ipv4.h

Go to the documentation of this file.

/*
 * Copyright 2015 Didier Barvaux
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

/**
 * @file   ipv4.h
 * @brief  The IPv4 header
 * @author Didier Barvaux <didier@barvaux.org>
 */

#ifndef ROHC_PROTOCOLS_IPV4_H
#define ROHC_PROTOCOLS_IPV4_H

#include "rohc_utils.h"

#include <stdint.h>

#ifdef __KERNEL__
#  include <endian.h>
#else
#  include "config.h" /* for WORDS_BIGENDIAN */
#endif


/** The format to print an IPv4 address */
#define IPV4_ADDR_FORMAT \
        "%02x%02x%02x%02x (%u.%u.%u.%u)"


/** The data to print an IPv4 address in raw format */
#define IPV4_ADDR_RAW(x) \
        (x)[0], (x)[1], (x)[2], (x)[3], \
        (x)[0], (x)[1], (x)[2], (x)[3]


/**
 * @brief The IPv4 header
 */
struct ipv4_hdr
{
#if WORDS_BIGENDIAN == 1
        uint8_t version:4;          /**< The IP version */
        uint8_t ihl:4;              /**< The IP Header Length (IHL) in 32-bit words */
#else
        uint8_t ihl:4;
        uint8_t version:4;
#endif

        /* service may be read as TOS or DSCP + ECN */
        union
        {
                uint8_t tos;             /**< The Type Of Service (TOS) */
                uint8_t dscp_ecn;        /**< The combined DSCP and ECN fields */
                struct
                {
#if WORDS_BIGENDIAN == 1
                        uint8_t dscp:6;       /**< The Differentiated Services Code Point (DSCP) */
                        uint8_t ecn:2;        /**< The Explicit Congestion Notification (ECN) */
#else
                        uint8_t ecn:2;
                        uint8_t dscp:6;
#endif
                } __attribute__((packed));
        } __attribute__((packed));

        uint16_t tot_len;           /**< The Total Length (header + payload) */
        uint16_t id;                /**< The IDentification of the packet */

        /* IP flags and Fragment Offset may be read in 2 ways */
        union
        {
                uint16_t frag_off;       /**< The IP flags + Fragment Offset in 64-bit words */
#define IPV4_RF      0x8000    /**< Mask for reserved flag */
#define IPV4_DF      0x4000    /**< Mask for Don't Fragment (DF) flag */
#define IPV4_MF      0x2000    /**< Mask for More Fragments (MF) flag */
#define IPV4_OFFMASK 0x1fff    /**< mask for Fragment Offset field */
                struct
                {
#if WORDS_BIGENDIAN == 1
                        uint8_t reserved:1;   /**< A reserved flag */
                        uint8_t df:1;         /**< The Don't Fragment (DF) flag */
                        uint8_t mf:1;         /**< The More Fragments (MF) flag */
                        uint8_t frag_off1:5;  /**< The Fragment Offset in 64-bit words (part 1) */
#else
                        uint8_t frag_off1:5;
                        uint8_t mf:1;
                        uint8_t df:1;
                        uint8_t reserved:1;
#endif
                        uint8_t frag_off2;    /**< The Fragment Offset in 64-bit words (part 2) */
                } __attribute__((packed));
        } __attribute__((packed));

        uint8_t ttl;                /**< The Time To Live (TTL) */
        uint8_t protocol;           /**< The Protocol of the next header */
        uint16_t check;             /**< The checksum over the IP header */
        uint32_t saddr;             /**< The source IP address */
        uint32_t daddr;             /**< The destination IP address */

        uint8_t options[0];         /**< The IP options start here */

} __attribute__((packed));


/* compiler sanity check for C11-compliant compilers and GCC >= 4.6 */
#if ((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || \
     (defined(__GNUC__) && defined(__GNUC_MINOR__) && \
      (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))))
_Static_assert(sizeof(struct ipv4_hdr) == 20,
               "IPv4 header should exactly 20-byte long");
#endif


static inline bool ipv4_is_fragment(const struct ipv4_hdr *const ipv4_hdr)
        __attribute__((warn_unused_result, nonnull(1), pure));

/**
 * @brief Whether the IPv4 packet is fragmented or not
 *
 * The IPv4 packet shall be at least sizeof(struct ipv4_hdr) long.
 *
 * @param ipv4  The IPv4 packet to check
 * @return      true if the IPv4 packet is a fragment,
 *              false if the IPv4 packet is not a fragment
 */
static inline bool ipv4_is_fragment(const struct ipv4_hdr *const ipv4)
{
        return !!((rohc_ntoh16(ipv4->frag_off) & (~IPV4_DF)) != 0);
}


#endif