/* vi: set sw=4 ts=4: */
/*
 * A simple tftp client/server for busybox.
 * Tries to follow RFC1350.
 * Only "octet" mode supported.
 * Optional blocksize negotiation (RFC2347 + RFC2348)
 *
 * Copyright (C) 2001 Magnus Damm <damm@opensource.se>
 *
 * Parts of the code based on:
 *
 * atftp:  Copyright (C) 2000 Jean-Pierre Lefebvre <helix@step.polymtl.ca>
 *                        and Remi Lefebvre <remi@debian.org>
 *
 * utftp:  Copyright (C) 1999 Uwe Ohse <uwe@ohse.de>
 *
 * tftpd added by Denys Vlasenko & Vladimir Dronnikov
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
#include "libbb.h"

#if ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT

#define TFTP_BLKSIZE_DEFAULT       512  /* according to RFC 1350, don't change */
#define TFTP_BLKSIZE_DEFAULT_STR "512"
/* Was 50 ms but users asked to bump it up a bit */
#define TFTP_TIMEOUT_MS            100
#define TFTP_MAXTIMEOUT_MS        2000
#define TFTP_NUM_RETRIES            12  /* number of backed-off retries */

/* opcodes we support */
#define TFTP_RRQ   1
#define TFTP_WRQ   2
#define TFTP_DATA  3
#define TFTP_ACK   4
#define TFTP_ERROR 5
#define TFTP_OACK  6

/* error codes sent over network (we use only 0, 1, 3 and 8) */
/* generic (error message is included in the packet) */
#define ERR_UNSPEC   0
#define ERR_NOFILE   1
#define ERR_ACCESS   2
/* disk full or allocation exceeded */
#define ERR_WRITE    3
#define ERR_OP       4
#define ERR_BAD_ID   5
#define ERR_EXIST    6
#define ERR_BAD_USER 7
#define ERR_BAD_OPT  8

/* masks coming from getopt32 */
enum {
        TFTP_OPT_GET = (1 << 0),
        TFTP_OPT_PUT = (1 << 1),
        /* pseudo option: if set, it's tftpd */
        TFTPD_OPT = (1 << 7) * ENABLE_TFTPD,
        TFTPD_OPT_r = (1 << 8) * ENABLE_TFTPD,
        TFTPD_OPT_c = (1 << 9) * ENABLE_TFTPD,
        TFTPD_OPT_u = (1 << 10) * ENABLE_TFTPD,
};

#if ENABLE_FEATURE_TFTP_GET && !ENABLE_FEATURE_TFTP_PUT
#define IF_GETPUT(...)
#define CMD_GET(cmd) 1
#define CMD_PUT(cmd) 0
#elif !ENABLE_FEATURE_TFTP_GET && ENABLE_FEATURE_TFTP_PUT
#define IF_GETPUT(...)
#define CMD_GET(cmd) 0
#define CMD_PUT(cmd) 1
#else
#define IF_GETPUT(...) __VA_ARGS__
#define CMD_GET(cmd) ((cmd) & TFTP_OPT_GET)
#define CMD_PUT(cmd) ((cmd) & TFTP_OPT_PUT)
#endif
/* NB: in the code below
 * CMD_GET(cmd) and CMD_PUT(cmd) are mutually exclusive
 */


struct globals {
        /* u16 TFTP_ERROR; u16 reason; both network-endian, then error text: */
        uint8_t error_pkt[4 + 32];
        char *user_opt;
        /* used in tftpd_main(), a bit big for stack: */
        char block_buf[TFTP_BLKSIZE_DEFAULT];
#if ENABLE_FEATURE_TFTP_PROGRESS_BAR
        off_t pos;
        off_t size;
        const char *file;
        bb_progress_t pmt;
#endif
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
struct BUG_G_too_big {
        char BUG_G_too_big[sizeof(G) <= COMMON_BUFSIZE ? 1 : -1];
};
#define block_buf        (G.block_buf   )
#define user_opt         (G.user_opt    )
#define error_pkt        (G.error_pkt   )
#define INIT_G() do { } while (0)

#define error_pkt_reason (error_pkt[3])
#define error_pkt_str    (error_pkt + 4)

#if ENABLE_FEATURE_TFTP_PROGRESS_BAR
static void tftp_progress_update(void)
{
        bb_progress_update(&G.pmt, G.file, 0, G.pos, G.size);
}
static void tftp_progress_init(void)
{
        bb_progress_init(&G.pmt);
        tftp_progress_update();
}
static void tftp_progress_done(void)
{
        if (G.pmt.inited) {
                tftp_progress_update();
                bb_putchar_stderr('\n');
                G.pmt.inited = 0;
        }
}
#else
# define tftp_progress_init() ((void)0)
# define tftp_progress_done() ((void)0)
#endif

#if ENABLE_FEATURE_TFTP_BLOCKSIZE

static int tftp_blksize_check(const char *blksize_str, int maxsize)
{
        /* Check if the blksize is valid:
         * RFC2348 says between 8 and 65464,
         * but our implementation makes it impossible
         * to use blksizes smaller than 22 octets. */
        unsigned blksize = bb_strtou(blksize_str, NULL, 10);
        if (errno
         || (blksize < 24) || (blksize > maxsize)
        ) {
                bb_error_msg("bad blocksize '%s'", blksize_str);
                return -1;
        }
# if ENABLE_TFTP_DEBUG
        bb_error_msg("using blksize %u", blksize);
# endif
        return blksize;
}

static char *tftp_get_option(const char *option, char *buf, int len)
{
        int opt_val = 0;
        int opt_found = 0;
        int k;

        /* buf points to:
         * "opt_name<NUL>opt_val<NUL>opt_name2<NUL>opt_val2<NUL>..." */

        while (len > 0) {
                /* Make sure options are terminated correctly */
                for (k = 0; k < len; k++) {
                        if (buf[k] == '\0') {
                                goto nul_found;
                        }
                }
                return NULL;
 nul_found:
                if (opt_val == 0) { /* it's "name" part */
                        if (strcasecmp(buf, option) == 0) {
                                opt_found = 1;
                        }
                } else if (opt_found) {
                        return buf;
                }

                k++;
                buf += k;
                len -= k;
                opt_val ^= 1;
        }

        return NULL;
}

#endif

static int tftp_protocol(
                /* NULL if tftp, !NULL if tftpd: */
                len_and_sockaddr *our_lsa,
                len_and_sockaddr *peer_lsa,
                const char *local_file
                IF_TFTP(, const char *remote_file)
#if !ENABLE_TFTP
# define remote_file NULL
#endif
                /* 1 for tftp; 1/0 for tftpd depending whether client asked about it: */
                IF_FEATURE_TFTP_BLOCKSIZE(, int want_transfer_size)
                IF_FEATURE_TFTP_BLOCKSIZE(, int blksize))
{
#if !ENABLE_FEATURE_TFTP_BLOCKSIZE
        enum { blksize = TFTP_BLKSIZE_DEFAULT };
#endif

        struct pollfd pfd[1];
#define socket_fd (pfd[0].fd)
        int len;
        int send_len;
        IF_FEATURE_TFTP_BLOCKSIZE(smallint expect_OACK = 0;)
        smallint finished = 0;
        uint16_t opcode;
        uint16_t block_nr;
        uint16_t recv_blk;
        int open_mode, local_fd;
        int retries, waittime_ms;
        int io_bufsize = blksize + 4;
        char *cp;
        /* Can't use RESERVE_CONFIG_BUFFER here since the allocation
         * size varies meaning BUFFERS_GO_ON_STACK would fail.
         *
         * We must keep the transmit and receive buffers separate
         * in case we rcv a garbage pkt - we need to rexmit the last pkt.
         */
        char *xbuf = xmalloc(io_bufsize);
        char *rbuf = xmalloc(io_bufsize);

        socket_fd = xsocket(peer_lsa->u.sa.sa_family, SOCK_DGRAM, 0);
        setsockopt_reuseaddr(socket_fd);

        if (!ENABLE_TFTP || our_lsa) { /* tftpd */
                /* Create a socket which is:
                 * 1. bound to IP:port peer sent 1st datagram to,
                 * 2. connected to peer's IP:port
                 * This way we will answer from the IP:port peer
                 * expects, will not get any other packets on
                 * the socket, and also plain read/write will work. */
                xbind(socket_fd, &our_lsa->u.sa, our_lsa->len);
                xconnect(socket_fd, &peer_lsa->u.sa, peer_lsa->len);

                /* Is there an error already? Send pkt and bail out */
                if (error_pkt_reason || error_pkt_str[0])
                        goto send_err_pkt;

                if (user_opt) {
                        struct passwd *pw = xgetpwnam(user_opt);
                        change_identity(pw); /* initgroups, setgid, setuid */
                }
        }

        /* Prepare open mode */
        if (CMD_PUT(option_mask32)) {
                open_mode = O_RDONLY;
        } else {
                open_mode = O_WRONLY | O_TRUNC | O_CREAT;
#if ENABLE_TFTPD
                if ((option_mask32 & (TFTPD_OPT+TFTPD_OPT_c)) == TFTPD_OPT) {
                        /* tftpd without -c */
                        open_mode = O_WRONLY | O_TRUNC;
                }
#endif
        }

        /* Examples of network traffic.
         * Note two cases when ACKs with block# of 0 are sent.
         *
         * Download without options:
         * tftp -> "\0\1FILENAME\0octet\0"
         *         "\0\3\0\1FILEDATA..." <- tftpd
         * tftp -> "\0\4\0\1"
         * ...
         * Download with option of blksize 16384:
         * tftp -> "\0\1FILENAME\0octet\0blksize\00016384\0"
         *         "\0\6blksize\00016384\0" <- tftpd
         * tftp -> "\0\4\0\0"
         *         "\0\3\0\1FILEDATA..." <- tftpd
         * tftp -> "\0\4\0\1"
         * ...
         * Upload without options:
         * tftp -> "\0\2FILENAME\0octet\0"
         *         "\0\4\0\0" <- tftpd
         * tftp -> "\0\3\0\1FILEDATA..."
         *         "\0\4\0\1" <- tftpd
         * ...
         * Upload with option of blksize 16384:
         * tftp -> "\0\2FILENAME\0octet\0blksize\00016384\0"
         *         "\0\6blksize\00016384\0" <- tftpd
         * tftp -> "\0\3\0\1FILEDATA..."
         *         "\0\4\0\1" <- tftpd
         * ...
         */
        block_nr = 1;
        cp = xbuf + 2;

        if (!ENABLE_TFTP || our_lsa) { /* tftpd */
                /* Open file (must be after changing user) */
                local_fd = open(local_file, open_mode, 0666);
                if (local_fd < 0) {
                        error_pkt_reason = ERR_NOFILE;
                        strcpy((char*)error_pkt_str, "can't open file");
                        goto send_err_pkt;
                }
/* gcc 4.3.1 would NOT optimize it out as it should! */
#if ENABLE_FEATURE_TFTP_BLOCKSIZE
                if (blksize != TFTP_BLKSIZE_DEFAULT || want_transfer_size) {
                        /* Create and send OACK packet. */
                        /* For the download case, block_nr is still 1 -
                         * we expect 1st ACK from peer to be for (block_nr-1),
                         * that is, for "block 0" which is our OACK pkt */
                        opcode = TFTP_OACK;
                        goto add_blksize_opt;
                }
#endif
                if (CMD_GET(option_mask32)) {
                        /* It's upload and we don't send OACK.
                         * We must ACK 1st packet (with filename)
                         * as if it is "block 0" */
                        block_nr = 0;
                }

        } else { /* tftp */
                /* Open file (must be after changing user) */
                local_fd = CMD_GET(option_mask32) ? STDOUT_FILENO : STDIN_FILENO;
                if (NOT_LONE_DASH(local_file))
                        local_fd = xopen(local_file, open_mode);
/* Removing #if, or using if() statement instead of #if may lead to
 * "warning: null argument where non-null required": */
#if ENABLE_TFTP
                /* tftp */

                /* We can't (and don't really need to) bind the socket:
                 * we don't know from which local IP datagrams will be sent,
                 * but kernel will pick the same IP every time (unless routing
                 * table is changed), thus peer will see dgrams consistently
                 * coming from the same IP.
                 * We would like to connect the socket, but since peer's
                 * UDP code can be less perfect than ours, _peer's_ IP:port
                 * in replies may differ from IP:port we used to send
                 * our first packet. We can connect() only when we get
                 * first reply. */

                /* build opcode */
                opcode = TFTP_WRQ;
                if (CMD_GET(option_mask32)) {
                        opcode = TFTP_RRQ;
                }
                /* add filename and mode */
                /* fill in packet if the filename fits into xbuf */
                len = strlen(remote_file) + 1;
                if (2 + len + sizeof("octet") >= io_bufsize) {
                        bb_error_msg("remote filename is too long");
                        goto ret;
                }
                strcpy(cp, remote_file);
                cp += len;
                /* add "mode" part of the packet */
                strcpy(cp, "octet");
                cp += sizeof("octet");

# if ENABLE_FEATURE_TFTP_BLOCKSIZE
                if (blksize == TFTP_BLKSIZE_DEFAULT && !want_transfer_size)
                        goto send_pkt;

                /* Need to add option to pkt */
                if ((&xbuf[io_bufsize - 1] - cp) < sizeof("blksize NNNNN tsize ") + sizeof(off_t)*3) {
                        bb_error_msg("remote filename is too long");
                        goto ret;
                }
                expect_OACK = 1;
# endif
#endif /* ENABLE_TFTP */

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
 add_blksize_opt:
                if (blksize != TFTP_BLKSIZE_DEFAULT) {
                        /* add "blksize", <nul>, blksize, <nul> */
                        strcpy(cp, "blksize");
                        cp += sizeof("blksize");
                        cp += snprintf(cp, 6, "%d", blksize) + 1;
                }
                if (want_transfer_size) {
                        /* add "tsize", <nul>, size, <nul> (see RFC2349) */
                        /* if tftp and downloading, we send "0" (since we opened local_fd with O_TRUNC)
                         * and this makes server to send "tsize" option with the size */
                        /* if tftp and uploading, we send file size (maybe dont, to not confuse old servers???) */
                        /* if tftpd and downloading, we are answering to client's request */
                        /* if tftpd and uploading: !want_transfer_size, this code is not executed */
                        struct stat st;
                        strcpy(cp, "tsize");
                        cp += sizeof("tsize");
                        st.st_size = 0;
                        fstat(local_fd, &st);
                        cp += sprintf(cp, "%"OFF_FMT"u", (off_t)st.st_size) + 1;
# if ENABLE_FEATURE_TFTP_PROGRESS_BAR
                        /* Save for progress bar. If 0 (tftp downloading),
                         * we look at server's reply later */
                        G.size = st.st_size;
                        if (remote_file && st.st_size)
                                tftp_progress_init();
# endif
                }
#endif
                /* First packet is built, so skip packet generation */
                goto send_pkt;
        }

        /* Using mostly goto's - continue/break will be less clear
         * in where we actually jump to */
        while (1) {
                /* Build ACK or DATA */
                cp = xbuf + 2;
                *((uint16_t*)cp) = htons(block_nr);
                cp += 2;
                block_nr++;
                opcode = TFTP_ACK;
                if (CMD_PUT(option_mask32)) {
                        opcode = TFTP_DATA;
                        len = full_read(local_fd, cp, blksize);
                        if (len < 0) {
                                goto send_read_err_pkt;
                        }
                        if (len != blksize) {
                                finished = 1;
                        }
                        cp += len;
                }
 send_pkt:
                /* Send packet */
                *((uint16_t*)xbuf) = htons(opcode); /* fill in opcode part */
                send_len = cp - xbuf;
                /* NB: send_len value is preserved in code below
                 * for potential resend */

                retries = TFTP_NUM_RETRIES;  /* re-initialize */
                waittime_ms = TFTP_TIMEOUT_MS;

 send_again:
#if ENABLE_TFTP_DEBUG
                fprintf(stderr, "sending %u bytes\n", send_len);
                for (cp = xbuf; cp < &xbuf[send_len]; cp++)
                        fprintf(stderr, "%02x ", (unsigned char) *cp);
                fprintf(stderr, "\n");
#endif
                xsendto(socket_fd, xbuf, send_len, &peer_lsa->u.sa, peer_lsa->len);

#if ENABLE_FEATURE_TFTP_PROGRESS_BAR
                if (ENABLE_TFTP && remote_file) /* tftp */
                        G.pos = (block_nr - 1) * (uoff_t)blksize;
                if (G.pmt.inited)
                        tftp_progress_update();
#endif
                /* Was it final ACK? then exit */
                if (finished && (opcode == TFTP_ACK))
                        goto ret;

 recv_again:
                /* Receive packet */
                /*pfd[0].fd = socket_fd;*/
                pfd[0].events = POLLIN;
                switch (safe_poll(pfd, 1, waittime_ms)) {
                default:
                        /*bb_perror_msg("poll"); - done in safe_poll */
                        goto ret;
                case 0:
                        retries--;
                        if (retries == 0) {
                                tftp_progress_done();
                                bb_error_msg("timeout");
                                goto ret; /* no err packet sent */
                        }

                        /* exponential backoff with limit */
                        waittime_ms += waittime_ms/2;
                        if (waittime_ms > TFTP_MAXTIMEOUT_MS) {
                                waittime_ms = TFTP_MAXTIMEOUT_MS;
                        }

                        goto send_again; /* resend last sent pkt */
                case 1:
                        if (!our_lsa) {
                                /* tftp (not tftpd!) receiving 1st packet */
                                our_lsa = ((void*)(ptrdiff_t)-1); /* not NULL */
                                len = recvfrom(socket_fd, rbuf, io_bufsize, 0,
                                                &peer_lsa->u.sa, &peer_lsa->len);
                                /* Our first dgram went to port 69
                                 * but reply may come from different one.
                                 * Remember and use this new port (and IP) */
                                if (len >= 0)
                                        xconnect(socket_fd, &peer_lsa->u.sa, peer_lsa->len);
                        } else {
                                /* tftpd, or not the very first packet:
                                 * socket is connect()ed, can just read from it. */
                                /* Don't full_read()!
                                 * This is not TCP, one read == one pkt! */
                                len = safe_read(socket_fd, rbuf, io_bufsize);
                        }
                        if (len < 0) {
                                goto send_read_err_pkt;
                        }
                        if (len < 4) { /* too small? */
                                goto recv_again;
                        }
                }

                /* Process recv'ed packet */
                opcode = ntohs( ((uint16_t*)rbuf)[0] );
                recv_blk = ntohs( ((uint16_t*)rbuf)[1] );
#if ENABLE_TFTP_DEBUG
                fprintf(stderr, "received %d bytes: %04x %04x\n", len, opcode, recv_blk);
#endif
                if (opcode == TFTP_ERROR) {
                        static const char errcode_str[] ALIGN1 =
                                "\0"
                                "file not found\0"
                                "access violation\0"
                                "disk full\0"
                                "bad operation\0"
                                "unknown transfer id\0"
                                "file already exists\0"
                                "no such user\0"
                                "bad option";

                        const char *msg = "";

                        if (len > 4 && rbuf[4] != '\0') {
                                msg = &rbuf[4];
                                rbuf[io_bufsize - 1] = '\0'; /* paranoia */
                        } else if (recv_blk <= 8) {
                                msg = nth_string(errcode_str, recv_blk);
                        }
                        bb_error_msg("server error: (%u) %s", recv_blk, msg);
                        goto ret;
                }

#if ENABLE_FEATURE_TFTP_BLOCKSIZE
                if (expect_OACK) {
                        expect_OACK = 0;
                        if (opcode == TFTP_OACK) {
                                /* server seems to support options */
                                char *res;

                                res = tftp_get_option("blksize", &rbuf[2], len - 2);
                                if (res) {
                                        blksize = tftp_blksize_check(res, blksize);
                                        if (blksize < 0) {
                                                error_pkt_reason = ERR_BAD_OPT;
                                                goto send_err_pkt;
                                        }
                                        io_bufsize = blksize + 4;
                                }
# if ENABLE_FEATURE_TFTP_PROGRESS_BAR
                                if (remote_file && G.size == 0) { /* if we don't know it yet */
                                        res = tftp_get_option("tsize", &rbuf[2], len - 2);
                                        if (res) {
                                                G.size = bb_strtoull(res, NULL, 10);
                                                if (G.size)
                                                        tftp_progress_init();
                                        }
                                }
# endif
                                if (CMD_GET(option_mask32)) {
                                        /* We'll send ACK for OACK,
                                         * such ACK has "block no" of 0 */
                                        block_nr = 0;
                                }
                                continue;
                        }
                        /* rfc2347:
                         * "An option not acknowledged by the server
                         * must be ignored by the client and server
                         * as if it were never requested." */
                        if (blksize != TFTP_BLKSIZE_DEFAULT)
                                bb_error_msg("falling back to blocksize "TFTP_BLKSIZE_DEFAULT_STR);
                        blksize = TFTP_BLKSIZE_DEFAULT;
                        io_bufsize = TFTP_BLKSIZE_DEFAULT + 4;
                }
#endif
                /* block_nr is already advanced to next block# we expect
                 * to get / block# we are about to send next time */

                if (CMD_GET(option_mask32) && (opcode == TFTP_DATA)) {
                        if (recv_blk == block_nr) {
                                int sz = full_write(local_fd, &rbuf[4], len - 4);
                                if (sz != len - 4) {
                                        strcpy((char*)error_pkt_str, bb_msg_write_error);
                                        error_pkt_reason = ERR_WRITE;
                                        goto send_err_pkt;
                                }
                                if (sz != blksize) {
                                        finished = 1;
                                }
                                continue; /* send ACK */
                        }
/* Disabled to cope with servers with Sorcerer's Apprentice Syndrome */
#if 0
                        if (recv_blk == (block_nr - 1)) {
                                /* Server lost our TFTP_ACK.  Resend it */
                                block_nr = recv_blk;
                                continue;
                        }
#endif
                }

                if (CMD_PUT(option_mask32) && (opcode == TFTP_ACK)) {
                        /* did peer ACK our last DATA pkt? */
                        if (recv_blk == (uint16_t) (block_nr - 1)) {
                                if (finished)
                                        goto ret;
                                continue; /* send next block */
                        }
                }
                /* Awww... recv'd packet is not recognized! */
                goto recv_again;
                /* why recv_again? - rfc1123 says:
                 * "The sender (i.e., the side originating the DATA packets)
                 *  must never resend the current DATA packet on receipt
                 *  of a duplicate ACK".
                 * DATA pkts are resent ONLY on timeout.
                 * Thus "goto send_again" will ba a bad mistake above.
                 * See:
                 * http://en.wikipedia.org/wiki/Sorcerer's_Apprentice_Syndrome
                 */
        } /* end of "while (1)" */
 ret:
        if (ENABLE_FEATURE_CLEAN_UP) {
                close(local_fd);
                close(socket_fd);
                free(xbuf);
                free(rbuf);
        }
        return finished == 0; /* returns 1 on failure */

 send_read_err_pkt:
        strcpy((char*)error_pkt_str, bb_msg_read_error);
 send_err_pkt:
        if (error_pkt_str[0])
                bb_error_msg("%s", (char*)error_pkt_str);
        error_pkt[1] = TFTP_ERROR;
        xsendto(socket_fd, error_pkt, 4 + 1 + strlen((char*)error_pkt_str),
                        &peer_lsa->u.sa, peer_lsa->len);
        return EXIT_FAILURE;
#undef remote_file
}

#if ENABLE_TFTP

int tftp_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tftp_main(int argc UNUSED_PARAM, char **argv)
{
        len_and_sockaddr *peer_lsa;
        const char *local_file = NULL;
        const char *remote_file = NULL;
# if ENABLE_FEATURE_TFTP_BLOCKSIZE
        const char *blksize_str = TFTP_BLKSIZE_DEFAULT_STR;
        int blksize;
# endif
        int result;
        int port;
        IF_GETPUT(int opt;)

        INIT_G();

        /* -p or -g is mandatory, and they are mutually exclusive */
        opt_complementary = "" IF_FEATURE_TFTP_GET("g:") IF_FEATURE_TFTP_PUT("p:")
                        IF_GETPUT("g--p:p--g:");

        IF_GETPUT(opt =) getopt32(argv,
                        IF_FEATURE_TFTP_GET("g") IF_FEATURE_TFTP_PUT("p")
                                "l:r:" IF_FEATURE_TFTP_BLOCKSIZE("b:"),
                        &local_file, &remote_file
                        IF_FEATURE_TFTP_BLOCKSIZE(, &blksize_str));
        argv += optind;

# if ENABLE_FEATURE_TFTP_BLOCKSIZE
        /* Check if the blksize is valid:
         * RFC2348 says between 8 and 65464 */
        blksize = tftp_blksize_check(blksize_str, 65564);
        if (blksize < 0) {
                //bb_error_msg("bad block size");
                return EXIT_FAILURE;
        }
# endif

        if (remote_file) {
                if (!local_file) {
                        const char *slash = strrchr(remote_file, '/');
                        local_file = slash ? slash + 1 : remote_file;
                }
        } else {
                remote_file = local_file;
        }

        /* Error if filename or host is not known */
        if (!remote_file || !argv[0])
                bb_show_usage();

        port = bb_lookup_port(argv[1], "udp", 69);
        peer_lsa = xhost2sockaddr(argv[0], port);

# if ENABLE_TFTP_DEBUG
        fprintf(stderr, "using server '%s', remote_file '%s', local_file '%s'\n",
                        xmalloc_sockaddr2dotted(&peer_lsa->u.sa),
                        remote_file, local_file);
# endif

# if ENABLE_FEATURE_TFTP_PROGRESS_BAR
        G.file = remote_file;
# endif
        result = tftp_protocol(
                NULL /*our_lsa*/, peer_lsa,
                local_file, remote_file
                IF_FEATURE_TFTP_BLOCKSIZE(, 1 /* want_transfer_size */)
                IF_FEATURE_TFTP_BLOCKSIZE(, blksize)
        );
        tftp_progress_done();

        if (result != EXIT_SUCCESS && NOT_LONE_DASH(local_file) && CMD_GET(opt)) {
                unlink(local_file);
        }
        return result;
}

#endif /* ENABLE_TFTP */

#if ENABLE_TFTPD
int tftpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tftpd_main(int argc UNUSED_PARAM, char **argv)
{
        len_and_sockaddr *our_lsa;
        len_and_sockaddr *peer_lsa;
        char *local_file, *mode;
        const char *error_msg;
        int opt, result, opcode;
        IF_FEATURE_TFTP_BLOCKSIZE(int blksize = TFTP_BLKSIZE_DEFAULT;)
        IF_FEATURE_TFTP_BLOCKSIZE(int want_transfer_size = 0;)

        INIT_G();

        our_lsa = get_sock_lsa(STDIN_FILENO);
        if (!our_lsa) {
                /* This is confusing:
                 *bb_error_msg_and_die("stdin is not a socket");
                 * Better: */
                bb_show_usage();
                /* Help text says that tftpd must be used as inetd service,
                 * which is by far the most usual cause of get_sock_lsa
                 * failure */
        }
        peer_lsa = xzalloc(LSA_LEN_SIZE + our_lsa->len);
        peer_lsa->len = our_lsa->len;

        /* Shifting to not collide with TFTP_OPTs */
        opt = option_mask32 = TFTPD_OPT | (getopt32(argv, "rcu:", &user_opt) << 8);
        argv += optind;
        if (argv[0])
                xchdir(argv[0]);

        result = recv_from_to(STDIN_FILENO, block_buf, sizeof(block_buf),
                        0 /* flags */,
                        &peer_lsa->u.sa, &our_lsa->u.sa, our_lsa->len);

        error_msg = "malformed packet";
        opcode = ntohs(*(uint16_t*)block_buf);
        if (result < 4 || result >= sizeof(block_buf)
         || block_buf[result-1] != '\0'
         || (IF_FEATURE_TFTP_PUT(opcode != TFTP_RRQ) /* not download */
             IF_GETPUT(&&)
             IF_FEATURE_TFTP_GET(opcode != TFTP_WRQ) /* not upload */
            )
        ) {
                goto err;
        }
        local_file = block_buf + 2;
        if (local_file[0] == '.' || strstr(local_file, "/.")) {
                error_msg = "dot in file name";
                goto err;
        }
        mode = local_file + strlen(local_file) + 1;
        if (mode >= block_buf + result || strcmp(mode, "octet") != 0) {
                goto err;
        }
# if ENABLE_FEATURE_TFTP_BLOCKSIZE
        {
                char *res;
                char *opt_str = mode + sizeof("octet");
                int opt_len = block_buf + result - opt_str;
                if (opt_len > 0) {
                        res = tftp_get_option("blksize", opt_str, opt_len);
                        if (res) {
                                blksize = tftp_blksize_check(res, 65564);
                                if (blksize < 0) {
                                        error_pkt_reason = ERR_BAD_OPT;
                                        /* will just send error pkt */
                                        goto do_proto;
                                }
                        }
                        if (opcode != TFTP_WRQ /* download? */
                        /* did client ask us about file size? */
                         && tftp_get_option("tsize", opt_str, opt_len)
                        ) {
                                want_transfer_size = 1;
                        }
                }
        }
# endif

        if (!ENABLE_FEATURE_TFTP_PUT || opcode == TFTP_WRQ) {
                if (opt & TFTPD_OPT_r) {
                        /* This would mean "disk full" - not true */
                        /*error_pkt_reason = ERR_WRITE;*/
                        error_msg = bb_msg_write_error;
                        goto err;
                }
                IF_GETPUT(option_mask32 |= TFTP_OPT_GET;) /* will receive file's data */
        } else {
                IF_GETPUT(option_mask32 |= TFTP_OPT_PUT;) /* will send file's data */
        }

        /* NB: if error_pkt_str or error_pkt_reason is set up,
         * tftp_protocol() just sends one error pkt and returns */

 do_proto:
        close(STDIN_FILENO); /* close old, possibly wildcard socket */
        /* tftp_protocol() will create new one, bound to particular local IP */
        result = tftp_protocol(
                our_lsa, peer_lsa,
                local_file IF_TFTP(, NULL /*remote_file*/)
                IF_FEATURE_TFTP_BLOCKSIZE(, want_transfer_size)
                IF_FEATURE_TFTP_BLOCKSIZE(, blksize)
        );

        return result;
 err:
        strcpy((char*)error_pkt_str, error_msg);
        goto do_proto;
}

#endif /* ENABLE_TFTPD */

#endif /* ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT */