/* $Id$ */

/*
 *   Copyright (c) 2001-2010 Aaron Turner <aturner at synfin dot net>
 *   Copyright (c) 2013-2025 Fred Klassen <tcpreplay at appneta dot com> - AppNeta
 *
 *   The Tcpreplay Suite of tools is free software: you can redistribute it
 *   and/or modify it under the terms of the GNU General Public License as
 *   published by the Free Software Foundation, either version 3 of the
 *   License, or with the authors permission any later version.
 *
 *   The Tcpreplay Suite is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with the Tcpreplay Suite.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "null.h"
#include "dlt_utils.h"
#include "tcpedit.h"
#include "tcpedit_stub.h"
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h> // PF_* values

static char dlt_name[] = "null";
static char _U_ dlt_prefix[] = "null";
static uint16_t dlt_value = DLT_NULL;

/*
 * From the libpcap man page:
 * DLT_NULL aka BSD loopback encapsulation; the link layer header is a 4-byte
 * field,  in  host  byte  order,  containing  a  PF_ value from
 * socket.h for the network-layer protocol of the packet.
 *
 * Note that ``host byte  order''  is  the  byte  order  of  the
 * machine on which the packets are captured, and the PF_ values
 * are for the OS of the machine on which the packets  are  captured;
 * if  a live capture is being done, ``host byte order''
 * is the byte order of the machine capturing the  packets,  and
 * the  PF_  values are those of the OS of the machine capturing
 * the packets, but if a ``savefile'' is being  read,  the  byte
 * order and PF_ values are not necessarily those of the machine
 * reading the capture file.
 */

/*
 * Function to register ourselves.  This function is always called, regardless
 * of what DLT types are being used, so it shouldn't be allocating extra buffers
 * or anything like that (use the dlt_null_init() function below for that).
 * Tasks:
 * - Create a new plugin struct
 * - Fill out the provides/requires bit masks.  Note:  Only specify which fields are
 *   actually in the header.
 * - Add the plugin to the context's plugin chain
 * Returns: TCPEDIT_ERROR | TCPEDIT_OK | TCPEDIT_WARN
 */
int
dlt_null_register(tcpeditdlt_t *ctx)
{
    tcpeditdlt_plugin_t *plugin;
    assert(ctx);

    /* create  a new plugin structure */
    plugin = tcpedit_dlt_newplugin();

    /* set what we provide & require */
    plugin->provides += PLUGIN_MASK_PROTO;
    plugin->
        requires
    += 0;

    /* what is our DLT value? */
    plugin->dlt = dlt_value;

    /* set the prefix name of our plugin.  This is also used as the prefix for our options */
    plugin->name = safe_strdup(dlt_prefix);

    /*
     * Point to our functions, note, you need a function for EVERY method.
     * Even if it is only an empty stub returning success.
     */
    plugin->plugin_init = dlt_null_init;
    plugin->plugin_cleanup = dlt_null_cleanup;
    plugin->plugin_parse_opts = dlt_null_parse_opts;
    plugin->plugin_decode = dlt_null_decode;
    plugin->plugin_encode = dlt_null_encode;
    plugin->plugin_proto = dlt_null_proto;
    plugin->plugin_l2addr_type = dlt_null_l2addr_type;
    plugin->plugin_l2len = dlt_null_l2len;
    plugin->plugin_get_layer3 = dlt_null_get_layer3;
    plugin->plugin_merge_layer3 = dlt_null_merge_layer3;

    /* add it to the available plugin list */
    return tcpedit_dlt_addplugin(ctx, plugin);
}

/*
 * Initializer function.  This function is called only once, if and only if
 * this plugin will be utilized.  Remember, if you need to keep track of any state,
 * store it in your plugin->config, not a global!
 * Returns: TCPEDIT_ERROR | TCPEDIT_OK | TCPEDIT_WARN
 */
int
dlt_null_init(tcpeditdlt_t *ctx)
{
    tcpeditdlt_plugin_t *plugin;
    assert(ctx);

    if ((plugin = tcpedit_dlt_getplugin(ctx, dlt_value)) == NULL) {
        tcpedit_seterr(ctx->tcpedit, "Unable to initialize unregistered plugin %s", dlt_name);
        return TCPEDIT_ERROR;
    }

    return TCPEDIT_OK; /* success */
}

/*
 * Since this is used in a library, we should manually clean up after ourselves
 * Unless you allocated some memory in dlt_null_init(), this is just an stub.
 * Returns: TCPEDIT_ERROR | TCPEDIT_OK | TCPEDIT_WARN
 */
int
dlt_null_cleanup(tcpeditdlt_t *ctx)
{
    tcpeditdlt_plugin_t *plugin;
    assert(ctx);

    if ((plugin = tcpedit_dlt_getplugin(ctx, dlt_value)) == NULL) {
        tcpedit_seterr(ctx->tcpedit, "Unable to cleanup unregistered plugin %s", dlt_name);
        return TCPEDIT_ERROR;
    }

    safe_free(plugin->name);
    plugin->name = NULL;
    safe_free(plugin->config);
    plugin->config = NULL;
    plugin->config_size = 0;

    return TCPEDIT_OK; /* success */
}

/*
 * This is where you should define all your AutoGen AutoOpts option parsing.
 * Any user specified option should have it's bit turned on in the 'provides'
 * bit mask.
 * Returns: TCPEDIT_ERROR | TCPEDIT_OK | TCPEDIT_WARN
 */
int
dlt_null_parse_opts(tcpeditdlt_t *ctx)
{
    assert(ctx);

    /* nothing to parse here, move along */
    return TCPEDIT_OK; /* success */
}

/*
 * Function to decode the layer 2 header in the packet.
 * You need to fill out:
 * - ctx->l2len
 * - ctx->srcaddr
 * - ctx->dstaddr
 * - ctx->proto
 * - ctx->decoded_extra
 * Returns: TCPEDIT_ERROR | TCPEDIT_OK | TCPEDIT_WARN
 */
int
dlt_null_decode(tcpeditdlt_t *ctx, const u_char *packet, int pktlen)
{
    int proto;
    assert(ctx);
    assert(packet);

    if ((proto = dlt_null_proto(ctx, packet, pktlen)) == TCPEDIT_ERROR)
        return TCPEDIT_ERROR;

    ctx->proto = (uint16_t)proto;
    ctx->l2len = 4;

    return TCPEDIT_OK; /* success */
}

/*
 * Function to encode the layer 2 header back into the packet.
 * Returns: total packet len or TCPEDIT_ERROR
 */
int
dlt_null_encode(tcpeditdlt_t *ctx, u_char *packet, _U_ int pktlen, _U_ tcpr_dir_t dir)
{
    assert(ctx);
    assert(packet);

    tcpedit_seterr(ctx->tcpedit, "%s", "DLT_NULL and DLT_LOOP plugins do not support packet encoding");
    return TCPEDIT_ERROR;
}

/*
 * Function returns the Layer 3 protocol type of the given packet, or TCPEDIT_ERROR on error
 */
int
dlt_null_proto(tcpeditdlt_t *ctx, const u_char *packet, int pktlen)
{
    assert(ctx);
    assert(packet);
    uint32_t *af_type;
    int protocol = 0;

    if (pktlen < 4)
        return TCPEDIT_ERROR;

    /* PF_INET is always 2 but PF_INET6 varies based on platform, i.e
     * Linux - 10
     * NetBSD,OpenBSD,BSD/OS - 24
     * NetBSD,OpenBSD,BSD/OS - 28
     * Darwin/macOS - 30
     * See https://gitlab.com/wireshark/wireshark/-/wikis/NullLoopback
     */
    af_type = (uint32_t *)packet;
    if (*af_type == PF_INET || SWAPLONG(*af_type) == PF_INET) {
        protocol = ETHERTYPE_IP;
    } else if (*af_type == PF_INET6 || SWAPLONG(*af_type) == PF_INET6 || *af_type == 10 || SWAPLONG(*af_type) == 10 ||
               *af_type == 24 || SWAPLONG(*af_type) == 24 || *af_type == 28 || SWAPLONG(*af_type) == 28 ||
               *af_type == 30 || SWAPLONG(*af_type) == 30) {
        protocol = ETHERTYPE_IP6;
    } else {
        tcpedit_seterr(ctx->tcpedit, "Unsupported DLT_NULL/DLT_LOOP PF_ type: 0x%04x", *af_type);
        return TCPEDIT_ERROR;
    }

    return htons(protocol);
}

/*
 * Function returns a pointer to the layer 3 protocol header or NULL on error
 */
u_char *
dlt_null_get_layer3(tcpeditdlt_t *ctx, u_char *packet, int pktlen)
{
    int l2len;
    assert(ctx);
    assert(packet);

    l2len = dlt_null_l2len(ctx, packet, pktlen);

    if (pktlen < l2len)
        return NULL;

    return tcpedit_dlt_l3data_copy(ctx, packet, pktlen, l2len);
}

/*
 * function merges the packet (containing L2 and old L3) with the l3data buffer
 * containing the new l3 data.  Note, if L2 % 4 == 0, then they're pointing to the
 * same buffer, otherwise there was a memcpy involved on strictly aligned architectures
 * like SPARC
 */
u_char *
dlt_null_merge_layer3(tcpeditdlt_t *ctx, u_char *packet, int pktlen, u_char *ipv4_data, u_char *ipv6_data)
{
    int l2len;
    assert(ctx);
    assert(packet);
    assert(ipv4_data || ipv6_data);

    l2len = dlt_null_l2len(ctx, packet, pktlen);
    if (pktlen < l2len)
        return NULL;

    return tcpedit_dlt_l3data_merge(ctx, packet, pktlen, ipv4_data ?: ipv6_data, l2len);
}

/*
 * return the length of the L2 header of the current packet
 */
int
dlt_null_l2len(tcpeditdlt_t *ctx, const u_char *packet, int pktlen)
{
    assert(ctx);
    assert(packet);

    if (pktlen < 4)
        return 0;

    /* always is 4 */
    return 4;
}

/*
 * return a static pointer to the source/destination MAC address
 * return NULL on error/address doesn't exist
 */
u_char *
dlt_null_get_mac(tcpeditdlt_t *ctx, _U_ tcpeditdlt_mac_type_t mac, const u_char *packet, _U_ int pktlen)
{
    assert(ctx);
    assert(packet);

    return (NULL);
}

tcpeditdlt_l2addr_type_t
dlt_null_l2addr_type(void)
{
    return NONE;
}
