/* packet-sapni.c
 * Routines for SAP NI (Network Interface) dissection
 * Copyright 2022, Martin Gallo <martin.gallo [AT] gmail.com>
 * Code contributed by SecureAuth Corp.
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * This is a simple dissector for the SAP NI protocol, mainly responsible for reassembly and calling the right registered dissector
 * based on the port number.
 *
 * Some details and example requests can be found in pysap's documentation: https://pysap.readthedocs.io/en/latest/protocols/SAPNI.html.
 */

#include <config.h>

#include <epan/packet.h>
#include <epan/prefs.h>
#include <epan/expert.h>
#include "packet-tcp.h"
#include <epan/next_tvb.h>
#include <epan/conversation.h>
#include <wsutil/wmem/wmem.h>

#include "packet-sapni.h"


/*
 * Define default ports. The right range should be 32NN and 4NNNN, but as port numbers are proprietary and not
 * IANA assigned, we leave only the ones corresponding to the instance 00.
 */
#define SAP_PROTOCOL_PORT_RANGE "3200,40000"

/*
 * Length of the frame header
 */
#define SAP_PROTOCOL_HEADER_LEN 4

static int proto_sap_protocol;

static int hf_sap_protocol_length;
static int hf_sap_protocol_payload;

static int hf_sap_protocol_ping;
static int hf_sap_protocol_pong;

static int ett_sap_protocol;

/* Expert info */
static expert_field ei_sap_invalid_length;

/* Global port preference */
static range_t *global_sap_protocol_port_range;

/* Global reassemble preference */
static bool global_sap_protocol_desegment = true;

/* Protocol handle */
static dissector_handle_t sap_protocol_handle;
static dissector_handle_t sap_router_handle;

/* Sub-dissectors table */
static dissector_table_t sub_dissectors_table;
static heur_dissector_list_t heur_subdissector_list;

/*
 *
 */
void proto_reg_handoff_sap_protocol(void);
void proto_register_sap_protocol(void);


/*
 * Get the SAPNI pdu length
 */
static unsigned
get_sap_protocol_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int offset _U_, void *dissector_data _U_)
{
	return ((unsigned)tvb_get_ntohl(tvb, 0) + 4);
}


/*
 * Dissect the payload of a packet using a registered SAP protocol. It uses
 * heuristics as a first try as some protocols uses the same TCP ports
 * (e.g. 3200/tcp for Enqueue Server and Diag).
 */
void
dissect_sap_protocol_payload(tvbuff_t *tvb, uint32_t offset, packet_info *pinfo, proto_tree *tree, uint16_t sport, uint16_t dport){
	uint16_t low_port = 0, high_port = 0;
	tvbuff_t *next_tvb = NULL;
	heur_dtbl_entry_t *hdtbl_entry = NULL;

	/* Set the new tvb for further dissection of the payload */
	next_tvb = tvb_new_subset_remaining(tvb, offset);

	/* Determine if this packet is part of a conversation and call dissector
	 * for the conversation if available.
	 */
	if (try_conversation_dissector(&pinfo->dst, &pinfo->src, CONVERSATION_TCP,
			dport, sport, next_tvb, pinfo, tree, NULL, 0)) {
		return;
	}

	/* Try with the heuristic dissectors first */
	/* TODO: When the protocol is guessed via heuristic dissector (Enqueue
	 * Server), the NI Protocol tree is missed. */
	if (dissector_try_heuristic(heur_subdissector_list, next_tvb, pinfo, tree, &hdtbl_entry, NULL)) {
		return;
	}

	/* Call the dissector in the subdissectors table according to the port number */
	if (sport > dport) {
		low_port = dport; high_port = sport;
	} else {
		low_port = sport; high_port = dport;
	}
	if ((low_port != 0 && dissector_try_uint(sub_dissectors_table, low_port, next_tvb, pinfo, tree)) ||
		(high_port != 0 && dissector_try_uint(sub_dissectors_table, high_port, next_tvb, pinfo, tree))){
		return;
	}
}


/*
 * Dissect a SAPNI packet, adding the length field to the protocol tree and
 * calling the sub-dissector according to the port number. It also identifies
 * PING/PONG packets at the SAPNI layer.
 */
static int
dissect_sap_protocol_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
{
	uint32_t length = 0;
	proto_item *ti = NULL, *sap_protocol_length = NULL;
	proto_tree *sap_protocol_tree = NULL;
	conversation_t *conversation = NULL;
	tvbuff_t *next_tvb = NULL;

	/* Add the protocol to the column */
	col_set_str(pinfo->cinfo, COL_PROTOCOL, "SAPNI");
	/* Clear out stuff in the info column */
	col_clear(pinfo->cinfo,COL_INFO);

	/* Get the length field */
	length = tvb_get_ntohl(tvb, 0);

	/* Add the payload length to the info column */
	col_add_fstr(pinfo->cinfo, COL_INFO, "Length=%d ", length);

	/* Add the main SAP Protocol subtree */
	ti = proto_tree_add_item(tree, proto_sap_protocol, tvb, 0, -1, ENC_NA);
	sap_protocol_tree = proto_item_add_subtree(ti, ett_sap_protocol);

	/* Add the length item */
	proto_item_append_text(ti, ", Len: %u", length);
	sap_protocol_length = proto_tree_add_item(sap_protocol_tree, hf_sap_protocol_length, tvb, 0, 4, ENC_BIG_ENDIAN);

	/* Add expert info in case of no match between the given length and the actual one */
	if (tvb_reported_length(tvb) != length + 4) {
		expert_add_info(pinfo, sap_protocol_length, &ei_sap_invalid_length);
	}

	/* Add the payload subtree */
	if (length > 0){
		proto_tree_add_item(sap_protocol_tree, hf_sap_protocol_payload, tvb, 4, -1, ENC_NA);
	}

	/* Check for NI_PING */
	if ((length == 8)&&(tvb_strneql(tvb, 4, "NI_PING\00", 8) == 0)){
		col_set_str(pinfo->cinfo, COL_INFO, "Ping message");

		proto_item_append_text(ti, ", Ping message (keep-alive request)");
		proto_tree_add_item(sap_protocol_tree, hf_sap_protocol_ping, tvb, 4, -1, ENC_NA);

	/* Chek for NI_PONG */
	} else if ((length == 8)&&(tvb_strneql(tvb, 4, "NI_PONG\00", 8) == 0)){
		col_set_str(pinfo->cinfo, COL_INFO, "Pong message");
		proto_item_append_text(ti, ", Pong message");

		/* We need to check if this is a keep-alive response, or it's part of
		 * a SAP Router conversation and thus a route accepted message.
		 */
		conversation = find_conversation_pinfo(pinfo, 0);
		if (conversation == NULL){
			col_append_str(pinfo->cinfo, COL_INFO, " (keep-alive response)");
			proto_item_append_text(ti, " (keep-alive response)");
			proto_tree_add_item(sap_protocol_tree, hf_sap_protocol_pong, tvb, 4, -1, ENC_NA);

		} else {
			col_append_str(pinfo->cinfo, COL_INFO, " (route accepted)");
			proto_item_append_text(ti, " (route accepted)");

			/* Call the SAP Router dissector */
			if (sap_router_handle){
				/* Create a new tvb buffer and call the dissector */
				next_tvb = tvb_new_subset_remaining(tvb, 4);
				call_dissector_only(sap_router_handle, next_tvb, pinfo, tree, NULL);
			}
		}

	/* Dissect the payload */
	} else if (length > 0){
		dissect_sap_protocol_payload(tvb, 4, pinfo, tree, pinfo->srcport, pinfo->destport);
	}

	/* TODO: We need to return the *actual* length processed */
	return (length);
}

/*
 * Performs the TCP reassembling and dissects the packet.
 */
static int
dissect_sap_protocol(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data)
{
	tcp_dissect_pdus(tvb, pinfo, tree, global_sap_protocol_desegment, SAP_PROTOCOL_HEADER_LEN,
		get_sap_protocol_pdu_len, dissect_sap_protocol_message, data);
	return tvb_reported_length(tvb);
}

void
proto_register_sap_protocol(void)
{
	static hf_register_info hf[] = {
		{ &hf_sap_protocol_length,
			{ "Length", "sapni.length", FT_UINT32, BASE_DEC, NULL, 0x0, NULL, HFILL }},
		{ &hf_sap_protocol_payload,
			{ "Payload", "sapni.payload", FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }},
		{ &hf_sap_protocol_ping,
			{ "Ping", "sapni.ping", FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }},
		{ &hf_sap_protocol_pong,
			{ "Pong", "sapni.pong", FT_NONE, BASE_NONE, NULL, 0x0, NULL, HFILL }},
	};

	/* Setup protocol subtree array */
	static int *ett[] = {
		&ett_sap_protocol
	};

	/* Register the expert info */
	static ei_register_info ei[] = {
		{ &ei_sap_invalid_length, { "sapni.length.invalid", PI_MALFORMED, PI_WARN, "The reported length is incorrect", EXPFILL }},
	};

	module_t *sap_protocol_module;
	expert_module_t* sap_protocol_expert;

	/* Register the protocol */
	proto_sap_protocol = proto_register_protocol("SAP NI Protocol", "SAPNI", "sapni");

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

	sap_protocol_expert = expert_register_protocol(proto_sap_protocol);
	expert_register_field_array(sap_protocol_expert, ei, array_length(ei));

	register_dissector("sapni", dissect_sap_protocol, proto_sap_protocol);

	/* Sub dissector code */
	sub_dissectors_table = register_dissector_table("sapni.port", "SAP Protocol Port", proto_sap_protocol, FT_UINT16, BASE_DEC);
	heur_subdissector_list = register_heur_dissector_list_with_description("sapni", "SAP NI payload", proto_sap_protocol);

	/* Register the preferences */
	sap_protocol_module = prefs_register_protocol(proto_sap_protocol, proto_reg_handoff_sap_protocol);

	range_convert_str(wmem_epan_scope(), &global_sap_protocol_port_range, SAP_PROTOCOL_PORT_RANGE, MAX_TCP_PORT);
	prefs_register_range_preference(sap_protocol_module, "tcp_ports", "SAP NI Protocol TCP port numbers", "Port numbers used for SAP NI Protocol (default " SAP_PROTOCOL_PORT_RANGE ")", &global_sap_protocol_port_range, MAX_TCP_PORT);

	prefs_register_bool_preference(sap_protocol_module, "desegment", "Reassemble SAP NI Protocol messages spanning multiple TCP segments", "Whether the SAP NI Protocol dissector should reassemble messages spanning multiple TCP segments.", &global_sap_protocol_desegment);
}

/**
 * Helpers for dealing with the port range
 */
static void range_delete_callback (uint32_t port, void *ptr _U_)
{
	dissector_delete_uint("tcp.port", port, sap_protocol_handle);
}

static void range_add_callback (uint32_t port, void *ptr _U_)
{
	dissector_add_uint("tcp.port", port, sap_protocol_handle);
}

/**
 * Register Hand off for the SAP NI Protocol
 */
void
proto_reg_handoff_sap_protocol(void)
{
	static range_t *sap_protocol_port_range;
	static bool initialized = false;

	if (!initialized) {
		sap_protocol_handle = find_dissector("sapni");
		initialized = true;
	} else {
		range_foreach(sap_protocol_port_range, range_delete_callback, NULL);
		wmem_free(wmem_epan_scope(), sap_protocol_port_range);
	}

	sap_protocol_port_range = range_copy(wmem_epan_scope(), global_sap_protocol_port_range);
	range_foreach(sap_protocol_port_range, range_add_callback, NULL);

	sap_router_handle = find_dissector("saprouter");

}

/*
 * 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:
 */