ISA/ftprot.h at main · MarekPazur/ISA · GitHub

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/*
 * File: ftprot.h
 * Date: 14.10.2025
 * Author: Marek Pazúr
 * Login: xpazurm00
 */

#pragma once

#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>

#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/icmp6.h>

/* Encryption key string */
#define KEY "xpazurm00"

/* Initialisation vector size */
#define IV_SIZE 16

/* Encryption key size, 32B = 256bit */
#define KEY_SIZE 32

/* Fragment/Packet window circular buffer capacity, 22.4KB - 24KB */
#define WINDOW_SIZE 16

/* Macros for getting protocol header sizes statically */
#define IPV4_SIZE sizeof(struct ip)
#define IPV6_SIZE 0  // Considered 0, since kernel doesn't include it in recv/recvfrom
#define ICMP_SIZE sizeof(struct icmphdr)
#define ICMPV6_SIZE sizeof(struct icmp6_hdr)

/* Inline functions for getting protocol header sizes dynamically */
static inline int ipvh_size(int v) { return (v == AF_INET) ? IPV4_SIZE : IPV6_SIZE; }
static inline int icmph_size(int v) { return (v == AF_INET) ? ICMP_SIZE : ICMPV6_SIZE; }

/* Secret protocol diagram
 *
 * |             |               |             |         |
 * | IPv* header | ICMPv* header | SFTP header | Payload |
 * |             |               |             |         |
 *   20/40 bytes     8 bytes        8 bytes      ~1.4 kb
*/

/* Packet type */
enum type {
	META,        // Metadata packet (necessary file info)
	FILE_CHUNK,  // Data packet
	ACK,         // Acknowledgement
	ERROR,       // Error message
	FIN          // Communication finalization
};

/* Secret file transfer header, 8 bytes*/
struct sftp_hdr {
	uint16_t type;  // SFTP packet type
	uint16_t seq;   // Packet ID - sequence number
	uint16_t s_id;  // Session id - client server communication
	uint16_t size;  // Data size
};

#define SFTP_SIZE sizeof(struct sftp_hdr)

/**** Protocol functions ****/

/* Checksum */
uint16_t calculate_checksum(void *addr, size_t size);

/* Add icmp header */
void add_icmph(uint8_t *packet, const int ip_v, bool request);

/* Add sftp header */
void add_sftp_hdr(uint8_t *packet, const uint16_t type, const  uint16_t seq, const uint16_t size, const uint16_t s_id);

/* Helper functions */
void set_session_id(uint8_t *packet, uint16_t s_id);

uint16_t get_seq(uint8_t *packet);

uint16_t get_type(uint8_t *packet);

uint16_t get_size(uint8_t *packet);

/* Create state message to server  */
size_t msg_pkt(uint8_t *packet, int ip_v, int type, uint16_t seq, uint16_t s_id);