File content as of revision 6:66c4cd9073aa:

#ifndef IP_H
#define IP_H

#include "net.h"

/**
  \file ip.h
  \brief IP Packet header
  
  This file contains the memory map and associated functions for IP packet header
  creation and deconstruction. 
*/

#define ETHERTYPE_IPV4 0x0800
#define ETHERTYPE_IPV6 0x86DD

/// IP Address memory map
typedef struct {
  unsigned char octet[4]; ///< Individual address octets
} IP_Address;

/// IP Packet memory map
typedef struct {
  /// 4 bits that contain the version, that specifies if it's an IPv4 or IPv6 packet,
  unsigned version:4; // Only 0x4 supported
  /// 4 bits that contain the Internet Header Length which is the length of the header in multiples of 4 bytes (eg. 5 means 20 bytes).
  unsigned header_bytes_div4:4;
  /// 8 bits that contain the Type of Service, also referred to as Quality of Service (QoS), which describes what priority the packet should have,
  unsigned tos:8;
  /// 16 bits that contain the total length of the IP packet (datagram) in bytes,
  u16 packet_bytes;
  /// 16 bits that contain an identification tag to help reconstruct the packet from several fragments,
  u16 fragment_id;
  /// 3 bits that contain a zero, a flag that says whether the packet is allowed to be fragmented or not (DF: Don't fragment), and a flag to state whether more fragments of a packet follow (MF: More Fragments)
  unsigned unused_0:1;
  unsigned dont_fragment:1;
  unsigned more_follow:1;
  /// 13 bits that contain the fragment offset, a field to identify position of fragment within original packet
  unsigned fragment_offset:13; ///< This and the ones above may not work properly due to endianness
  /// 8 bits that contain the Time to live (TTL) which is the number of hops (router, computer or device along a network) the packet is allowed to pass before it dies (for example, a packet with a TTL of 16 will be allowed to go across 16 routers to get to its destination before it is discarded),
  unsigned ttl:8;
  /// 8 bits that contain the protocol (TCP, UDP, ICMP, etc...)
  ///   0x01 ICMP
  ///   0x06 TCP
  ///   0x11 UDP
  unsigned protocol:8;
  /// 16 bits that contain the Header Checksum, a number used in error detection,
  u16 header_checksum;
  /// 32 bits that contain the source IP address,
  IP_Address source;
  /// 32 bits that contain the destination address.
  IP_Address destination;
  /// Zero-length field for memory mapping the packet data
  unsigned char data[];
} IP_PacketHeader;

/// Convert from wire to host or host to wire endianness
inline void fix_endian_ip(IP_PacketHeader *packet)
{
  packet->version ^= packet->header_bytes_div4;
  packet->header_bytes_div4 ^= packet->version;
  packet->version ^= packet->header_bytes_div4;
  fix_endian_u16(&packet->packet_bytes);
  fix_endian_u16(&packet->fragment_id);
  // Don't fix checksums; they are done bitwise
}

/// Get a constant string of the given IP protocol (e.g. "ICMP", "TCP", "UDP") if known
inline const char *ipproto2name(u8 proto)
{
  switch (proto)
  {
    case 0x01: return "ICMP";
    case 0x02: return "IGMP";
    case 0x06: return "TCP";
    case 0x11: return "UDP";
  }
  return "<UNKNOWN>";
}

/// Print the IP packet
inline void print_ip(IP_PacketHeader *packet)
{
  main_log.printf("IPv%d Packet:", packet->version);
  if (packet->version != 4)
  {
    main_log.printf("Not an IPv4 packet (skipping)");
    return;
  }
    
  u8 *dst = packet->destination.octet;
  u8 *src = packet->source.octet;
  main_log.printf("  Source:    IP - %03d.%03d.%03d.%03d", src[0], src[1], src[2], src[3]);
  main_log.printf("  Dest:      IP - %03d.%03d.%03d.%03d", dst[0], dst[1], dst[2], dst[3]);
  main_log.printf("  TTL:       %d", packet->ttl);
  main_log.printf("  Protocol:  0x%02X (%s)", packet->protocol, ipproto2name(packet->protocol));
  main_log.printf("  ToS:       0x%02X", packet->tos);
  main_log.printf("  Header:    %d bytes", packet->header_bytes_div4*4);
  main_log.printf("  Packet:    %d bytes", packet->packet_bytes);
  main_log.printf("  Fragment:  0x%04X DF=%d MF=%d OFFSET=0x04X", packet->fragment_id, packet->dont_fragment, packet->more_follow, packet->fragment_offset);
  main_log.printf("  Checksum:  0x%04X", packet->header_checksum);
}

/// Parse the string (in decimal triple-dot notation) into the IP address structure
inline void str2ipaddr(const char *ip, IP_Address *addr)
{
  static short a,b,c,d;
  sscanf(ip, "%3hd.%3hd.%3hd.%3hd", &a, &b, &c, &d);
  addr->octet[0] = a;
  addr->octet[1] = b;
  addr->octet[2] = c;
  addr->octet[3] = d;
}

#endif