1 files changed, 56 insertions, 0 deletions
diff --git a/include/wireframe/net/ipv4.hpp b/include/wireframe/net/ipv4.hpp
new file mode 100644
index 0000000..f53b4f2
--- /dev/null
+++ b/include/wireframe/net/ipv4.hpp
@@ -0,0 +1,56 @@
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <cstdint>
+#include <optional>
+#include <span>
+
+#include "wireframe/byteio.hpp"
+
+namespace wireframe::net {
+
+inline constexpr std::uint8_t kProtoIcmp = 1;
+inline constexpr std::uint8_t kProtoTcp = 6;
+inline constexpr std::uint8_t kProtoUdp = 17;
+
+struct Ipv4Address {
+    std::array<unsigned char, 4> bytes;
+};
+
+struct Ipv4Header {
+    std::uint8_t version;
+    std::uint8_t ihl;  // header length in 32-bit words
+    std::uint16_t total_length;
+    std::uint8_t ttl;
+    std::uint8_t protocol;
+    Ipv4Address src;
+    Ipv4Address dst;
+};
+
+struct Ipv4Packet {
+    Ipv4Header header;
+    std::span<const unsigned char> payload;
+};
+
+inline std::optional<Ipv4Packet> parse_ipv4(std::span<const unsigned char> bytes) {
+    if (bytes.size() < 20) return std::nullopt;
+
+    std::uint8_t version = static_cast<std::uint8_t>(bytes[0] >> 4);
+    std::uint8_t ihl = bytes[0] & 0x0F;
+    std::size_t header_len = static_cast<std::size_t>(ihl) * 4;
+    if (version != 4 || header_len < 20 || bytes.size() < header_len) return std::nullopt;
+
+    Ipv4Header header{};
+    header.version = version;
+    header.ihl = ihl;
+    header.total_length = read_be16(bytes, 2);
+    header.ttl = bytes[8];
+    header.protocol = bytes[9];
+    std::copy_n(bytes.begin() + 12, 4, header.src.bytes.begin());
+    std::copy_n(bytes.begin() + 16, 4, header.dst.bytes.begin());
+
+    return Ipv4Packet{header, bytes.subspan(header_len)};
+}
+
+}  // namespace wireframe::net