HandleGeneric.java

/*
 * This file is part of ComputerCraft - http://www.computercraft.info
 * Copyright Daniel Ratcliffe, 2011-2020. Do not distribute without permission.
 * Send enquiries to dratcliffe@gmail.com
 */
package dan200.computercraft.core.apis.handles;

import dan200.computercraft.api.lua.LuaException;
import dan200.computercraft.api.lua.LuaFunction;
import dan200.computercraft.shared.util.IoUtil;

import javax.annotation.Nonnull;
import java.io.Closeable;
import java.io.IOException;
import java.nio.channels.Channel;
import java.nio.channels.SeekableByteChannel;
import java.util.Optional;

public abstract class HandleGeneric
{
    private Closeable closable;
    private boolean open = true;

    protected HandleGeneric( @Nonnull Closeable closable )
    {
        this.closable = closable;
    }

    protected void checkOpen() throws LuaException
    {
        if( !open ) throw new LuaException( "attempt to use a closed file" );
    }

    protected final void close()
    {
        open = false;

        IoUtil.closeQuietly( closable );
        closable = null;
    }

    /**
     * Close this file, freeing any resources it uses.
     *
     * Once a file is closed it may no longer be read or written to.
     *
     * @throws LuaException If the file has already been closed.
     */
    @LuaFunction( "close" )
    public final void doClose() throws LuaException
    {
        checkOpen();
        close();
    }


    /**
     * Shared implementation for various file handle types.
     *
     * @param channel The channel to seek in
     * @param whence  The seeking mode.
     * @param offset  The offset to seek to.
     * @return The new position of the file, or null if some error occurred.
     * @throws LuaException If the arguments were invalid
     * @see <a href="https://www.lua.org/manual/5.1/manual.html#pdf-file:seek">{@code file:seek} in the Lua manual.</a>
     */
    protected static Object[] handleSeek( SeekableByteChannel channel, Optional<String> whence, Optional<Long> offset ) throws LuaException
    {
        long actualOffset = offset.orElse( 0L );
        try
        {
            switch( whence.orElse( "cur" ) )
            {
                case "set":
                    channel.position( actualOffset );
                    break;
                case "cur":
                    channel.position( channel.position() + actualOffset );
                    break;
                case "end":
                    channel.position( channel.size() + actualOffset );
                    break;
                default:
                    throw new LuaException( "bad argument #1 to 'seek' (invalid option '" + whence + "'" );
            }

            return new Object[] { channel.position() };
        }
        catch( IllegalArgumentException e )
        {
            return new Object[] { null, "Position is negative" };
        }
        catch( IOException e )
        {
            return null;
        }
    }

    protected static SeekableByteChannel asSeekable( Channel channel )
    {
        if( !(channel instanceof SeekableByteChannel) ) return null;

        SeekableByteChannel seekable = (SeekableByteChannel) channel;
        try
        {
            seekable.position( seekable.position() );
            return seekable;
        }
        catch( IOException | UnsupportedOperationException e )
        {
            return null;
        }
    }
}