wireshark/epan/dissectors/packet-coap.c

/* packet-coap.c
 * Routines for CoAP packet disassembly
 * draft-ietf-core-coap-14.txt
 * draft-ietf-core-block-10.txt
 * draft-ietf-core-observe-07.txt
 * draft-ietf-core-link-format-06.txt
 * Shoichi Sakane <sakane@tanu.org>
 *
 * $Id$
 *
 * 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/prefs.h>
#include <expert.h>

void proto_register_coap(void);

static dissector_table_t media_type_dissector_table;

static int proto_coap = -1;

static int hf_coap_version		= -1;
static int hf_coap_ttype		= -1;
static int hf_coap_opt_count		= -1;
static int hf_coap_code			= -1;
static int hf_coap_tid			= -1;
static int hf_coap_payload_desc		= -1;
static int hf_coap_opt_name		= -1;
static int hf_coap_opt_desc		= -1;
static int hf_coap_opt_jump		= -1;
static int hf_coap_opt_delta		= -1;
static int hf_coap_opt_length		= -1;
static int hf_coap_opt_ctype		= -1;
static int hf_coap_opt_max_age		= -1;
static int hf_coap_opt_proxy_uri	= -1;
static int hf_coap_opt_etag		= -1;
static int hf_coap_opt_uri_host 	= -1;
static int hf_coap_opt_location_path	= -1;
static int hf_coap_opt_uri_port		= -1;
static int hf_coap_opt_location_query	= -1;
static int hf_coap_opt_uri_path		= -1;
static int hf_coap_opt_observe		= -1;
static int hf_coap_opt_token		= -1;
static int hf_coap_opt_accept		= -1;
static int hf_coap_opt_if_match		= -1;
static int hf_coap_opt_block_number	= -1;
static int hf_coap_opt_block_mflag	= -1;
static int hf_coap_opt_block_size	= -1;
static int hf_coap_opt_uri_query	= -1;
static int hf_coap_opt_unknown		= -1;

static gint ett_coap			= -1;
static gint ett_coap_option		= -1;
static gint ett_coap_payload		= -1;

/* CoAP's IANA-assigned port number */
#define DEFAULT_COAP_PORT	5683

/* indicators whether those are to be showed or not */
#define DEFAULT_COAP_CTYPE_VALUE	~0
#define DEFAULT_COAP_BLOCK_NUMBER	~0

static const gchar *coap_ctype_str   = NULL;
static gint coap_ctype_value = DEFAULT_COAP_CTYPE_VALUE;
static guint global_coap_port_number = DEFAULT_COAP_PORT;
static gint coap_block_number = DEFAULT_COAP_BLOCK_NUMBER;
static guint coap_block_mflag = 0;
static gchar coap_uri_str[1024];	/* the maximum is 1024 > 510 = Uri-Host:255 + Uri-Path:255 x 2 */
static gchar coap_uri_query[1024];	/* the maximum is 1024 > 765 = Uri-Query:255 x 3 */
static gchar coap_token_str[128];

/*
 * Transaction Type
 */
static const value_string vals_ttype[] = {
	{ 0, "Confirmable" },
	{ 1, "Non-Confirmable" },
	{ 2, "Acknowledgement" },
	{ 3, "Reset" },
	{ 0, NULL },
};
static const value_string vals_ttype_short[] = {
	{ 0, "CON" },
	{ 1, "NON" },
	{ 2, "ACK" },
	{ 3, "RST" },
	{ 0, NULL },
};

/*
 * Method Code
 * Response Code
 */
static const value_string vals_code[] = {
	{ 0, "Empty Message" },

	/* method code */
	{ 1, "GET" },
	{ 2, "POST" },
	{ 3, "PUT" },
	{ 4, "DELETE" },

	/* response code */
	{  65, "2.01 Created" },
	{  66, "2.02 Deleted" },
	{  67, "2.03 Valid" },
	{  68, "2.04 Changed" },
	{  69, "2.05 Content" },
	{ 128, "4.00 Bad Request" },
	{ 129, "4.01 Unauthorized" },
	{ 130, "4.02 Bad Option" },
	{ 131, "4.03 Forbidden" },
	{ 132, "4.04 Not Found" },
	{ 133, "4.05 Method Not Allowed" },
	{ 134, "4.06 Not Acceptable" },
	{ 136, "4.08 Request Entity Incomplete" },	/* core-block-10 */
	{ 140, "4.12 Precondition Failed" },
	{ 141, "4.13 Request Entity Too Large" },
	{ 143, "4.15 Unsupported Content-Format" },
	{ 160, "5.00 Internal Server Error" },
	{ 161, "5.01 Not Implemented" },
	{ 162, "5.02 Bad Gateway" },
	{ 163, "5.03 Service Unavailable" },
	{ 164, "5.04 Gateway Timeout" },
	{ 165, "5.05 Proxying Not Supported" },

	{ 0, NULL },
};

/*
 * Option Headers
 * No-Option must not be included in this structure, is handled in the function
 * of the dissector, especially.
 */
#define COAP_OPT_IF_MATCH	 1
#define COAP_OPT_URI_HOST	 3
#define COAP_OPT_ETAG		 4
#define COAP_OPT_IF_NONE_MATCH	 5
#define COAP_OPT_OBSERVE	 6	/* core-observe-07 */
#define COAP_OPT_URI_PORT	 7
#define COAP_OPT_LOCATION_PATH	 8
#define COAP_OPT_URI_PATH	11
#define COAP_OPT_CONTENT_TYPE	12
#define COAP_OPT_MAX_AGE	14
#define COAP_OPT_URI_QUERY	15
#define COAP_OPT_ACCEPT		16
#define COAP_OPT_TOKEN		19
#define COAP_OPT_LOCATION_QUERY	20
#define COAP_OPT_BLOCK2		23	/* core-block-10 */
#define COAP_OPT_BLOCK_SIZE	28	/* core-block-10 */
#define COAP_OPT_BLOCK1		27	/* core-block-10 */
#define COAP_OPT_PROXY_URI	35

static const value_string vals_opt_type[] = {
	{ COAP_OPT_IF_MATCH,       "If-Match" },
	{ COAP_OPT_URI_HOST,       "Uri-Host" },
	{ COAP_OPT_ETAG,           "Etag" },
	{ COAP_OPT_IF_NONE_MATCH,  "If-None-Match" },
	{ COAP_OPT_URI_PORT,       "Uri-Port" },
	{ COAP_OPT_LOCATION_PATH,  "Location-Path" },
	{ COAP_OPT_URI_PATH,       "Uri-Path" },
	{ COAP_OPT_CONTENT_TYPE,   "Content-Format" },
	{ COAP_OPT_MAX_AGE,        "Max-age" },
	{ COAP_OPT_URI_QUERY,      "Uri-Query" },
	{ COAP_OPT_ACCEPT,         "Accept" },
	{ COAP_OPT_TOKEN,          "Token" },
	{ COAP_OPT_LOCATION_QUERY, "Location-Query" },
	{ COAP_OPT_PROXY_URI,      "Proxy-Uri" },
	{ COAP_OPT_OBSERVE,        "Observe" },
	{ COAP_OPT_BLOCK2,         "Block2" },
	{ COAP_OPT_BLOCK1,         "Block1" },
	{ COAP_OPT_BLOCK_SIZE,     "Block Size" },
	{ 0, NULL },
};

struct coap_option_range_t {
	guint type;
	gint min;
	gint max;
} coi[] = {
    { COAP_OPT_IF_MATCH,       0,   8 },
    { COAP_OPT_URI_HOST,       1, 255 },
    { COAP_OPT_ETAG,           1,   8 },
    { COAP_OPT_IF_NONE_MATCH,  0,   0 },
    { COAP_OPT_URI_PORT,       0,   2 },
    { COAP_OPT_LOCATION_PATH,  0, 255 },
    { COAP_OPT_URI_PATH,       0, 255 },
    { COAP_OPT_CONTENT_TYPE,   0,   2 },
    { COAP_OPT_MAX_AGE,        0,   4 },
    { COAP_OPT_URI_QUERY,      1, 255 },
    { COAP_OPT_ACCEPT,         0,   2 },
    { COAP_OPT_TOKEN,          1,   8 },
    { COAP_OPT_LOCATION_QUERY, 0, 255 },
    { COAP_OPT_PROXY_URI,      1,1034 },
    { COAP_OPT_OBSERVE,        0,   2 },
    { COAP_OPT_BLOCK2,         0,   3 },
    { COAP_OPT_BLOCK1,         0,   3 },
    { COAP_OPT_BLOCK_SIZE,     0,   4 },
    { 0, 0, 0 },
};

static const value_string vals_ctype[] = {
	{ 0, "text/plain; charset=utf-8" },
	{ 40, "application/link-format" },
	{ 41, "application/xml" },
	{ 42, "application/octet-stream" },
	{ 47, "application/exi" },
	{ 50, "application/json" },
	{ 0, NULL },
};

static const char *nullstr = "(null)";

void proto_reg_handoff_coap(void);

static int
coap_is_str_ipv6addr(guint8 *str)
{
	size_t len   = strlen(str);
	int    colon = 0;

	while (len--) {
		if (*str++ == ':')
			colon++;
	}

	return colon > 1 ? 1 : 0;
}

static gint
coap_get_opt_uint(tvbuff_t *tvb, gint offset, gint length)
{
	switch (length) {
	case 0:
		return 0;
	case 1:
		return (guint)tvb_get_guint8(tvb, offset);
	case 2:
		return (guint)tvb_get_ntohs(tvb, offset);
	case 3:
		return (guint)tvb_get_ntoh24(tvb, offset);
	case 4:
		return (guint)tvb_get_ntohl(tvb, offset);
	default:
		return -1;
	}
}

static gint
coap_opt_check(packet_info *pinfo, proto_tree *subtree, guint opt_num, gint opt_length)
{
	int i;

	for (i = 0; i < (int)(array_length(coi)); i++) {
		if (coi[i].type == opt_num)
			break;
	}
	if (i == (int)(array_length(coi))) {
		expert_add_info_format(pinfo, subtree, PI_MALFORMED, PI_WARN,
		    "Invalid Option Number %d", opt_num);
		return -1;
	}
	if (opt_length < coi[i].min || opt_length > coi[i].max) {
		expert_add_info_format(pinfo, subtree, PI_MALFORMED,
		    PI_WARN, "Invalid Option Range: %d (%d < x < %d)",
		    opt_length, coi[i].min, coi[i].max);
	}

	return 0;
}

static void
dissect_coap_opt_hex_string(tvbuff_t *tvb, proto_item *item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length, int hf)
{
	const guint8 *str;
	gint dp = offset + opt_hlen;

	if (opt_length == 0)
		str = nullstr;
	else
		str = tvb_bytes_to_str_punct(tvb, dp, opt_length, ' ');

	proto_tree_add_string(subtree, hf, tvb, dp, opt_length, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(item, ": %s", str);
}

static void
dissect_coap_opt_uint(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length, int hf)
{
	guint i = 0;
	gint dp, len;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		i = 0;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		i = coap_get_opt_uint(tvb, dp, len);
	}

	proto_tree_add_uint(subtree, hf, tvb, dp, len, i);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %d", i);
}

static void
dissect_coap_opt_uri_host(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	guint8 *str = NULL;
	gint dp = offset + opt_hlen;

	str = tvb_get_ephemeral_string(tvb, dp, opt_length);

	proto_tree_add_string(subtree, hf_coap_opt_uri_host, tvb, dp, opt_length, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);

	/* forming a uri-string */
	g_strlcat(coap_uri_str, "coap://", sizeof(coap_uri_str));
	/*
	 * if the string looks an IPv6 address, assuming that it has
	 * to be enclosed by brackets.
	 */
	if (coap_is_str_ipv6addr(str)) {
		g_strlcat(coap_uri_str, "[", sizeof(coap_uri_str));
		g_strlcat(coap_uri_str, str, sizeof(coap_uri_str));
		g_strlcat(coap_uri_str, "]", sizeof(coap_uri_str));
	} else
		g_strlcat(coap_uri_str, str, sizeof(coap_uri_str));
}

static void
dissect_coap_opt_uri_path(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	const guint8 *str = NULL;
	gint dp, len;

	g_strlcat(coap_uri_str, "/", sizeof(coap_uri_str));

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		str = nullstr;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		str = tvb_get_ephemeral_string(tvb, dp, len);
		g_strlcat(coap_uri_str, str, sizeof(coap_uri_str));
	}

	proto_tree_add_string(subtree, hf_coap_opt_uri_path, tvb, dp, len, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);
}

static void
dissect_coap_opt_uri_query(tvbuff_t *tvb, proto_item *head_item,proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	const guint8 *str = NULL;
	gint dp, len;

	if (coap_uri_query[0] == '\0')
		g_strlcat(coap_uri_query, "?", sizeof(coap_uri_str));
	else
		g_strlcat(coap_uri_query, "&", sizeof(coap_uri_str));

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		str = nullstr;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		str = tvb_get_ephemeral_string(tvb, dp, len);
		g_strlcat(coap_uri_str, str, sizeof(coap_uri_str));
	}

	proto_tree_add_string(subtree, hf_coap_opt_uri_query, tvb, dp, len, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);
}

static void
dissect_coap_opt_location_path(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	const guint8 *str = NULL;
	gint dp, len;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		str = nullstr;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		str = tvb_get_ephemeral_string(tvb, dp, len);
	}

	proto_tree_add_string(subtree, hf_coap_opt_location_path, tvb, dp, len, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);
}

static void
dissect_coap_opt_location_query(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	const guint8 *str = NULL;
	gint dp, len;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		str = nullstr;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		str = tvb_get_ephemeral_string(tvb, dp, len);
	}

	proto_tree_add_string(subtree, hf_coap_opt_location_query, tvb, dp, len, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);
}

static void
dissect_coap_opt_proxy_uri(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	const guint8 *str = NULL;
	gint dp, len;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		str = nullstr;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		str = tvb_get_ephemeral_string(tvb, dp, len);
	}

	proto_tree_add_string(subtree, hf_coap_opt_proxy_uri, tvb, dp, len, str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", str);
}

static void
dissect_coap_opt_token(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	gint dp = offset + opt_hlen;

	/* forming a token */
	g_strlcat(coap_token_str, tvb_bytes_to_str_punct(tvb, dp, opt_length, ' '), sizeof(coap_token_str));

	proto_tree_add_string(subtree, hf_coap_opt_token, tvb, dp, opt_length, coap_token_str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", coap_token_str);
}

static void
dissect_coap_opt_ctype(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length, int hf)
{
	gint dp, len;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		coap_ctype_value = 0;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		coap_ctype_value = coap_get_opt_uint(tvb, dp, len);
	}

	coap_ctype_str = val_to_str(coap_ctype_value, vals_ctype, "Unknown Type %d");

	proto_tree_add_string(subtree, hf, tvb, dp, len, coap_ctype_str);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": %s", coap_ctype_str);
}

static void
dissect_coap_opt_block(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	guint8      val                = 0;
	guint       encoded_block_size = 0;
	guint       block_esize;
	gint dp, len;
	gint dp2;

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		coap_block_number = 0;
		val = 0;
		dp2 = dp;
	} else {
		dp = offset + opt_hlen;
		len = opt_length;
		coap_block_number = coap_get_opt_uint(tvb, dp, len) >> 4;
		val = tvb_get_guint8(tvb, offset + opt_length - 1) & 0x0f;
		dp2 = dp + opt_length - 1;
	}

	proto_tree_add_uint(subtree, hf_coap_opt_block_number,
	    tvb, dp, len, coap_block_number);

	/* More flag in the end of the option */
	coap_block_mflag = val & 0x08;
	proto_tree_add_uint(subtree, hf_coap_opt_block_mflag,
	    tvb, dp2, 1, coap_block_mflag);

	/* block size */
	encoded_block_size = val & 0x07;
	block_esize = 1 << (encoded_block_size + 4);
	proto_tree_add_uint_format(subtree, hf_coap_opt_block_size,
	    tvb, dp2, 1, encoded_block_size, "Block Size: %d (%d encoded)", block_esize, encoded_block_size);

	/* add info to the head of the packet detail */
	proto_item_append_text(head_item, ": NUM:%d, M:%d, SZX:%d",
	    coap_block_number, coap_block_mflag, block_esize);
}

static void
dissect_coap_opt_uri_port(tvbuff_t *tvb, proto_item *head_item, proto_tree *subtree, gint offset, gint opt_hlen, gint opt_length)
{
	guint port = 0;
	char portstr[6];
	gint dp, len;

	memset(portstr, '\0', sizeof(portstr));

	if (opt_length == 0) {
		dp = offset;
		len = opt_hlen;
		port = 0;
	} else {
		dp = offset;
		len = opt_hlen;
		port = coap_get_opt_uint(tvb, dp, len);
	}

	proto_tree_add_uint(subtree, hf_coap_opt_uri_port, tvb, dp, len, port);

	proto_item_append_text(head_item, ": %d", port);

	/* forming a uri-string */
	g_snprintf(portstr, sizeof(portstr), "%u", port);
	g_strlcat(coap_uri_str, ":", sizeof(coap_uri_str));
	g_strlcat(coap_uri_str, portstr, sizeof(coap_uri_str));
}

/*
 * dissector for each option of CoAP.
 * return the total length of the option including the header (e.g. delta and length).
 */
static int
dissect_coap_options_main(tvbuff_t *tvb, packet_info *pinfo, proto_tree *coap_tree, gint offset, guint8 opt_count, guint *opt_num, gint coap_length)
{
	guint8      opt_jump;
	gint        opt_length, tmp_length, jump_length;
	proto_tree *subtree    = NULL;
	proto_item *item       = NULL;
	gint        opt_hlen, max_hlen;
	tvbuff_t   *tvb_lenbuf = NULL;
	char strbuf[56];

	opt_jump = tvb_get_guint8(tvb, offset);

	/* option jump */
	/*
	 * seciton 3.2 in coap-12:
	 * If the Option Count field in the CoAP header is 15 and the Option
	 * Header byte is 0xf0 (the Option Delta is 15 and the Option Length is
	 * 0), the option is interpreted as the end-of-options marker instead of
	 * the option with the resulting Option Number.  (In other words, the
	 * end-of-options marker always is just a single byte valued 0xf0.)
	 *
	 * section 3.3 in coap-12:
	 * An Option Jump MUST be followed by an actual Option, i.e., it MUST
	 * NOT be followed by another Option Jump or an end-of-options
	 * indicator.  A message violating this MUST be treated as an encoding
	 * error.
	 * Option Jumps do NOT count as Options in the Option Count field of the
	 * header (i.e., they cannot by themselves end the Option sequence).
	 */
	switch (opt_jump) {
	case 0xf0:
		if (opt_count != 15) {
			expert_add_info_format(pinfo, subtree,
			    PI_MALFORMED, PI_WARN,
			    "end-of-options marker found, but OC isn't 15");
			return -1;
		}
		proto_tree_add_string(coap_tree, hf_coap_opt_jump,
		    tvb, offset, 1, "end-of-options marker");
		return ++offset;
	case 0xf1:
		jump_length = 15;
		proto_tree_add_uint_format(coap_tree, hf_coap_opt_jump,
		    tvb, offset, 1, jump_length, "Option Jump (0xf1): %d", jump_length);
		*opt_num += jump_length;
		offset++;
		opt_jump = tvb_get_guint8(tvb, offset);
		break;
	case 0xf2:
		jump_length = (tvb_get_guint8(tvb, offset + 1) + 2) * 8;
		proto_tree_add_uint_format(coap_tree, hf_coap_opt_jump,
		    tvb, offset, 2, jump_length, "Option Jump (0xf2): %d", jump_length);
		*opt_num += jump_length;
		offset += 2;
		opt_jump = tvb_get_guint8(tvb, offset);
		break;
	case 0xf3:
		jump_length = (tvb_get_ntohs(tvb, offset + 1) + 258) * 8;
		proto_tree_add_uint_format(coap_tree, hf_coap_opt_jump,
		    tvb, offset, 3, jump_length, "Option Jump (0xf3): %d", jump_length);
		*opt_num += jump_length;
		offset += 3;
		opt_jump = tvb_get_guint8(tvb, offset);
		break;
	}

	/*
	 * Length:
	 *   Normally Length is a 4-bit unsigned integer allowing values of
	 *   0-14 octets.  The Length field can be extended for options with
	 *   values longer than 14 bytes by adding extension bytes.
	 *   The maximum length for an option is 1034 bytes.
	 */
	max_hlen = 4;
	opt_hlen = 1;
	opt_length = opt_jump & 0x0f;
	if (opt_length == 0x0f) {
		do {
			tmp_length = tvb_get_guint8(tvb, offset + opt_hlen);
			opt_length += tmp_length;
			opt_hlen++;
		} while (!(opt_hlen == max_hlen || tmp_length != 0xff));
	}
	if (max_hlen < opt_hlen) {
		expert_add_info_format(pinfo, subtree, PI_MALFORMED, PI_WARN,
		    "Invalid Option Length: all %d bits are set, which is not"
		    " allowed by the spec 12", max_hlen * 8 - 4);
		return -1;
	}
	if (coap_length < offset) {
		expert_add_info_format(pinfo, subtree, PI_MALFORMED, PI_WARN,
		    "Invalid length: coap payload length(%d) < offset(%d)",
		    coap_length, offset);
		return -1;
	}

	*opt_num += ((opt_jump & 0xf0) >> 4);

	coap_opt_check(pinfo, subtree, *opt_num, opt_length);

	g_snprintf(strbuf, sizeof(strbuf), 
	    "#%u: %s", opt_count, val_to_str_const(*opt_num, vals_opt_type,
	    *opt_num % 14 == 0 ? "No-Op" : "Unknown Option"));
	item = proto_tree_add_string(coap_tree, hf_coap_opt_name,
	    tvb, offset, opt_hlen + opt_length, strbuf);

	subtree = proto_item_add_subtree(item, ett_coap_option);
	g_snprintf(strbuf, sizeof(strbuf), 
	    "Type %u, %s, %s%s", *opt_num,
	    (*opt_num & 1) ? "Critical" : "Elective",
	    (*opt_num & 2) ? "Unsafe" : "Safe",
	    ((*opt_num & 0x1e) == 0x1c) ? ", NoCacheKey" : "");
	proto_tree_add_string(subtree, hf_coap_opt_desc,
	    tvb, offset, opt_hlen + opt_length, strbuf);
	proto_tree_add_item(subtree, hf_coap_opt_delta, tvb, offset, 1,
	    ENC_BIG_ENDIAN);

	tvb_lenbuf = tvb_new_subset(tvb, offset, opt_hlen, opt_hlen);
	proto_tree_add_uint_bits_format_value(subtree, hf_coap_opt_length,
	    tvb_lenbuf, 4, 4 + ((opt_hlen - 1) * 8), opt_length, "%d",
	    opt_length);

	/* offset points the next to its option header */
	switch (*opt_num) {
	case COAP_OPT_CONTENT_TYPE:
		dissect_coap_opt_ctype(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_ctype);
		break;
	case COAP_OPT_MAX_AGE:
		dissect_coap_opt_uint(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_max_age);
		break;
	case COAP_OPT_PROXY_URI:
		dissect_coap_opt_proxy_uri(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_ETAG:
		dissect_coap_opt_hex_string(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_etag);
		break;
	case COAP_OPT_URI_HOST:
		dissect_coap_opt_uri_host(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_LOCATION_PATH:
		dissect_coap_opt_location_path(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_URI_PORT:
		dissect_coap_opt_uri_port(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_LOCATION_QUERY:
		dissect_coap_opt_location_query(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_URI_PATH:
		dissect_coap_opt_uri_path(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_OBSERVE:
		dissect_coap_opt_uint(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_observe);
		break;
	case COAP_OPT_TOKEN:
		dissect_coap_opt_token(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_ACCEPT:
		dissect_coap_opt_ctype(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_accept);
		break;
	case COAP_OPT_IF_MATCH:
		dissect_coap_opt_hex_string(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_if_match);
		break;
	case COAP_OPT_URI_QUERY:
		dissect_coap_opt_uri_query(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_BLOCK2:
		dissect_coap_opt_block(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_BLOCK1:
		dissect_coap_opt_block(tvb, item, subtree, offset,
		    opt_hlen, opt_length);
		break;
	case COAP_OPT_IF_NONE_MATCH:
		break;
	case COAP_OPT_BLOCK_SIZE:
		dissect_coap_opt_uint(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_block_size);
		break;
	default:
		dissect_coap_opt_hex_string(tvb, item, subtree, offset,
		    opt_hlen, opt_length, hf_coap_opt_unknown);
		break;
	}

	return offset + opt_hlen + opt_length;
}

/*
 * options dissector.
 * return offset pointing the next of options. (i.e. the top of the paylaod
 * or the end of the data.
 */
static int
dissect_coap_options(tvbuff_t *tvb, packet_info *pinfo, proto_tree *coap_tree, gint offset, gint coap_length, guint8 opt_count)
{
	guint      opt_num = 0;
	int         i;

	/* loop for dissecting options */
	for (i = 1; i <= opt_count; i++) {
		offset = dissect_coap_options_main(tvb, pinfo, coap_tree,
		    offset, i, &opt_num, coap_length);
		if (offset == -1)
			return -1;
	}

	return offset;
}

static void
dissect_coap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *parent_tree)
{
	gint        offset      = 0;
	proto_item *coap_root   = NULL;
	proto_tree *coap_tree   = NULL;
	guint8      ttype       = 0;
	guint8      opt_count   = 0;
	guint8      code        = 0;
	guint16     tid         = 0;
	gint        coap_length = 0;

	/* initialize the CoAP length and the content-Format */
	/*
	 * the length of CoAP message is not specified in the CoAP header.
	 * It has to be from the lower layer.  the iplen of packet_info is not accurate.
	 * Currently, the length is just copied from the reported length of the tvbuffer.
	 */
	coap_length = tvb_reported_length(tvb);
	coap_ctype_str = "";
	coap_ctype_value = DEFAULT_COAP_CTYPE_VALUE;

	coap_root = proto_tree_add_item(parent_tree, proto_coap, tvb, offset, -1, ENC_NA);
	coap_tree = proto_item_add_subtree(coap_root, ett_coap);

	proto_tree_add_item(coap_tree, hf_coap_version, tvb, offset, 1, ENC_BIG_ENDIAN);

	proto_tree_add_item(coap_tree, hf_coap_ttype, tvb, offset, 1, ENC_BIG_ENDIAN);
	ttype = (tvb_get_guint8(tvb, offset) & 0x30) >> 4;

	proto_tree_add_item(coap_tree, hf_coap_opt_count, tvb, offset, 1, ENC_BIG_ENDIAN);
	opt_count = tvb_get_guint8(tvb, offset) & 0x0f;
	offset += 1;

	proto_tree_add_item(coap_tree, hf_coap_code, tvb, offset, 1, ENC_BIG_ENDIAN);
	code = tvb_get_guint8(tvb, offset);
	offset += 1;

	proto_tree_add_item(coap_tree, hf_coap_tid, tvb, offset, 2, ENC_BIG_ENDIAN);
	tid = tvb_get_ntohs(tvb, offset);
	offset += 2;

	/* append the header information */
	proto_item_append_text(coap_tree, ", %s, %s, TID:%u", val_to_str(ttype, vals_ttype, "Unkown %d"), val_to_str(code, vals_code, "Unknown %d"), tid);

	/* initialize the external value */
	coap_block_number = DEFAULT_COAP_BLOCK_NUMBER;
	coap_block_mflag = 0;
	coap_uri_str[0] = '\0';
	coap_uri_query[0] = '\0';
	coap_token_str[0] = '\0';

	/* process options */
	offset = dissect_coap_options(tvb, pinfo, coap_tree, offset, coap_length, opt_count);
	if (offset == -1)
		return;

	/* add informations to the packet list */
	col_set_str(pinfo->cinfo, COL_PROTOCOL, "CoAP");
	col_clear(pinfo->cinfo, COL_INFO);
	col_add_fstr(pinfo->cinfo, COL_INFO, "%s", val_to_str(ttype, vals_ttype_short, "Unknown %d"));
	col_append_fstr(pinfo->cinfo, COL_INFO, ", TID:%u", tid);
	col_append_fstr(pinfo->cinfo, COL_INFO, ", %s", val_to_str(code, vals_code, "Unknown %d"));
	if (coap_token_str[0] != '\0')
		col_append_fstr(pinfo->cinfo, COL_INFO, ", TKN:%s", coap_token_str);
	if (coap_block_number != DEFAULT_COAP_BLOCK_NUMBER)
		col_append_fstr(pinfo->cinfo, COL_INFO, ", %sBlock #%d", coap_block_mflag ? "" : "End of ", coap_block_number);
	if (coap_uri_str[0] != '\0')
		col_append_fstr(pinfo->cinfo, COL_INFO, ", %s", coap_uri_str);
	if (coap_uri_query[0] != '\0')
		col_append_fstr(pinfo->cinfo, COL_INFO, "%s", coap_uri_query);

	/* dissect the payload */
	if (coap_length > offset) {
		proto_tree *payload_tree = NULL;
		proto_item *payload_item = NULL;
		tvbuff_t *payload_tvb;
		guint payload_length = coap_length - offset;
		char str_payload[80];

		/*
		 * 5.5.2.  Diagnostic Payload
		 *
		 * If no Content-Format option is given, the payload of responses
		 * indicating a client or server error is a brief human-readable
		 * diagnostic message, explaining the error situation. This diagnostic
		 * message MUST be encoded using UTF-8 [RFC3629], more specifically
		 * using Net-Unicode form [RFC5198].
		 */
		if (coap_ctype_value == DEFAULT_COAP_CTYPE_VALUE)
			coap_ctype_str = "text/plain; charset=utf-8";

		g_snprintf(str_payload, sizeof(str_payload), 
		    "Payload Content-Format: %s%s, Length: %u, offset: %u",
		    coap_ctype_str, coap_ctype_value == DEFAULT_COAP_CTYPE_VALUE ?
		    " (no Content-Format)" : "", payload_length, offset);
		proto_tree_add_string(coap_tree, hf_coap_payload_desc,
		    tvb, offset, -1, coap_ctype_str);
		payload_tree = proto_item_add_subtree(payload_item, ett_coap_payload);
		payload_tvb = tvb_new_subset(tvb, offset, payload_length, payload_length);

		dissector_try_string(media_type_dissector_table, coap_ctype_str, payload_tvb, pinfo, payload_tree);
	}
}

/*
 * Protocol initialization
 */
void
proto_register_coap(void)
{
	static hf_register_info hf[] = {
		{ &hf_coap_version,
                  { "Version", "coap.version",
                    FT_UINT8, BASE_DEC, NULL, 0xc0,
                    "CoAP Version", HFILL }
                },
		{ &hf_coap_ttype,
                  { "Type", "coap.type",
                    FT_UINT8, BASE_DEC, VALS(vals_ttype), 0x30,
                    "CoAP Transaction Type", HFILL }
                },
		{ &hf_coap_opt_count,
                  { "Opt Count", "coap.ocount",
                    FT_UINT8, BASE_DEC, NULL, 0x0f,
                    "CoAP Option Count", HFILL }
                },
		{ &hf_coap_code,
                  { "Code", "coap.code",
                    FT_UINT8, BASE_DEC, VALS(vals_code), 0x0,
                    "CoAP Method or Response Code", HFILL }
                },
		{ &hf_coap_tid,
                  { "Transaction ID", "coap.tid",
                    FT_UINT16, BASE_DEC, NULL, 0x0,
                    "CoAP Transaction ID", HFILL }
                },
		{ &hf_coap_payload_desc,
                  { "Payload Desc", "coap.opt.payload_desc",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Payload Description", HFILL }
                },
		{ &hf_coap_opt_name,
                  { "Opt Name", "coap.opt.name",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Name", HFILL }
                },
		{ &hf_coap_opt_desc,
                  { "Opt Desc", "coap.opt.desc",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Description", HFILL }
                },
		{ &hf_coap_opt_jump,
                  { "Opt Jump", "coap.opt.jump",
                    FT_UINT8, BASE_DEC, NULL, 0xf0,
                    "CoAP Option Jump", HFILL }
                },
		{ &hf_coap_opt_delta,
                  { "Opt Delta", "coap.opt.delta",
                    FT_UINT8, BASE_DEC, NULL, 0xf0,
                    "CoAP Option Delta", HFILL }
                },
		{ &hf_coap_opt_length,
                  { "Opt Length", "coap.opt.length",
                    FT_UINT16, BASE_DEC, NULL, 0x0,
                    "CoAP Option Length", HFILL }
                },
		{ &hf_coap_opt_ctype,
                  { "Content-type", "coap.opt.ctype",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Content Type", HFILL }
                },
		{ &hf_coap_opt_max_age,
                  { "Max-age", "coap.opt.max_age",
                    FT_UINT32, BASE_DEC, NULL, 0x0,
                    "CoAP Option Max-age", HFILL }
                },
		{ &hf_coap_opt_proxy_uri,
                  { "Proxy-Uri", "coap.opt.proxy_uri",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Proxy-Uri", HFILL }
                },
		{ &hf_coap_opt_etag,
                  { "Etag", "coap.opt.etag",
                    FT_BYTES, BASE_NONE, NULL, 0x0,
                    "CoAP Option Etag", HFILL }
                },
		{ &hf_coap_opt_uri_host,
                  { "Uri-Host", "coap.opt.uri_host",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Uri-Host", HFILL }
                },
		{ &hf_coap_opt_location_path,
                  { "Location-Path", "coap.opt.location_path",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Uri-Path", HFILL }
                },
		{ &hf_coap_opt_uri_port,
                  { "Uri-Port", "coap.opt.uri_port",
                    FT_UINT16, BASE_DEC, NULL, 0x0,
                    "CoAP Option Uri-Port", HFILL }
                },
		{ &hf_coap_opt_location_query,
                  { "Location-Query", "coap.opt.location_query",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Uri-Query", HFILL }
                },
		{ &hf_coap_opt_uri_path,
                  { "Uri-Path", "coap.opt.uri_path",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Uri-Path", HFILL }
                },
		{ &hf_coap_opt_observe,
                  { "Lifetime", "coap.opt.subscr_lifetime",
                    FT_INT32, BASE_DEC, NULL, 0x0,
                    "CoAP Option Observe", HFILL }
                },
		{ &hf_coap_opt_token,
                  { "Token", "coap.opt.token",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Token", HFILL }
                },
		{ &hf_coap_opt_accept,
                  { "Accept", "coap.opt.accept",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Acceptable Content Type", HFILL }
                },
		{ &hf_coap_opt_if_match,
                  { "If-Match", "coap.opt.if_match",
                    FT_BYTES, BASE_NONE, NULL, 0x0,
                    "CoAP Option If-Match", HFILL }
                },
		{ &hf_coap_opt_block_number,
                  { "Block Number", "coap.opt.block_number",
                    FT_UINT32, BASE_DEC, NULL, 0x0,
                    "CoAP Option Block Number", HFILL }
                },
		{ &hf_coap_opt_block_mflag,
                  { "More Flag", "coap.opt.block_mflag",
                    FT_UINT8, BASE_DEC, NULL, 0x08,
                    "CoAP Option Block More Size", HFILL }
                },
		{ &hf_coap_opt_block_size,
                  { "Encoded Block Size", "coap.opt.block_size",
                    FT_UINT8, BASE_DEC, NULL, 0x07,
                    "CoAP Option Encoded Block Size", HFILL }
                },
		{ &hf_coap_opt_uri_query,
                  { "Uri-Query", "coap.opt.uri_query",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "CoAP Option Uri-Query", HFILL }
                },
		{ &hf_coap_opt_unknown,
                  { "Unknown", "coap.opt.unknown",
                    FT_STRING, BASE_NONE, NULL, 0x0,
                    "Coap Unknown Option", HFILL }
                },
	};

	static gint *ett[] = {
		&ett_coap,
		&ett_coap_option,
		&ett_coap_payload,
	};

	module_t *coap_module;

	proto_coap = proto_register_protocol("Constrained Application Protocol", "CoAP", "coap");
	proto_register_field_array(proto_coap, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));

	register_dissector("coap", dissect_coap, proto_coap);

	/* Register our configuration options */
	coap_module = prefs_register_protocol (proto_coap, proto_reg_handoff_coap);

	prefs_register_uint_preference (coap_module, "udp_port",
					"CoAP port number",
					"Port number used for CoAP traffic",
					10, &global_coap_port_number);
}

void
proto_reg_handoff_coap(void)
{
	static gboolean coap_prefs_initialized = FALSE;
	static dissector_handle_t coap_handle;
	static guint coap_port_number;

	if (!coap_prefs_initialized) {
		coap_handle = find_dissector("coap");
		media_type_dissector_table = find_dissector_table("media_type");
		coap_prefs_initialized = TRUE;
	} else {
		dissector_delete_uint("udp.port", coap_port_number, coap_handle);
		dissector_delete_uint("tcp.port", coap_port_number, coap_handle);
	}

	coap_port_number = global_coap_port_number;
	dissector_add_uint("udp.port", coap_port_number, coap_handle);
	dissector_add_uint("tcp.port", coap_port_number, coap_handle);
}