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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache 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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package org.jboss.netty.channel;

import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;

import org.jboss.netty.util.ExternalResourceReleasable;

/**
 * A region of a file that is sent via a {@link Channel} which supports
 * zero-copy file transfer.
 *
 * Upgrade your JDK / JRE
 *
 * {@link FileChannel#transferTo(long, long, WritableByteChannel)} has at least
 * four known bugs in the old versions of Sun JDK and perhaps its derived ones.
 * Please upgrade your JDK to 1.6.0_18 or later version if you are going to use
 * zero-copy file transfer.
 * 
 * 5103988
 *   - FileChannel.transferTo() should return -1 for EAGAIN instead throws IOException
 * 6253145
 *   - FileChannel.transferTo() on Linux fails when going beyond 2GB boundary
 * 6427312
 *   - FileChannel.transferTo() throws IOException "system call interrupted"
 * 6470086
 *   - FileChannel.transferTo(2147483647, 1, channel) causes "Value too large" exception
 * 
 *
 * Check your operating system and JDK / JRE
 *
 * If your operating system (or JDK / JRE) does not support zero-copy file
 * transfer, sending a file with {@link FileRegion} might fail or yield worse
 * performance.  For example, sending a large file doesn't work well in Windows.
 *
 * Not all transports support it
 *
 * Currently, the NIO transport is the only transport that supports {@link FileRegion}.
 * Attempting to write a {@link FileRegion} to non-NIO {@link Channel} will trigger
 * a {@link ClassCastException} or a similar exception.
 */
public interface FileRegion extends ExternalResourceReleasable {

    // FIXME Make sure all transports support writing a FileRegion
    //       Even if zero copy cannot be achieved, all transports should emulate it.

    /**
     * Returns the offset in the file where the transfer began.
     */
    long getPosition();

    /**
     * Returns the number of bytes to transfer.
     */
    long getCount();

    /**
     * Transfers the content of this file region to the specified channel.
     *
     * @param target    the destination of the transfer
     * @param position  the relative offset of the file where the transfer
     *                  begins from.  For example, 0 will make the
     *                  transfer start from {@link #getPosition()}th byte and
     *                  {@link #getCount()} - 1 will make the last
     *                  byte of the region transferred.
     */
    long transferTo(WritableByteChannel target, long position) throws IOException;
}