated.");
		return;
	    }
	    qdatatype = sucknetword(c);
	    qclass = sucknetword(c);
	    if (qclass != C_IN) {
		ddebug2(RES_ERR "Received unsupported query class: %u (%s)",
			qclass, qclass < CLASSTYPES_COUNT ?
					classtypes[qclass] :
					classtypes[CLASSTYPES_COUNT]);
	    }
	    switch (qdatatype) {
	    case T_PTR:
		if (!IS_PTR(rp)) {
		    ddebug0(RES_WRN "Ignoring response with unexpected query type \"PTR\".");
		    return;
		}
		break;
	    case T_A:
		if (!IS_A(rp)) {
		    ddebug0(RES_WRN "Ignoring response with unexpected query type \"PTR\".");
		    return;
		}
		break;
	    default:
		ddebug2(RES_ERR "Received unimplemented query type: %u (%s)",
			qdatatype,
			qdatatype < RESOURCETYPES_COUNT ?
				resourcetypes[qdatatype] :
				resourcetypes[RESOURCETYPES_COUNT]);
	    }
	    for (rr = hp->ancount + hp->nscount + hp->arcount; rr; rr--) {
		if (c > eob) {
		    ddebug0(RES_ERR "Packet does not contain all specified resouce records.");
		    return;
		}
		*namestring = '\0';
		r = dn_expand(s, s + l, c, namestring, MAXDNAME);
		if (r == -1) {
		    ddebug0(RES_ERR "dn_expand() failed while expanding answer domain.");
		    return;
		}
		namestring[strlen(stackstring)] = '\0';
		if (egg_strcasecmp(stackstring, namestring))
		    usefulanswer = 0;
		else
		    usefulanswer = 1;
		ddebug1(RES_MSG "answered domain query: \"%s\"", namestring);
		c += r;
		if (c + 10 > eob) {
		    ddebug0(RES_ERR "Resource record truncated.");
		    return;
		}
		datatype = sucknetword(c);
		myclass = sucknetword(c);
		ttl = sucknetlong(c);
		rdatalength = sucknetword(c);
		if (myclass != qclass) {
		    ddebug2(RES_MSG "query class: %u (%s)",
			    qclass,
			    qclass < CLASSTYPES_COUNT ?
				classtypes[qclass] :
				classtypes[CLASSTYPES_COUNT]);
		    ddebug2(RES_MSG "rr class: %u (%s)", myclass,
			    myclass < CLASSTYPES_COUNT ?
				classtypes[myclass] :
				classtypes[CLASSTYPES_COUNT]);
		    ddebug0(RES_ERR "Answered class does not match queried class.");
		    return;
		}
		if (!rdatalength) {
		    ddebug0(RES_ERR "Zero size rdata.");
		    return;
		}
		if (c + rdatalength > eob) {
		    ddebug0(RES_ERR "Specified rdata length exceeds packet size.");
		    return;
		}
		if (datatype == qdatatype) {
		    ddebug1(RES_MSG "TTL: %s", strtdiff(sendstring, ttl));
		    ddebug1(RES_MSG "TYPE: %s", datatype < RESOURCETYPES_COUNT ?
			    resourcetypes[datatype] :
			    resourcetypes[RESOURCETYPES_COUNT]);
		    if (usefulanswer)
			switch (datatype) {
			case T_A:
			    if (rdatalength != 4) {
				ddebug1(RES_ERR "Unsupported rdata format for \"A\" type. (%u bytes)", rdatalength);
				return;
			    }
			    egg_memcpy(&rp->ip, (IP *) c, sizeof(IP));
			    linkresolveip(rp);
			    passrp(rp, ttl, T_A);
			    return;
			case T_PTR:
			    *namestring = '\0';
			    r =	dn_expand(s, s + l, c, namestring, MAXDNAME);
			    if (r == -1) {
				ddebug0(RES_ERR "dn_expand() failed while expanding domain in rdata.");
				return;
			    }
			    ddebug1(RES_MSG "Answered domain: \"%s\"",
				   namestring);
			    if (r > HOSTNAMELEN) {
				ddebug0(RES_ERR "Domain name too long.");
				failrp(rp, T_PTR);
				return;
			    }
			    if (!rp->hostn) {
                                rp->hostn = strdup(namestring);
				linkresolvehost(rp);
				passrp(rp, ttl, T_PTR);
				return;
			    }
			    break;
			default:
			    ddebug2(RES_ERR "Received unimplemented data type: %u (%s)",
				    datatype,
				    datatype < RESOURCETYPES_COUNT ?
					resourcetypes[datatype] :
					resourcetypes[RESOURCETYPES_COUNT]);
			}
		} else if (datatype == T_CNAME) {
		    *namestring = '\0';
		    r =	dn_expand(s, s + l, c, namestring, MAXDNAME);
		    if (r == -1) {
			ddebug0(RES_ERR "dn_expand() failed while expanding domain in rdata.");
			return;
		    }
		    ddebug1(RES_MSG "answered domain is CNAME for: %s",
			   namestring);
		    /* The next responses will be related to the domain
		     * pointed to by CNAME, so we need to update which
		     * respones we regard as important.
		     */
		    strncpy(stackstring, namestring, 1024);
		} else {
		    ddebug2(RES_MSG "Ignoring resource type %u. (%s)",
			   datatype, datatype < RESOURCETYPES_COUNT ?
				resourcetypes[datatype] :
				resourcetypes[RESOURCETYPES_COUNT]);
		}
		c += rdatalength;
	    }
	} else {
	    ddebug0(RES_ERR "No error returned but no answers given.");
        }
	break;
    case NXDOMAIN:
	ddebug0(RES_MSG "Host not found.");
	switch (rp->state) {
	case STATE_PTRREQ:
		failrp(rp, T_PTR);
		break;
	case STATE_AREQ:
		failrp(rp, T_A);
		break;
	default:
		failrp(rp, 0);
		break;
	}
	break;
    default:
	ddebug2(RES_MSG "Received error response %u. (%s)",
		getheader_rcode(hp),
		getheader_rcode(hp) < RESPONSECODES_COUNT ?
			responsecodes[getheader_rcode(hp)] :
			responsecodes[RESPONSECODES_COUNT]);
    }
}

/* Read data received on our dns socket. This function is called
 * as soon as traffic is detected.
 */
static void dns_ack(void)
{
    struct sockaddr_in from;
    unsigned int fromlen = sizeof(struct sockaddr_in);
    int r, i;

    r =	recvfrom(resfd, (u_8bit_t *) resrecvbuf, MAX_PACKETSIZE, 0,
		 (struct sockaddr *) &from, &fromlen);
    if (r <= 0) {
	ddebug1(RES_MSG "Socket error: %s", strerror(errno));
	return;
    }
    /* Check to see if this server is actually one we sent to */
    if (from.sin_addr.s_addr == localhost) {
        for (i = 0; i < _res.nscount; i++)
	    /* 0.0.0.0 replies as 127.0.0.1 */
	    if ((_res.nsaddr_list[i].sin_addr.s_addr == from.sin_addr.s_addr)
		|| (!_res.nsaddr_list[i].sin_addr.s_addr))
		break;
    } else {
        for (i = 0; i < _res.nscount; i++)
	    if (_res.nsaddr_list[i].sin_addr.s_addr == from.sin_addr.s_addr)
		break;
    }
    if (i == _res.nscount) {
        ddebug1(RES_ERR "Received reply from unknown source: %s",
	       iptostr(from.sin_addr.s_addr));
    } else
        parserespacket((u_8bit_t *) resrecvbuf, (size_t) r);
}

/* Remove or resend expired requests. Called once a second.
 */
static void dns_check_expires(void)
{
    struct resolve *rp = NULL, *nextrp = NULL;

    /* Walk through sorted list ... */
    for (rp = expireresolves; (rp) && (now >= rp->expiretime);
	 rp = nextrp) {
	nextrp = rp->next;
	untieresolve(rp);
	switch (rp->state) {
	case STATE_FINISHED:	/* TTL has expired */
	case STATE_FAILED:	/* Fake TTL has expired */
	    ddebug4(RES_MSG "Cache record for \"%s\" (%s) has expired. (state: %u)  Marked for expire at: %ld.",
		   nonull(rp->hostn), iptostr(rp->ip), rp->state,
		   rp->expiretime);
	    unlinkresolve(rp);
	    break;
	case STATE_PTRREQ:	/* T_PTR send timed out */
	    if (rp->sends <= RES_MAXSENDS) {
	      ddebug1(RES_MSG "Resend #%d for \"PTR\" query...", rp->sends - 1);
	      resendrequest(rp, T_PTR);
	    } else {
	      ddebug0(RES_MSG "\"PTR\" query timed out.");
	      failrp(rp, T_PTR);
	    }
	    break;
	case STATE_AREQ:	/* T_A send timed out */
	    if (rp->sends <= RES_MAXSENDS) {
	      ddebug1(RES_MSG "Resend #%d for \"A\" query...", rp->sends - 1);
	      resendrequest(rp, T_A);
	    } else {
	      ddebug0(RES_MSG "\"A\" query timed out.");
	      failrp(rp, T_A);
	    }
	    break;
	default:		/* Unknown state, let it expire */
	    ddebug1(RES_WRN "Unknown request state %d. Request expired.",
		   rp->state);
	    failrp(rp, 0);
	}
    }
}

/* Start searching for a host-name, using it's ip-address.
 */
void dns_hostbyip(IP ip)
{
    struct resolve *rp = NULL;

    ip = htonl(ip);
    if ((rp = findip(ip))) {
	if (rp->state == STATE_FINISHED || rp->state == STATE_FAILED) {
	    if (rp->state == STATE_FINISHED && rp->hostn) {
		ddebug2(RES_MSG "Used cached record: %s == \"%s\".",
			    iptostr(ip), rp->hostn);
		dns_event_success(rp, T_PTR);
	    } else {
		ddebug1(RES_MSG "Used failed record: %s == ???", iptostr(ip));
		dns_event_failure(rp, T_PTR);
	    }
	}
	return;
    }

    ddebug0(RES_MSG "Creating new record");
    rp = allocresolve();
    rp->state = STATE_PTRREQ;
    rp->sends = 1;
    rp->ip = ip;
    linkresolveip(rp);
    sendrequest(rp, T_PTR);
}

/* Start searching for an ip-address, using it's host-name.
 */
void dns_ipbyhost(char *hostn)
{
    struct resolve *rp = NULL;
    struct in_addr inaddr;

    /* Check if someone passed us an IP address as hostname
     * and return it straight away.
     */
    if (egg_inet_aton(hostn, &inaddr)) {
      call_ipbyhost(hostn, ntohl(inaddr.s_addr), 1);
      return;
    }
    if ((rp = findhost(hostn))) {
	if (rp->state == STATE_FINISHED || rp->state == STATE_FAILED) {
	    if (rp->state == STATE_FINISHED && rp->ip) {
		ddebug2(RES_MSG "Used cached record: %s == \"%s\".", hostn,
		       iptostr(rp->ip));
		dns_event_success(rp, T_A);
	    } else {
		ddebug1(RES_MSG "Used failed record: %s == ???", hostn);
		dns_event_failure(rp, T_A);
	    }
	}
	return;
    }
    ddebug0(RES_MSG "Creating new record");
    rp = allocresolve();
    rp->state = STATE_AREQ;
    rp->sends = 1;
    rp->hostn = strdup(hostn);
    linkresolvehost(rp);
    sendrequest(rp, T_A);
}

/* Initialise the network.
 */
static int init_dns_network(void)
{
    int option;
    struct in_addr inaddr;

    resfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (resfd == -1) {
	putlog(LOG_MISC, "*",
		"Unable to allocate socket for nameserver communication: %s",
		strerror(errno));
	return 0;
    }
    (void) allocsock(resfd, SOCK_PASS);
    option = 1;
    if (setsockopt(resfd, SOL_SOCKET, SO_BROADCAST, (char *) &option,
	 sizeof(option))) {
	putlog(LOG_MISC, "*",
		"Unable to setsockopt() on nameserver communication socket: %s",
		strerror(errno));
	killsock(resfd);
	return 0;
    }

    egg_inet_aton("127.0.0.1", &inaddr);
    localhost = inaddr.s_addr;
    return 1;
}

/* Initialise the core dns system, returns 1 if all goes well, 0 if not.
 */
static int init_dns_core(void)
{
    int i;

    /* Initialise the resolv library. */
    res_init();
    if (!_res.nscount) {
	putlog(LOG_MISC, "*", "No nameservers defined.");
	return 0;
    }

    for (i = 0; i < _res.nscount; i++) {
      char s[102] = "";
      egg_inet_ntop(AF_INET, &_res.nsaddr_list[i].sin_addr, s, 101);
      sdprintf("added ns: %s", s);
      _res.nsaddr_list[i].sin_family = AF_INET;
    }


    if (!init_dns_network())
	return 0;

    /* Initialise the hash tables. */
    aseed = time(NULL) ^ (time(NULL) << 3) ^ (u_32bit_t) getpid();
    for (i = 0; i < BASH_SIZE; i++) {
	idbash[i] = NULL;
	ipbash[i] = NULL;
	hostbash[i] = NULL;
    }
    expireresolves = NULL;
    return 1;
}