/*
 * 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.channel.socket.nio;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelException;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelOutboundBuffer;
import io.netty.channel.ChannelPromise;
import io.netty.channel.EventLoop;
import io.netty.channel.FileRegion;
import io.netty.channel.RecvByteBufAllocator;
import io.netty.channel.nio.AbstractNioByteChannel;
import io.netty.channel.socket.DefaultSocketChannelConfig;
import io.netty.channel.socket.ServerSocketChannel;
import io.netty.channel.socket.SocketChannelConfig;
import io.netty.util.concurrent.GlobalEventExecutor;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.SocketUtils;
import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.concurrent.Executor;

import static io.netty.channel.internal.ChannelUtils.MAX_BYTES_PER_GATHERING_WRITE_ATTEMPTED_LOW_THRESHOLD;

/**
 * {@link io.netty.channel.socket.SocketChannel} which uses NIO selector based implementation.使用基于NIO选择器的实现的socket.socketchannel。
 */
public class NioSocketChannel extends AbstractNioByteChannel implements io.netty.channel.socket.SocketChannel {
    private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioSocketChannel.class);
    private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();

    private static SocketChannel newSocket(SelectorProvider provider) {
        try {
            /**
             *  Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
             *  {@link SelectorProvider#provider()} which is called by each SocketChannel.open() otherwise.
             *
             *  See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.
             */
            return provider.openSocketChannel();
        } catch (IOException e) {
            throw new ChannelException("Failed to open a socket.", e);
        }
    }

    private final SocketChannelConfig config;

    /**
     * Create a new instance
     */
    public NioSocketChannel() {
        this(DEFAULT_SELECTOR_PROVIDER);
    }

    /**
     * Create a new instance using the given {@link SelectorProvider}.
     */
    public NioSocketChannel(SelectorProvider provider) {
        this(newSocket(provider));
    }

    /**
     * Create a new instance using the given {@link SocketChannel}.
     */
    public NioSocketChannel(SocketChannel socket) {
        this(null, socket);
    }

    /**
     * Create a new instance
     *
     * @param parent    the {@link Channel} which created this instance or {@code null} if it was created by the user
     * @param socket    the {@link SocketChannel} which will be used
     */
    public NioSocketChannel(Channel parent, SocketChannel socket) {
        super(parent, socket);
        config = new NioSocketChannelConfig(this, socket.socket());
    }

    @Override
    public ServerSocketChannel parent() {
        return (ServerSocketChannel) super.parent();
    }

    @Override
    public SocketChannelConfig config() {
        return config;
    }

    @Override
    protected SocketChannel javaChannel() {
        return (SocketChannel) super.javaChannel();
    }

    @Override
    public boolean isActive() {
        SocketChannel ch = javaChannel();
        return ch.isOpen() && ch.isConnected();
    }

    @Override
    public boolean isOutputShutdown() {
        return javaChannel().socket().isOutputShutdown() || !isActive();
    }

    @Override
    public boolean isInputShutdown() {
        return javaChannel().socket().isInputShutdown() || !isActive();
    }

    @Override
    public boolean isShutdown() {
        Socket socket = javaChannel().socket();
        return socket.isInputShutdown() && socket.isOutputShutdown() || !isActive();
    }

    @Override
    public InetSocketAddress localAddress() {
        return (InetSocketAddress) super.localAddress();
    }

    @Override
    public InetSocketAddress remoteAddress() {
        return (InetSocketAddress) super.remoteAddress();
    }

    @UnstableApi
    @Override
    protected final void doShutdownOutput() throws Exception {
        if (PlatformDependent.javaVersion() >= 7) {
            javaChannel().shutdownOutput();
        } else {
            javaChannel().socket().shutdownOutput();
        }
    }

    @Override
    public ChannelFuture shutdownOutput() {
        return shutdownOutput(newPromise());
    }

    @Override
    public ChannelFuture shutdownOutput(final ChannelPromise promise) {
        final EventLoop loop = eventLoop();
        if (loop.inEventLoop()) {
            ((AbstractUnsafe) unsafe()).shutdownOutput(promise);
        } else {
            loop.execute(new Runnable() {
                @Override
                public void run() {
                    ((AbstractUnsafe) unsafe()).shutdownOutput(promise);
                }
            });
        }
        return promise;
    }

    @Override
    public ChannelFuture shutdownInput() {
        return shutdownInput(newPromise());
    }

    @Override
    protected boolean isInputShutdown0() {
        return isInputShutdown();
    }

    @Override
    public ChannelFuture shutdownInput(final ChannelPromise promise) {
        EventLoop loop = eventLoop();
        if (loop.inEventLoop()) {
            shutdownInput0(promise);
        } else {
            loop.execute(new Runnable() {
                @Override
                public void run() {
                    shutdownInput0(promise);
                }
            });
        }
        return promise;
    }

    @Override
    public ChannelFuture shutdown() {
        return shutdown(newPromise());
    }

    @Override
    public ChannelFuture shutdown(final ChannelPromise promise) {
        ChannelFuture shutdownOutputFuture = shutdownOutput();
        if (shutdownOutputFuture.isDone()) {
            shutdownOutputDone(shutdownOutputFuture, promise);
        } else {
            shutdownOutputFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(final ChannelFuture shutdownOutputFuture) throws Exception {
                    shutdownOutputDone(shutdownOutputFuture, promise);
                }
            });
        }
        return promise;
    }

    private void shutdownOutputDone(final ChannelFuture shutdownOutputFuture, final ChannelPromise promise) {
        ChannelFuture shutdownInputFuture = shutdownInput();
        if (shutdownInputFuture.isDone()) {
            shutdownDone(shutdownOutputFuture, shutdownInputFuture, promise);
        } else {
            shutdownInputFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture shutdownInputFuture) throws Exception {
                    shutdownDone(shutdownOutputFuture, shutdownInputFuture, promise);
                }
            });
        }
    }

    private static void shutdownDone(ChannelFuture shutdownOutputFuture,
                                     ChannelFuture shutdownInputFuture,
                                     ChannelPromise promise) {
        Throwable shutdownOutputCause = shutdownOutputFuture.cause();
        Throwable shutdownInputCause = shutdownInputFuture.cause();
        if (shutdownOutputCause != null) {
            if (shutdownInputCause != null) {
                logger.debug("Exception suppressed because a previous exception occurred.",
                        shutdownInputCause);
            }
            promise.setFailure(shutdownOutputCause);
        } else if (shutdownInputCause != null) {
            promise.setFailure(shutdownInputCause);
        } else {
            promise.setSuccess();
        }
    }
    private void shutdownInput0(final ChannelPromise promise) {
        try {
            shutdownInput0();
            promise.setSuccess();
        } catch (Throwable t) {
            promise.setFailure(t);
        }
    }

    private void shutdownInput0() throws Exception {
        if (PlatformDependent.javaVersion() >= 7) {
            javaChannel().shutdownInput();
        } else {
            javaChannel().socket().shutdownInput();
        }
    }

    @Override
    protected SocketAddress localAddress0() {
        return javaChannel().socket().getLocalSocketAddress();
    }

    @Override
    protected SocketAddress remoteAddress0() {
        return javaChannel().socket().getRemoteSocketAddress();
    }

    @Override
    protected void doBind(SocketAddress localAddress) throws Exception {
        doBind0(localAddress);
    }

    private void doBind0(SocketAddress localAddress) throws Exception {
        if (PlatformDependent.javaVersion() >= 7) {
            SocketUtils.bind(javaChannel(), localAddress);
        } else {
            SocketUtils.bind(javaChannel().socket(), localAddress);
        }
    }

    @Override
    protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
        if (localAddress != null) {
//            调用java底层的socketChannel的bind方法
            doBind0(localAddress);
        }

        boolean success = false;
        try {
//            调用java底层的socketChannel的connect方法
            boolean connected = SocketUtils.connect(javaChannel(), remoteAddress);
            if (!connected) {
//                如果没有连接成功注册OP_CONNECT事件
                selectionKey().interestOps(SelectionKey.OP_CONNECT);
            }
            success = true;
            return connected;
        } finally {
            if (!success) {
//                如果连接失败调用java底层channel close
                doClose();
            }
        }
    }

    @Override
    protected void doFinishConnect() throws Exception {
        if (!javaChannel().finishConnect()) {
            throw new Error();
        }
    }

    @Override
    protected void doDisconnect() throws Exception {
        doClose();
    }

    @Override
    protected void doClose() throws Exception {
        super.doClose();
        javaChannel().close();
    }

    @Override
    protected int doReadBytes(ByteBuf byteBuf) throws Exception {
        final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle();
        allocHandle.attemptedBytesRead(byteBuf.writableBytes());
        return byteBuf.writeBytes(javaChannel(), allocHandle.attemptedBytesRead());
    }

    @Override
    protected int doWriteBytes(ByteBuf buf) throws Exception {
        final int expectedWrittenBytes = buf.readableBytes();
        return buf.readBytes(javaChannel(), expectedWrittenBytes);
    }

    @Override
    protected long doWriteFileRegion(FileRegion region) throws Exception {
        final long position = region.transferred();
        return region.transferTo(javaChannel(), position);
    }

    private void adjustMaxBytesPerGatheringWrite(int attempted, int written, int oldMaxBytesPerGatheringWrite) {
        // By default we track the SO_SNDBUF when ever it is explicitly set. However some OSes may dynamically change
        // SO_SNDBUF (and other characteristics that determine how much data can be written at once) so we should try
        // make a best effort to adjust as OS behavior changes.//默认情况下，当SO_SNDBUF被显式设置时，我们会跟踪它
// SO_SNDBUF(以及决定一次可以写入多少数据的其他特性)，因此我们应该尝试一下
//当操作系统的行为改变时，尽最大的努力去调整。
        if (attempted == written) {
            if (attempted << 1 > oldMaxBytesPerGatheringWrite) {
                ((NioSocketChannelConfig) config).setMaxBytesPerGatheringWrite(attempted << 1);
            }
        } else if (attempted > MAX_BYTES_PER_GATHERING_WRITE_ATTEMPTED_LOW_THRESHOLD && written < attempted >>> 1) {
            ((NioSocketChannelConfig) config).setMaxBytesPerGatheringWrite(attempted >>> 1);
        }
    }

    @Override
    protected void doWrite(ChannelOutboundBuffer in) throws Exception {
//        获取java底层channel
        SocketChannel ch = javaChannel();
//        写循环次数
        int writeSpinCount = config().getWriteSpinCount();
        do {
            if (in.isEmpty()) {
                // All written so clear OP_WRITE都写得很清楚，OP_WRITE
//                清楚写事件
                clearOpWrite();
                // Directly return here so incompleteWrite(...) is not called.直接返回这里，所以incompleteWrite(…)没有被调用。
                return;
            }

            // Ensure the pending writes are made of ByteBufs only.确保挂起的写操作仅由ByteBufs组成。
            int maxBytesPerGatheringWrite = ((NioSocketChannelConfig) config).getMaxBytesPerGatheringWrite();
            ByteBuffer[] nioBuffers = in.nioBuffers(1024, maxBytesPerGatheringWrite);
//            有待处理的字节数
            int nioBufferCnt = in.nioBufferCount();

            // Always us nioBuffers() to workaround data-corruption.总是使用nioBuffers()来解决数据损坏的问题。
            // See https://github.com/netty/netty/issues/2761
            switch (nioBufferCnt) {
                case 0:
                    // We have something else beside ByteBuffers to write so fallback to normal writes.除了ByteBuffers，我们还需要写些别的东西，这样就可以退回到正常的写操作
                    writeSpinCount -= doWrite0(in);
                    break;
                case 1: {
                    // Only one ByteBuf so use non-gathering write
                    // Zero length buffers are not added to nioBuffers by ChannelOutboundBuffer, so there is no need
                    // to check if the total size of all the buffers is non-zero.//只有一个字节buf，所以使用非聚集写入
// 0长度的缓冲区不是通过ChannelOutboundBuffer添加到nioBuffers的，所以没有必要这样做
//检查所有缓冲区的总大小是否为非零。
                    ByteBuffer buffer = nioBuffers[0];
                    int attemptedBytes = buffer.remaining();
                    final int localWrittenBytes = ch.write(buffer);
                    if (localWrittenBytes <= 0) {
                        incompleteWrite(true);
                        return;
                    }
                    adjustMaxBytesPerGatheringWrite(attemptedBytes, localWrittenBytes, maxBytesPerGatheringWrite);
                    in.removeBytes(localWrittenBytes);
                    --writeSpinCount;
                    break;
                }
                default: {
                    // Zero length buffers are not added to nioBuffers by ChannelOutboundBuffer, so there is no need
                    // to check if the total size of all the buffers is non-zero.
                    // We limit the max amount to int above so cast is safe// 0长度的缓冲区不是通过ChannelOutboundBuffer添加到nioBuffers的，所以没有必要这样做
//检查所有缓冲区的总大小是否为非零。
//我们限制最大数量的int以上，以使铸造是安全的
                    long attemptedBytes = in.nioBufferSize();
                    final long localWrittenBytes = ch.write(nioBuffers, 0, nioBufferCnt);
                    if (localWrittenBytes <= 0) {
                        incompleteWrite(true);
                        return;
                    }
                    // Casting to int is safe because we limit the total amount of data in the nioBuffers to int above.
                    adjustMaxBytesPerGatheringWrite((int) attemptedBytes, (int) localWrittenBytes,
                            maxBytesPerGatheringWrite);
                    in.removeBytes(localWrittenBytes);
                    --writeSpinCount;
                    break;
                }
            }
        } while (writeSpinCount > 0);

        incompleteWrite(writeSpinCount < 0);
    }

    @Override
    protected AbstractNioUnsafe newUnsafe() {
        return new NioSocketChannelUnsafe();
    }

    private final class NioSocketChannelUnsafe extends NioByteUnsafe {
        @Override
        protected Executor prepareToClose() {
            try {
                if (javaChannel().isOpen() && config().getSoLinger() > 0) {
                    // We need to cancel this key of the channel so we may not end up in a eventloop spin
                    // because we try to read or write until the actual close happens which may be later due
                    // SO_LINGER handling.
                    // See https://github.com/netty/netty/issues/4449
                    doDeregister();
                    return GlobalEventExecutor.INSTANCE;
                }
            } catch (Throwable ignore) {
                // Ignore the error as the underlying channel may be closed in the meantime and so
                // getSoLinger() may produce an exception. In this case we just return null.
                // See https://github.com/netty/netty/issues/4449
            }
            return null;
        }
    }

    private final class NioSocketChannelConfig extends DefaultSocketChannelConfig {
        private volatile int maxBytesPerGatheringWrite = Integer.MAX_VALUE;

        private NioSocketChannelConfig(NioSocketChannel channel, Socket javaSocket) {
            super(channel, javaSocket);
            calculateMaxBytesPerGatheringWrite();
        }

        @Override
        protected void autoReadCleared() {
            clearReadPending();
        }

        @Override
        public NioSocketChannelConfig setSendBufferSize(int sendBufferSize) {
            super.setSendBufferSize(sendBufferSize);
            calculateMaxBytesPerGatheringWrite();
            return this;
        }

        void setMaxBytesPerGatheringWrite(int maxBytesPerGatheringWrite) {
            this.maxBytesPerGatheringWrite = maxBytesPerGatheringWrite;
        }

        int getMaxBytesPerGatheringWrite() {
            return maxBytesPerGatheringWrite;
        }

        private void calculateMaxBytesPerGatheringWrite() {
            // Multiply by 2 to give some extra space in case the OS can process write data faster than we can provide.
            int newSendBufferSize = getSendBufferSize() << 1;
            if (newSendBufferSize > 0) {
                setMaxBytesPerGatheringWrite(getSendBufferSize() << 1);
            }
        }
    }
}