/*
 * Copyright (c) 1983, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * @(#) Copyright (c) 1983, 1993 The Regents of the University of California.  All rights reserved.
 * @(#)tftpd.c  8.1 (Berkeley) 6/4/93
 * $FreeBSD: src/libexec/tftpd/tftpd.c,v 1.15.2.5 2003/04/06 19:42:56 dwmalone Exp $
 */

/*
 * Trivial file transfer protocol server.
 *
 * This version includes many modifications by Jim Guyton
 * <guyton@rand-unix>.
 */

#include <sys/param.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/types.h>

#include <netinet/in.h>
#include <arpa/tftp.h>
#include <arpa/inet.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <libutil.h>
#include <netdb.h>
#include <pwd.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "tftpsubs.h"

#define TIMEOUT         5
#define MAX_TIMEOUTS    5

static int      peer;
static int      rexmtval = TIMEOUT;
static int      max_rexmtval = 2*TIMEOUT;

#define PKTSIZE SEGSIZE+4
static char     buf[PKTSIZE];
static char     ackbuf[PKTSIZE];
static struct   sockaddr_storage from;
static int      fromlen;

static void tftp(struct tftphdr *, int) __dead2;
static void unmappedaddr(struct sockaddr_in6 *);

/*
 * Null-terminated directory prefix list for absolute pathname requests and
 * search list for relative pathname requests.
 *
 * MAXDIRS should be at least as large as the number of arguments that
 * inetd allows (currently 20).
 */
#define MAXDIRS 20
static struct dirlist {
        const char      *name;
        int     len;
} dirs[MAXDIRS+1];
static int      suppress_naks;
static int      logging;
static int      ipchroot;

static const char *errtomsg(int);
static void  nak(int);
static void  oack(void);

static void  timer(int);
static void  justquit(int);

int
main(int argc, char *argv[])
{
        struct tftphdr *tp;
        int n;
        int ch, on;
        struct sockaddr_storage me;
        int len;
        char *chroot_dir = NULL;
        struct passwd *nobody;
        const char *chuser = "nobody";

        openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
        while ((ch = getopt(argc, argv, "cClns:u:")) != -1) {
                switch (ch) {
                case 'c':
                        ipchroot = 1;
                        break;
                case 'C':
                        ipchroot = 2;
                        break;
                case 'l':
                        logging = 1;
                        break;
                case 'n':
                        suppress_naks = 1;
                        break;
                case 's':
                        chroot_dir = optarg;
                        break;
                case 'u':
                        chuser = optarg;
                        break;
                default:
                        syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
                }
        }
        if (optind < argc) {
                struct dirlist *dirp;

                /* Get list of directory prefixes. Skip relative pathnames. */
                for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
                     optind++) {
                        if (argv[optind][0] == '/') {
                                dirp->name = argv[optind];
                                dirp->len  = strlen(dirp->name);
                                dirp++;
                        }
                }
        }
        else if (chroot_dir) {
                dirs->name = "/";
                dirs->len = 1;
        }
        if (ipchroot && chroot_dir == NULL) {
                syslog(LOG_ERR, "-c requires -s");
                exit(1);
        }

        on = 1;
        if (ioctl(0, FIONBIO, &on) < 0) {
                syslog(LOG_ERR, "ioctl(FIONBIO): %m");
                exit(1);
        }
        fromlen = sizeof (from);
        n = recvfrom(0, buf, sizeof (buf), 0,
            (struct sockaddr *)&from, &fromlen);
        if (n < 0) {
                syslog(LOG_ERR, "recvfrom: %m");
                exit(1);
        }
        /*
         * Now that we have read the message out of the UDP
         * socket, we fork and exit.  Thus, inetd will go back
         * to listening to the tftp port, and the next request
         * to come in will start up a new instance of tftpd.
         *
         * We do this so that inetd can run tftpd in "wait" mode.
         * The problem with tftpd running in "nowait" mode is that
         * inetd may get one or more successful "selects" on the
         * tftp port before we do our receive, so more than one
         * instance of tftpd may be started up.  Worse, if tftpd
         * break before doing the above "recvfrom", inetd would
         * spawn endless instances, clogging the system.
         */
        {
                int pid;
                int i, j;

                for (i = 1; i < 20; i++) {
                    pid = fork();
                    if (pid < 0) {
                                sleep(i);
                                /*
                                 * flush out to most recently sent request.
                                 *
                                 * This may drop some request, but those
                                 * will be resent by the clients when
                                 * they timeout.  The positive effect of
                                 * this flush is to (try to) prevent more
                                 * than one tftpd being started up to service
                                 * a single request from a single client.
                                 */
                                j = sizeof from;
                                i = recvfrom(0, buf, sizeof (buf), 0,
                                    (struct sockaddr *)&from, &j);
                                if (i > 0) {
                                        n = i;
                                        fromlen = j;
                                }
                    } else {
                                break;
                    }
                }
                if (pid < 0) {
                        syslog(LOG_ERR, "fork: %m");
                        exit(1);
                } else if (pid != 0) {
                        exit(0);
                }
        }

        /*
         * Since we exit here, we should do that only after the above
         * recvfrom to keep inetd from constantly forking should there
         * be a problem.  See the above comment about system clogging.
         */
        if (chroot_dir) {
                if (ipchroot) {
                        char *tempchroot;
                        struct stat sb;
                        int statret;
                        struct sockaddr_storage ss;
                        char hbuf[NI_MAXHOST];

                        memcpy(&ss, &from, from.ss_len);
                        unmappedaddr((struct sockaddr_in6 *)&ss);
                        getnameinfo((struct sockaddr *)&ss, ss.ss_len,
                                    hbuf, sizeof(hbuf), NULL, 0,
                                    NI_NUMERICHOST | NI_WITHSCOPEID);
                        asprintf(&tempchroot, "%s/%s", chroot_dir, hbuf);
                        statret = stat(tempchroot, &sb);
                        if ((sb.st_mode & S_IFDIR) &&
                            (statret == 0 || (statret == -1 && ipchroot == 1)))
                                chroot_dir = tempchroot;
                }
                /* Must get this before chroot because /etc might go away */
                if ((nobody = getpwnam(chuser)) == NULL) {
                        syslog(LOG_ERR, "%s: no such user", chuser);
                        exit(1);
                }
                if (chroot(chroot_dir)) {
                        syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
                        exit(1);
                }
                chdir( "/" );
                setuid(nobody->pw_uid);
                setgroups(1, &nobody->pw_gid);
        }

        len = sizeof(me);
        if (getsockname(0, (struct sockaddr *)&me, &len) == 0) {
                switch (me.ss_family) {
                case AF_INET:
                        ((struct sockaddr_in *)&me)->sin_port = 0;
                        break;
                case AF_INET6:
                        ((struct sockaddr_in6 *)&me)->sin6_port = 0;
                        break;
                default:
                        /* unsupported */
                        break;
                }
        } else {
                memset(&me, 0, sizeof(me));
                me.ss_family = from.ss_family;
                me.ss_len = from.ss_len;
        }
        alarm(0);
        close(0);
        close(1);
        peer = socket(from.ss_family, SOCK_DGRAM, 0);
        if (peer < 0) {
                syslog(LOG_ERR, "socket: %m");
                exit(1);
        }
        if (bind(peer, (struct sockaddr *)&me, me.ss_len) < 0) {
                syslog(LOG_ERR, "bind: %m");
                exit(1);
        }
        if (connect(peer, (struct sockaddr *)&from, from.ss_len) < 0) {
                syslog(LOG_ERR, "connect: %m");
                exit(1);
        }
        tp = (struct tftphdr *)buf;
        tp->th_opcode = ntohs(tp->th_opcode);
        if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
                tftp(tp, n);
        exit(1);
}

struct formats;
static int      validate_access(char **, int);
static void     xmitfile(struct formats *);
static void     recvfile(struct formats *);

static struct formats {
        const char      *f_mode;
        int     (*f_validate)(char **, int);
        void    (*f_send)(struct formats *);
        void    (*f_recv)(struct formats *);
        int     f_convert;
} formats[] = {
        { "netascii",   validate_access,        xmitfile,       recvfile, 1 },
        { "octet",      validate_access,        xmitfile,       recvfile, 0 },
#ifdef notdef
        { "mail",       validate_user,          sendmail,       recvmail, 1 },
#endif
        { 0,            NULL,                   NULL,           NULL,     0 }
};

static struct options {
        const char      *o_type;
        char    *o_request;
        int     o_reply;        /* turn into union if need be */
} options[] = {
        { "tsize",      NULL, 0 },              /* OPT_TSIZE */
        { "timeout",    NULL, 0 },              /* OPT_TIMEOUT */
        { NULL,         NULL, 0 }
};

enum opt_enum {
        OPT_TSIZE = 0,
        OPT_TIMEOUT,
};

/*
 * Handle initial connection protocol.
 */
static void
tftp(struct tftphdr *tp, int size)
{
        char *cp;
        size_t i;
        int first = 1, has_options = 0, ecode;
        struct formats *pf;
        char *filename, *mode = NULL, *option, *ccp;
        char fnbuf[MAXPATHLEN];

        cp = tp->th_stuff;
again:
        while (cp < buf + size) {
                if (*cp == '\0')
                        break;
                cp++;
        }
        if (*cp != '\0') {
                nak(EBADOP);
                exit(1);
        }
        i = cp - tp->th_stuff;
        if (i >= sizeof(fnbuf)) {
                nak(EBADOP);
                exit(1);
        }
        memcpy(fnbuf, tp->th_stuff, i);
        fnbuf[i] = '\0';
        filename = fnbuf;
        if (first) {
                mode = ++cp;
                first = 0;
                goto again;
        }
        for (cp = mode; *cp; cp++)
                if (isupper(*cp))
                        *cp = tolower(*cp);
        for (pf = formats; pf->f_mode; pf++)
                if (strcmp(pf->f_mode, mode) == 0)
                        break;
        if (pf->f_mode == NULL) {
                nak(EBADOP);
                exit(1);
        }
        while (++cp < buf + size) {
                for (i = 2, ccp = cp; i > 0; ccp++) {
                        if (ccp >= buf + size) {
                                /*
                                 * Don't reject the request, just stop trying
                                 * to parse the option and get on with it.
                                 * Some Apple OpenFirmware versions have
                                 * trailing garbage on the end of otherwise
                                 * valid requests.
                                 */
                                goto option_fail;
                        } else if (*ccp == '\0')
                                i--;
                }
                for (option = cp; *cp; cp++)
                        if (isupper(*cp))
                                *cp = tolower(*cp);
                for (i = 0; options[i].o_type != NULL; i++)
                        if (strcmp(option, options[i].o_type) == 0) {
                                options[i].o_request = ++cp;
                                has_options = 1;
                        }
                cp = ccp-1;
        }

option_fail:
        if (options[OPT_TIMEOUT].o_request) {
                int to = atoi(options[OPT_TIMEOUT].o_request);
                if (to < 1 || to > 255) {
                        nak(EBADOP);
                        exit(1);
                }
                else if (to <= max_rexmtval)
                        options[OPT_TIMEOUT].o_reply = rexmtval = to;
                else
                        options[OPT_TIMEOUT].o_request = NULL;
        }

        ecode = (*pf->f_validate)(&filename, tp->th_opcode);
        if (has_options)
                oack();
        if (logging) {
                char hbuf[NI_MAXHOST];

                getnameinfo((struct sockaddr *)&from, from.ss_len,
                            hbuf, sizeof(hbuf), NULL, 0, 
                            NI_WITHSCOPEID);
                syslog(LOG_INFO, "%s: %s request for %s: %s", hbuf,
                        tp->th_opcode == WRQ ? "write" : "read",
                        filename, errtomsg(ecode));
        }
        if (ecode) {
                /*
                 * Avoid storms of naks to a RRQ broadcast for a relative
                 * bootfile pathname from a diskless Sun.
                 */
                if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
                        exit(0);
                nak(ecode);
                exit(1);
        }
        if (tp->th_opcode == WRQ)
                (*pf->f_recv)(pf);
        else
                (*pf->f_send)(pf);
        exit(0);
}


static FILE *file;

/*
 * Validate file access.  Since we
 * have no uid or gid, for now require
 * file to exist and be publicly
 * readable/writable.
 * If we were invoked with arguments
 * from inetd then the file must also be
 * in one of the given directory prefixes.
 * Note also, full path name must be
 * given as we have no login directory.
 */
static int
validate_access(char **filep, int mode)
{
        struct stat stbuf;
        int     fd;
        struct dirlist *dirp;
        static char pathname[MAXPATHLEN];
        char *filename = *filep;

        /*
         * Prevent tricksters from getting around the directory restrictions
         */
        if (strstr(filename, "/../"))
                return (EACCESS);

        if (*filename == '/') {
                /*
                 * Allow the request if it's in one of the approved locations.
                 * Special case: check the null prefix ("/") by looking
                 * for length = 1 and relying on the arg. processing that
                 * it's a /.
                 */
                for (dirp = dirs; dirp->name != NULL; dirp++) {
                        if (dirp->len == 1 ||
                            (!strncmp(filename, dirp->name, dirp->len) &&
                             filename[dirp->len] == '/'))
                                    break;
                }
                /* If directory list is empty, allow access to any file */
                if (dirp->name == NULL && dirp != dirs)
                        return (EACCESS);
                if (stat(filename, &stbuf) < 0)
                        return (errno == ENOENT ? ENOTFOUND : EACCESS);
                if ((stbuf.st_mode & S_IFMT) != S_IFREG)
                        return (ENOTFOUND);
                if (mode == RRQ) {
                        if ((stbuf.st_mode & S_IROTH) == 0)
                                return (EACCESS);
                } else {
                        if ((stbuf.st_mode & S_IWOTH) == 0)
                                return (EACCESS);
                }
        } else {
                int err;

                /*
                 * Relative file name: search the approved locations for it.
                 * Don't allow write requests that avoid directory
                 * restrictions.
                 */

                if (!strncmp(filename, "../", 3))
                        return (EACCESS);

                /*
                 * If the file exists in one of the directories and isn't
                 * readable, continue looking. However, change the error code
                 * to give an indication that the file exists.
                 */
                err = ENOTFOUND;
                for (dirp = dirs; dirp->name != NULL; dirp++) {
                        snprintf(pathname, sizeof(pathname), "%s/%s",
                                dirp->name, filename);
                        if (stat(pathname, &stbuf) == 0 &&
                            (stbuf.st_mode & S_IFMT) == S_IFREG) {
                                if ((stbuf.st_mode & S_IROTH) != 0) {
                                        break;
                                }
                                err = EACCESS;
                        }
                }
                if (dirp->name == NULL)
                        return (err);
                *filep = filename = pathname;
        }
        if (options[OPT_TSIZE].o_request) {
                if (mode == RRQ) 
                        options[OPT_TSIZE].o_reply = stbuf.st_size;
                else
                        /* XXX Allows writes of all sizes. */
                        options[OPT_TSIZE].o_reply =
                                atoi(options[OPT_TSIZE].o_request);
        }
        fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
        if (fd < 0)
                return (errno + 100);
        file = fdopen(fd, (mode == RRQ)? "r":"w");
        if (file == NULL) {
                return errno+100;
        }
        return (0);
}

static int      timeouts;
static jmp_buf  timeoutbuf;

static void
timer(int sig __unused)
{
        if (++timeouts > MAX_TIMEOUTS)
                exit(1);
        longjmp(timeoutbuf, 1);
}

/*
 * Send the requested file.
 */
static void
xmitfile(struct formats *pf)
{
        struct tftphdr *dp;
        struct tftphdr *ap;    /* ack packet */
        int size, n;
        volatile unsigned short block;

        signal(SIGALRM, timer);
        dp = r_init();
        ap = (struct tftphdr *)ackbuf;
        block = 1;
        do {
                size = readit(file, &dp, pf->f_convert);
                if (size < 0) {
                        nak(errno + 100);
                        goto abort;
                }
                dp->th_opcode = htons((u_short)DATA);
                dp->th_block = htons((u_short)block);
                timeouts = 0;
                (void)setjmp(timeoutbuf);

send_data:
                {
                        int i, t = 1;
                        for (i = 0; ; i++){
                                if (send(peer, dp, size + 4, 0) != size + 4) {
                                        sleep(t);
                                        t = (t < 32) ? t<< 1 : t;
                                        if (i >= 12) {
                                                syslog(LOG_ERR, "write: %m");
                                                goto abort;
                                        }
                                }
                                break;
                        }
                }
                read_ahead(file, pf->f_convert);
                for ( ; ; ) {
                        alarm(rexmtval);        /* read the ack */
                        n = recv(peer, ackbuf, sizeof (ackbuf), 0);
                        alarm(0);
                        if (n < 0) {
                                syslog(LOG_ERR, "read: %m");
                                goto abort;
                        }
                        ap->th_opcode = ntohs((u_short)ap->th_opcode);
                        ap->th_block = ntohs((u_short)ap->th_block);

                        if (ap->th_opcode == ERROR)
                                goto abort;

                        if (ap->th_opcode == ACK) {
                                if (ap->th_block == block)
                                        break;
                                /* Re-synchronize with the other side */
                                (void) synchnet(peer);
                                if (ap->th_block == (block -1))
                                        goto send_data;
                        }

                }
                block++;
        } while (size == SEGSIZE);
abort:
        (void) fclose(file);
}

static void
justquit(int sig __unused)
{
        exit(0);
}


/*
 * Receive a file.
 */
static void
recvfile(struct formats *pf)
{
        struct tftphdr *dp;
        struct tftphdr *ap;    /* ack buffer */
        int n, size;
        volatile unsigned short block;

        signal(SIGALRM, timer);
        dp = w_init();
        ap = (struct tftphdr *)ackbuf;
        block = 0;
        do {
                timeouts = 0;
                ap->th_opcode = htons((u_short)ACK);
                ap->th_block = htons((u_short)block);
                block++;
                (void) setjmp(timeoutbuf);
send_ack:
                if (send(peer, ackbuf, 4, 0) != 4) {
                        syslog(LOG_ERR, "write: %m");
                        goto abort;
                }
                write_behind(file, pf->f_convert);
                for ( ; ; ) {
                        alarm(rexmtval);
                        n = recv(peer, dp, PKTSIZE, 0);
                        alarm(0);
                        if (n < 0) {            /* really? */
                                syslog(LOG_ERR, "read: %m");
                                goto abort;
                        }
                        dp->th_opcode = ntohs((u_short)dp->th_opcode);
                        dp->th_block = ntohs((u_short)dp->th_block);
                        if (dp->th_opcode == ERROR)
                                goto abort;
                        if (dp->th_opcode == DATA) {
                                if (dp->th_block == block) {
                                        break;   /* normal */
                                }
                                /* Re-synchronize with the other side */
                                (void) synchnet(peer);
                                if (dp->th_block == (block-1))
                                        goto send_ack;          /* rexmit */
                        }
                }
                /*  size = write(file, dp->th_data, n - 4); */
                size = writeit(file, &dp, n - 4, pf->f_convert);
                if (size != (n-4)) {                    /* ahem */
                        if (size < 0) nak(errno + 100);
                        else nak(ENOSPACE);
                        goto abort;
                }
        } while (size == SEGSIZE);
        write_behind(file, pf->f_convert);
        (void) fclose(file);            /* close data file */

        ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
        ap->th_block = htons((u_short)(block));
        (void) send(peer, ackbuf, 4, 0);

        signal(SIGALRM, justquit);      /* just quit on timeout */
        alarm(rexmtval);
        n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
        alarm(0);
        if (n >= 4 &&                   /* if read some data */
            dp->th_opcode == DATA &&    /* and got a data block */
            block == dp->th_block) {    /* then my last ack was lost */
                (void) send(peer, ackbuf, 4, 0);     /* resend final ack */
        }
abort:
        return;
}

static struct errmsg {
        int     e_code;
        const char      *e_msg;
} errmsgs[] = {
        { EUNDEF,       "Undefined error code" },
        { ENOTFOUND,    "File not found" },
        { EACCESS,      "Access violation" },
        { ENOSPACE,     "Disk full or allocation exceeded" },
        { EBADOP,       "Illegal TFTP operation" },
        { EBADID,       "Unknown transfer ID" },
        { EEXISTS,      "File already exists" },
        { ENOUSER,      "No such user" },
        { EOPTNEG,      "Option negotiation" },
        { -1,           0 }
};

static const char *
errtomsg(int error)
{
        static char ebuf[20];
        struct errmsg *pe;

        if (error == 0)
                return "success";
        for (pe = errmsgs; pe->e_code >= 0; pe++)
                if (pe->e_code == error)
                        return pe->e_msg;
        snprintf(ebuf, sizeof(ebuf), "error %d", error);
        return ebuf;
}

/*
 * Send a nak packet (error message).
 * Error code passed in is one of the
 * standard TFTP codes, or a UNIX errno
 * offset by 100.
 */
static void
nak(int error)
{
        struct tftphdr *tp;
        int length;
        struct errmsg *pe;

        tp = (struct tftphdr *)buf;
        tp->th_opcode = htons((u_short)ERROR);
        tp->th_code = htons((u_short)error);
        for (pe = errmsgs; pe->e_code >= 0; pe++)
                if (pe->e_code == error)
                        break;
        if (pe->e_code < 0) {
                pe->e_msg = strerror(error - 100);
                tp->th_code = EUNDEF;   /* set 'undef' errorcode */
        }
        strcpy(tp->th_msg, pe->e_msg);
        length = strlen(pe->e_msg);
        tp->th_msg[length] = '\0';
        length += 5;
        if (send(peer, buf, length, 0) != length)
                syslog(LOG_ERR, "nak: %m");
}

/* translate IPv4 mapped IPv6 address to IPv4 address */
static void
unmappedaddr(struct sockaddr_in6 *sin6)
{
        struct sockaddr_in *sin4;
        void *addr;
        int port;

        if (sin6->sin6_family != AF_INET6 ||
            !IN6_IS_ADDR_V4MAPPED(&sin6->sin6_addr))
                return;
        sin4 = (struct sockaddr_in *)sin6;
        addr = &sin6->sin6_addr.s6_addr[12];
        port = sin6->sin6_port;
        memset(sin4, 0, sizeof(struct sockaddr_in));
        sin4->sin_addr.s_addr = *(uint32_t *)addr;
        sin4->sin_port = port;
        sin4->sin_family = AF_INET;
        sin4->sin_len = sizeof(struct sockaddr_in);
}

/*
 * Send an oack packet (option acknowledgement).
 */
static void
oack(void)
{
        struct tftphdr *tp, *ap;
        int size, i, n;
        char *bp;

        tp = (struct tftphdr *)buf;
        bp = buf + 2;
        size = sizeof(buf) - 2;
        tp->th_opcode = htons((u_short)OACK);
        for (i = 0; options[i].o_type != NULL; i++) {
                if (options[i].o_request) {
                        n = snprintf(bp, size, "%s%c%d", options[i].o_type,
                                     0, options[i].o_reply);
                        bp += n+1;
                        size -= n+1;
                        if (size < 0) {
                                syslog(LOG_ERR, "oack: buffer overflow");
                                exit(1);
                        }
                }
        }
        size = bp - buf;
        ap = (struct tftphdr *)ackbuf;
        signal(SIGALRM, timer);
        timeouts = 0;

        (void)setjmp(timeoutbuf);
        if (send(peer, buf, size, 0) != size) {
                syslog(LOG_INFO, "oack: %m");
                exit(1);
        }

        for (;;) {
                alarm(rexmtval);
                n = recv(peer, ackbuf, sizeof (ackbuf), 0);
                alarm(0);
                if (n < 0) {
                        syslog(LOG_ERR, "recv: %m");
                        exit(1);
                }
                ap->th_opcode = ntohs((u_short)ap->th_opcode);
                ap->th_block = ntohs((u_short)ap->th_block);
                if (ap->th_opcode == ERROR)
                        exit(1);
                if (ap->th_opcode == ACK && ap->th_block == 0)
                        break;
        }
}