serenity/Kernel/Net/IP/IPv4.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <[email protected]>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Assertions.h>
#include <AK/Endian.h>
#include <AK/IPv4Address.h>
#include <AK/Types.h>

namespace Kernel {

enum class IPv4PacketFlags : u16 {
    DontFragment = 0x4000,
    MoreFragments = 0x2000,
};

NetworkOrdered<u16> internet_checksum(void const*, size_t);

class [[gnu::packed]] IPv4Packet {
public:
    u8 version() const { return (m_version_and_ihl >> 4) & 0xf; }
    void set_version(u8 version) { m_version_and_ihl = (m_version_and_ihl & 0x0f) | (version << 4); }

    u8 dscp_and_ecn() const { return m_dscp_and_ecn; }
    void set_dscp_and_ecn(u8 dscp_and_ecn) { m_dscp_and_ecn = dscp_and_ecn; }

    u8 internet_header_length() const { return m_version_and_ihl & 0xf; }
    void set_internet_header_length(u8 ihl) { m_version_and_ihl = (m_version_and_ihl & 0xf0) | (ihl & 0x0f); }

    u16 length() const { return m_length; }
    void set_length(u16 length) { m_length = length; }

    u16 ident() const { return m_ident; }
    void set_ident(u16 ident) { m_ident = ident; }

    u8 ttl() const { return m_ttl; }
    void set_ttl(u8 ttl) { m_ttl = ttl; }

    u8 protocol() const { return m_protocol; }
    void set_protocol(u8 protocol) { m_protocol = protocol; }

    u16 checksum() const { return m_checksum; }
    void set_checksum(u16 checksum) { m_checksum = checksum; }

    IPv4Address const& source() const { return m_source; }
    void set_source(IPv4Address const& address) { m_source = address; }

    IPv4Address const& destination() const { return m_destination; }
    void set_destination(IPv4Address const& address) { m_destination = address; }

    void* payload() { return this + 1; }
    void const* payload() const { return this + 1; }

    u16 flags_and_fragment() const { return m_flags_and_fragment; }
    u16 fragment_offset() const { return ((u16)m_flags_and_fragment & 0x1fff); }
    u16 flags() const { return (((u16)m_flags_and_fragment) & (((u16)IPv4PacketFlags::MoreFragments) | ((u16)IPv4PacketFlags::DontFragment))); }

    void set_has_more_fragments(bool more_fragments)
    {
        if (more_fragments)
            m_flags_and_fragment = (u16)m_flags_and_fragment | ((u16)IPv4PacketFlags::MoreFragments);
        else
            m_flags_and_fragment = (u16)m_flags_and_fragment & ((u16)IPv4PacketFlags::MoreFragments);
    }
    void set_fragment_offset(u16 offset)
    {
        m_flags_and_fragment = flags() | (offset & 0x1fff);
    }

    bool is_a_fragment() const
    {
        // either has More-Fragments set, or has a fragment offset
        return (((u16)m_flags_and_fragment) & ((u16)IPv4PacketFlags::MoreFragments)) || ((u16)m_flags_and_fragment & 0x1fff);
    }

    u16 payload_size() const { return m_length - sizeof(IPv4Packet); }

    NetworkOrdered<u16> compute_checksum() const
    {
        VERIFY(!m_checksum);
        return internet_checksum(this, sizeof(IPv4Packet));
    }

private:
    u8 m_version_and_ihl { 0 };
    u8 m_dscp_and_ecn { 0 };
    NetworkOrdered<u16> m_length;
    NetworkOrdered<u16> m_ident;
    NetworkOrdered<u16> m_flags_and_fragment;
    u8 m_ttl { 0 };
    NetworkOrdered<u8> m_protocol;
    NetworkOrdered<u16> m_checksum;
    IPv4Address m_source;
    IPv4Address m_destination;
};

static_assert(AssertSize<IPv4Packet, 20>());

inline NetworkOrdered<u16> internet_checksum(void const* ptr, size_t count)
{
    u32 checksum = 0;
    auto* w = (u16 const*)ptr;
    while (count > 1) {
        checksum += AK::convert_between_host_and_network_endian(*w++);
        if (checksum & 0x80000000)
            checksum = (checksum & 0xffff) | (checksum >> 16);
        count -= 2;
    }
    while (checksum >> 16)
        checksum = (checksum & 0xffff) + (checksum >> 16);
    return ~checksum & 0xffff;
}

}