/*
 * tftp.c - a simple, read-only tftp server for qemu
 *
 * Copyright (c) 2004 Magnus Damm <damm@opensource.se>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <slirp.h>


static void tftp_session_update(PNATState pData, struct tftp_session *spt)
{
    spt->timestamp = curtime;
    spt->in_use = 1;
}

static void tftp_session_terminate(struct tftp_session *spt)
{
    spt->in_use = 0;
}

static int tftp_session_allocate(PNATState pData, struct tftp_t *tp)
{
    struct tftp_session *spt;
    int k;

    for (k = 0; k < TFTP_SESSIONS_MAX; k++)
    {
        spt = &tftp_sessions[k];

        if (!spt->in_use)
            goto found;

        /* sessions time out after 5 inactive seconds */
        if ((int)(curtime - spt->timestamp) > 5000)
            goto found;
    }

    return -1;

 found:
    memset(spt, 0, sizeof(*spt));
    memcpy(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip));
    spt->client_port = tp->udp.uh_sport;

    tftp_session_update(pData, spt);

    return k;
}

static int tftp_session_find(PNATState pData, struct tftp_t *tp)
{
    struct tftp_session *spt;
    int k;

    for (k = 0; k < TFTP_SESSIONS_MAX; k++)
    {
        spt = &tftp_sessions[k];

        if (spt->in_use)
        {
            if (!memcmp(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip)))
            {
                if (spt->client_port == tp->udp.uh_sport)
                    return k;
            }
        }
    }

    return -1;
}

static int tftp_read_data(PNATState pData, struct tftp_session *spt, u_int16_t block_nr,
                          u_int8_t *buf, int len)
{
    int fd;
    int bytes_read = 0;
    char buffer[1024];
    int n;

    n = RTStrPrintf(buffer, sizeof(buffer), "%s/%s",
                    tftp_prefix, spt->filename);
    if (n >= sizeof(buffer))
        return -1;

    fd = open(buffer, O_RDONLY | O_BINARY);
    if (fd < 0)
        return -1;

    if (len)
    {
        lseek(fd, block_nr * 512, SEEK_SET);
        bytes_read = read(fd, buf, len);
    }

    close(fd);

    return bytes_read;
}

static int tftp_send_oack(PNATState pData,
                          struct tftp_session *spt,
                          const char *key, uint32_t value,
                          struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int n = 0;

    m = m_get(pData);
    if (!m)
        return -1;

    memset(m->m_data, 0, m->m_size);

    m->m_data += if_maxlinkhdr;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_OACK);
    n += RTStrPrintf((char *)tp->x.tp_buf + n, M_FREEROOM(m), "%s", key) + 1;
    n += RTStrPrintf((char *)tp->x.tp_buf + n, M_FREEROOM(m), "%u", value) + 1;

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    m->m_len = sizeof(struct tftp_t) - 514 + n -
        sizeof(struct ip) - sizeof(struct udphdr);
    udp_output2(pData, NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    return 0;
}



static int tftp_send_error(PNATState pData,
                           struct tftp_session *spt,
                           u_int16_t errorcode, const char *msg,
                           struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int nobytes;

    m = m_get(pData);
    if (!m)
        return -1;

    memset(m->m_data, 0, m->m_size);

    m->m_data += if_maxlinkhdr;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_ERROR);
    tp->x.tp_error.tp_error_code = htons(errorcode);
    strcpy((char *)tp->x.tp_error.tp_msg, msg);

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    nobytes = 2;

    m->m_len = sizeof(struct tftp_t) 
             - 514
             + 3 
             + strlen(msg)
             - sizeof(struct ip) 
             - sizeof(struct udphdr);

    udp_output2(pData, NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    tftp_session_terminate(spt);

    return 0;
}

static int tftp_send_data(PNATState pData,
                          struct tftp_session *spt,
                          u_int16_t block_nr,
                          struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int nobytes;

    if (block_nr < 1)
        return -1;

    m = m_get(pData);
    if (!m)
        return -1;

    memset(m->m_data, 0, m->m_size);

    m->m_data += if_maxlinkhdr;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_DATA);
    tp->x.tp_data.tp_block_nr = htons(block_nr);

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    nobytes = tftp_read_data(pData, spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
    if (nobytes < 0)
    {
        m_free(pData, m);
        /* send "file not found" error back */
        tftp_send_error(pData, spt, 1, "File not found", tp);
        return -1;
    }

    m->m_len = sizeof(struct tftp_t) 
             - (512 - nobytes) 
             - sizeof(struct ip) 
             - sizeof(struct udphdr);

    udp_output2(pData, NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    if (nobytes == 512)
        tftp_session_update(pData, spt);
    else
        tftp_session_terminate(spt);

    return 0;
}

static void tftp_handle_rrq(PNATState pData, struct tftp_t *tp, int pktlen)
{
    struct tftp_session *spt;
    int s, k, n;
    u_int8_t *src, *dst;

    s = tftp_session_allocate(pData, tp);
    if (s < 0)
        return;

    spt = &tftp_sessions[s];

    src = tp->x.tp_buf;
    dst = spt->filename;
    n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);

    /* get name */
    for (k = 0; k < n; k++)
    {
        if (k < TFTP_FILENAME_MAX)
            dst[k] = src[k];
        else
            return;

        if (src[k] == '\0')
            break;
    }

    if (k >= n)
        return;

    k++;

    /* check mode */
    if ((n - k) < 6)
        return;

    if (memcmp(&src[k], "octet\0", 6) != 0)
    {
        tftp_send_error(pData, spt, 4, "Unsupported transfer mode", tp);
        return;
    }

    k += 6; /* skipping octet */

    /* do sanity checks on the filename */
    if (   !strncmp((const char*)spt->filename, "../", 3)
        || (spt->filename[strlen((const char *)spt->filename) - 1] == '/')
        ||  strstr((const char *)spt->filename, "/../"))
    {
        tftp_send_error(pData, spt, 2, "Access violation", tp);
        return;
    }

    /* only allow exported prefixes */
    if (!tftp_prefix)
    {
        tftp_send_error(pData, spt, 2, "Access violation", tp);
        return;
    }

    /* check if the file exists */
    if (tftp_read_data(pData, spt, 0, spt->filename, 0) < 0)
    {
        tftp_send_error(pData, spt, 1, "File not found", tp);
        return;
    }

    if (src[n - 1] != 0)
    {
        tftp_send_error(pData, spt, 2, "Access violation", tp);
        return;
    }

    while (k < n)
    {
        const char *key, *value;

        key = (const char *)src + k;
        k += strlen(key) + 1;

        if (k >= n)
        {
            tftp_send_error(pData, spt, 2, "Access violation", tp);
            return;
        }

        value = (const char *)src + k;
        k += strlen(value) + 1;

        if (strcmp(key, "tsize") == 0)
        {
            int tsize = atoi(value);
            struct stat stat_p;

            if (tsize == 0 && tftp_prefix)
            {
                char buffer[1024];
                int len;

                len = RTStrPrintf(buffer, sizeof(buffer), "%s/%s",
                                  tftp_prefix, spt->filename);
                if (stat(buffer, &stat_p) == 0)
                    tsize = stat_p.st_size;
                else
                {
                    tftp_send_error(pData, spt, 1, "File not found", tp);
                    return;
                }
            }

            tftp_send_oack(pData, spt, "tsize", tsize, tp);
            return;
        }
    }

    tftp_send_data(pData, spt, 1, tp);
}

static void tftp_handle_ack(PNATState pData, struct tftp_t *tp, int pktlen)
{
    int s;

    s = tftp_session_find(pData, tp);
    if (s < 0)
        return;

    if (tftp_send_data(pData, &tftp_sessions[s],
                       ntohs(tp->x.tp_data.tp_block_nr) + 1, tp) < 0)
    {
        /* XXX */
    }
}

void tftp_input(PNATState pData, struct mbuf *m)
{
    struct tftp_t *tp = (struct tftp_t *)m->m_data;

    switch(ntohs(tp->tp_op))
    {
        case TFTP_RRQ:
            tftp_handle_rrq(pData, tp, m->m_len);
            break;

        case TFTP_ACK:
            tftp_handle_ack(pData, tp, m->m_len);
            break;
    }
}