populate.h

#include <netinet/if_ether.h>
#include <netinet/in.h>
#include <pcap.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>


#define SIZE_MAC_ADDRESS 6
#define SIZE_IPV4_ADDRESS 4
#define SIZE_ETHERNET_HEADER 14
#define SIZE_UDP_HEADER 8
#define SIZE_TLS_HEADER 5

#define IPV4_ADDR_LEN_STR 16

#define ARP_PROTOCOL 2054
#define IPV4_PROTOCOL 2048
#define IPV6_PROTOCOL 34525
#define UDP_PROTOCOL 17
#define TCP_PROTOCOL 6

#define HTTP_PORT 80
#define HTTPS_PORT 443
#define FTP_DATA_TRANSFER 20
#define FTP_CONTROL 21

#define IP_RF 0x8000          /* reserved fragment flag */
#define IP_DF 0x4000          /* don't fragment flag */
#define IP_MF 0x2000          /* more fragments flag */
#define IP_OFFSET_MASK 0x1fff /* mask for fragmenting bits */

// NOTE: the endianness should be converted after using IP_OFFSET_VALUE
#define IP_OFFSET_VALUE(ip) (((ip)->ip_offset_and_flags) & (IP_OFFSET_MASK))
#define IP_FLAG_VALUE(ip, mask) ((((ip)->ip_offset_and_flags) & (mask)) ? 1 : 0)

#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
#define TH_PUSH 0x08
#define TH_ACK 0x10
#define TH_URG 0x20
#define TH_ECE 0x40
#define TH_CWR 0x80

#define TCP_OFFSET_VALUE(tcp) ((((tcp)->th_offset_flag_ns) & 0xf0) >> 4)
#define TCP_FLAG_NS_VALUE(tcp) (((tcp)->th_offset_flag_ns) & 0x01)
#define TCP_FLAG_VALUE(tcp, mask) ((((tcp)->th_flags) & (mask)) ? 1 : 0)


enum http_request_method {
    Http_Connect,
    Http_Delete,
    Http_Get,
    Http_Head,
    Http_Options,
    Http_Patch,
    Http_Post,
    Http_Put,
    Http_Trace,
} typedef HttpRequestMethod;


struct ethernet_frame {
    u_char mac_destination[ETHER_ADDR_LEN];
    u_char mac_source[ETHER_ADDR_LEN];
    u_short ether_protocol_type;
} typedef EthernetFrame;
///////////////////////////////////////////////////////////////////////////////
// NOTE: the order of the fields might seem weird, it's because of how the   //
//       compiler places the fields                                          //
//         0       1       2       3                                         //
//         01234567012345670123456701234567                                  //
// ip:     |ver|len|...                                                      //
// struct: |len|ver|...                                                      //
///////////////////////////////////////////////////////////////////////////////
struct ipv4_datagram {
    u_char ip_header_length : 4;
    u_char ip_version : 4;
    u_char ip_type_of_service;
    u_short ip_total_length;
    u_short ip_identification;
    u_short ip_offset_and_flags;
    u_char ip_time_to_live;
    u_char ip_protocol;
    u_short ip_checksum;
    u_int ip_source;
    u_int ip_destination;
} typedef Ipv4Datagram;
struct tcp_segment {
    u_short th_source_port;
    u_short th_destination_port;
    u_int th_sequence_num;
    u_int th_acknowledgement_num;
    u_char th_offset_flag_ns;
    u_char th_flags;
    u_short th_window;
    u_short th_checksum;
    u_short th_urgent_pointer;
} typedef TcpSegment;
struct udp_segment {
    u_short port_source;
    u_short port_destination;
    u_short length;
    u_short checksum;
} typedef UdpSegment;
struct http_data {
    bool is_response;
    HttpRequestMethod request_method;  // only for requests
    size_t status_code;                // only for responses
    size_t content_length;
    void *header;
    void *data;
} typedef HttpData;
struct tls_data {
    u_char content_type;
    u_short version;
    u_short length;
    void *header;
    void *data;
} __attribute__((packed)) typedef TlsData;


enum populate_protocol {
    // NOTE: "PP" stands for "Populate Protocol"
    PP_None,
    PP_Ethernet,
    PP_Ipv4,
    PP_Ipv6,
    PP_Arp,
    PP_Tcp,
    PP_Udp,
    PP_Http,
    PP_Tls,
    PP_Ftp,
} typedef PopulateProtocol;

struct packet {
    PopulateProtocol data_link_protocol;
    PopulateProtocol network_protocol;
    PopulateProtocol transport_protocol;
    PopulateProtocol application_protocol;

    void *data_link_header;
    void *network_header;
    void *transport_header;
    void *application_header;
    // NOTE: the application layer's header is the only one that need to be
    // allocated, it's because it doesn't have a fixed size.

    struct pcap_pkthdr *packet_header;
} typedef Packet;


void populate_packet(void *body, Packet *packet);
void print_packet_headers(Packet *packet);
void print_packet_data(Packet *packet);