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 * License Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.eclipse.org/legal/epl-v20.html
 *
 * Software distributed under the License is distributed on an "AS
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 * implied. See the License for the specific language governing
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 * Copyright (C) 2008 JRuby project
 *
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package org.jruby.ext.ffi.io;

import org.jruby.Ruby;
import jnr.posix.LibC;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ByteChannel;

import static com.headius.backport9.buffer.Buffers.positionBuffer;

/**
 * An implementation of ByteChannel that reads from and writes to a native unix
 * file descriptor.
 */
public class FileDescriptorByteChannel implements ByteChannel {
    private final LibC libc;
    private final int fd;
    private volatile boolean isOpen = true;

    private static LibC libc(Ruby runtime) {
        LibC libc = runtime.getPosix().libc();
        if (libc == null) {
            throw runtime.newNotImplementedError("native access not enabled");
        }
        return libc;
    }

    /**
     * Creates a new <tt>FileDescriptorByteChannel</tt>.
     *
     * @param fd The native unix fd to read/write.
     */
    public FileDescriptorByteChannel(Ruby runtime, int fd) {
        this.fd = fd;
        this.libc = libc(runtime);
    }

    /**
     * Reads data from the native unix file descriptor.
     * @param dst The destination <tt>ByteBuffer</tt> to place read bytes in.
     * @return The number of bytes read.
     *
     * @throws java.io.IOException If an error occurred during reading.
     */
    public int read(ByteBuffer dst) throws IOException {
        if (!isOpen) {
            throw new IOException("Not open");
        }
        int n = libc.read(fd, dst, dst.remaining());
        if (n > 0) {
            positionBuffer(dst, dst.position() + n);
        } else if (n == 0) {
            return -1; // EOF
        }
        return n;
    }

    /**
     * Writes data to the native unix file descriptor.
     *
     * @param src The source <tt>ByteBuffer</tt> to write to the file descriptor.
     * @return The number of bytes written.
     *
     * @throws java.io.IOException If an error occurred during writing.
     */
    public int write(ByteBuffer src) throws IOException {
        if (!isOpen) {
            throw new IOException("Not open");
        }
        int n = libc.write(fd, src, src.remaining());
        if (n > 0) {
            positionBuffer(src, src.position() + n);
        }
        return n;
    }

    /**
     * Tests if the ByteChannel is open.
     *
     * @return <tt>true</tt> if the Channel is still open
     */
    public boolean isOpen() {
        return isOpen;
    }
    /**
     * Closes the <tt>Channel</tt>.
     * <p>
     * This closes the underlying native file descriptor.
     * </p>
     * @throws java.io.IOException
     */
    public void close() throws IOException {
        if (!isOpen) {
            throw new IllegalStateException("file already closed");
        }
        isOpen = false;
        libc.close(fd);
    }
}
