VDEFileItemCodec.cpp

/**
 * @internal
 *
 * Create a Codec instance for VDEFileItem records.
 */
static Codec<VDEFileItem> fileItemCodec () {
    using namespace codecs;

    const auto varLengthBytes = eager(variableSizeBytes(uint32L, identityBytes));

    const auto vdeRecordVersion = (
        ("compat_version"            | codecs::uint8        ) &
        ("feature_version"           | codecs::uint8        )
    ).as<VDERecordVersion>();

    const auto vdeSection = (
        ("offset"                    | uint64L              ) &
        ("length"                    | uint64L              )
    ).as<VDESectionRecord>();

    const auto vdeHeader = (
        ("magic"                     | vdeFileMagicCodec    ) >>
        ("file_version"              | vdeRecordVersion     ) &
        ("vde_encrypted_sect"        | vdeSection           ) &
        ("vde_session_sect"          | vdeSection           )
    ).as<VDEFileHeader>();

    const auto pbkdf2Params = (
        ("iters"                     | uint32L              ) &
        ("salt"                      | varLengthBytes       )
    ).as<VDESessionMasterKeyParameters>();

    // TODO: Until we generalize Codec::as(), we have to lift the single Codec to a TupledCodec here
    const auto hkdfParams = TupledCodec<std::vector<uint8_t>>(
        ("salt"                      | varLengthBytes       )
    ).as<VDESessionSubkeyParameters>();

    const auto keyParams = (
        ("master_key_params"         | pbkdf2Params         ) &
        ("sub_key_params"            | hkdfParams           )
    ).as<VDESessionKeyParameters>();

    const auto vdeSession = (
        ("version"                   | vdeRecordVersion     ) &
        ("key_params"                | keyParams            ) &
        ("dpk"                       | varLengthBytes       )
    ).as<VDESession>();

    return (
        ("vde_header"                | vdeHeader            ) >>= [vdeSession](const VDEFileHeader &hdr) {
            auto padding1Length = hdr.encryptedSection().offset() - VDE_FILE_HEADER_SIZE;
            auto encryptedLength = hdr.encryptedSection().length();
            auto padding2Length = hdr.sessionSection().offset() - (hdr.encryptedSection().offset() + encryptedLength);
            auto sessionLength = hdr.sessionSection().length();
            return (
                ("padding_1"         | ignore(size_t(padding1Length))                    ) >>
                ("encrypted_data"    | eager(bytes(size_t(encryptedLength)))             ) &
                ("padding_2"         | ignore(size_t(padding2Length))                    ) >>
                ("vde_session"       | fixedSizeBytes(size_t(sessionLength), vdeSession) )
            );
        }
    ).as<VDEFileItem>();
}