ADDED: TCP Source file

Author: president-xd

src/parsers/tcp.cpp

@@ -0,0 +1,76 @@
+#include "parsers/tcp.h"
+
+#include <sstream>
+#include <iomanip>
+#include <stdexcept>
+#include <cstring>
+#include <arpa/inet.h>
+#include <iostream>
+
+namespace parsers {
+
+    TCPHeader parse_tcp_header(const uint8_t* buffer, std::size_t length) {
+        TCPHeader tcp{};
+
+        // Minimum TCP header size is 20 bytes (without options)
+        if (length < 20) {
+            std::cerr << "Buffer too short for TCP header\n";
+            return tcp;
+        }
+
+        // Parse fixed header fields
+        tcp.src_port = ntohs(*reinterpret_cast<const uint16_t*>(buffer));
+        tcp.dest_port = ntohs(*reinterpret_cast<const uint16_t*>(buffer + 2));
+        tcp.seq_num = ntohl(*reinterpret_cast<const uint32_t*>(buffer + 4));
+        tcp.ack_num = ntohl(*reinterpret_cast<const uint32_t*>(buffer + 8));
+
+        uint8_t data_offset_reserved_ns = buffer[12];
+        uint8_t flags_byte = buffer[13];
+
+        // Extract Data Offset (upper 4 bits) - number of 32-bit words
+        tcp.data_offset = (data_offset_reserved_ns >> 4) & 0x0F;  
+        // Calculate header length in bytes
+        size_t header_length_bytes = tcp.data_offset * 4;
+
+        // Extract Reserved (3 bits)
+        tcp.reserved = (data_offset_reserved_ns >> 1) & 0x07;
+
+        // Extract NS flag (least significant bit of byte 12)
+        tcp.ns_flag = (data_offset_reserved_ns & 0x01) != 0;
+
+        // Extract flags (byte 13)
+        tcp.cwr_flag = (flags_byte & 0x80) != 0;
+        tcp.ece_flag = (flags_byte & 0x40) != 0;
+        tcp.urg_flag = (flags_byte & 0x20) != 0;
+        tcp.ack_flag = (flags_byte & 0x10) != 0;
+        tcp.psh_flag = (flags_byte & 0x08) != 0;
+        tcp.rst_flag = (flags_byte & 0x04) != 0;
+        tcp.syn_flag = (flags_byte & 0x02) != 0;
+        tcp.fin_flag = (flags_byte & 0x01) != 0;
+
+        tcp.window_size = ntohs(*reinterpret_cast<const uint16_t*>(buffer + 14));
+        tcp.checksum = ntohs(*reinterpret_cast<const uint16_t*>(buffer + 16));
+        tcp.urgent_pointer = ntohs(*reinterpret_cast<const uint16_t*>(buffer + 18));
+
+        // Validate header length
+        if (length < header_length_bytes) {
+            std::cerr << "TCP header length field exceeds buffer length\n";
+            return tcp;
+        }
+
+        // Calculate options length (header length minus fixed 20 bytes)
+        tcp.options_length = static_cast<uint8_t>(header_length_bytes - 20);
+
+        // Copy options if present
+        if (tcp.options_length > 0) {
+            tcp.options.assign(buffer + 20, buffer + 20 + tcp.options_length);
+        }
+
+        // Set payload pointer and length
+        tcp.payload = buffer + header_length_bytes;
+        tcp.payload_length = static_cast<uint16_t>(length - header_length_bytes);
+
+        return tcp;
+    }
+
+} // namespace parsers