feat: yeah lots of things

gitignore

@@ -0,0 +1 @@
+./npcap

nethdr.h

@@ -0,0 +1,18 @@
+#ifndef NETHDR_H
+#define NETHDR_H
+#include <stdint.h> 
+
+struct arphdr_c {
+    uint16_t htype;
+    uint16_t ptype;
+    uint8_t hlen;
+    uint8_t plen;
+    uint16_t opcode;
+    uint8_t sender_mac[6];
+    uint8_t sender_ip[4];
+    uint8_t target_mac[6];
+    uint8_t target_ip[4];
+} __attribute__((packed));
+
+
+#endif

npcap.c

@@ -0,0 +1,124 @@
+//
+// Created by ako on 8/22/25.
+//
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <netinet/ip.h>
+#include <netinet/if_ether.h>
+#include <netpacket/packet.h>
+#include <net/ethernet.h>
+#include <errno.h>
+#include "nethdr.h"
+#include "npcap_handle.h"
+#include <netpacket/packet.h>
+#include <net/if.h> // if_nametoindex()
+
+void cleanup(int socket, unsigned char* buffer) {
+    close(socket);
+    free(buffer);
+}
+
+int main()
+{
+    if (geteuid() != 0)
+    {
+        printf("Please run me as root.\n");
+        return 1;
+    }
+
+    int sock_raw = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
+    if (sock_raw < 0)
+    {
+        fprintf(stderr, "Unable to connect to network socket.\n");
+        return -1;
+    }
+
+    unsigned char *buffer = (unsigned char *) calloc(65536, sizeof(unsigned char));
+
+    if (buffer == NULL) {
+        fprintf(stderr, "Unable to connect to allocate memory.\n");
+        cleanup(sock_raw, buffer);
+        return 1;
+    }
+
+    struct sockaddr_ll sourceaddr;
+    socklen_t sourceaddr_len = sizeof(sourceaddr);
+
+    int loopback_ifindex = if_nametoindex("lo");
+    if (loopback_ifindex == 0) {
+        perror("if_nametoindex for lo");
+        cleanup(sock_raw, buffer);
+        return 1;
+    }
+
+    while (1) {
+        ssize_t buflen = recvfrom(sock_raw, buffer, 65536, 0, (struct sockaddr *)&sourceaddr, &sourceaddr_len);
+
+        if (buflen == -1) {
+            perror("Couldn't read from socket");
+            cleanup(sock_raw, buffer);
+            return 1;
+        }
+
+        if (sourceaddr.sll_ifindex == loopback_ifindex) {
+            continue;
+        }
+        printf("\n===== Paquet reçu =====\n");
+        printf("Paquet de %ld octets\n", buflen);
+
+        // Debug
+        printf("Hexdump des 32 premiers octets:\n");
+        for (int i = 0; i < 32 && i < buflen; i++) {
+            printf("%02x ", buffer[i]);
+            if ((i + 1) % 8 == 0) printf("  ");
+        }
+        printf("\n");
+
+        //
+        // COUCHE 2
+        //
+        // Décodage entête Ethernet
+        struct ethhdr *eth = (struct ethhdr *)buffer;
+        handle_eth(eth);
+
+
+        //
+        // COUCHE 3
+        //
+        switch (ntohs(eth->h_proto)) 
+        {
+            // Décodage entête ARP
+            case ETH_P_ARP:
+                struct arphdr_c *arp = (struct arphdr_c *) (buffer + sizeof(struct ethhdr));
+                handle_arp(arp);
+                break;
+
+            case ETH_P_IP:
+                struct iphdr *ip = (struct iphdr *) (buffer + sizeof(struct ethhdr));
+                handle_ip(ip);
+
+                switch (ip->protocol) {
+                    case 0x01:
+                        handle_icmp();
+                        break;
+                    case 0x06:
+                        handle_tcp();
+                        break;
+                    case 0x11:
+                        handle_udp();
+                        break;
+                    default:
+                        break;
+                }
+                
+                break;
+        }
+
+        // printf("\n=======================\n");
+    }
+    cleanup(sock_raw, buffer);
+}

npcap_handle.c

@@ -0,0 +1,69 @@
+#include "npcap_handle.h"
+
+int handle_eth(struct ethhdr* eth) {
+    printf("\nEthernet:\n");
+    printf("\tSource        : %02x:%02x:%02x:%02x:%02x:%02x\n",
+           eth->h_source[0], eth->h_source[1], eth->h_source[2],
+           eth->h_source[3], eth->h_source[4], eth->h_source[5]);
+    printf("\tDestination   : %02x:%02x:%02x:%02x:%02x:%02x\n",
+           eth->h_dest[0], eth->h_dest[1], eth->h_dest[2],
+           eth->h_dest[3], eth->h_dest[4], eth->h_dest[5]);
+    printf("\tProtocole     : 0x%04x\n", ntohs(eth->h_proto));
+    return 0;
+}
+
+int handle_arp(struct arphdr_c* arp) {
+    printf("\n\tARP:\n");
+    printf("\t\tCode d'opération ARP   : %d\n", arp->opcode);
+    printf("\t\tMAC Source             : %02x:%02x:%02x:%02x:%02x:%02x\n",
+        arp->sender_mac[0], arp->sender_mac[1], arp->sender_mac[2],
+        arp->sender_mac[3], arp->sender_mac[4], arp->sender_mac[5]);
+    printf("\t\tIP Source              : %d.%d.%d.%d\n",
+        arp->sender_ip[0], arp->sender_ip[1], arp->sender_ip[2], arp->sender_ip[3]);
+    printf("\t\tMAC Destination        : %02x:%02x:%02x:%02x:%02x:%02x\n",
+        arp->target_mac[0], arp->target_mac[1], arp->target_mac[2],
+        arp->target_mac[3], arp->target_mac[4], arp->target_mac[5]);
+    printf("\t\tIP Destination         : %d.%d.%d.%d\n",
+        arp->target_ip[0], arp->target_ip[1], arp->target_ip[2], arp->target_ip[3]);
+    return 0;
+
+}
+
+int handle_ip(struct iphdr* ip) {
+
+    char srcip[INET_ADDRSTRLEN];
+    char dstip[INET_ADDRSTRLEN];
+    inet_ntop(AF_INET, &ip->saddr, srcip, INET_ADDRSTRLEN);
+    inet_ntop(AF_INET, &ip->daddr, dstip, INET_ADDRSTRLEN);
+    char* protostr;
+    switch (ip->protocol) {
+        case 0x01:
+            protostr = "ICMP";
+            break;
+        case 0x06:
+            protostr = "TCP";
+            break;
+        case 0x11:
+            protostr = "UDP";
+            break;
+        default:
+            protostr = "Unexpected";
+            break;
+    }
+
+    printf("\n\tIPv4:\n");
+    printf("\t\tVersion    : %d\n", ip->version);
+    printf("\t\tIHL        : %d\n", ip->ihl);
+    printf("\t\tToS        : %d\n", ip->tos);
+    printf("\t\tLongueur   : %d\n", ip->tot_len);
+    printf("\t\tID         : %d\n", ip->id);
+    // printf("\t\tFlags      : %d%d%d\n");
+    // printf("\t\tFragment offset:");
+    printf("\t\tTTL        : %d\n", ip->ttl);
+    printf("\t\tProtocole  : 0x%02x (%s)\n", ip->protocol, protostr);
+    printf("\t\tHeader cksm: %d\n", ip->check);
+    printf("\t\tIP Source  : %s\n", srcip);
+    printf("\t\tIP Dest.   : %s\n", dstip);
+    return 0;
+
+}

npcap_handle.h

@@ -0,0 +1,13 @@
+#ifndef NPCAP_HANDLE_H
+#define NPCAP_HANDLE_H
+#include <linux/if_ether.h>
+#include "nethdr.h"
+#include <stdio.h>
+#include <arpa/inet.h>
+#include <netinet/ip.h>
+
+int handle_eth(struct ethhdr* eth);
+int handle_arp(struct arphdr_c* arp);
+int handle_ip(struct iphdr* ip);
+
+#endif