/* packet-ehdlc.c
 * Routines for packet dissection of Ericsson HDLC as used in A-bis over IP
 * Copyright 2010-2012 by Harald Welte <laforge@gnumonks.org>
 *
 * $Id$
 *
 * This code is based on pure educational guesses while looking at protocol
 * traces, as there is no publicly available protocol description by Ericsson.
 * Even the name is a guess, since it looks quite a bit like HDLC and is used
 * by Ericsson, I called it EHDLC.
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * This program 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 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "config.h"

#include <glib.h>

#include <epan/packet.h>
#include <epan/ipproto.h>
#include <epan/xdlc.h>

void proto_register_ehdlc(void);
void proto_reg_handoff_ehdlc(void);

/* Initialize the protocol and registered fields */
static int proto_ehdlc = -1;

static int hf_ehdlc_data_len = -1;
static int hf_ehdlc_protocol = -1;
/* static int hf_ehdlc_sapi = -1; */
/* static int hf_ehdlc_c_r = -1; */

static int hf_ehdlc_xid_payload = -1;
static int hf_ehdlc_control = -1;

static int hf_ehdlc_p = -1;
static int hf_ehdlc_f = -1;
static int hf_ehdlc_u_modifier_cmd = -1;
static int hf_ehdlc_u_modifier_resp = -1;
static int hf_ehdlc_ftype_s_u = -1;

static int hf_ehdlc_n_r = -1;
static int hf_ehdlc_n_s = -1;
static int hf_ehdlc_p_ext = -1;
static int hf_ehdlc_f_ext = -1;
static int hf_ehdlc_s_ftype = -1;
static int hf_ehdlc_ftype_i = -1;
static int hf_ehdlc_ftype_s_u_ext = -1;

/* Used only for U frames */
static const xdlc_cf_items ehdlc_cf_items = {
	NULL,
	NULL,
	&hf_ehdlc_p,
	&hf_ehdlc_f,
	NULL,
	&hf_ehdlc_u_modifier_cmd,
	&hf_ehdlc_u_modifier_resp,
	NULL,
	&hf_ehdlc_ftype_s_u
};

/* Used only for I and S frames */
static const xdlc_cf_items ehdlc_cf_items_ext = {
	&hf_ehdlc_n_r,
	&hf_ehdlc_n_s,
	&hf_ehdlc_p_ext,
	&hf_ehdlc_f_ext,
	&hf_ehdlc_s_ftype,
	NULL,
	NULL,
	&hf_ehdlc_ftype_i,
	&hf_ehdlc_ftype_s_u_ext,
};

/* Initialize the subtree pointers */
static gint ett_ehdlc = -1;
static gint ett_ehdlc_control = -1;

static const value_string ehdlc_protocol_vals[] = {
	{ 0x20,		"RSL" },
	{ 0xa0,		"ACK" },
	{ 0xc0,		"OML" },
	{ 0, 		NULL }
};

enum {
	SUB_RSL,
	SUB_OML,
	SUB_DATA,

	SUB_MAX
};

static dissector_handle_t sub_handles[SUB_MAX];

/* Code to actually dissect the packets */
static void
dissect_ehdlc(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
	int  offset = 4;

	col_set_str(pinfo->cinfo, COL_PROTOCOL, "EHDLC");
	col_clear(pinfo->cinfo, COL_INFO);

	while (tvb_reported_length_remaining(tvb, offset) > 0) {
		proto_item *ti            = NULL;
		proto_tree *ehdlc_tree    = NULL;
		guint16     len, msg_type;
		tvbuff_t   *next_tvb;
		guint16     control;
		gboolean    is_response   = FALSE, is_extended = TRUE;
		gint        header_length = 2; /* Address + Length field */

		msg_type      = tvb_get_guint8(tvb, offset);
		len           = tvb_get_guint8(tvb, offset+1);
#if 0
		col_append_fstr(pinfo->cinfo, COL_INFO, "%s ",
		                val_to_str(msg_type, ehdlc_protocol_vals,
		                           "unknown 0x%02x"));
#endif
		if (tree) {
			/* Use MIN(...,...) in the following to prevent a premature */
			/* exception before we try to dissect whatever is available. */
			ti = proto_tree_add_protocol_format(tree, proto_ehdlc,
					tvb, offset, MIN(len, tvb_length_remaining(tvb,offset)),
					"Ericsson HDLC protocol, type: %s",
					val_to_str(msg_type, ehdlc_protocol_vals,
						   "unknown 0x%02x"));
			ehdlc_tree = proto_item_add_subtree(ti, ett_ehdlc);
			proto_tree_add_item(ehdlc_tree, hf_ehdlc_protocol,
					    tvb, offset, 1, ENC_BIG_ENDIAN);
#if 0
			proto_tree_add_item(ehdlc_tree, hf_ehdlc_sapi,
					    tvb, offset, 1, ENC_BIG_ENDIAN);
			proto_tree_add_item(ehdlc_tree, hf_ehdlc_c_r,
					    tvb, offset, 1, ENC_BIG_ENDIAN);
#endif
			proto_tree_add_item(ehdlc_tree, hf_ehdlc_data_len,
					    tvb, offset+1, 1, ENC_BIG_ENDIAN);
		}

		control = dissect_xdlc_control(tvb, offset+2, pinfo, ehdlc_tree, hf_ehdlc_control,
					       ett_ehdlc_control, &ehdlc_cf_items, &ehdlc_cf_items_ext,
					       NULL, NULL, is_response, is_extended, FALSE);
		header_length += XDLC_CONTROL_LEN(control, is_extended);

		if (XDLC_IS_INFORMATION(control)) {
			next_tvb = tvb_new_subset(tvb, offset+header_length,
						  len-header_length, len-header_length);

			switch (msg_type) {
			case 0x20:
				/* len == 4 seems to be some kind of ACK */
				if (len <= 4)
					break;
				call_dissector(sub_handles[SUB_RSL], next_tvb, pinfo, tree);
				break;
			case 0xbc:
			case 0xdc:
			case 0xa0:
			case 0xc0:
				/* len == 4 seems to be some kind of ACK */
				if (len <= 4)
					break;
				call_dissector(sub_handles[SUB_OML], next_tvb, pinfo, tree);
				break;
			default:
				call_dissector(sub_handles[SUB_DATA], next_tvb, pinfo, tree);
				break;
			}
		} else if (control == (XDLC_U | XDLC_XID)) {
			/* XID is formatted like ISO 8885, typically we see
 			 * something like
			 * 82		format identifier
			 * 80		group identifier
			 * 00 09 	length
			 * 07 01 05 	Window Size Tx
			 * 09 01 04	Ack Timer (msec)
			 * 08 01 05	Window Size Rx */
			proto_tree_add_item(ehdlc_tree, hf_ehdlc_xid_payload,
					    tvb, offset+header_length,
					    len-header_length, ENC_NA);
		}

		if (len == 0)
			len = 1;
		offset += len;
	}
}

void
proto_register_ehdlc(void)
{
	static hf_register_info hf[] = {
		{ &hf_ehdlc_data_len,
		  { "DataLen", "ehdlc.data_len",
		    FT_UINT8, BASE_DEC, NULL, 0x0,
		    "The length of the data (in bytes)", HFILL }
		},
		{ &hf_ehdlc_protocol,
		  { "Protocol", "ehdlc.protocol",
		    FT_UINT8, BASE_HEX, VALS(ehdlc_protocol_vals), 0x0,
		    "The HDLC Sub-Protocol", HFILL }
		},
#if 0
		{ &hf_ehdlc_sapi,
		  { "SAPI", "ehdlc.sapi",
		    FT_UINT8, BASE_DEC, NULL, 0x1f,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_c_r,
		  { "C/R", "ehdlc.c_r",
		    FT_UINT8, BASE_HEX, NULL, 0x20,
		    NULL, HFILL }
		},
#endif
		{ &hf_ehdlc_xid_payload,
		  { "XID Payload", "ehdlc.xid_payload",
		    FT_BYTES, BASE_NONE, NULL, 0,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_control,
		  { "Control Field", "ehdlc.control",
		    FT_UINT16, BASE_HEX, NULL, 0,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_n_r,
		  { "N(R)", "ehdlc.control.n_r",
		    FT_UINT16, BASE_DEC, NULL, XDLC_N_R_EXT_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_n_s,
		  { "N(S)", "ehdlc.control.n_s",
		    FT_UINT16, BASE_DEC, NULL, XDLC_N_S_EXT_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_p,
		  { "Poll", "ehdlc.control.p",
		    FT_BOOLEAN, 8, TFS(&tfs_set_notset), XDLC_P_F,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_p_ext,
		  { "Poll", "ehdlc.control.p",
		    FT_BOOLEAN, 16, TFS(&tfs_set_notset), XDLC_P_F_EXT,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_f,
		  { "Final", "ehdlc.control.f",
		    FT_BOOLEAN, 8, TFS(&tfs_set_notset), XDLC_P_F,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_f_ext,
		  { "Final", "ehdlc.control.f",
		    FT_BOOLEAN, 16, TFS(&tfs_set_notset), XDLC_P_F_EXT,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_s_ftype,
		  { "Supervisory frame type", "ehdlc.control.s_ftype",
		    FT_UINT16, BASE_HEX, VALS(stype_vals), XDLC_S_FTYPE_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_u_modifier_cmd,
		  { "Command", "ehdlc.control.u_modifier_cmd",
		    FT_UINT8, BASE_HEX, VALS(modifier_vals_cmd), XDLC_U_MODIFIER_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_u_modifier_resp,
		  { "Response", "ehdlc.control.u_modifier_resp",
		    FT_UINT8, BASE_HEX, VALS(modifier_vals_resp), XDLC_U_MODIFIER_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_ftype_i,
		  { "Frame Type", "ehdlc.control.ftype",
		    FT_UINT16, BASE_HEX, VALS(ftype_vals), XDLC_I_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_ftype_s_u,
		  { "Frame Type", "ehdlc.control.ftype",
		    FT_UINT8, BASE_HEX, VALS(ftype_vals), XDLC_S_U_MASK,
		    NULL, HFILL }
		},
		{ &hf_ehdlc_ftype_s_u_ext,
		  { "Frame Type", "ehdlc.control.ftype",
		    FT_UINT16, BASE_HEX, VALS(ftype_vals), XDLC_S_U_MASK,
		    NULL, HFILL }
		},
	};

	static gint *ett[] = {
		&ett_ehdlc,
		&ett_ehdlc_control,
	};

	proto_ehdlc =
	    proto_register_protocol("Ericsson HDLC",
				    "Ericsson HDLC as used in A-bis over IP", "ehdlc");

	proto_register_field_array(proto_ehdlc, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));

	register_dissector("ehdlc", dissect_ehdlc, proto_ehdlc);
}

void
proto_reg_handoff_ehdlc(void)
{
	sub_handles[SUB_RSL]  = find_dissector("gsm_abis_rsl");
	sub_handles[SUB_OML]  = find_dissector("gsm_abis_oml");
	sub_handles[SUB_DATA] = find_dissector("data");
}
