/*
    * Copyright 2014 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:
    *
    *   https://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.epoll;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.AbstractChannel;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.ChannelException;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.ConnectTimeoutException;
  import io.netty.channel.EventLoop;
  import io.netty.channel.IoEvent;
  import io.netty.channel.IoEventLoop;
  import io.netty.channel.IoRegistration;
  import io.netty.channel.RecvByteBufAllocator;
  import io.netty.channel.socket.ChannelInputShutdownEvent;
  import io.netty.channel.socket.ChannelInputShutdownReadComplete;
  import io.netty.channel.socket.SocketChannelConfig;
  import io.netty.channel.unix.FileDescriptor;
  import io.netty.channel.unix.IovArray;
  import io.netty.channel.unix.Socket;
  import io.netty.channel.unix.UnixChannel;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.concurrent.Future;
  
  import java.io.IOException;
  import java.io.UncheckedIOException;
  import java.net.InetSocketAddress;
  import java.net.SocketAddress;
  import java.nio.ByteBuffer;
  import java.nio.channels.AlreadyConnectedException;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.ConnectionPendingException;
  import java.nio.channels.NotYetConnectedException;
  import java.nio.channels.UnresolvedAddressException;
  import java.util.concurrent.TimeUnit;
  
  import static io.netty.channel.epoll.EpollIoOps.EPOLL_ERR_IN_MASK;
  import static io.netty.channel.epoll.EpollIoOps.EPOLL_ERR_OUT_MASK;
  import static io.netty.channel.epoll.EpollIoOps.EPOLL_RDHUP_MASK;
  import static io.netty.channel.internal.ChannelUtils.WRITE_STATUS_SNDBUF_FULL;
  import static io.netty.channel.unix.UnixChannelUtil.computeRemoteAddr;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  abstract class AbstractEpollChannel extends AbstractChannel implements UnixChannel {
      private static final ChannelMetadata METADATA = new ChannelMetadata(false);
      protected final LinuxSocket socket;
      private final EpollIoOps initial;
  
      /**
       * The future of the current connection attempt.  If not null, subsequent
       * connection attempts will fail.
       */
      private ChannelPromise connectPromise;
      private Future<?> connectTimeoutFuture;
      private SocketAddress requestedRemoteAddress;
      private volatile SocketAddress local;
      private volatile SocketAddress remote;
  
      private IoRegistration registration;
      boolean inputClosedSeenErrorOnRead;
      private EpollIoOps ops;
  
      protected volatile boolean active;
  
      AbstractEpollChannel(Channel parent, LinuxSocket fd, boolean active, EpollIoOps initialOps) {
          super(parent);
          this.socket = checkNotNull(fd, "fd");
          this.active = active;
          if (active) {
              // Directly cache the remote and local addresses
              // See https://github.com/netty/netty/issues/2359
              this.local = fd.localAddress();
              this.remote = fd.remoteAddress();
          }
          this.initial = initialOps;
          this.ops = initialOps;
      }
 
     AbstractEpollChannel(Channel parent, LinuxSocket fd, SocketAddress remote, EpollIoOps initialOps) {
         super(parent);
         this.socket = checkNotNull(fd, "fd");
         this.active = true;
         // Directly cache the remote and local addresses
         // See https://github.com/netty/netty/issues/2359
         this.remote = remote;
         this.local = fd.localAddress();
         this.initial = initialOps;
         this.ops = initialOps;
     }
 
     static boolean isSoErrorZero(Socket fd) {
         try {
             return fd.getSoError() == 0;
         } catch (IOException e) {
             throw new ChannelException(e);
         }
     }
 
     protected void setFlag(int flag) throws IOException {
         if (ops.contains(flag)) {
             // we can save a syscall if the ops did not change
             return;
         }
         ops = ops.with(EpollIoOps.valueOf(flag));
         if (isRegistered()) {
             IoRegistration registration = registration();
             registration.submit(ops);
         } else {
             ops = ops.with(EpollIoOps.valueOf(flag));
         }
     }
 
     void clearFlag(int flag) throws IOException {
         IoRegistration registration = registration();
         if (!ops.contains(flag)) {
             // we can save a syscall if the ops did not change
             return;
         }
         ops = ops.without(EpollIoOps.valueOf(flag));
         registration.submit(ops);
     }
 
     protected final IoRegistration registration() {
         assert registration != null;
         return registration;
     }
 
     boolean isFlagSet(int flag) {
         return (ops.value & flag) != 0;
     }
 
     @Override
     public final FileDescriptor fd() {
         return socket;
     }
 
     @Override
     public abstract EpollChannelConfig config();
 
     @Override
     public boolean isActive() {
         return active;
     }
 
     @Override
     public ChannelMetadata metadata() {
         return METADATA;
     }
 
     @Override
     protected void doClose() throws Exception {
         active = false;
         // Even if we allow half closed sockets we should give up on reading. Otherwise we may allow a read attempt on a
         // socket which has not even been connected yet. This has been observed to block during unit tests.
         inputClosedSeenErrorOnRead = true;
         try {
             ChannelPromise promise = connectPromise;
             if (promise != null) {
                 // Use tryFailure() instead of setFailure() to avoid the race against cancel().
                 promise.tryFailure(new ClosedChannelException());
                 connectPromise = null;
             }
 
             Future<?> future = connectTimeoutFuture;
             if (future != null) {
                 future.cancel(false);
                 connectTimeoutFuture = null;
             }
 
             if (isRegistered()) {
                 // Need to check if we are on the EventLoop as doClose() may be triggered by the GlobalEventExecutor
                 // if SO_LINGER is used.
                 //
                 // See https://github.com/netty/netty/issues/7159
                 EventLoop loop = eventLoop();
                 if (loop.inEventLoop()) {
                     doDeregister();
                 } else {
                     loop.execute(new Runnable() {
                         @Override
                         public void run() {
                             try {
                                 doDeregister();
                             } catch (Throwable cause) {
                                 pipeline().fireExceptionCaught(cause);
                             }
                         }
                     });
                 }
             }
         } finally {
             socket.close();
         }
     }
 
     void resetCachedAddresses() {
         local = socket.localAddress();
         remote = socket.remoteAddress();
     }
 
     @Override
     protected void doDisconnect() throws Exception {
         doClose();
     }
 
     @Override
     public boolean isOpen() {
         return socket.isOpen();
     }
 
     @Override
     protected void doDeregister() throws Exception {
         IoRegistration registration = this.registration;
         if (registration != null) {
             ops = initial;
             registration.cancel();
         }
     }
 
     @Override
     protected boolean isCompatible(EventLoop loop) {
         return loop instanceof IoEventLoop && ((IoEventLoop) loop).isCompatible(AbstractEpollUnsafe.class);
     }
 
     @Override
     protected void doBeginRead() throws Exception {
         // Channel.read() or ChannelHandlerContext.read() was called
         final AbstractEpollUnsafe unsafe = (AbstractEpollUnsafe) unsafe();
         unsafe.readPending = true;
 
         // We must set the read flag here as it is possible the user didn't read in the last read loop, the
         // executeEpollInReadyRunnable could read nothing, and if the user doesn't explicitly call read they will
         // never get data after this.
         setFlag(Native.EPOLLIN);
     }
 
     final boolean shouldBreakEpollInReady(ChannelConfig config) {
         return socket.isInputShutdown() && (inputClosedSeenErrorOnRead || !isAllowHalfClosure(config));
     }
 
     private static boolean isAllowHalfClosure(ChannelConfig config) {
         if (config instanceof EpollDomainSocketChannelConfig) {
             return ((EpollDomainSocketChannelConfig) config).isAllowHalfClosure();
         }
         return config instanceof SocketChannelConfig &&
                 ((SocketChannelConfig) config).isAllowHalfClosure();
     }
 
     final void clearEpollIn() {
         // Only clear if registered with an EventLoop as otherwise
         if (isRegistered()) {
             final EventLoop loop = eventLoop();
             final AbstractEpollUnsafe unsafe = (AbstractEpollUnsafe) unsafe();
             if (loop.inEventLoop()) {
                 unsafe.clearEpollIn0();
             } else {
                 // schedule a task to clear the EPOLLIN as it is not safe to modify it directly
                 loop.execute(new Runnable() {
                     @Override
                     public void run() {
                         if (!unsafe.readPending && !config().isAutoRead()) {
                             // Still no read triggered so clear it now
                             unsafe.clearEpollIn0();
                         }
                     }
                 });
             }
         } else  {
             // The EventLoop is not registered atm so just update the flags so the correct value
             // will be used once the channel is registered
             ops = ops.without(EpollIoOps.EPOLLIN);
         }
     }
 
     @Override
     protected void doRegister(ChannelPromise promise) {
         ((IoEventLoop) eventLoop()).register((AbstractEpollUnsafe) unsafe()).addListener(f -> {
             if (f.isSuccess()) {
                 registration = (IoRegistration) f.getNow();
                 if (isActive()) {
                     // The channel is active, register with current ops now as we are ready to start receiving events.
                     submitCurrentOps();
                 }
                 promise.setSuccess();
             } else {
                 promise.setFailure(f.cause());
             }
         });
     }
 
     @Override
     protected abstract AbstractEpollUnsafe newUnsafe();
 
     /**
      * Returns an off-heap copy of the specified {@link ByteBuf}, and releases the original one.
      */
     protected final ByteBuf newDirectBuffer(ByteBuf buf) {
         return newDirectBuffer(buf, buf);
     }
 
     /**
      * Returns an off-heap copy of the specified {@link ByteBuf}, and releases the specified holder.
      * The caller must ensure that the holder releases the original {@link ByteBuf} when the holder is released by
      * this method.
      */
     protected final ByteBuf newDirectBuffer(Object holder, ByteBuf buf) {
         final int readableBytes = buf.readableBytes();
         if (readableBytes == 0) {
             ReferenceCountUtil.release(holder);
             return Unpooled.EMPTY_BUFFER;
         }
 
         final ByteBufAllocator alloc = alloc();
         if (alloc.isDirectBufferPooled()) {
             return newDirectBuffer0(holder, buf, alloc, readableBytes);
         }
 
         final ByteBuf directBuf = ByteBufUtil.threadLocalDirectBuffer();
         if (directBuf == null) {
             return newDirectBuffer0(holder, buf, alloc, readableBytes);
         }
 
         directBuf.writeBytes(buf, buf.readerIndex(), readableBytes);
         ReferenceCountUtil.safeRelease(holder);
         return directBuf;
     }
 
     private static ByteBuf newDirectBuffer0(Object holder, ByteBuf buf, ByteBufAllocator alloc, int capacity) {
         final ByteBuf directBuf = alloc.directBuffer(capacity);
         directBuf.writeBytes(buf, buf.readerIndex(), capacity);
         ReferenceCountUtil.safeRelease(holder);
         return directBuf;
     }
 
     protected static void checkResolvable(InetSocketAddress addr) {
         if (addr.isUnresolved()) {
             throw new UnresolvedAddressException();
         }
     }
 
     /**
      * Read bytes into the given {@link ByteBuf} and return the amount.
      */
     protected final int doReadBytes(ByteBuf byteBuf) throws Exception {
         int writerIndex = byteBuf.writerIndex();
         int localReadAmount;
         unsafe().recvBufAllocHandle().attemptedBytesRead(byteBuf.writableBytes());
         if (byteBuf.hasMemoryAddress()) {
             localReadAmount = socket.recvAddress(byteBuf.memoryAddress(), writerIndex, byteBuf.capacity());
         } else {
             ByteBuffer buf = byteBuf.internalNioBuffer(writerIndex, byteBuf.writableBytes());
             localReadAmount = socket.recv(buf, buf.position(), buf.limit());
         }
         if (localReadAmount > 0) {
             byteBuf.writerIndex(writerIndex + localReadAmount);
         }
         return localReadAmount;
     }
 
     protected final int doWriteBytes(ChannelOutboundBuffer in, ByteBuf buf) throws Exception {
         if (buf.hasMemoryAddress()) {
             int localFlushedAmount = socket.sendAddress(buf.memoryAddress(), buf.readerIndex(), buf.writerIndex());
             if (localFlushedAmount > 0) {
                 in.removeBytes(localFlushedAmount);
                 return 1;
             }
         } else {
             final ByteBuffer nioBuf = buf.nioBufferCount() == 1 ?
                     buf.internalNioBuffer(buf.readerIndex(), buf.readableBytes()) : buf.nioBuffer();
             int localFlushedAmount = socket.send(nioBuf, nioBuf.position(), nioBuf.limit());
             if (localFlushedAmount > 0) {
                 nioBuf.position(nioBuf.position() + localFlushedAmount);
                 in.removeBytes(localFlushedAmount);
                 return 1;
             }
         }
         return WRITE_STATUS_SNDBUF_FULL;
     }
 
     /**
      * Write bytes to the socket, with or without a remote address.
      * Used for datagram and TCP client fast open writes.
      */
     final long doWriteOrSendBytes(ByteBuf data, InetSocketAddress remoteAddress, boolean fastOpen)
             throws IOException {
         assert !(fastOpen && remoteAddress == null) : "fastOpen requires a remote address";
         if (data.hasMemoryAddress()) {
             long memoryAddress = data.memoryAddress();
             if (remoteAddress == null) {
                 return socket.sendAddress(memoryAddress, data.readerIndex(), data.writerIndex());
             }
             return socket.sendToAddress(memoryAddress, data.readerIndex(), data.writerIndex(),
                     remoteAddress.getAddress(), remoteAddress.getPort(), fastOpen);
         }
 
         if (data.nioBufferCount() > 1) {
             IovArray array = ((NativeArrays) registration.attachment()).cleanIovArray();
             array.add(data, data.readerIndex(), data.readableBytes());
             int cnt = array.count();
             assert cnt != 0;
 
             if (remoteAddress == null) {
                 return socket.writevAddresses(array.memoryAddress(0), cnt);
             }
             return socket.sendToAddresses(array.memoryAddress(0), cnt,
                     remoteAddress.getAddress(), remoteAddress.getPort(), fastOpen);
         }
 
         ByteBuffer nioData = data.internalNioBuffer(data.readerIndex(), data.readableBytes());
         if (remoteAddress == null) {
             return socket.send(nioData, nioData.position(), nioData.limit());
         }
         return socket.sendTo(nioData, nioData.position(), nioData.limit(),
                 remoteAddress.getAddress(), remoteAddress.getPort(), fastOpen);
     }
 
     protected abstract class AbstractEpollUnsafe extends AbstractUnsafe implements EpollIoHandle {
         boolean readPending;
         private EpollRecvByteAllocatorHandle allocHandle;
 
         Channel channel() {
             return AbstractEpollChannel.this;
         }
 
         @Override
         public FileDescriptor fd() {
             return AbstractEpollChannel.this.fd();
         }
 
         @Override
         public void close() {
             close(voidPromise());
         }
 
         @Override
         public void handle(IoRegistration registration, IoEvent event) {
             EpollIoEvent epollEvent = (EpollIoEvent) event;
             int ops = epollEvent.ops().value;
 
             // Don't change the ordering of processing EPOLLOUT | EPOLLRDHUP / EPOLLIN if you're not 100%
             // sure about it!
             // Re-ordering can easily introduce bugs and bad side-effects, as we found out painfully in the
             // past.
 
             // First check for EPOLLOUT as we may need to fail the connect ChannelPromise before try
             // to read from the file descriptor.
             // See https://github.com/netty/netty/issues/3785
             //
             // It is possible for an EPOLLOUT or EPOLLERR to be generated when a connection is refused.
             // In either case epollOutReady() will do the correct thing (finish connecting, or fail
             // the connection).
             // See https://github.com/netty/netty/issues/3848
             if ((ops & EPOLL_ERR_OUT_MASK) != 0) {
                 // Force flush of data as the epoll is writable again
                 epollOutReady();
             }
 
             // Check EPOLLIN before EPOLLRDHUP to ensure all data is read before shutting down the input.
             // See https://github.com/netty/netty/issues/4317.
             //
             // If EPOLLIN or EPOLLERR was received and the channel is still open call epollInReady(). This will
             // try to read from the underlying file descriptor and so notify the user about the error.
             if ((ops & EPOLL_ERR_IN_MASK) != 0) {
                 // The Channel is still open and there is something to read. Do it now.
                 epollInReady();
             }
 
             // Check if EPOLLRDHUP was set, this will notify us for connection-reset in which case
             // we may close the channel directly or try to read more data depending on the state of the
             // Channel and als depending on the AbstractEpollChannel subtype.
             if ((ops & EPOLL_RDHUP_MASK) != 0) {
                 epollRdHupReady();
             }
         }
 
         /**
          * Called once EPOLLIN event is ready to be processed
          */
         abstract void epollInReady();
 
         final boolean shouldStopReading(ChannelConfig config) {
             // Check if there is a readPending which was not processed yet.
             // This could be for two reasons:
             // * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method
             // * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method
             //
             // See https://github.com/netty/netty/issues/2254
             return !readPending && !config.isAutoRead();
         }
 
         /**
          * Called once EPOLLRDHUP event is ready to be processed
          */
         final void epollRdHupReady() {
             // This must happen before we attempt to read. This will ensure reading continues until an error occurs.
             recvBufAllocHandle().receivedRdHup();
 
             if (isActive()) {
                 // If it is still active, we need to call epollInReady as otherwise we may miss to
                 // read pending data from the underlying file descriptor.
                 // See https://github.com/netty/netty/issues/3709
                 epollInReady();
             } else {
                 // Just to be safe make sure the input marked as closed.
                 shutdownInput(false);
             }
 
             // Clear the EPOLLRDHUP flag to prevent continuously getting woken up on this event.
             clearEpollRdHup();
         }
 
         /**
          * Clear the {@link Native#EPOLLRDHUP} flag from EPOLL, and close on failure.
          */
         private void clearEpollRdHup() {
             try {
                 clearFlag(Native.EPOLLRDHUP);
             } catch (IOException e) {
                 pipeline().fireExceptionCaught(e);
                 close(voidPromise());
             }
         }
 
         /**
          * Shutdown the input side of the channel.
          */
         void shutdownInput(boolean allDataRead) {
             if (!socket.isInputShutdown()) {
                 if (isAllowHalfClosure(config())) {
                     try {
                         socket.shutdown(true, false);
                     } catch (IOException ignored) {
                         // We attempted to shutdown and failed, which means the input has already effectively been
                         // shutdown.
                         fireEventAndClose(ChannelInputShutdownEvent.INSTANCE);
                         return;
                     } catch (NotYetConnectedException ignore) {
                         // We attempted to shutdown and failed, which means the input has already effectively been
                         // shutdown.
                     }
                     if (shouldStopReading(config())) {
                         clearEpollIn0();
                     }
                     pipeline().fireUserEventTriggered(ChannelInputShutdownEvent.INSTANCE);
                 } else {
                     close(voidPromise());
                     return;
                 }
             }
 
             if (allDataRead && !inputClosedSeenErrorOnRead) {
                 inputClosedSeenErrorOnRead = true;
                 pipeline().fireUserEventTriggered(ChannelInputShutdownReadComplete.INSTANCE);
             }
         }
 
         private void fireEventAndClose(Object evt) {
             pipeline().fireUserEventTriggered(evt);
             close(voidPromise());
         }
 
         @Override
         public EpollRecvByteAllocatorHandle recvBufAllocHandle() {
             if (allocHandle == null) {
                 allocHandle = newEpollHandle((RecvByteBufAllocator.ExtendedHandle) super.recvBufAllocHandle());
             }
             return allocHandle;
         }
 
         /**
          * Create a new {@link EpollRecvByteAllocatorHandle} instance.
          * @param handle The handle to wrap with EPOLL specific logic.
          */
         EpollRecvByteAllocatorHandle newEpollHandle(RecvByteBufAllocator.ExtendedHandle handle) {
             return new EpollRecvByteAllocatorHandle(handle);
         }
 
         @Override
         protected final void flush0() {
             // Flush immediately only when there's no pending flush.
             // If there's a pending flush operation, event loop will call forceFlush() later,
             // and thus there's no need to call it now.
             if (!isFlagSet(Native.EPOLLOUT)) {
                 super.flush0();
             }
         }
 
         /**
          * Called once a EPOLLOUT event is ready to be processed
          */
         final void epollOutReady() {
             if (connectPromise != null) {
                 // pending connect which is now complete so handle it.
                 finishConnect();
             } else if (!socket.isOutputShutdown()) {
                 // directly call super.flush0() to force a flush now
                 super.flush0();
             }
         }
 
         protected final void clearEpollIn0() {
             assert eventLoop().inEventLoop();
             try {
                 readPending = false;
                 if (!ops.contains(EpollIoOps.EPOLLIN)) {
                     return;
                 }
                 ops = ops.without(EpollIoOps.EPOLLIN);
                 IoRegistration registration = registration();
                 registration.submit(ops);
             } catch (UncheckedIOException e) {
                 // When this happens there is something completely wrong with either the filedescriptor or epoll,
                 // so fire the exception through the pipeline and close the Channel.
                 pipeline().fireExceptionCaught(e);
                 unsafe().close(unsafe().voidPromise());
             }
         }
 
         @Override
         public void connect(
                 final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) {
             // Don't mark the connect promise as uncancellable as in fact we can cancel it as it is using
             // non-blocking io.
             if (promise.isDone() || !ensureOpen(promise)) {
                 return;
             }
 
             try {
                 if (connectPromise != null) {
                     throw new ConnectionPendingException();
                 }
 
                 boolean wasActive = isActive();
                 if (doConnect(remoteAddress, localAddress)) {
                     fulfillConnectPromise(promise, wasActive);
                 } else {
                     connectPromise = promise;
                     requestedRemoteAddress = remoteAddress;
 
                     // Schedule connect timeout.
                     final int connectTimeoutMillis = config().getConnectTimeoutMillis();
                     if (connectTimeoutMillis > 0) {
                         connectTimeoutFuture = eventLoop().schedule(new Runnable() {
                             @Override
                             public void run() {
                                 ChannelPromise connectPromise = AbstractEpollChannel.this.connectPromise;
                                 if (connectPromise != null && !connectPromise.isDone()
                                         && connectPromise.tryFailure(new ConnectTimeoutException(
                                                 "connection timed out after " + connectTimeoutMillis + " ms: " +
                                                         remoteAddress))) {
                                     close(voidPromise());
                                 }
                             }
                         }, connectTimeoutMillis, TimeUnit.MILLISECONDS);
                     }
 
                     promise.addListener(new ChannelFutureListener() {
                         @Override
                         public void operationComplete(ChannelFuture future) {
                             // If the connect future is cancelled we also cancel the timeout and close the
                             // underlying socket.
                             if (future.isCancelled()) {
                                 if (connectTimeoutFuture != null) {
                                     connectTimeoutFuture.cancel(false);
                                 }
                                 connectPromise = null;
                                 close(voidPromise());
                             }
                         }
                     });
                 }
             } catch (Throwable t) {
                 closeIfClosed();
                 promise.tryFailure(annotateConnectException(t, remoteAddress));
             }
         }
 
         private void fulfillConnectPromise(ChannelPromise promise, boolean wasActive) {
             if (promise == null) {
                 // Closed via cancellation and the promise has been notified already.
                 return;
             }
             active = true;
 
             // The channel is active, register with current ops now as we are ready to start receiving events.
             submitCurrentOps();
 
             // Get the state as trySuccess() may trigger an ChannelFutureListener that will close the Channel.
             // We still need to ensure we call fireChannelActive() in this case.
             boolean active = isActive();
 
             // trySuccess() will return false if a user cancelled the connection attempt.
             boolean promiseSet = promise.trySuccess();
 
             // Regardless if the connection attempt was cancelled, channelActive() event should be triggered,
             // because what happened is what happened.
             if (!wasActive && active) {
                 pipeline().fireChannelActive();
             }
 
             // If a user cancelled the connection attempt, close the channel, which is followed by channelInactive().
             if (!promiseSet) {
                 close(voidPromise());
             }
         }
 
         private void fulfillConnectPromise(ChannelPromise promise, Throwable cause) {
             if (promise == null) {
                 // Closed via cancellation and the promise has been notified already.
                 return;
             }
 
             // Use tryFailure() instead of setFailure() to avoid the race against cancel().
             promise.tryFailure(cause);
             closeIfClosed();
         }
 
         private void finishConnect() {
             // Note this method is invoked by the event loop only if the connection attempt was
             // neither cancelled nor timed out.
 
             assert eventLoop().inEventLoop();
 
             boolean connectStillInProgress = false;
             try {
                 boolean wasActive = isActive();
                 if (!doFinishConnect()) {
                     connectStillInProgress = true;
                     return;
                 }
                 fulfillConnectPromise(connectPromise, wasActive);
             } catch (Throwable t) {
                 fulfillConnectPromise(connectPromise, annotateConnectException(t, requestedRemoteAddress));
             } finally {
                 if (!connectStillInProgress) {
                     // Check for null as the connectTimeoutFuture is only created if a connectTimeoutMillis > 0 is used
                     // See https://github.com/netty/netty/issues/1770
                     if (connectTimeoutFuture != null) {
                         connectTimeoutFuture.cancel(false);
                     }
                     connectPromise = null;
                 }
             }
         }
 
         /**
          * Finish the connect
          */
         private boolean doFinishConnect() throws Exception {
             if (socket.finishConnect()) {
                 clearFlag(Native.EPOLLOUT);
                 if (requestedRemoteAddress instanceof InetSocketAddress) {
                     remote = computeRemoteAddr((InetSocketAddress) requestedRemoteAddress, socket.remoteAddress());
                 }
                 requestedRemoteAddress = null;
 
                 return true;
             }
             setFlag(Native.EPOLLOUT);
             return false;
         }
     }
 
     @Override
     protected void doBind(SocketAddress local) throws Exception {
         if (local instanceof InetSocketAddress) {
             checkResolvable((InetSocketAddress) local);
         }
         socket.bind(local);
         this.local = socket.localAddress();
     }
 
     /**
      * Connect to the remote peer
      */
     protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
         if (localAddress instanceof InetSocketAddress) {
             checkResolvable((InetSocketAddress) localAddress);
         }
 
         InetSocketAddress remoteSocketAddr = remoteAddress instanceof InetSocketAddress
                 ? (InetSocketAddress) remoteAddress : null;
         if (remoteSocketAddr != null) {
             checkResolvable(remoteSocketAddr);
         }
 
         if (remote != null) {
             // Check if already connected before trying to connect. This is needed as connect(...) will not return -1
             // and set errno to EISCONN if a previous connect(...) attempt was setting errno to EINPROGRESS and finished
             // later.
             throw new AlreadyConnectedException();
         }
 
         if (localAddress != null) {
             socket.bind(localAddress);
         }
 
         boolean connected = doConnect0(remoteAddress);
         if (connected) {
             remote = remoteSocketAddr == null ?
                     remoteAddress : computeRemoteAddr(remoteSocketAddr, socket.remoteAddress());
         }
         // We always need to set the localAddress even if not connected yet as the bind already took place.
         //
         // See https://github.com/netty/netty/issues/3463
         local = socket.localAddress();
         return connected;
     }
 
     boolean doConnect0(SocketAddress remote) throws Exception {
         boolean success = false;
         try {
             boolean connected = socket.connect(remote);
             if (!connected) {
                 setFlag(Native.EPOLLOUT);
             }
             success = true;
             return connected;
         } finally {
             if (!success) {
                 doClose();
             }
         }
     }
 
     final void submitCurrentOps() {
         IoRegistration registration = registration();
         registration.submit(ops);
     }
 
     @Override
     protected SocketAddress localAddress0() {
         return local;
     }
 
     @Override
     protected SocketAddress remoteAddress0() {
         return remote;
     }
 }