UnixFdEncoder.java

/*
 * SPDX-FileCopyrightText: 2023-2025 Lucimber UG
 * SPDX-License-Identifier: Apache-2.0
 */
package com.lucimber.dbus.codec.encoder;

import com.lucimber.dbus.type.DBusUnixFD;
import com.lucimber.dbus.type.Type;
import com.lucimber.dbus.util.LoggerUtils;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Objects;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * An encoder which encodes a file-descriptor to the D-Bus marshalling format using ByteBuffer.
 *
 * @see Encoder
 * @see DBusUnixFD
 */
public final class UnixFdEncoder implements Encoder<DBusUnixFD, ByteBuffer> {

    private static final Logger LOGGER = LoggerFactory.getLogger(UnixFdEncoder.class);

    private static final int TYPE_SIZE = 4;
    private final ByteOrder order;

    /**
     * Constructs a new instance with mandatory parameter.
     *
     * @param order The byte order of the produced bytes.
     */
    public UnixFdEncoder(ByteOrder order) {
        this.order = Objects.requireNonNull(order, "order must not be null");
    }

    @Override
    public EncoderResult<ByteBuffer> encode(DBusUnixFD value, int offset) throws EncoderException {
        Objects.requireNonNull(value, "value must not be null");

        try {
            int padding =
                    EncoderUtils.calculateAlignmentPadding(Type.UNIX_FD.getAlignment(), offset);
            int totalSize = padding + TYPE_SIZE;

            ByteBuffer buffer = ByteBuffer.allocate(totalSize).order(order);
            for (int i = 0; i < padding; i++) {
                buffer.put((byte) 0);
            }
            buffer.putInt(value.getDelegate());
            buffer.flip();

            EncoderResult<ByteBuffer> result = new EncoderResultImpl<>(totalSize, buffer);

            LOGGER.debug(
                    LoggerUtils.MARSHALLING,
                    "UNIX_FD: {}; Offset: {}; Padding: {}; Produced bytes: {};",
                    value,
                    offset,
                    padding,
                    totalSize);

            return result;
        } catch (Exception ex) {
            throw new EncoderException("Could not encode UNIX_FD.", ex);
        }
    }
}