#pragma once

#pragma pack(1)

// Ethernet Header

#define ETH_ALEN        6      /* Octets in one ethernet addr  */

#define ETH_P_IP        0x0800 /* Internet Protocol packet     */
#define ETH_P_ARP       0x0806 /* Address Resolution packet    */

typedef struct _ethhdr {
  UCHAR  h_dest[ETH_ALEN];     /* destination eth addr         */
  UCHAR  h_source[ETH_ALEN];   /* source ether addr            */
  USHORT h_proto;              /* packet type ID field         */
} EthHdr;


// ARP Header

#define ARPOP_REQUEST   1      /* ARP request                  */
#define ARPOP_REPLY     2      /* ARP reply                    */

typedef struct _arphdr {
  USHORT  ar_hrd;              /* format of hardware address   */
  USHORT  ar_pro;              /* format of protocol address   */
  UCHAR   ar_hln;              /* length of hardware address   */
  UCHAR   ar_pln;              /* length of protocol address   */
  USHORT  ar_op;               /* ARP opcode (command)         */
  UCHAR   ar_sha[ETH_ALEN];    /* sender hardware address      */
  ULONG   ar_sip;              /* sender IP address            */
  UCHAR   ar_tha[ETH_ALEN];    /* target hardware address      */
  ULONG   ar_tip;              /* target IP address            */
} ArpHdr;


// IP Header

#define IPPROTO_ICMP 1   /* Internet Control Message Protocol. */
#define IPPROTO_TCP  6   /* Transmission Control Protocol.     */
#define IPPROTO_UDP 17   /* User Datagram Protocol.            */

typedef struct _iphdr {
  UCHAR ihl:4;
  UCHAR version:4;
  UCHAR tos;
  USHORT tot_len;
  USHORT id;
  USHORT frag_off;
  UCHAR ttl;
  UCHAR protocol;
  USHORT check;
  ULONG saddr;
  ULONG daddr;
} IpHdr;


// ICMP Header

#define ICMP_ECHOREPLY     0    /* Echo Reply         */
#define ICMP_ECHO          8    /* Echo Request       */

typedef struct _icmphdr {
  UCHAR  type;                  /* message type       */
  UCHAR  code;                  /* type sub-code      */
  USHORT checksum;
  union {
    struct {
      USHORT id;
      USHORT sequence;
    } echo;                     /* echo datagram      */
    
    ULONG gateway;              /* gateway address    */
    struct {
      USHORT __unused;
      USHORT mtu;
    } frag;                     /* path mtu discovery */
  } un;
} IcmpHdr;