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#pragma once
#include <cstdint>
#include <optional>
#include <span>
#include "wireframe/byteio.hpp"
namespace wireframe::net {
// Lower 6 bits of the flags byte: URG ACK PSH RST SYN FIN. CWR/ECE (the
// top 2 bits) are masked off - not needed for now.
inline constexpr std::uint8_t kTcpFin = 0x01;
inline constexpr std::uint8_t kTcpSyn = 0x02;
inline constexpr std::uint8_t kTcpRst = 0x04;
inline constexpr std::uint8_t kTcpPsh = 0x08;
inline constexpr std::uint8_t kTcpAck = 0x10;
inline constexpr std::uint8_t kTcpUrg = 0x20;
struct TcpHeader {
std::uint16_t src_port;
std::uint16_t dst_port;
std::uint32_t seq;
std::uint32_t ack;
std::uint8_t data_offset; // header length in 32-bit words
std::uint8_t flags;
std::uint16_t window;
};
struct TcpSegment {
TcpHeader header;
std::span<const unsigned char> payload;
};
inline std::optional<TcpSegment> parse_tcp(std::span<const unsigned char> bytes) {
if (bytes.size() < 20) return std::nullopt;
std::uint8_t data_offset = static_cast<std::uint8_t>(bytes[12] >> 4);
std::size_t header_len = static_cast<std::size_t>(data_offset) * 4;
if (header_len < 20 || bytes.size() < header_len) return std::nullopt;
TcpHeader header{};
header.src_port = read_be16(bytes, 0);
header.dst_port = read_be16(bytes, 2);
header.seq = read_be32(bytes, 4);
header.ack = read_be32(bytes, 8);
header.data_offset = data_offset;
header.flags = bytes[13] & 0x3F;
header.window = read_be16(bytes, 14);
return TcpSegment{header, bytes.subspan(header_len)};
}
} // namespace wireframe::net
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