feat: added simple reading of packets from file and printing the payloads. TODO: utilize TCP sequence number to make sure the stream is read in order and parse the packets without reassemblying the entire stream (which might be enormous), but keeping in mind that entire fight result might be accross multiple segments

2 files changed, 49 insertions, 0 deletions

diff --git a/analyzer/utils/pcap.c b/analyzer/utils/pcap.c
new file mode 100644
index 0000000..cdefba7
--- /dev/null
+++ b/analyzer/utils/pcap.c
@@ -0,0 +1,36 @@
+#include "pcap.h"
+
+#include <netinet/if_ether.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+
+const unsigned char *get_payload_from_packet(const unsigned char *packet, const struct pcap_pkthdr *packet_data, int *payload_len) {
+    // get Ethernet header
+    const struct ether_header *eth_header = (const struct ether_header *)packet;
+    int eth_header_len = sizeof(struct ether_header);
+
+    // check if it's IP
+    if (ntohs(eth_header->ether_type) != ETHERTYPE_IP) {
+        *payload_len = -1;
+        return NULL;
+    }
+
+    // get IP header
+    const struct ip *ip_header = (const struct ip *)(packet + eth_header_len);
+    int ip_header_len = ip_header->ip_hl * 4;
+
+    // check if it's TCP
+    if (ip_header->ip_p != IPPROTO_TCP) {
+        *payload_len = -1;
+        return NULL;
+    }
+
+    // get TCP header
+    const struct tcphdr *tcp_header = (const struct tcphdr *)(packet + eth_header_len + ip_header_len);
+    int tcp_header_len = tcp_header->th_off * 4;
+
+    // get payload
+    int total_header_len = eth_header_len + ip_header_len + tcp_header_len;
+    *payload_len = packet_data->caplen - total_header_len;
+    return packet + total_header_len;
+}
diff --git a/analyzer/utils/pcap.h b/analyzer/utils/pcap.h
new file mode 100644
index 0000000..d31b961
--- /dev/null
+++ b/analyzer/utils/pcap.h
@@ -0,0 +1,13 @@
+// utils/pcap.h
+// helper functions for usage of libpcap
+
+#include <pcap.h>
+
+// get payload from a TCP/IP packet
+// params:
+//      - packet - captured packet
+//      - packet_data - metadata about packet
+//      - payload_len - pointer to save the payload length to or -1 if not a correct packet
+// returns:
+//      pointer to the payload or NULL if not a correct packet
+extern const unsigned char *get_payload_from_packet(const unsigned char *packet, const struct pcap_pkthdr *packet_data, int *payload_len);