/* packet-gsm_um.c
 * Routines for GSM Um packet disassembly
 * Duncan Salerno <duncan.salerno@googlemail.com>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */


#include "config.h"

#include <epan/packet.h>
#include <epan/prefs.h>
#include <wiretap/wtap.h>

void proto_register_gsm_um(void);
void proto_reg_handoff_gsm_um(void);

static int proto_gsm_um;
static int hf_gsm_um_direction;
static int hf_gsm_um_channel;
static int hf_gsm_um_bsic;
static int hf_gsm_um_arfcn;
static int hf_gsm_um_band;
static int hf_gsm_um_frequency;
static int hf_gsm_um_frame;
static int hf_gsm_um_error;
static int hf_gsm_um_timeshift;
static int hf_gsm_um_l2_pseudo_len;

static int ett_gsm_um;

static dissector_handle_t gsm_um_handle;

static dissector_handle_t lapdm_handle;
static dissector_handle_t dtap_handle;

static bool dcs1800_gsm = true;

#define	GSM_UM_L2_PSEUDO_LEN		0xfc


static void
decode_arfcn(uint16_t arfcn, const char **band, unsigned *uplink, unsigned *downlink)
{
	/* Decode ARFCN to frequency using GSM 05.05 */
	if( arfcn >= 1 && arfcn <= 124 ) {
		*band = "P-GSM 900";
		*uplink = 890000 + 200 * arfcn;
		*downlink = *uplink + 45000;
	}
	else if( arfcn == 0 ) {
		*band = "E-GSM 900";
		*uplink = 890000 + 200 * arfcn;
		*downlink = *uplink + 45000;
	}
	else if( arfcn >= 975 && arfcn <= 1023 ) {
		*band = "E-GSM 900";
		*uplink = 890000 + 200 * (arfcn - 1024);
		*downlink = *uplink + 45000;
	}
	else if( arfcn >= 955 && arfcn <= 974 ) {
		*band = "R-GSM 900";
		*uplink = 890000 + 200 * (arfcn - 1024);
		*downlink = *uplink + 45000;
	}
	else if( arfcn >= 512 && arfcn <= 885 && dcs1800_gsm) {
		*band = "DCS 1800";
		*uplink = 1710200 + 200 * (arfcn - 512);
		*downlink = *uplink + 95000;
	}
	else if( arfcn >= 512 && arfcn <= 810 && !dcs1800_gsm) {
		*band = "PCS 1900";
		*uplink = 1850200 + 200 * (arfcn - 512);
		*downlink = *uplink + 80000;
	}
	else if( arfcn >= 259 && arfcn <= 293 ) {
		*band = "GSM 450";
		*uplink = 450600 + 200 * (arfcn - 259);
		*downlink = *uplink + 10000;
	}
	else if( arfcn >= 306 && arfcn <= 340 ) {
		*band = "GSM 480";
		*uplink = 479000 + 200 * (arfcn - 306);
		*downlink = *uplink + 10000;
	}
	else if( arfcn >= 128 && arfcn <= 251 ) {
		*band = "GSM 850";
		*uplink = 824200 + 200 * (arfcn - 128);
		*downlink = *uplink + 45000;
	}
	else {
		*band = "Unknown";
		*uplink = *downlink = 0;
	}
}


static int
dissect_gsm_um(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
	proto_tree *gsm_um_tree = NULL;
	proto_item *ti;

	col_set_str(pinfo->cinfo, COL_PROTOCOL, "GSM Um");

	if (pinfo->pseudo_header->gsm_um.uplink) {
		col_set_str(pinfo->cinfo, COL_RES_DL_DST, "BTS");
		col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "MS");
	}
	else {
		switch (pinfo->pseudo_header->gsm_um.channel) {
			case GSM_UM_CHANNEL_BCCH:
			case GSM_UM_CHANNEL_CCCH:
			case GSM_UM_CHANNEL_PCH:
			case GSM_UM_CHANNEL_AGCH:
				col_set_str(pinfo->cinfo, COL_RES_DL_DST, "Broadcast");
				break;
			default:
				col_set_str(pinfo->cinfo, COL_RES_DL_DST, "MS");
				break;
		}
		col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "BTS");
	}

	if (tree) {
		const char *channel;

		ti = proto_tree_add_item(tree, proto_gsm_um, tvb, 0, 0, ENC_NA);
		gsm_um_tree = proto_item_add_subtree(ti, ett_gsm_um);

		switch( pinfo->pseudo_header->gsm_um.channel ) {
			case GSM_UM_CHANNEL_BCCH: channel = "BCCH"; break;
			case GSM_UM_CHANNEL_CCCH: channel = "CCCH"; break;
			case GSM_UM_CHANNEL_PCH: channel = "PCH"; break;
			case GSM_UM_CHANNEL_AGCH: channel = "AGCH"; break;
			case GSM_UM_CHANNEL_SACCH: channel = "SACCH"; break;
			case GSM_UM_CHANNEL_FACCH: channel = "FACCH"; break;
			case GSM_UM_CHANNEL_SDCCH: channel = "SDCCH"; break;
			default: channel = "Unknown"; break;
		}

		if( pinfo->pseudo_header->gsm_um.uplink ) {
			proto_tree_add_string(gsm_um_tree, hf_gsm_um_direction, tvb, 0, 0, "Uplink");
		}
		else {
			proto_tree_add_string(gsm_um_tree, hf_gsm_um_direction, tvb, 0, 0, "Downlink");
		}

		proto_tree_add_string(gsm_um_tree, hf_gsm_um_channel, tvb, 0, 0, channel);

		/* Show the other fields, if we have them (ie. downlink, BTS->MS) */
		if( !pinfo->pseudo_header->gsm_um.uplink ) {
			const char *band;
			unsigned downlink, uplink;

			decode_arfcn(pinfo->pseudo_header->gsm_um.arfcn, &band, &uplink, &downlink);

			proto_tree_add_uint(gsm_um_tree, hf_gsm_um_arfcn, tvb, 0, 0,
				pinfo->pseudo_header->gsm_um.arfcn);
			proto_tree_add_string(gsm_um_tree, hf_gsm_um_band, tvb, 0, 0,
				band);
			proto_tree_add_uint_format_value(gsm_um_tree, hf_gsm_um_frequency, tvb, 0, 0,
				downlink, "%u.%03uMHz", downlink / 1000, downlink % 1000);
			proto_tree_add_uint(gsm_um_tree, hf_gsm_um_bsic, tvb, 0, 0,
				pinfo->pseudo_header->gsm_um.bsic);
			proto_tree_add_uint(gsm_um_tree, hf_gsm_um_frame, tvb, 0, 0,
				pinfo->pseudo_header->gsm_um.tdma_frame);
			proto_tree_add_uint(gsm_um_tree, hf_gsm_um_error, tvb, 0, 0,
				pinfo->pseudo_header->gsm_um.error);
			proto_tree_add_uint(gsm_um_tree, hf_gsm_um_timeshift, tvb, 0, 0,
				pinfo->pseudo_header->gsm_um.timeshift);
		}
	}

	/* TODO: If CCCH downlink could work out of PCH or AGCH by peeking at next bytes, uplink is RACH */

	switch( pinfo->pseudo_header->gsm_um.channel ) {
		case GSM_UM_CHANNEL_BCCH:
		case GSM_UM_CHANNEL_CCCH:
		case GSM_UM_CHANNEL_PCH:
		case GSM_UM_CHANNEL_AGCH:
			if( !pinfo->pseudo_header->gsm_um.uplink ) {
				tvbuff_t *next_tvb;
				uint8_t pseudo_len, len_left, len_byte;

				len_left = tvb_reported_length(tvb);
				len_byte = tvb_get_uint8(tvb, 0);
				pseudo_len = len_byte >> 2;
				next_tvb = tvb_new_subset_length_caplen(tvb, 1, MIN(len_left, pseudo_len), -1);

				if (tree) {
					proto_tree_add_uint(gsm_um_tree, hf_gsm_um_l2_pseudo_len, tvb, 0, 1,
						len_byte);
				}

				/* Only dissect non-empty frames */
				if( tvb_reported_length(next_tvb) ) {
					call_dissector(dtap_handle, next_tvb, pinfo, tree);
				}
			}
			else {
				/* Either RACH, or something invalid */
				call_data_dissector(tvb, pinfo, tree);
			}
			break;
		case GSM_UM_CHANNEL_SACCH:
		case GSM_UM_CHANNEL_FACCH:
		case GSM_UM_CHANNEL_SDCCH:
			call_dissector(lapdm_handle, tvb, pinfo, tree);
			break;
		default:
			call_data_dissector(tvb, pinfo, tree);
			break;
	}
	return tvb_captured_length(tvb);
}

void
proto_register_gsm_um(void)
{
	static hf_register_info hf[] = {
		{ &hf_gsm_um_direction,
		{ "Direction",	"gsm_um.direction", FT_STRINGZ, BASE_NONE,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_channel,
		{ "Channel",	"gsm_um.channel", FT_STRINGZ, BASE_NONE,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_bsic,
		{ "BSIC",	"gsm_um.bsic", FT_UINT8, BASE_DEC,
		  NULL, 0x0, "Base station identity code", HFILL }},

		{ &hf_gsm_um_arfcn,
		{ "ARFCN",	"gsm_um.arfcn", FT_UINT16, BASE_DEC,
		  NULL, 0x0, "Absolute radio frequency channel number", HFILL }},

		{ &hf_gsm_um_band,
		{ "Band",	"gsm_um.band", FT_STRING, BASE_NONE,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_frequency,
		{ "Frequency",	"gsm_um.frequency", FT_UINT32, BASE_DEC,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_frame,
		{ "TDMA Frame",	"gsm_um.frame", FT_UINT32, BASE_DEC,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_error,
		{ "Error",	"gsm_um.error", FT_UINT8, BASE_DEC,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_timeshift,
		{ "Timeshift",	"gsm_um.timeshift", FT_UINT16, BASE_DEC,
		  NULL, 0x0, NULL, HFILL }},

		{ &hf_gsm_um_l2_pseudo_len,
		{ "L2 Pseudo Length",	"gsm_um.l2_pseudo_len", FT_UINT8, BASE_DEC,
		  NULL, GSM_UM_L2_PSEUDO_LEN, NULL, HFILL }}

	};
	static int *ett[] = {
		&ett_gsm_um
	};
	module_t *gsm_um_module;

	proto_gsm_um = proto_register_protocol("GSM Um Interface", "GSM Um", "gsm_um");
	proto_register_field_array(proto_gsm_um, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));

	gsm_um_module = prefs_register_protocol(proto_gsm_um, NULL);
	prefs_register_bool_preference(gsm_um_module, "dcs1800",
				   "Treat ARFCN 512-810 as DCS 1800 rather than PCS 1900",
				   "Treat ARFCN 512-810 as DCS 1800 rather than PCS 1900",
				   &dcs1800_gsm);

	gsm_um_handle = register_dissector("gsm_um", dissect_gsm_um, proto_gsm_um);
}

void
proto_reg_handoff_gsm_um(void)
{
	lapdm_handle = find_dissector_add_dependency("lapdm", proto_gsm_um);
	dtap_handle = find_dissector_add_dependency("gsm_a_dtap", proto_gsm_um);

	dissector_add_uint("wtap_encap", WTAP_ENCAP_GSM_UM, gsm_um_handle);
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 8
 * tab-width: 8
 * indent-tabs-mode: t
 * End:
 *
 * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 * :indentSize=8:tabSize=8:noTabs=false:
 */
