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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 io.netty.handler.stream;

import io.netty.buffer.ByteBuf;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

/**
 * A {@link ChunkedByteInput} that fetches data from a file chunk by chunk using
 * NIO {@link FileChannel}.
 * 
 * If your operating system supports
 * zero-copy file transfer
 * such as {@code sendfile()}, you might want to use {@link FileRegion} instead.
 */
public class ChunkedNioFile implements ChunkedByteInput {

    private final FileChannel in;
    private final long startOffset;
    private final long endOffset;
    private final int chunkSize;
    private long offset;

    /**
     * Creates a new instance that fetches data from the specified file.
     */
    public ChunkedNioFile(File in) throws IOException {
        this(new FileInputStream(in).getChannel());
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param chunkSize the number of bytes to fetch on each
     *                  {@link #nextChunk()} call
     */
    public ChunkedNioFile(File in, int chunkSize) throws IOException {
        this(new FileInputStream(in).getChannel(), chunkSize);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     */
    public ChunkedNioFile(FileChannel in) throws IOException {
        this(in, ChunkedStream.DEFAULT_CHUNK_SIZE);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param chunkSize the number of bytes to fetch on each
     *                  {@link #nextChunk()} call
     */
    public ChunkedNioFile(FileChannel in, int chunkSize) throws IOException {
        this(in, 0, in.size(), chunkSize);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param offset the offset of the file where the transfer begins
     * @param length the number of bytes to transfer
     * @param chunkSize the number of bytes to fetch on each
     *                  {@link #nextChunk()} call
     */
    public ChunkedNioFile(FileChannel in, long offset, long length, int chunkSize)
            throws IOException {
        if (in == null) {
            throw new NullPointerException("in");
        }
        if (offset < 0) {
            throw new IllegalArgumentException(
                    "offset: " + offset + " (expected: 0 or greater)");
        }
        if (length < 0) {
            throw new IllegalArgumentException(
                    "length: " + length + " (expected: 0 or greater)");
        }
        if (chunkSize <= 0) {
            throw new IllegalArgumentException(
                    "chunkSize: " + chunkSize +
                    " (expected: a positive integer)");
        }

        if (offset != 0) {
            in.position(offset);
        }
        this.in = in;
        this.chunkSize = chunkSize;
        this.offset = startOffset = offset;
        endOffset = offset + length;
    }

    /**
     * Returns the offset in the file where the transfer began.
     */
    public long getStartOffset() {
        return startOffset;
    }

    /**
     * Returns the offset in the file where the transfer will end.
     */
    public long getEndOffset() {
        return endOffset;
    }

    /**
     * Returns the offset in the file where the transfer is happening currently.
     */
    public long getCurrentOffset() {
        return offset;
    }

    @Override
    public boolean isEndOfInput() throws Exception {
        return !(offset < endOffset && in.isOpen());
    }

    @Override
    public void close() throws Exception {
        in.close();
    }

    @Override
    public boolean readChunk(ByteBuf buffer) throws Exception {
        long offset = this.offset;
        if (offset >= endOffset) {
            return false;
        }

        int chunkSize = (int) Math.min(this.chunkSize, endOffset - offset);
        int readBytes = 0;
        for (;;) {
            int localReadBytes = buffer.writeBytes(in, chunkSize - readBytes);
            if (localReadBytes < 0) {
                break;
            }
            readBytes += localReadBytes;
            if (readBytes == chunkSize) {
                break;
            }
        }
        this.offset += readBytes;

        return true;
    }
}