icmp.h


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#pragma once

#include <stdint.h>


#define IP_HEADER_SIZE 40

#define MIN_MTU 576
#define MAX_IP_PACKET_SIZE 65535
#define MAX_DATAGRAM_SIZE (MAX_IP_PACKET_SIZE - IP_HEADER_SIZE)

#define ICMP_PAYLOAD_OFFSET 8

struct __attribute__((packed)) icmp_echo {
	uint8_t type;
	uint8_t code;
	uint16_t checksum;
	uint16_t id;
	uint16_t seqnum;
	uint8_t payload[MAX_DATAGRAM_SIZE - ICMP_PAYLOAD_OFFSET];
};

#define ICMP_MAX_PAYLOAD_LENGTH (MAX_DATAGRAM_SIZE - ICMP_PAYLOAD_OFFSET)
#define ICMP_SAFE_PAYLOAD_LENGTH (MIN_MTU - IP_HEADER_SIZE - ICMP_PAYLOAD_OFFSET)


struct icmp_incoming {
	const uint8_t *data;  // points to internal buffer
	size_t length;  // length of 'data'

	int id, seqnum;
	uint32_t source_addr;
};