nonamed.c

Go to the documentation of this file.

/*      nonamed - Not a name daemon, but plays one on TV.
 *                                                      Author: Kees J. Bot
 *                                                              29 Nov 1994
 */
static const char version[] = "2.7";

/* Use the file reading gethostent() family of functions. */
#define sethostent      _sethostent
#define gethostent      _gethostent
#define endhostent      _endhostent

#define nil ((void*)0)
#include <sys/types.h>
#include <stdio.h>
#include <syslog.h>
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <time.h>
#include <limits.h>
#include <signal.h>
#include <assert.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/asynchio.h>
#include <net/hton.h>
#include <net/netlib.h>
#include <net/gen/in.h>
#include <net/gen/inet.h>
#include <net/gen/nameser.h>
#include <net/gen/resolv.h>
#include <net/gen/netdb.h>
#include <net/gen/socket.h>
#include <net/gen/tcp.h>
#include <net/gen/tcp_io.h>
#include <net/gen/udp.h>
#include <net/gen/udp_hdr.h>
#include <net/gen/udp_io.h>
#include <net/gen/dhcp.h>

#include <minix/paths.h>

#define HTTL            3600L   /* Default time to live for /etc/hosts data. */
#define SHORT_TIMEOUT      2    /* If you expect an answer soon. */
#define MEDIUM_TIMEOUT     4    /* Soon, but not that soon. */
#define LONG_TIMEOUT     300    /* For stream connections to a real named. */
#define N_IDS            256    /* Keep track of this many queries. */
#define N_DATAMAX (4096*sizeof(char *)) /* Default response cache size. */
#define N_NAMEDS           8    /* Max # name daemons we can keep track of. */
#define NO_FD           (-1)    /* No name daemon channel here. */
#define T_NXD   ((u16_t) -1)    /* A "type" signalling a nonexistent domain. */

/* Can't do async I/O under standard Minix, so forget about TCP. */
#define DO_TCP (__minix_vmd || !__minix)

/* Host data, file to store our process id in, our cache, DHCP's cache. */
static char HOSTS[]=    _PATH_HOSTS;
static char PIDFILE[]=  "/usr/run/nonamed.pid";
static char NNCACHE[]=  "/usr/adm/nonamed.cache";
static char DHCPCACHE[]= _PATH_DHCPCACHE;

/* Magic string to head the cache file. */
static char MAGIC[4]=   "NND\2";

#define arraysize(a)    (sizeof(a) / sizeof((a)[0]))
#define arraylimit(a)   ((a) + arraysize(a))
#define between(a, c, z) ((unsigned) ((c) - (a)) <= (unsigned) ((z) - (a)))

/* The start of time and the far future. */
#define IMMEDIATE       ((time_t) 0)
#define NEVER           ((time_t) ((time_t) -1 < 0 ? LONG_MAX : ULONG_MAX))

static unsigned debug;          /* Debug level. */
static time_t now;              /* Current time. */
static u32_t stale;             /* Extension time for stale data. */
static u32_t httl;              /* TTL for /etc/hosts data. */
static int reinit, done;        /* Reinit config / program is done. */
static int single;              /* Run single on a nondefault interface. */
static int localonly;           /* Only accept local queries. */
#define LOCALHOST       0x7F000001

static void report(const char *label)
{
    fprintf(stderr, "nonamed: %s: %s\n", label, strerror(errno));
}

static void fatal(const char *label)
{
    report(label);
    if (debug >= 3) { fflush(nil); abort(); }
    exit(1);
}

static void *allocate(void *mem, size_t size)
{
    if ((mem= realloc(mem, size)) == nil) fatal("malloc()");
    return mem;
}

static void deallocate(void *mem)
{
    free(mem);
}

static char *timegmt(time_t t)
/* Simple "time in seconds to GMT time today" converter. */
{
    unsigned h, m, s;
    static char asctime[sizeof("00:00:00")];

    s= t % 60;
    t /= 60;
    m= t % 60;
    t /= 60;
    h= t % 24;
    sprintf(asctime, "%02u:%02u:%02u", h, m, s);
    return asctime;
}

static char *nowgmt(void)
{
    return timegmt(now);
}

#define PC(n)   ((void) sizeof(char [sizeof(*(n)) == 1]), (char *) (n))
#define namecpy(n1, n2)         strcpy(PC(n1), PC(n2))
#define namecat(n1, n2)         strcat(PC(n1), PC(n2))
#define namechr(n, c)           ((u8_t *) strchr(PC(n), (c)))
#define namecmp(n1, n2)         strcasecmp(PC(n1), PC(n2))
#define namencmp(n1, n2, len)   strncasecmp(PC(n1), PC(n2), len)

typedef struct dns {            /* A DNS packet. */
        dns_hdr_t       hdr;            /* DNS header. */
        u8_t            data[PACKETSZ - sizeof(dns_hdr_t)];     /* DNS data. */
} dns_t;

/* Addres of DNS packet to octet address, or vv. */
#define dns2oct(dp)             ((u8_t *) (dp))
#define oct2dns(dp)             ((dns_t *) (dp))

typedef struct query {          /* One cached answer to a query. */
        struct query    *less;          /* Less recently used. */
        struct query    *more;          /* More recently used. */
        time_t          age;            /* Time it was added. */
        time_t          stale;          /* Time it goes stale by TTL. */
        u16_t           usage;          /* Counts of queries answered. */
        u8_t            flags;          /* QF_REFRESH. */
        size_t          size;           /* Size of DNS packet. */
        dns_t           dns;            /* Answer to query as a DNS packet. */
} query_t;

#define QF_REFRESH      0x01            /* This stale data must be refreshed. */
#define QU_SHIFT        1               /* To shift usage by when evicting. */

/* Size of new query_t or existing query_t. */
#define query_allocsize(dnssize)        (offsetof(query_t, dns) + (dnssize))
#define query_size(qp)                  query_allocsize((qp)->size)

static query_t *mru, *lru;      /* Most and least recently used answers. */
static int q_refresh;           /* Set when an entry needs refreshing. */

static void pack16(u8_t *buf, u16_t s)
/* Pack a 16 bit value into a byte array. */
{
    buf[0]= ((u8_t *) &s)[0];
    buf[1]= ((u8_t *) &s)[1];
}

static void pack32(u8_t *buf, u32_t l)
/* Pack a 32 bit value into a byte array. */
{
    buf[0]= ((u8_t *) &l)[0];
    buf[1]= ((u8_t *) &l)[1];
    buf[2]= ((u8_t *) &l)[2];
    buf[3]= ((u8_t *) &l)[3];
}

static u16_t upack16(u8_t *buf)
/* Unpack a 16 bit value from a byte array. */
{
    u16_t s;

    ((u8_t *) &s)[0]= buf[0];
    ((u8_t *) &s)[1]= buf[1];
    return s;
}

static u32_t upack32(u8_t *buf)
/* Unpack a 32 bit value from a byte array. */
{
    u32_t l;

    ((u8_t *) &l)[0]= buf[0];
    ((u8_t *) &l)[1]= buf[1];
    ((u8_t *) &l)[2]= buf[2];
    ((u8_t *) &l)[3]= buf[3];
    return l;
}

/* Encoding of RRs: i(paddr), d(omain), l(ong), c(har), s(tring), (s)h(ort). */
static char *encoding[] = {
        "c*",           /* anything unknown is c* */
        "i",            /* A */
        "d",            /* NS */
        "d",            /* MD */
        "d",            /* MF */
        "d",            /* CNAME */
        "ddlllll",      /* SOA */
        "d",            /* MB */
        "d",            /* MG */
        "d",            /* MR */
        "c*",           /* NULL */
        "icc*",         /* WKS */
        "d",            /* PTR */
        "ss",           /* HINFO */
        "dd",           /* MINFO */
        "hd",           /* MX */
        "s*",           /* TXT */
};

static char *itoa(char *fmt, u32_t i)
{
    static char output[32 + 3 * sizeof(i)];

    sprintf(output, fmt, (unsigned long) i);
    return output;
}

static char *classname(unsigned class)
/* Class name of a resource record, for debug purposes. */
{
    static char *classes[] = { "IN", "CS", "CHAOS", "HS" };

    if ((class - C_IN) < arraysize(classes)) return classes[class - C_IN];
    return itoa("C_%u", class);
}

static char *typename(unsigned type)
/* Type name of a resource record, for debug purposes. */
{
    static char type_A[][6] = {
        "A", "NS", "MD", "MF", "CNAME", "SOA", "MB", "MG", "MR", "NULL",
        "WKS", "PTR", "HINFO", "MINFO", "MX", "TXT",
    };
    static char type_AXFR[][6] = {
        "AXFR", "MAILB", "MAILA", "ANY",
    };
    if ((type - T_A) < arraysize(type_A)) return type_A[type - T_A];
    if ((type - T_AXFR) < arraysize(type_AXFR)) return type_AXFR[type - T_AXFR];
    return itoa("T_%u", type);
}

static int print_qrr(dns_t *dp, size_t size, u8_t *cp0, int q)
/* Print a query (q) or resource record (!q) from 'cp0' in a DNS packet for
 * debug purposes.  Return number of bytes skipped or -1 on error.
 */
{
    u8_t name[MAXDNAME+1];
    u8_t *cp;
    char *ep;
    u8_t *dlim, *rlim;
    u16_t type, class, rdlength;
    u32_t ttl;
    int r;

    cp= cp0;
    dlim= dns2oct(dp) + size;
    r= dn_expand(dns2oct(dp), dlim, cp, name, MAXDNAME);
    if (r == -1) return -1;
    cp += r;
    if (cp + 2 * sizeof(u16_t) > dlim) return -1;
    type= ntohs(upack16(cp));
    cp += sizeof(u16_t);
    class= ntohs(upack16(cp));
    cp += sizeof(u16_t);
    printf("%-25s", (char *) name);
    if (q) {
        /* We're just printing a query segment, stop right here. */
        printf(" %8s", classname(class));
        printf(" %-5s", typename(type));
        return cp - cp0;
    }
    if (cp + sizeof(u32_t) + sizeof(u16_t) > dlim) return -1;
    ttl= ntohl(upack32(cp));
    cp += sizeof(u32_t);
    rdlength= ntohs(upack16(cp));
    cp += sizeof(u16_t);
    if (cp + rdlength > dlim) return -1;
    rlim = cp + rdlength;
    printf(" %5lu", (unsigned long) ttl);
    printf(" %s", classname(class));
    printf(" %-5s", typename(type));
    ep= type < arraysize(encoding) ? encoding[type] : encoding[0];
    while (*ep != 0) {
        switch (*ep++) {
        case 'i':
            if (cp + sizeof(u32_t) > rlim) return -1;
            printf(" %s", inet_ntoa(upack32(cp)));
            cp += sizeof(u32_t);
            break;
        case 'l':
            if (cp + sizeof(u32_t) > rlim) return -1;
            printf(" %ld", (long)(i32_t) ntohl(upack32(cp)));
            cp += sizeof(u32_t);
            break;
        case 'd':
            r= dn_expand(dns2oct(dp), dlim, cp, name, MAXDNAME);
            if (r == -1) return -1;
            printf(" %s", (char *) name);
            cp += r;
            break;
        case 'c':
            if (cp >= rlim) return -1;
            printf(" %02X", *cp++);
            break;
        case 's':
            r= *cp + 1;
            if (cp + r > rlim) return -1;
            printf(" \"%.*s\"", *cp, (char *) (cp + 1));
            cp += r;
            break;
        case 'h':
            if (cp + sizeof(u16_t) > rlim) return -1;
            printf(" %u", ntohs(upack16(cp)));
            cp += sizeof(u16_t);
            break;
        }
        if (*ep == '*') ep= cp < rlim ? ep-1 : ep+1;
    }
    return cp - cp0;
}

static void dns_tell(int indent, dns_t *dp, size_t size)
/* Explain a DNS packet, for debug purposes. */
{
    u8_t *cp;
    int r, i;
    unsigned count[4];
    static char label[4][4]= { "QD:", "AN:", "NS:", "AR:" };
    static char rcodes[][9] = {
        "NOERROR", "FORMERR", "SERVFAIL", "NXDOMAIN", "NOTIMP", "REFUSED"
    };

    if (size < sizeof(dns_hdr_t)) return;

    printf("%*s", indent, "");
    printf("DNS %s:", (dp->hdr.dh_flag1 & DHF_QR) ? "reply" : "query");
    r= dp->hdr.dh_flag2 & DHF_RCODE;
    printf(" %s", r < arraysize(rcodes) ? rcodes[r] : itoa("ERR_%lu", r));
    if (dp->hdr.dh_flag1 & DHF_AA) printf(" AA");
    if (dp->hdr.dh_flag1 & DHF_TC) printf(" TC");
    if (dp->hdr.dh_flag1 & DHF_RD) printf(" RD");
    if (dp->hdr.dh_flag2 & DHF_RA) printf(" RA");
#ifdef DHF_AD
    if (dp->hdr.dh_flag2 & DHF_AD) printf(" AD");
    if (dp->hdr.dh_flag2 & DHF_CD) printf(" CD");
#endif
    fputc('\n', stdout);

    count[0]= ntohs(dp->hdr.dh_qdcount);
    count[1]= ntohs(dp->hdr.dh_ancount);
    count[2]= ntohs(dp->hdr.dh_nscount);
    count[3]= ntohs(dp->hdr.dh_arcount);
    cp = dp->data;
    for (i= 0; i < 4; i++) {
        while (count[i] > 0) {
            printf("%*s", indent, "");
            printf(" %s ", label[i]);
            r= print_qrr(dp, size, cp, (i == 0));
            fputc('\n', stdout);
            if (r == -1) return;
            cp += r;
            count[i]--;
        }
    }
}

static u32_t dns_ttl(dns_t *dp, size_t size, u32_t delta)
/* Compute the minimum TTL of all RRs in a DNS packet and subtract delta from
 * all TTLs.  (We are actually only interested in the minimum (delta = 0) or
 * the subtraction (delta > 0).  It was easier to roll this into one routine.)
 */
{
    u8_t *cp, *rdp, *dlim;
    int r, i, hasttl, hassoa;
    unsigned type, count[4];
    u32_t ttl, minimum, minttl;
    unsigned rcode;
    u8_t name[MAXDNAME+1];

    hasttl= hassoa= 0;
    minttl= 365*24*3600L;
    dlim= dns2oct(dp) + size;
    if (size < sizeof(dns_hdr_t)) return 0;

    rcode= dp->hdr.dh_flag2 & DHF_RCODE;
    count[0]= ntohs(dp->hdr.dh_qdcount);
    count[1]= ntohs(dp->hdr.dh_ancount);
    count[2]= ntohs(dp->hdr.dh_nscount);
    count[3]= ntohs(dp->hdr.dh_arcount);
    cp = dp->data;
    for (i= 0; i < 4 && cp < dlim; i++) {
        while (count[i] > 0) {
            r= dn_expand(dns2oct(dp), dlim, cp, name, MAXDNAME);
            if (r == -1) break;
            cp += r + 2 * sizeof(u16_t);
            if (i != 0) {
                if (cp + sizeof(u32_t) + sizeof(u16_t) > dlim) break;
                type= upack16(cp - 2 * sizeof(u16_t));
                ttl= ntohl(upack32(cp));
                ttl= ttl < delta ? 0 : ttl - delta;
                if (rcode == NXDOMAIN && i == 2 && type == HTONS(T_SOA)) {
                    rdp= cp + sizeof(u32_t) + sizeof(u16_t);
                    r= dn_expand(dns2oct(dp), dlim, rdp, name, MAXDNAME);
                    if (r == -1) break;
                    rdp += r;
                    r= dn_expand(dns2oct(dp), dlim, rdp, name, MAXDNAME);
                    if (r == -1) break;
                    rdp += r + 4 * sizeof(u32_t);
                    if (rdp + sizeof(u32_t) > dlim) break;
                    minimum= ntohl(upack32(rdp));
                    if (ttl > minimum) ttl= minimum;
                    hassoa= 1;
                }
                if (delta != 0) pack32(cp, htonl(ttl));
                if (ttl < minttl) minttl= ttl;
                hasttl= 1;
                cp += sizeof(u32_t);
                cp += sizeof(u16_t) + ntohs(upack16(cp));
            }
            count[i]--;
        }
    }
    return ((rcode == NOERROR && hasttl) || (rcode == NXDOMAIN && hassoa))
                ? minttl : 0;
}

/* Total cached query data. */
static size_t n_datamax= N_DATAMAX;
static size_t n_data;

static query_t *extract_query(query_t *qp)
/* Take a query out of the query cache. */
{
    assert(qp != nil);
    *(qp->less != nil ? &qp->less->more : &lru) = qp->more;
    *(qp->more != nil ? &qp->more->less : &mru) = qp->less;
    n_data -= query_size(qp);
    return qp;
}

static query_t *get_query(u8_t *name, unsigned type)
/* Find a query and if so remove it from the cache and return it. */
{
    query_t *qp, *less;
    u8_t qname[MAXDNAME+1];
    int r;

    for (qp= mru; qp != nil; qp= less) {
        less= qp->less;
        if (qp->stale <= now - stale) {
            /* This answer has expired. */
            deallocate(extract_query(qp));
        } else {
            r= dn_expand(dns2oct(&qp->dns), dns2oct(&qp->dns) + qp->size,
                qp->dns.data, qname, MAXDNAME);
            if (r == -1) continue;
            if (namecmp(qname, name) == 0 && upack16(qp->dns.data+r) == type) {
                /* Found an answer to the query. */
                return extract_query(qp);
            }
        }
    }
    return nil;
}

static void insert_query(query_t *qp)
/* (Re)insert a query into the cache. */
{
    *(qp->less != nil ? &qp->less->more : &lru) = qp;
    *(qp->more != nil ? &qp->more->less : &mru) = qp;
    n_data += query_size(qp);

    /* Try to delete the LRU while there is too much memory in use.  If
     * its usage count is too high then it gets a second chance.
     */
    while (n_data > n_datamax && lru != nil) {
        if ((lru->usage >>= QU_SHIFT) == 0 || lru->stale <= now - stale) {
            deallocate(extract_query(lru));
        } else {
            lru->less= mru;     /* Make list circular. */
            mru->more= lru;
            mru= lru;           /* Move one over, making LRU the MRU. */
            lru= lru->more;
            lru->less= nil;     /* Break the circle. */
            mru->more= nil;
        }
    }

    if (debug >= 2) {
        unsigned n= 0;
        for (qp= mru; qp != nil; qp= qp->less) n++;
        printf("%u cached repl%s, %u bytes, sbrk(0) = %u\n",
            n, n == 1 ? "y" : "ies",
            (unsigned) n_data,
            (unsigned) sbrk(0));
    }
}

static void put_query(query_t *qp)
/* Add a new query to the cache as the MRU. */
{
    qp->less= mru;
    qp->more= nil;
    insert_query(qp);
}

static void cache2file(void)
/* Store the cached data into the cache file. */
{
    FILE *fp;
    query_t *qp;
    u8_t data[4+1+2+2];
    u16_t usage;
    char newcache[sizeof(NNCACHE) + sizeof(".new")];

    if (single) return;

    strcpy(newcache, NNCACHE);
    strcat(newcache, ".new");

    if ((fp= fopen(newcache, "w")) == nil) {
        if ((errno != ENOENT && errno != EROFS) || debug >= 2) report(newcache);
        return;
    }
    if (debug >= 2) printf("Writing %s:\n", newcache);

    /* Magic number: */
    fwrite(MAGIC, 1, sizeof(MAGIC), fp);

    for (qp= lru; qp != nil; qp= qp->more) {
        if (qp->stale <= now - stale) continue;
        if (debug >= 2) {
            printf("Usage = %u, Age = %ld, Flags = %02X:\n",
                qp->usage, (long) (now - qp->age), qp->flags);
            dns_tell(2, &qp->dns, qp->size);
        }
        pack32(data+0, htonl(qp->age));
        data[4]= qp->flags;
        pack16(data+5, htons(qp->size));
        pack16(data+7, htons(qp->usage));
        fwrite(data, 1, sizeof(data), fp);
        fwrite(&qp->dns, 1, qp->size, fp);
        if (ferror(fp)) break;
    }

    if (ferror(fp) || fclose(fp) == EOF) {
        report(newcache);
        (void) unlink(newcache);
        return;
    }

    if (debug >= 2) printf("mv %s %s\n", newcache, NNCACHE);
    if (rename(newcache, NNCACHE) < 0) {
        fprintf(stderr, "nonamed: mv %s %s: %s\n",
            newcache, NNCACHE, strerror(errno));
        (void) unlink(newcache);
    }
}

static void file2cache(void)
/* Read cached data from the cache file. */
{
    query_t *qp;
    FILE *fp;
    u8_t data[4+1+2+2];
    size_t dlen;

    if (single) return;

    if ((fp= fopen(NNCACHE, "r")) == nil) {
        if (errno != ENOENT || debug >= 2) report(NNCACHE);
        return;
    }
    if (debug >= 2) printf("Reading %s:\n", NNCACHE);

    /* Magic number? */
    fread(data, 1, sizeof(MAGIC), fp);
    if (ferror(fp) || memcmp(MAGIC, data, sizeof(MAGIC)) != 0) goto err;

    for (;;) {
        fread(data, 1, sizeof(data), fp);
        if (feof(fp) || ferror(fp)) break;
        dlen= ntohs(upack16(data+5));
        qp= allocate(nil, query_allocsize(dlen));
        qp->age= htonl(upack32(data+0));
        qp->flags= data[4];
        if (qp->flags & QF_REFRESH) q_refresh= 1;
        qp->size= dlen;
        qp->usage= htons(upack16(data+7));
        fread(&qp->dns, 1, qp->size, fp);
        if (feof(fp) || ferror(fp)) {
            deallocate(qp);
            goto err;
        }
        qp->stale= qp->age + dns_ttl(&qp->dns, dlen, 0);
        if (debug >= 2) {
            printf("Usage = %u, Age = %ld, Flags = %02X:\n",
                qp->usage, (long) (now - qp->age), qp->flags);
            dns_tell(2, &qp->dns, dlen);
        }
        put_query(qp);
    }
    if (ferror(fp)) {
    err:
        /* The cache file did not end at EOF or is otherwise a mess. */
        fprintf(stderr, "nonamed: %s: %s\n", NNCACHE,
                ferror(fp) ? strerror(errno) : "Corrupt");
        while (lru != nil) deallocate(extract_query(lru));
    }
    fclose(fp);
}

typedef int handler_t(void *data, int expired);

/* All actions are in the form of "jobs". */
typedef struct job {
        struct job      *next, **prev;  /* To make a job queue. */
        handler_t       *handler;       /* Function to handle this job. */
        time_t          timeout;        /* Moment it times out. */
        void            *data;          /* Data associated with the job. */
} job_t;

static job_t *queue;            /* Main job queue. */

static void newjob(handler_t *handler, time_t timeout, void *data)
/* Create a new job with the given handler, timeout time and data. */
{
    job_t *job, **prev;

    job= allocate(nil, sizeof(*job));
    job->handler= handler;
    job->timeout= timeout;
    job->data= data;

    for (prev= &queue; *prev != nil; prev= &(*prev)->next) {
        if (job->timeout < (*prev)->timeout) break;
    }
    job->next= *prev;
    job->prev= prev;
    *prev= job;
    if (job->next != nil) job->next->prev= &job->next;
}

static int execjob(job_t *job, int expired)
/* Execute a job by calling the handler.  Remove the job if it returns true,
 * indicating that it is done.  Expired is set if the job timed out.  It is
 * otherwise called to check for I/O.
 */
{
    if ((*job->handler)(job->data, expired)) {
        *job->prev= job->next;
        if (job->next != nil) job->next->prev= job->prev;
        deallocate(job);
        return 1;
    }
    return 0;
}

static void force_expire(handler_t *handler)
/* Force jobs to expire immediately, the named searcher for instance. */
{
    job_t *job, **prev= &queue;

    while ((job= *prev) != nil) {
        if (job->handler == handler && job->timeout != IMMEDIATE) {
            *prev= job->next;
            if (job->next != nil) job->next->prev= prev;
            newjob(job->handler, IMMEDIATE, job->data);
            deallocate(job);
        } else {
            prev= &job->next;
        }
    }
}

static int nxdomain(u8_t *name)
/* True iff the two top level components in a name are repeated in the name,
 * or if in-addr.arpa is found within a name.  Such things happen often in a
 * search for an already fully qualified local name.  For instance:
 * flotsam.cs.vu.nl.cs.vu.nl.  (We don't want this at boot time.)
 */
{
    u8_t *end, *top, *p;
    size_t n;

    end= namechr(name, 0);
    top= end;
    while (top > name && *--top != '.') {}
    while (top > name && *--top != '.') {}
    n= end - top;
    p= top;
    for (;;) {
        if (p == name) return 0;
        if (*--p == '.') {
            if (namencmp(p, top, n) == 0 && p[n] == '.') return 1;
            if (namencmp(p, ".in-addr.arpa.", 14) == 0) return 1;
        }
    }
}

typedef struct id2id {
        u16_t           id;             /* ID of old query. */
        u16_t           port;           /* Reply port. */
        ipaddr_t        ip;             /* Reply address. */
} id2id_t;

static id2id_t id2id[N_IDS];
static u16_t id_counter;

static u16_t new_id(u16_t in_id, u16_t in_port, ipaddr_t in_ip)
/* An incoming UDP query must be relabeled with a new ID before it can be
 * send on to a real name daemon.
 */
{
    id2id_t *idp;
    u16_t id;

    id= id_counter++;
    idp= &id2id[id % N_IDS];
    idp->id= in_id;
    idp->port= in_port;
    idp->ip= in_ip;
    return htons(id);
}

static int old_id(u16_t id, u16_t *out_id, u16_t *out_port, ipaddr_t *out_ip)
/* Translate a reply id back to the id, port, and address used in the query.
 * Return true if the translation is possible.
 */
{
    id= ntohs(id);
    if ((u16_t) (id_counter - id) > N_IDS) {
        /* Too old. */
        return 0;
    } else {
        /* We know this one. */
        id2id_t *idp= &id2id[id % N_IDS];

        if (idp->port == 0) return 0;   /* Named is trying to fool us? */
        *out_id= idp->id;
        *out_port= idp->port;
        *out_ip= idp->ip;
        idp->port= 0;
        return 1;
    }
}

/* IDs used to mark my own queries to name servers, must be new_id translated
 * to make them unique "on the wire".
 */
#define ID_IPSELF       HTONL(0)        /* "I did it myself" address. */
#define ID_PROBE        HTONS(0)        /* Name server probe. */
#define ID_REFRESH      HTONS(1)        /* Query to refresh a cache entry. */

static char *tcp_device, *udp_device;   /* TCP and UDP device names. */
static int udp_fd;                      /* To send or receive UDP packets. */
static asynchio_t asyn;                 /* For I/O in progress. */
static ipaddr_t my_ip;                  /* My IP address. */
static u16_t my_port, named_port;       /* Port numbers, normally "domain". */

static ipaddr_t named[N_NAMEDS];        /* Addresses of all name servers. */
static unsigned n_nameds;               /* Number of configured name daemons. */
static unsigned i_named;                /* Index to current name server. */
static int expect;                      /* Set when we expect an answer. */
static int search_ct= -1;               /* Named search count and state. */
static int dirty;                       /* True when new entry put in cache. */

#define current_named()         (+named[i_named])
#define searching()             (search_ct > 0)
#define start_searching()       ((void) (search_ct= -1))
#define stop_searching()        ((void) (search_ct= 0))
#define expecting()             (+expect)
#define start_expecting()       ((void) (expect= 1))
#define stop_expecting()        ((void) (expect= 0))

static time_t filetime(const char *file)
/* Get the modified time of a file. */
{
    struct stat st;

    return stat(file, &st) == 0 ? st.st_mtime : 0;
}

static void init_config(ipaddr_t ifip)
/* Read name daemon list and other special stuff from the hosts file. */
{
    struct hostent *he;
    u32_t nip, hip;
    static time_t hosts_time, dhcp_time;
    time_t ht, dt;

    /* See if anything really changed. */
    if (((ifip ^ HTONL(LOCALHOST)) & HTONL(0xFF000000)) == 0) ifip= my_ip;
    ht= filetime(HOSTS);
    dt= filetime(DHCPCACHE);
    if (ifip == my_ip && ht == hosts_time && dt == dhcp_time) return;
    my_ip= ifip;
    hosts_time= ht;
    dhcp_time= dt;

    if (debug >= 2) {
        printf("%s: I am nonamed %s at %s:%u\n",
            nowgmt(), version, inet_ntoa(my_ip), ntohs(my_port));
    }

    httl= HTONL(HTTL);
    stale= 0;
    n_nameds= 0;

    if (!single) {
        sethostent(0);
        while ((he= gethostent()) != nil) {
            memcpy(&nip, he->h_addr, sizeof(u32_t));
            hip= ntohl(nip);
            if (namecmp(he->h_name, "%ttl") == 0) httl= nip;
            if (namecmp(he->h_name, "%stale") == 0) stale= hip;
            if (namecmp(he->h_name, "%memory") == 0) n_datamax= hip;
            if (namecmp(he->h_name, "%nameserver") == 0) {
                if (nip != my_ip || named_port != my_port) {
                    if (n_nameds < N_NAMEDS) named[n_nameds++]= nip;
                }
            }
        }
        endhostent();
    }

    if (n_nameds == 0) {
        /* No name daemons found in the host file.  What about DHCP? */
        int fd;
        dhcp_t d;
        ssize_t r;
        u8_t *data;
        size_t len;

        if ((fd= open(DHCPCACHE, O_RDONLY)) < 0) {
            if (errno != ENOENT) fatal(DHCPCACHE);
        } else {
            while ((r= read(fd, &d, sizeof(d))) == sizeof(d)) {
                if (d.yiaddr == my_ip) break;
            }
            if (r < 0) fatal(DHCPCACHE);
            close(fd);

            if (r == sizeof(d) && dhcp_gettag(&d, DHCP_TAG_DNS, &data, &len)) {
                while (len >= sizeof(nip)) {
                    memcpy(&nip, data, sizeof(nip));
                    data += sizeof(nip);
                    len -= sizeof(nip);
                    if (nip != my_ip || named_port != my_port) {
                        if (n_nameds < N_NAMEDS) named[n_nameds++]= nip;
                    }
                }
            }
        }
    }
    i_named= 0;
}

static handler_t job_save_cache, job_read_udp, job_find_named, job_expect_named;
#if DO_TCP
static handler_t job_setup_listen, job_listen, job_setup_connect, job_connect;
static handler_t job_read_query, job_write_query;
static handler_t job_read_reply, job_write_reply;
#endif

static int query_hosts(u8_t *qname, unsigned type, dns_t *dp, size_t *pdlen)
/* Read the /etc/hosts file to try and answer an A or PTR query.  Return
 * true iff an answer can be found, with the answer copied to *dp.
 */
{
    struct hostent *he;
    int i, r;
    dns_t dns;
    u8_t *domain;
    u8_t *cp;
    u8_t name[MAXDNAME+1];
    u8_t *dnvec[40];
    unsigned ancount;
    struct hostent localhost;
    static char *noaliases[]= { nil };
    static ipaddr_t localaddr= HTONL(LOCALHOST);
    static char *localaddrlist[]= { (char *) &localaddr, nil };

    if (single) return 0;

    /* Assume we can answer. */
    dns.hdr.dh_flag1= DHF_QR | DHF_AA;
    dns.hdr.dh_flag2= DHF_RA;
    dns.hdr.dh_qdcount= HTONS(1);
    ancount= 0;
    dns.hdr.dh_nscount= HTONS(0);
    dns.hdr.dh_arcount= HTONS(0);

    dnvec[0]= dns2oct(&dns);
    dnvec[1]= nil;
    cp= dns.data;
    r= dn_comp(qname, cp, arraysize(dns.data), dnvec, arraylimit(dnvec));
    if (r == -1) return 0;
    cp += r;
    pack16(cp, type);
    cp += sizeof(u16_t);
    pack16(cp, HTONS(C_IN));
    cp += sizeof(u16_t);

    /* Localhost is fixed to 127.0.0.1. */
    localhost.h_name=
        namencmp(qname, "localhost.", 10) == 0 ? (char *) qname : "localhost";
    localhost.h_aliases= noaliases;
    localhost.h_addr_list= localaddrlist;
    he= &localhost;

    sethostent(0);
    do {
        switch (type) {
        case HTONS(T_A):
            if (namecmp(qname, he->h_name) == 0) {
              addA:
                r= dn_comp((u8_t *) he->h_name, cp, arraylimit(dns.data) - cp,
                    dnvec, arraylimit(dnvec));
                if (r == -1) return 0;
                cp += r;
                if (cp + 3 * sizeof(u16_t) + 2 * sizeof(u32_t)
                    > arraylimit(dns.data)) { r= -1; break; }
                pack16(cp, HTONS(T_A));
                cp += sizeof(u16_t);
                pack16(cp, HTONS(C_IN));
                cp += sizeof(u16_t);
                pack32(cp, httl);
                cp += sizeof(u32_t);
                pack16(cp, HTONS(sizeof(u32_t)));
                cp += sizeof(u16_t);
                memcpy(cp, he->h_addr, sizeof(u32_t));
                cp += sizeof(u32_t);
                ancount++;
                break;
            }
            /*FALL THROUGH*/
        case HTONS(T_CNAME):
            domain= namechr(he->h_name, '.');
            for (i= 0; he->h_aliases[i] != nil; i++) {
                namecpy(name, he->h_aliases[i]);
                if (domain != nil && namechr(name, '.') == nil) {
                    namecat(name, domain);
                }
                if (namecmp(qname, name) == 0) {
                    r= dn_comp(name, cp, arraylimit(dns.data) - cp,
                        dnvec, arraylimit(dnvec));
                    if (r == -1) break;
                    cp += r;
                    if (cp + 3 * sizeof(u16_t)
                        + 1 * sizeof(u32_t) > arraylimit(dns.data)) return 0;
                    pack16(cp, HTONS(T_CNAME));
                    cp += sizeof(u16_t);
                    pack16(cp, HTONS(C_IN));
                    cp += sizeof(u16_t);
                    pack32(cp, httl);
                    cp += sizeof(u32_t);
                    /* pack16(cp, htonl(RDLENGTH)) */
                    cp += sizeof(u16_t);
                    r= dn_comp((u8_t *) he->h_name, cp,
                        arraylimit(dns.data) - cp,
                        dnvec, arraylimit(dnvec));
                    if (r == -1) break;
                    pack16(cp - sizeof(u16_t), htons(r));
                    cp += r;
                    ancount++;
                    if (type == HTONS(T_A)) goto addA;  /* really wants A */
                    break;
                }
            }
            break;
        case HTONS(T_PTR):
            if (ancount > 0) break;
            if (he->h_name[0] == '%') break;
            sprintf((char *) name, "%d.%d.%d.%d.in-addr.arpa",
                    ((u8_t *) he->h_addr)[3],
                    ((u8_t *) he->h_addr)[2],
                    ((u8_t *) he->h_addr)[1],
                    ((u8_t *) he->h_addr)[0]);
            if (namecmp(qname, name) == 0) {
                r= dn_comp(name, cp, arraylimit(dns.data) - cp,
                    dnvec, arraylimit(dnvec));
                if (r == -1) break;
                cp += r;
                if (cp + 3 * sizeof(u16_t) + 1 * sizeof(u32_t)
                    > arraylimit(dns.data)) { r= -1; break; }
                pack16(cp, HTONS(T_PTR));
                cp += sizeof(u16_t);
                pack16(cp, HTONS(C_IN));
                cp += sizeof(u16_t);
                pack32(cp, httl);
                cp += sizeof(u32_t);
                /* pack16(cp, htonl(RDLENGTH)) */
                cp += sizeof(u16_t);
                r= dn_comp((u8_t *) he->h_name, cp,
                    arraylimit(dns.data) - cp, dnvec, arraylimit(dnvec));
                if (r == -1) return 0;
                pack16(cp - sizeof(u16_t), htons(r));
                cp += r;
                ancount++;
            }
            break;
        }
    } while (r != -1 && (he= gethostent()) != nil);
    endhostent();

    if (r == -1 || ancount == 0) return 0;

    dns.hdr.dh_ancount= htons(ancount);
    memcpy(dp, &dns, *pdlen= cp - dns2oct(&dns));
    return 1;
}

static int query_chaos(u8_t *qname, unsigned type, dns_t *dp, size_t *pdlen)
/* Report my version.  Can't let BIND take all the credit. :-) */
{
    int i, n, r;
    dns_t dns;
    u8_t *cp;
    u8_t *dnvec[40];

    if (type != HTONS(T_TXT) || namecmp(qname, "version.bind") != 0) return 0;

    dns.hdr.dh_flag1= DHF_QR | DHF_AA;
    dns.hdr.dh_flag2= DHF_RA;
    dns.hdr.dh_qdcount= HTONS(1);
    dns.hdr.dh_ancount= HTONS(1);
    dns.hdr.dh_nscount= HTONS(0);
    dns.hdr.dh_arcount= htons(n_nameds);

    dnvec[0]= dns2oct(&dns);
    dnvec[1]= nil;
    cp= dns.data;
    r= dn_comp(qname, cp, arraysize(dns.data), dnvec, arraylimit(dnvec));
    if (r == -1) return 0;
    cp += r;
    pack16(cp, type);
    cp += sizeof(u16_t);
    pack16(cp, HTONS(C_CHAOS));
    cp += sizeof(u16_t);

    r= dn_comp(qname, cp, arraylimit(dns.data) - cp, dnvec, arraylimit(dnvec));
    if (r == -1) return 0;
    cp += r;
    pack16(cp, HTONS(T_TXT));
    cp += sizeof(u16_t);
    pack16(cp, HTONS(C_CHAOS));
    cp += sizeof(u16_t);
    pack32(cp, HTONL(0));
    cp += sizeof(u32_t);
    /* pack16(cp, htonl(RDLENGTH)) */
    cp += sizeof(u16_t);
    sprintf((char *) cp + 1, "nonamed %s at %s:%u",
            version, inet_ntoa(my_ip), ntohs(my_port));
    r= strlen((char *) cp + 1) + 1;
    pack16(cp - sizeof(u16_t), htons(r));
    *cp= r-1;
    cp += r;
    for (n= 0, i= i_named; n < n_nameds; n++, i= (i+1) % n_nameds) {
        r= dn_comp((u8_t *) "%nameserver", cp, arraylimit(dns.data) - cp,
            dnvec, arraylimit(dnvec));
        if (r == -1) return 0;
        cp += r;
        if (cp + 3 * sizeof(u16_t)
            + 2 * sizeof(u32_t) > arraylimit(dns.data)) return 0;
        pack16(cp, HTONS(T_A));
        cp += sizeof(u16_t);
        pack16(cp, HTONS(C_IN));
        cp += sizeof(u16_t);
        pack32(cp, HTONL(0));
        cp += sizeof(u32_t);
        pack16(cp, HTONS(sizeof(u32_t)));
        cp += sizeof(u16_t);
        memcpy(cp, &named[i], sizeof(u32_t));
        cp += sizeof(u32_t);
    }

    memcpy(dp, &dns, *pdlen= cp - dns2oct(&dns));
    return 1;
}

static void cache_reply(dns_t *dp, size_t dlen)
/* Store a DNS packet in the cache. */
{
    int r;
    query_t *qp, *less, *more;
    unsigned usage;
    u16_t type;
    u8_t *cp;
    u8_t name[MAXDNAME];
    u32_t minttl;

    if ((dp->hdr.dh_flag1 & (DHF_RD | DHF_TC)) != DHF_RD) return;
    if (dp->hdr.dh_qdcount != HTONS(1)) return;
    cp= dp->data;
    r= dn_expand(dns2oct(dp), dns2oct(dp) + dlen, cp, name, MAXDNAME);
    if (r == -1) return;
    cp += r;
    type= upack16(cp);
    cp += sizeof(u16_t);
    if (upack16(cp) != HTONS(C_IN)) return;

    /* Delete old cached data, if any.  Note where it is in the LRU. */
    if ((qp= get_query(name, type)) != nil) {
        less= qp->less;
        more= qp->more;
        usage= qp->usage;
        deallocate(qp);
    } else {
        /* Not yet in the cache. */
        less= mru;
        more= nil;
        usage= 1;
    }

    /* Determine minimum TTL.  Discard if zero, never cache zero TTLs. */
    if ((minttl= dns_ttl(dp, dlen, 0)) == 0) return;

    /* Enter new reply in cache. */
    qp= allocate(nil, query_allocsize(dlen));
    qp->less= less;
    qp->more= more;
    qp->age= now;
    qp->flags= 0;
    qp->usage= usage;
    qp->size= dlen;
    memcpy(&qp->dns, dp, dlen);
    qp->stale= qp->age + minttl;
    insert_query(qp);
    if (debug >= 1) printf("Answer cached\n");

    /* Save the cache soon. */
    if (!dirty) {
        dirty= 1;
        newjob(job_save_cache, now + LONG_TIMEOUT, nil);
    }
}

static int job_save_cache(void *data, int expired)
/* Some time after the cache is changed it is written back to disk. */
{
    if (!expired) return 0;
    cache2file();
    dirty= 0;
}

static int compose_reply(dns_t *dp, size_t *pdlen)
/* Try to compose a reply to a request in *dp using the hosts file or
 * cached data.  Return answer in *dp with its size in *pdlen.  Return true
 * iff an answer is given.
 */
{
    size_t dlen= *pdlen;
    int r, rd;
    query_t *qp;
    unsigned id, type, class;
    u8_t *cp;
    u8_t name[MAXDNAME];

    cp= dp->data;
    r= dn_expand(dns2oct(dp), dns2oct(dp) + dlen, cp, name, MAXDNAME);
    if (r != -1) {
        cp += r;
        if (cp + 2 * sizeof(u16_t) > dns2oct(dp) + dlen) {
            r= -1;
        } else {
            type= upack16(cp);
            cp += sizeof(u16_t);
            class= upack16(cp);
            cp += sizeof(u16_t);
        }
    }

    /* Remember ID and RD. */
    id= dp->hdr.dh_id;
    rd= dp->hdr.dh_flag1 & DHF_RD;

    if (r == -1) {
        /* Malformed query, reply "FORMERR". */
        dp->hdr.dh_flag1 &= ~(DHF_TC);
        dp->hdr.dh_flag1 |= DHF_QR | DHF_AA;
        dp->hdr.dh_flag2 &= ~(DHF_UNUSED | DHF_RCODE);
        dp->hdr.dh_flag2 |= DHF_RA | FORMERR;
    } else
    if (class == HTONS(C_IN) && query_hosts(name, type, dp, pdlen)) {
        /* Answer to this query is in the hosts file. */
        dlen= *pdlen;
    } else
    if (class == HTONS(C_IN) && (qp= get_query(name, type)) != nil) {
        /* Answer to this query is present in the cache. */
        memcpy(dp, &qp->dns, dlen= qp->size);
        dp->hdr.dh_flag1 &= ~DHF_AA;
        (void) dns_ttl(dp, dlen, now - qp->age);
        if (rd) {
            if (qp->stale <= now) {
                qp->flags |= QF_REFRESH;
                q_refresh= 1;
            }
            qp->usage++;
        }
        put_query(qp);
    } else
    if (class == HTONS(C_CHAOS) && query_chaos(name, type, dp, pdlen)) {
        /* Return our version numbers. */
        dlen= *pdlen;
    } else
    if (n_nameds == 0 || nxdomain(name)) {
        /* No real name daemon present, or this name has a repeated top level
         * domain sequence.  Reply "no such domain".
         */
        dp->hdr.dh_flag1 &= ~(DHF_TC);
        dp->hdr.dh_flag1 |= DHF_QR | DHF_AA;
        dp->hdr.dh_flag2 &= ~(DHF_UNUSED | DHF_RCODE);
        dp->hdr.dh_flag2 |= DHF_RA | NXDOMAIN;
    } else
    if (!rd) {
        /* "Recursion Desired" is off, so don't bother to relay. */
        dp->hdr.dh_flag1 &= ~(DHF_TC);
        dp->hdr.dh_flag1 |= DHF_QR;
        dp->hdr.dh_flag2 &= ~(DHF_UNUSED | DHF_RCODE);
        dp->hdr.dh_flag2 |= DHF_RA | NOERROR;
    } else {
        /* Caller needs to consult with a real name daemon. */
        return 0;
    }

    /* Copy ID and RD back to answer. */
    dp->hdr.dh_id= id;
    dp->hdr.dh_flag1 &= ~DHF_RD;
    dp->hdr.dh_flag1 |= rd;
    *pdlen= dlen;
    return 1;
}

typedef struct udp_dns {        /* One DNS packet over UDP. */
        udp_io_hdr_t    hdr;            /* UDP header (source/destination). */
        dns_t           dns;            /* DNS packet. */
} udp_dns_t;

static void refresh_cache(void)
/* Find a stale entry in the cache that was used to answer a query, and send
 * a request to a name server that should refresh this entry.
 */
{
    query_t *qp;
    unsigned type;
    int r;
    u8_t *cp;
    size_t dlen, ulen;
    u8_t qname[MAXDNAME+1];
    u8_t *dnvec[40];
    udp_dns_t udp;

    if (!q_refresh) return;
    for (qp= lru; qp != nil; qp= qp->more) {
        if ((qp->flags & QF_REFRESH) && qp->stale > now - stale) break;
    }
    if (qp == nil) {
        q_refresh= 0;
        return;
    }

    /* Found one to refresh. */
    qp->flags &= ~QF_REFRESH;
    r= dn_expand(dns2oct(&qp->dns), dns2oct(&qp->dns) + qp->size,
        qp->dns.data, qname, MAXDNAME);
    if (r == -1) return;
    type= upack16(qp->dns.data+r);

    dnvec[0]= dns2oct(&udp.dns);
    dnvec[1]= nil;
    cp= udp.dns.data;
    r= dn_comp(qname, cp, arraysize(udp.dns.data), dnvec, arraylimit(dnvec));
    if (r == -1) return;
    cp += r;
    pack16(cp, type);
    cp += sizeof(u16_t);
    pack16(cp, HTONS(C_IN));
    cp += sizeof(u16_t);
    dlen= cp - dns2oct(&udp.dns);

    udp.dns.hdr.dh_id= new_id(ID_REFRESH, my_port, ID_IPSELF);
    udp.dns.hdr.dh_flag1= DHF_RD;
    udp.dns.hdr.dh_flag2= 0;
    udp.dns.hdr.dh_qdcount= HTONS(1);
    udp.dns.hdr.dh_ancount= HTONS(0);
    udp.dns.hdr.dh_nscount= HTONS(0);
    udp.dns.hdr.dh_arcount= HTONS(0);

    udp.hdr.uih_dst_addr= current_named();
    udp.hdr.uih_dst_port= named_port;
    udp.hdr.uih_ip_opt_len= 0;
    udp.hdr.uih_data_len= dlen;

    if (debug >= 1) {
        printf("Refresh to %s:%u:\n",
            inet_ntoa(current_named()), ntohs(named_port));
        dns_tell(0, &udp.dns, dlen);
    }
    ulen= offsetof(udp_dns_t, dns) + dlen;
    if (write(udp_fd, &udp, ulen) < 0) fatal(udp_device);
}

static int job_read_udp(void *data, int expired)
/* Read UDP queries and replies. */
{
    size_t ulen, dlen;
    static udp_dns_t udp;
    u16_t id, port;
    ipaddr_t ip;
    time_t dtime;

    assert(!expired);

    /* Try to read a packet. */
    ulen= asyn_read(&asyn, udp_fd, &udp, sizeof(udp));
    dlen= ulen - offsetof(udp_dns_t, dns);

    if (ulen == -1) {
        if (errno == EINPROGRESS && !expired) return 0;
        if (errno == EIO) fatal(udp_device);

        if (debug >= 2) {
            printf("%s: UDP read: %s\n", nowgmt(), strerror(errno));
        }
    } else {
        if (debug >= 2) {
            printf("%s: UDP read, %d bytes\n", nowgmt(), (int) ulen);
        }
    }

    /* Restart this job no matter what. */
    newjob(job_read_udp, NEVER, nil);

    if (ulen < (ssize_t) (sizeof(udp_io_hdr_t) + sizeof(dns_hdr_t))) return 1;

    if (debug >= 1) {
        printf("%s:%u UDP ", inet_ntoa(udp.hdr.uih_src_addr),
                                ntohs(udp.hdr.uih_src_port));
        dns_tell(0, &udp.dns, dlen);
    }

    /* Check, and if necessary reinitialize my configuration. */
    init_config(udp.hdr.uih_dst_addr);

    if (udp.dns.hdr.dh_flag1 & DHF_QR) {
        /* This is a remote named reply, not a query. */

        /* Response to a query previously relayed? */
        if (!old_id(udp.dns.hdr.dh_id, &id, &port, &ip)) return 1;

        if (ip == ID_IPSELF && id == ID_PROBE) {
            if (searching()) {
                /* We have found a name server! */
                int i;

                /* In my list? */
                for (i= 0; i < n_nameds; i++) {
                    if (named[i] == udp.hdr.uih_src_addr) {
                        i_named= i;
                        if (debug >= 1) {
                            printf("Current named = %s\n",
                                inet_ntoa(current_named()));
                        }
                        stop_searching();
                        force_expire(job_find_named);
                    }
                }
            }
        }

        /* We got an answer, so stop worrying. */
        if (expecting()) {
            stop_expecting();
            force_expire(job_expect_named);
        }

        /* Put the information in the cache. */
        cache_reply(&udp.dns, dlen);

        /* Refresh a cached entry that was used when stale. */
        refresh_cache();

        /* Discard reply to myself. */
        if (ip == ID_IPSELF) return 1;

        /* Send the reply to the process that asked for it. */
        udp.dns.hdr.dh_id= id;
        udp.hdr.uih_dst_addr= ip;
        udp.hdr.uih_dst_port= port;
        if (debug >= 1) printf("To client %s:%u\n", inet_ntoa(ip), ntohs(port));
    } else {
        /* A query. */
        if (udp.dns.hdr.dh_qdcount != HTONS(1)) return 1;

        if(localonly) {
                /* Check if it's a local query. */
                if(ntohl(udp.hdr.uih_src_addr) != LOCALHOST) {
                        syslog(LOG_WARNING, "nonamed: dropped query from %s",
                                inet_ntoa(udp.hdr.uih_src_addr));
                        return 1;
                }
        }

        /* Try to compose a reply from local data. */
        if (compose_reply(&udp.dns, &dlen)) {
            udp.hdr.uih_dst_addr= udp.hdr.uih_src_addr;
            udp.hdr.uih_dst_port= udp.hdr.uih_src_port;
            udp.hdr.uih_ip_opt_len= 0;
            udp.hdr.uih_data_len= dlen;
            ulen= offsetof(udp_dns_t, dns) + dlen;

            /* Send an UDP DNS reply. */
            if (debug >= 1) {
                printf("%s:%u UDP ", inet_ntoa(udp.hdr.uih_dst_addr),
                                            ntohs(udp.hdr.uih_dst_port));
                dns_tell(0, &udp.dns, dlen);
            }
        } else {
            /* Let a real name daemon handle the query. */
            udp.dns.hdr.dh_id= new_id(udp.dns.hdr.dh_id,
                                udp.hdr.uih_src_port, udp.hdr.uih_src_addr);
            udp.hdr.uih_dst_addr= current_named();
            udp.hdr.uih_dst_port= named_port;
            if (!expecting()) {
                start_expecting();
                newjob(job_expect_named, now + MEDIUM_TIMEOUT, nil);
            }
            if (debug >= 1) {
                printf("To named %s:%u\n",
                    inet_ntoa(current_named()), ntohs(named_port));
            }
        }
    }
    if (write(udp_fd, &udp, ulen) < 0) fatal(udp_device);
    return 1;
}

#if DO_TCP

typedef struct data_cl {        /* Data for connect or listen jobs. */
        int             fd;             /* Open TCP channel. */
        int             dn_fd;          /* TCP channel to the name daemon. */
        int             retry;          /* Retrying a connect? */
        nwio_tcpcl_t    tcpcl;          /* Flags. */
} data_cl_t;

typedef struct data_rw {        /* Data for TCP read or write jobs. */
        int             r_fd;           /* Read from this TCP channel. */
        int             w_fd;           /* And write to this TCP channel. */
        struct data_rw  *rev;           /* Optional reverse TCP channel. */
        u8_t            *buf;           /* Buffer for bytes to transfer. */
        ssize_t         offset;         /* Offset in buf to r/w at. */
        size_t          size;           /* Size of buf. */
} data_rw_t;

static int job_setup_listen(void *data, int expired)
/* Set up a listening channel for TCP DNS queries. */
{
    data_cl_t *data_cl= data;
    nwio_tcpconf_t tcpconf;
    nwio_tcpopt_t tcpopt;
    int fd;

    if (!expired) return 0;
    if (debug >= 2) printf("%s: Setup listen\n", nowgmt());

    if (data_cl == nil) {
        if ((fd= open(tcp_device, O_RDWR)) < 0) {
            if (errno != EMFILE) report(tcp_device);
            newjob(job_setup_listen, now + SHORT_TIMEOUT, nil);
            return 1;
        }

        tcpconf.nwtc_flags= NWTC_SHARED | NWTC_LP_SET | NWTC_UNSET_RA
                                                        | NWTC_UNSET_RP;
        tcpconf.nwtc_locport= my_port;
        if (ioctl(fd, NWIOSTCPCONF, &tcpconf) == -1) fatal(tcp_device);

        tcpopt.nwto_flags= NWTO_DEL_RST;
        if (ioctl(fd, NWIOSTCPOPT, &tcpopt) == -1) fatal(tcp_device);

        data_cl= allocate(nil, sizeof(*data_cl));
        data_cl->fd= fd;
        data_cl->tcpcl.nwtcl_flags= 0;
    }
    /* And listen. */
    newjob(job_listen, NEVER, data_cl);
    return 1;
}

static int job_listen(void *data, int expired)
/* A connection on the TCP DNS query channel. */
{
    data_cl_t *data_cl= data;

    /* Wait for a client. */
    if (asyn_ioctl(&asyn, data_cl->fd, NWIOTCPLISTEN, &data_cl->tcpcl) < 0) {
        if (errno == EINPROGRESS) return 0;
        report(tcp_device);

        /* Try again after a short time. */
        newjob(job_setup_listen, now + SHORT_TIMEOUT, data_cl);
        return 1;
    }
    if (debug >= 2) printf("%s: Listen\n", nowgmt());

    /* Immediately resume listening. */
    newjob(job_setup_listen, IMMEDIATE, nil);

    /* Set up a connect to the real name daemon. */
    data_cl->retry= 0;
    newjob(job_setup_connect, IMMEDIATE, data_cl);
    return 1;
}

static void start_relay(int fd, int dn_fd)
/* Start one or two read jobs after job_setup_connect() or job_connect(). */
{
    data_rw_t *query;   /* Client to DNS daemon relay. */
    data_rw_t *reply;   /* DNS daemon to client relay. */

    query= allocate(nil, sizeof(*query));
    query->r_fd= fd;
    query->buf= allocate(nil, sizeof(u16_t));
    query->offset= 0;
    query->size= sizeof(u16_t);
    if (dn_fd == NO_FD) {
        /* Answer mode. */
        query->w_fd= fd;
        query->rev= nil;
    } else {
        /* Relay mode. */
        reply= allocate(nil, sizeof(*reply));
        reply->r_fd= dn_fd;
        reply->w_fd= fd;
        reply->buf= allocate(nil, sizeof(u16_t));
        reply->offset= 0;
        reply->size= sizeof(u16_t);
        reply->rev= query;
        query->w_fd= dn_fd;
        query->rev= reply;
        newjob(job_read_reply, now + LONG_TIMEOUT, reply);
    }
    newjob(job_read_query, now + LONG_TIMEOUT, query);
}

static void close_relay(data_rw_t *data_rw)
/* Close a relay channel. */
{
    if (data_rw->rev != nil) {
        /* Other end still active, signal EOF. */
        (void) ioctl(data_rw->w_fd, NWIOTCPSHUTDOWN, nil);
        data_rw->rev->rev= nil;
    } else {
        /* Close both ends down. */
        asyn_close(&asyn, data_rw->r_fd);
        close(data_rw->r_fd);
        if (data_rw->w_fd != data_rw->r_fd) {
            asyn_close(&asyn, data_rw->w_fd);
            close(data_rw->w_fd);
        }
    }
    deallocate(data_rw->buf);
    deallocate(data_rw);
}

static int job_setup_connect(void *data, int expired)
/* Set up a connect for a TCP channel to the real name daemon. */
{
    nwio_tcpconf_t tcpconf;
    int dn_fd;
    data_cl_t *data_cl= data;

    if (!expired) return 0;
    if (debug >= 2) printf("%s: Setup connect\n", nowgmt());

    if (n_nameds == 0) {
        /* No name daemons to relay to, answer myself. */
        start_relay(data_cl->fd, NO_FD);
        deallocate(data_cl);
        return 1;
    }

    if ((dn_fd= open(tcp_device, O_RDWR)) < 0) {
        if (errno != EMFILE) report(tcp_device);
        if (++data_cl->retry < 5) {
            /* Retry. */
            newjob(job_setup_connect, now + SHORT_TIMEOUT, data_cl);
        } else {
            /* Reply myself (bound to fail). */
            start_relay(data_cl->fd, NO_FD);
            deallocate(data_cl);
        }
        return 1;
    }

    tcpconf.nwtc_flags= NWTC_LP_SEL | NWTC_SET_RA | NWTC_SET_RP;
    tcpconf.nwtc_remaddr= current_named();
    tcpconf.nwtc_remport= named_port;
    if (ioctl(dn_fd, NWIOSTCPCONF, &tcpconf) == -1) fatal(tcp_device);

    /* And connect. */
    data_cl->dn_fd= dn_fd;
    data_cl->tcpcl.nwtcl_flags= 0;
    newjob(job_connect, NEVER, data_cl);
    return 1;
}

static int job_connect(void *data, int expired)
/* Connect to a TCP DNS query channel. */
{
    data_cl_t *data_cl= data;

    /* Try to connect. */
    if (asyn_ioctl(&asyn, data_cl->dn_fd, NWIOTCPCONN, &data_cl->tcpcl) < 0) {
        if (errno == EINPROGRESS) return 0;
        if (errno == EIO) fatal(tcp_device);

        /* Connection refused. */
        if (debug >= 2) printf("%s: Connect: %s\n", nowgmt(), strerror(errno));
        asyn_close(&asyn, data_cl->dn_fd);
        close(data_cl->dn_fd);
        data_cl->dn_fd= NO_FD;
        if (++data_cl->retry < 5) {
            /* Search a new name daemon. */
            if (!searching()) {
                start_searching();
                force_expire(job_find_named);
            }
            newjob(job_setup_connect, NEVER, data_cl);
            return 1;
        }
        /* Reply with a failure eventually. */
    }
    if (debug >= 2) printf("%s: Connect\n", nowgmt());

    /* Read the query from the user, send on to the name daemon, etc. */
    start_relay(data_cl->fd, data_cl->dn_fd);
    deallocate(data_cl);
    return 1;
}

static void tcp_dns_tell(int fd, u8_t *buf)
/* Tell about a DNS packet on a TCP channel. */
{
    nwio_tcpconf_t tcpconf;

    if (ioctl(fd, NWIOGTCPCONF, &tcpconf) < 0) {
        printf("??\?:?? TCP ");
    } else {
        printf("%s:%u TCP ", inet_ntoa(tcpconf.nwtc_remaddr),
                                ntohs(tcpconf.nwtc_remport));
    }
    dns_tell(0, oct2dns(buf + sizeof(u16_t)), ntohs(upack16(buf)));
}

static int job_read_query(void *data, int expired)
/* Read TCP queries from the client. */
{
    data_rw_t *data_rw= data;
    ssize_t count;

    /* Try to read count bytes. */
    count= asyn_read(&asyn, data_rw->r_fd,
                                data_rw->buf + data_rw->offset,
                                data_rw->size - data_rw->offset);

    if (count < 0) {
        if (errno == EINPROGRESS && !expired) return 0;
        if (errno == EIO) fatal(tcp_device);

        /* Remote end is late, or an error occurred. */
        if (debug >= 2) {
            printf("%s: TCP read query: %s\n", nowgmt(), strerror(errno));
        }
        close_relay(data_rw);
        return 1;
    }

    if (debug >= 2) {
        printf("%s: TCP read query, %d/%u bytes\n",
            nowgmt(), data_rw->offset + count, data_rw->size);
    }
    if (count == 0) {
        /* EOF. */
        close_relay(data_rw);
        return 1;
    }
    data_rw->offset += count;
    if (data_rw->offset == data_rw->size) {
        data_rw->size= sizeof(u16_t) + ntohs(upack16(data_rw->buf));
        if (data_rw->size < sizeof(u16_t)) {
            /* Malformed. */
            close_relay(data_rw);
            return 1;
        }
        if (data_rw->offset < data_rw->size) {
            /* Query not complete, read more. */
            data_rw->buf= allocate(data_rw->buf, data_rw->size);
            newjob(job_read_query, now + LONG_TIMEOUT, data_rw);
            return 1;
        }
    }

    if (data_rw->size < sizeof(u16_t) + sizeof(dns_hdr_t)) {
        close_relay(data_rw);
        return 1;
    }
    if (debug >= 1) tcp_dns_tell(data_rw->r_fd, data_rw->buf);

    /* Relay or reply. */
    if (data_rw->w_fd != data_rw->r_fd) {
        /* We have a real name daemon to do the work. */
        data_rw->offset= 0;
        newjob(job_write_query, now + LONG_TIMEOUT, data_rw);
    } else {
        /* No real name daemons or none reachable, so use the hosts file. */
        dns_t *dp;
        size_t dlen;

        if (data_rw->size < sizeof(u16_t) + PACKETSZ) {
            data_rw->buf= allocate(data_rw->buf, sizeof(u16_t) + PACKETSZ);
        }

        /* Build a reply packet. */
        dp= oct2dns(data_rw->buf + sizeof(u16_t));
        dlen= data_rw->size - sizeof(u16_t);
        if (!compose_reply(dp, &dlen)) {
            /* We're told to ask a name daemon, but that won't work. */
            close_relay(data_rw);
            return 1;
        }

        /* Start a reply write. */
        pack16(data_rw->buf, htons(dlen));
        data_rw->size= sizeof(u16_t) + dlen;
        data_rw->buf= allocate(data_rw->buf, data_rw->size);
        data_rw->offset= 0;
        newjob(job_write_reply, now + LONG_TIMEOUT, data_rw);
    }
    return 1;
}

static int job_write_query(void *data, int expired)
/* Relay a TCP query to the name daemon. */
{
    data_rw_t *data_rw= data;
    ssize_t count;

    /* Try to write count bytes to the name daemon. */
    count= asyn_write(&asyn, data_rw->w_fd,
                                data_rw->buf + data_rw->offset,
                                data_rw->size - data_rw->offset);

    if (count <= 0) {
        if (errno == EINPROGRESS && !expired) return 0;
        if (errno == EIO) fatal(tcp_device);

        /* A write expired or failed (usually a broken connection.) */
        if (debug >= 2) {
            printf("%s: TCP write query: %s\n", nowgmt(), strerror(errno));
        }
        close_relay(data_rw);
        return 1;
    }

    if (debug >= 2) {
        printf("%s: TCP write query, %d/%u bytes\n",
            nowgmt(), data_rw->offset + count, data_rw->size);
    }
    data_rw->offset += count;
    if (data_rw->offset < data_rw->size) {
        /* Partial write, continue. */
        newjob(job_write_query, now + LONG_TIMEOUT, data_rw);
        return 1;
    }
    if (debug >= 1) tcp_dns_tell(data_rw->w_fd, data_rw->buf);

    /* Query fully send on, go read more queries. */
    data_rw->offset= 0;
    data_rw->size= sizeof(u16_t);
    newjob(job_read_query, now + LONG_TIMEOUT, data_rw);
    return 1;
}

static int job_read_reply(void *data, int expired)
/* Read a TCP reply from the real name daemon. */
{
    data_rw_t *data_rw= data;
    ssize_t count;

    /* Try to read count bytes. */
    count= asyn_read(&asyn, data_rw->r_fd,
                                data_rw->buf + data_rw->offset,
                                data_rw->size - data_rw->offset);

    if (count < 0) {
        if (errno == EINPROGRESS && !expired) return 0;
        if (errno == EIO) fatal(tcp_device);

        /* Remote end is late, or an error occurred. */
        if (debug >= 2) {
            printf("%s: TCP read reply: %s\n", nowgmt(), strerror(errno));
        }
        close_relay(data_rw);
        return 1;
    }

    if (debug >= 2) {
        printf("%s: TCP read reply, %d/%u bytes\n",
            nowgmt(), data_rw->offset + count, data_rw->size);
    }
    if (count == 0) {
        /* EOF. */
        close_relay(data_rw);
        return 1;
    }
    data_rw->offset += count;
    if (data_rw->offset == data_rw->size) {
        data_rw->size= sizeof(u16_t) + ntohs(upack16(data_rw->buf));
        if (data_rw->size < sizeof(u16_t)) {
            /* Malformed. */
            close_relay(data_rw);
            return 1;
        }
        if (data_rw->offset < data_rw->size) {
            /* Reply not complete, read more. */
            data_rw->buf= allocate(data_rw->buf, data_rw->size);
            newjob(job_read_reply, now + LONG_TIMEOUT, data_rw);
            return 1;
        }
    }
    if (debug >= 1) tcp_dns_tell(data_rw->r_fd, data_rw->buf);

    /* Reply fully read, send it on. */
    data_rw->offset= 0;
    newjob(job_write_reply, now + LONG_TIMEOUT, data_rw);
    return 1;
}

static int job_write_reply(void *data, int expired)
/* Send a TCP reply to the client. */
{
    data_rw_t *data_rw= data;
    ssize_t count;

    /* Try to write count bytes to the client. */
    count= asyn_write(&asyn, data_rw->w_fd,
                                data_rw->buf + data_rw->offset,
                                data_rw->size - data_rw->offset);

    if (count <= 0) {
        if (errno == EINPROGRESS && !expired) return 0;
        if (errno == EIO) fatal(tcp_device);

        /* A write expired or failed (usually a broken connection.) */
        if (debug >= 2) {
            printf("%s: TCP write reply: %s\n", nowgmt(), strerror(errno));
        }
        close_relay(data_rw);
        return 1;
    }

    if (debug >= 2) {
        printf("%s: TCP write reply, %d/%u bytes\n",
            nowgmt(), data_rw->offset + count, data_rw->size);
    }
    data_rw->offset += count;
    if (data_rw->offset < data_rw->size) {
        /* Partial write, continue. */
        newjob(job_write_reply, now + LONG_TIMEOUT, data_rw);
        return 1;
    }
    if (debug >= 1) tcp_dns_tell(data_rw->w_fd, data_rw->buf);

    /* Reply fully send on, go read more replies (or queries). */
    data_rw->offset= 0;
    data_rw->size= sizeof(u16_t);
    newjob(data_rw->w_fd != data_rw->r_fd ? job_read_reply : job_read_query,
                now + LONG_TIMEOUT, data_rw);
    return 1;
}
#else /* !DO_TCP */

static int job_dummy(void *data, int expired)
{
    return 1;
}
#define job_setup_listen        job_dummy
#define job_setup_connect       job_dummy
#endif /* !DO_TCP */

static void named_probe(ipaddr_t ip)
/* Send a probe to a name daemon, like 'host -r -t ns . <ip>'. */
{
    udp_dns_t udp;
#   define dlen (offsetof(dns_t, data) + 5)
#   define ulen (offsetof(udp_dns_t, dns) + dlen)

    /* Send a simple DNS query that all name servers can answer easily:
     * "What are the name servers for the root domain?"
     */
    udp.dns.hdr.dh_id= new_id(ID_PROBE, my_port, ID_IPSELF);
    udp.dns.hdr.dh_flag1= 0;
    udp.dns.hdr.dh_flag2= 0;
    udp.dns.hdr.dh_qdcount= HTONS(1);
    udp.dns.hdr.dh_ancount= HTONS(0);
    udp.dns.hdr.dh_nscount= HTONS(0);
    udp.dns.hdr.dh_arcount= HTONS(0);

    udp.dns.data[0] = 0;        /* Null name. */
    pack16(udp.dns.data+1, HTONS(T_NS));
    pack16(udp.dns.data+3, HTONS(C_IN));
    if (debug >= 1) {
        printf("PROBE %s ", inet_ntoa(ip));
        dns_tell(0, &udp.dns, dlen);
    }

    udp.hdr.uih_dst_addr= ip;
    udp.hdr.uih_dst_port= named_port;
    udp.hdr.uih_ip_opt_len= 0;
    udp.hdr.uih_data_len= dlen;

    if (write(udp_fd, &udp, ulen) < 0) fatal(udp_device);
#undef dlen
#undef ulen
}

static int job_find_named(void *data, int expired)
/* Look for a real name daemon to answer real DNS queries. */
{
    if (!expired) return 0;
    if (debug >= 2) printf("%s: Find named\n", nowgmt());

    /* New search? */
    if (search_ct < 0) {
        search_ct= n_nameds;
        i_named= -1;
    }

    if (--search_ct < 0) {
        /* Forced end of search (named response!), or end of search with
         * nothing found.  Search again after a long time.
         */
        newjob(job_find_named,
            (stale > 0 || i_named > 0) ? now + LONG_TIMEOUT : NEVER, nil);
        force_expire(job_setup_connect);
        return 1;
    }

    /* Send a named probe. */
    i_named= (i_named+1) % n_nameds;
    named_probe(current_named());

    /* Schedule the next call. */
    newjob(job_find_named, now + SHORT_TIMEOUT, nil);
    return 1;
}

static int job_expect_named(void *data, int expired)
/* The real name server is expected to answer by now. */
{
    if (!expired) return 0;
    if (debug >= 2) printf("%s: Expect named\n", nowgmt());

    if (expecting() && !searching()) {
        /* No answer yet, start searching. */
        start_searching();
        force_expire(job_find_named);
    }
    return 1;
}

static void sig_handler(int sig)
/* A signal forces a search for a real name daemon, etc. */
{
    switch (sig) {
    case SIGINT:
    case SIGTERM:       done= 1;                break;
    case SIGHUP:        reinit= 1;              break;
    case SIGUSR1:       debug++;                break;
    case SIGUSR2:       debug= 0;               break;
    }
}

static void usage(void)
{
    fprintf(stderr, "Usage: nonamed [-qs] [-d[level]] [-p port]\n");
    exit(1);
}

int main(int argc, char **argv)
{
    job_t *job;
    nwio_udpopt_t udpopt;
    int i;
    struct servent *servent;
    struct sigaction sa;
    FILE *fp;
    int quit= 0;

    /* Debug output must be line buffered. */
    setvbuf(stdout, nil, _IOLBF, 0);

    /* DNS service port number? */
    if ((servent= getservbyname("domain", nil)) == nil) {
        fprintf(stderr, "nonamed: \"domain\": unknown service\n");
        exit(1);
    }
    my_port= servent->s_port;
    named_port= servent->s_port;

    i= 1;
    while (i < argc && argv[i][0] == '-') {
        char *opt= argv[i++] + 1, *end;

        if (opt[0] == '-' && opt[1] == 0) break;

        switch (*opt++) {
        case 'd':               /* Debug level. */
            debug= 1;
            if (between('0', *opt, '9')) debug= strtoul(opt, &opt, 10);
            break;
        case 'p':               /* Port to listen to (for testing.) */
            if (*opt == 0) {
                if (i == argc) usage();
                opt= argv[i++];
            }
            my_port= htons(strtoul(opt, &end, 0));
            if (opt == end || *end != 0) usage();
            opt= end;
            break;
        case 's':
            single= 1;
            break;
        case 'q':               /* Quit after printing cache contents. */
            quit= 1;
            break;
        case 'L':
            localonly= 1;
            break;
        default:
            usage();
        }
    }
    if (i != argc) usage();

    if (quit) {
        /* Oops, just having a look at the cache. */
        debug= 2;
        now= time(nil);
        n_datamax= -1;
        file2cache();
        return 0;
    }

    /* Don't die on broken pipes, reinitialize on hangup, etc. */
    sa.sa_handler= SIG_IGN;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags= 0;
    sigaction(SIGPIPE, &sa, nil);
    sa.sa_handler= sig_handler;
    sigaction(SIGINT, &sa, nil);
    sigaction(SIGHUP, &sa, nil);
    sigaction(SIGUSR1, &sa, nil);
    sigaction(SIGUSR2, &sa, nil);
    sigaction(SIGTERM, &sa, nil);

    /* TCP and UDP device names. */
    if ((tcp_device= getenv("TCP_DEVICE")) == nil) tcp_device= TCP_DEVICE;
    if ((udp_device= getenv("UDP_DEVICE")) == nil) udp_device= UDP_DEVICE;

    /* Open an UDP channel for incoming DNS queries. */
    if ((udp_fd= open(udp_device, O_RDWR)) < 0) fatal(udp_device);

    udpopt.nwuo_flags= NWUO_EXCL | NWUO_LP_SET | NWUO_EN_LOC | NWUO_DI_BROAD
                | NWUO_RP_ANY | NWUO_RA_ANY | NWUO_RWDATALL | NWUO_DI_IPOPT;
    udpopt.nwuo_locport= my_port;
    if (ioctl(udp_fd, NWIOSUDPOPT, &udpopt) == -1
        || ioctl(udp_fd, NWIOGUDPOPT, &udpopt) == -1
    ) {
        fatal(udp_device);
    }

    /* The current time is... */
    now= time(nil);

    /* Read configuration and data cached by the previous nonamed. */
    init_config(udpopt.nwuo_locaddr);
    file2cache();

    if (!single) {
        /* Save process id. */
        if ((fp= fopen(PIDFILE, "w")) != nil) {
            fprintf(fp, "%u\n", (unsigned) getpid());
            fclose(fp);
        }
    }

    /* Jobs that start the ball rolling. */
    newjob(job_read_udp, NEVER, nil);
    newjob(job_setup_listen, IMMEDIATE, nil);
    newjob(job_find_named, IMMEDIATE, nil);

    /* Open syslog. */
    openlog("nonamed", LOG_PID, LOG_DAEMON);

    while (!done) {
        /* There is always something in the queue. */
        assert(queue != nil);

        /* Any expired jobs? */
        while (queue->timeout <= now) {
            (void) execjob(queue, 1);
            assert(queue != nil);
        }

        /* Check I/O jobs. */
        for (job= queue; job != nil; job= job->next) {
            if (execjob(job, 0)) break;
        }

        if (queue->timeout != IMMEDIATE) {
            struct timeval tv, *tvp;

            if (debug >= 2) printf("%s: I/O wait", nowgmt());

            if (queue->timeout != NEVER) {
                tv.tv_sec= queue->timeout;
                tv.tv_usec= 0;
                tvp= &tv;
                if (debug >= 2) printf(" (expires %s)\n", timegmt(tv.tv_sec));
            } else {
                tvp= nil;
                if (debug >= 2) fputc('\n', stdout);
            }
            fflush(stdout);

            if (asyn_wait(&asyn, 0, tvp) < 0) {
                if (errno != EINTR && errno != EAGAIN) fatal("fwait()");
            }
            now= time(nil);
        }

        if (reinit) {
            /* A hangup makes us go back to square one. */
            reinit= 0;
            if (ioctl(udp_fd, NWIOGUDPOPT, &udpopt) == -1) fatal(udp_device);
            init_config(udpopt.nwuo_locaddr);
            start_searching();
            force_expire(job_find_named);
        }
    }
    cache2file();
    (void) unlink(PIDFILE);
    if (debug >= 2) printf("sbrk(0) = %u\n", (unsigned) sbrk(0));
    return 0;
}

---