/*
    * 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:
    *
    *   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.local;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.AbstractChannel;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.DefaultChannelConfig;
  import io.netty.channel.EventLoop;
  import io.netty.channel.IoEvent;
  import io.netty.channel.IoEventLoop;
  import io.netty.channel.IoRegistration;
  import io.netty.channel.PreferHeapByteBufAllocator;
  import io.netty.channel.RecvByteBufAllocator;
  import io.netty.channel.SingleThreadEventLoop;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.SingleThreadEventExecutor;
  import io.netty.util.internal.InternalThreadLocalMap;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.net.ConnectException;
  import java.net.SocketAddress;
  import java.nio.channels.AlreadyConnectedException;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.ConnectionPendingException;
  import java.nio.channels.NotYetConnectedException;
  import java.util.Queue;
  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  
  /**
   * A {@link Channel} for the local transport.
   */
  public class LocalChannel extends AbstractChannel {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(LocalChannel.class);
      @SuppressWarnings({ "rawtypes" })
      private static final AtomicReferenceFieldUpdater<LocalChannel, Future> FINISH_READ_FUTURE_UPDATER =
              AtomicReferenceFieldUpdater.newUpdater(LocalChannel.class, Future.class, "finishReadFuture");
      private static final AtomicReferenceFieldUpdater<LocalChannel, State> STATE_UPDATER =
              AtomicReferenceFieldUpdater.newUpdater(LocalChannel.class, State.class, "state");
      private static final ChannelMetadata METADATA = new ChannelMetadata(false);
      private static final int MAX_READER_STACK_DEPTH = 8;
  
      private enum State { OPEN, BOUND, CONNECTED, CLOSED }
  
      private final ChannelConfig config = new DefaultChannelConfig(this);
      // To further optimize this we could write our own SPSC queue.
      final Queue<Object> inboundBuffer = PlatformDependent.newSpscQueue();
      private final Runnable readTask = new Runnable() {
          @Override
          public void run() {
              // Ensure the inboundBuffer is not empty as readInbound() will always call fireChannelReadComplete()
              if (!inboundBuffer.isEmpty()) {
                  readInbound();
              }
          }
      };
  
      private final Runnable finishReadTask = new Runnable() {
          @Override
          public void run() {
              finishPeerRead0(LocalChannel.this);
          }
      };
  
      private IoRegistration registration;
  
      private volatile State state;
      private volatile LocalChannel peer;
      private volatile LocalAddress localAddress;
      private volatile LocalAddress remoteAddress;
      private volatile ChannelPromise connectPromise;
      private volatile boolean readInProgress;
      private volatile boolean writeInProgress;
      private volatile Future<?> finishReadFuture;
  
      public LocalChannel() {
          super(null);
          config().setAllocator(new PreferHeapByteBufAllocator(config.getAllocator()));
     }
 
     protected LocalChannel(LocalServerChannel parent, LocalChannel peer) {
         super(parent);
         config().setAllocator(new PreferHeapByteBufAllocator(config.getAllocator()));
         this.peer = peer;
         localAddress = parent.localAddress();
         remoteAddress = peer.localAddress();
     }
 
     @Override
     public ChannelMetadata metadata() {
         return METADATA;
     }
 
     @Override
     public ChannelConfig config() {
         return config;
     }
 
     @Override
     public LocalServerChannel parent() {
         return (LocalServerChannel) super.parent();
     }
 
     @Override
     public LocalAddress localAddress() {
         return (LocalAddress) super.localAddress();
     }
 
     @Override
     public LocalAddress remoteAddress() {
         return (LocalAddress) super.remoteAddress();
     }
 
     @Override
     public boolean isOpen() {
         return state != State.CLOSED;
     }
 
     @Override
     public boolean isActive() {
         return state == State.CONNECTED;
     }
 
     @Override
     protected AbstractUnsafe newUnsafe() {
         return new LocalUnsafe();
     }
 
     @Override
     protected boolean isCompatible(EventLoop loop) {
         return loop instanceof SingleThreadEventLoop ||
                 (loop instanceof IoEventLoop && ((IoEventLoop) loop).isCompatible(LocalUnsafe.class));
     }
 
     @Override
     protected SocketAddress localAddress0() {
         return localAddress;
     }
 
     @Override
     protected SocketAddress remoteAddress0() {
         return remoteAddress;
     }
 
     @Override
     protected void doRegister(ChannelPromise promise) {
         EventLoop loop = eventLoop();
         if (loop instanceof IoEventLoop) {
             assert registration == null;
             ((IoEventLoop) loop).register((LocalUnsafe) unsafe()).addListener(f -> {
                if (f.isSuccess()) {
                    registration = (IoRegistration) f.getNow();
                    promise.setSuccess();
                } else {
                    promise.setFailure(f.cause());
                }
             });
         } else {
             try {
                 ((LocalUnsafe) unsafe()).registered();
             } catch (Throwable cause) {
                 promise.setFailure(cause);
             }
             promise.setSuccess();
         }
     }
 
     @Override
     protected void doDeregister() throws Exception {
         EventLoop loop = eventLoop();
         if (loop instanceof IoEventLoop) {
             IoRegistration registration = this.registration;
             if (registration != null) {
                 this.registration = null;
                 registration.cancel();
             }
         } else {
             ((LocalUnsafe) unsafe()).unregistered();
         }
     }
 
     @Override
     protected void doBind(SocketAddress localAddress) throws Exception {
         this.localAddress =
                 LocalChannelRegistry.register(this, this.localAddress,
                         localAddress);
         state = State.BOUND;
     }
 
     @Override
     protected void doDisconnect() throws Exception {
         doClose();
     }
 
     @Override
     protected void doClose() throws Exception {
         final LocalChannel peer = this.peer;
         State oldState = state;
         State closedFrom = oldState;
         try {
             if (oldState != State.CLOSED) {
                 // Update all internal state before the closeFuture is notified.
                 if (localAddress != null) {
                     if (parent() == null) {
                         LocalChannelRegistry.unregister(localAddress);
                     }
                     localAddress = null;
                 }
 
                 // State change must happen before finishPeerRead to ensure writes are released either in doWrite or
                 // channelRead.
                 // Use getAndSet() as an accepted channel may concurrently move this channel from BOUND to CONNECTED
                 // when it is registered. See LocalUnsafe.registered().
                 closedFrom = STATE_UPDATER.getAndSet(this, State.CLOSED);
 
                 // Preserve order of event and force a read operation now before the close operation is processed.
                 if (writeInProgress && peer != null) {
                     finishPeerRead(peer);
                 }
 
                 ChannelPromise promise = connectPromise;
                 if (promise != null) {
                     // Use tryFailure() instead of setFailure() to avoid the race against cancel().
                     promise.tryFailure(new ClosedChannelException());
                     connectPromise = null;
                 }
             }
 
             if (peer != null && parent() == null && closedFrom != State.CONNECTED) {
                 // The accepted channel did not complete the connection. Don't touch it: it may not have an event
                 // loop yet and is owned by the server channel or its own event loop. When it is registered it sees
                 // that this channel is closed and closes itself. If it was closed already, its close has notified
                 // this channel or will do so.
                 this.peer = null;
             } else if (peer != null) {
                 this.peer = null;
                 // Always call peer.eventLoop().execute() even if peer.eventLoop().inEventLoop() is true.
                 // This ensures that if both channels are on the same event loop, the peer's channelInActive
                 // event is triggered *after* this peer's channelInActive event
                 EventLoop peerEventLoop = peer.eventLoop();
                 final boolean peerIsActive = peer.isActive();
                 try {
                     peerEventLoop.execute(new Runnable() {
                         @Override
                         public void run() {
                             peer.tryClose(peerIsActive);
                         }
                     });
                 } catch (Throwable cause) {
                     logger.warn("Releasing Inbound Queues for channels {}-{} because exception occurred!",
                             this, peer, cause);
                     if (peerEventLoop.inEventLoop()) {
                         peer.releaseInboundBuffers();
                     } else {
                         // inboundBuffers is a SPSC so we may leak if the event loop is shutdown prematurely or
                         // rejects the close Runnable but give a best effort.
                         peer.close();
                     }
                     PlatformDependent.throwException(cause);
                 }
             }
         } finally {
             // Release all buffers if the Channel was already registered in the past and if it was not closed before.
             if (oldState != null && oldState != State.CLOSED) {
                 // We need to release all the buffers that may be put into our inbound queue since we closed the Channel
                 // to ensure we not leak any memory. This is fine as it basically gives the same guarantees as TCP which
                 // means even if the promise was notified before its not really guaranteed that the "remote peer" will
                 // see the buffer at all.
                 releaseInboundBuffers();
             }
         }
     }
 
     private void tryClose(boolean isActive) {
         if (isActive) {
             unsafe().close(unsafe().voidPromise());
         } else if (connectPromise != null) {
             // The accepted channel was closed before the connection was established, for example because the server
             // channel was closed. It is closed already, so don't notify it again. Fail the connect like a refused
             // connection and close this channel.
             ChannelPromise promise = connectPromise;
             connectPromise = null;
             peer = null;
             promise.tryFailure(new ConnectException("connection refused: the accepted channel was closed"));
             unsafe().close(unsafe().voidPromise());
         } else {
             releaseInboundBuffers();
         }
     }
 
     private void readInbound() {
         RecvByteBufAllocator.Handle handle = unsafe().recvBufAllocHandle();
         handle.reset(config());
         ChannelPipeline pipeline = pipeline();
         do {
             Object received = inboundBuffer.poll();
             if (received == null) {
                 break;
             }
             if (received instanceof ByteBuf && inboundBuffer.peek() instanceof ByteBuf) {
                 ByteBuf msg = (ByteBuf) received;
                 ByteBuf output = handle.allocate(alloc());
                 if (msg.readableBytes() < output.writableBytes()) {
                     // We have an opportunity to coalesce buffers.
                     output.writeBytes(msg, msg.readerIndex(), msg.readableBytes());
                     msg.release();
                     while ((received = inboundBuffer.peek()) instanceof ByteBuf &&
                             ((ByteBuf) received).readableBytes() < output.writableBytes()) {
                         inboundBuffer.poll();
                         msg = (ByteBuf) received;
                         output.writeBytes(msg, msg.readerIndex(), msg.readableBytes());
                         msg.release();
                     }
                     handle.lastBytesRead(output.readableBytes());
                     received = output; // Send the coalesced buffer down the pipeline.
                 } else {
                     // It won't be profitable to coalesce buffers this time around.
                     handle.lastBytesRead(output.capacity());
                     output.release();
                 }
             }
             handle.incMessagesRead(1);
             pipeline.fireChannelRead(received);
         } while (handle.continueReading());
         handle.readComplete();
         pipeline.fireChannelReadComplete();
     }
 
     @Override
     protected void doBeginRead() throws Exception {
         if (readInProgress) {
             return;
         }
 
         Queue<Object> inboundBuffer = this.inboundBuffer;
         if (inboundBuffer.isEmpty()) {
             readInProgress = true;
             return;
         }
 
         final InternalThreadLocalMap threadLocals = InternalThreadLocalMap.get();
         final int stackDepth = threadLocals.localChannelReaderStackDepth();
         if (stackDepth < MAX_READER_STACK_DEPTH) {
             threadLocals.setLocalChannelReaderStackDepth(stackDepth + 1);
             try {
                 readInbound();
             } finally {
                 threadLocals.setLocalChannelReaderStackDepth(stackDepth);
             }
         } else {
             try {
                 eventLoop().execute(readTask);
             } catch (Throwable cause) {
                 logger.warn("Closing Local channels {}-{} because exception occurred!", this, peer, cause);
                 close();
                 peer.close();
                 PlatformDependent.throwException(cause);
             }
         }
     }
 
     @Override
     protected void doWrite(ChannelOutboundBuffer in) throws Exception {
         switch (state) {
         case OPEN:
         case BOUND:
             throw new NotYetConnectedException();
         case CLOSED:
             throw new ClosedChannelException();
         case CONNECTED:
             break;
         }
 
         final LocalChannel peer = this.peer;
 
         writeInProgress = true;
         try {
             ClosedChannelException exception = null;
             for (;;) {
                 Object msg = in.current();
                 if (msg == null) {
                     break;
                 }
                 try {
                     // It is possible the peer could have closed while we are writing, and in this case we should
                     // simulate real socket behavior and ensure the write operation is failed.
                     if (peer.state == State.CONNECTED) {
                         peer.inboundBuffer.add(ReferenceCountUtil.retain(msg));
                         in.remove();
                     } else {
                         if (exception == null) {
                             exception = new ClosedChannelException();
                         }
                         in.remove(exception);
                     }
                 } catch (Throwable cause) {
                     in.remove(cause);
                 }
             }
         } finally {
             // The following situation may cause trouble:
             // 1. Write (with promise X)
             // 2. promise X is completed when in.remove() is called, and a listener on this promise calls close()
             // 3. Then the close event will be executed for the peer before the write events, when the write events
             // actually happened before the close event.
             writeInProgress = false;
         }
 
         finishPeerRead(peer);
     }
 
     private void finishPeerRead(final LocalChannel peer) {
         // If the peer is also writing, then we must schedule the event on the event loop to preserve read order.
         if (peer.eventLoop() == eventLoop() && !peer.writeInProgress) {
             finishPeerRead0(peer);
         } else {
             runFinishPeerReadTask(peer);
         }
     }
 
     private void runFinishTask0() {
         // If the peer is writing, we must wait until after reads are completed for that peer before we can read. So
         // we keep track of the task, and coordinate later that our read can't happen until the peer is done.
         if (writeInProgress) {
             finishReadFuture = eventLoop().submit(finishReadTask);
         } else {
             eventLoop().execute(finishReadTask);
         }
     }
 
     private void runFinishPeerReadTask(final LocalChannel peer) {
         try {
             peer.runFinishTask0();
         } catch (Throwable cause) {
             logger.warn("Closing Local channels {}-{} because exception occurred!", this, peer, cause);
             close();
             peer.close();
             PlatformDependent.throwException(cause);
         }
     }
 
     private void releaseInboundBuffers() {
         assert eventLoop() == null || eventLoop().inEventLoop();
         readInProgress = false;
         Queue<Object> inboundBuffer = this.inboundBuffer;
         Object msg;
         while ((msg = inboundBuffer.poll()) != null) {
             ReferenceCountUtil.release(msg);
         }
     }
 
     private void finishPeerRead0(LocalChannel peer) {
         Future<?> peerFinishReadFuture = peer.finishReadFuture;
         if (peerFinishReadFuture != null) {
             if (!peerFinishReadFuture.isDone()) {
                 runFinishPeerReadTask(peer);
                 return;
             } else {
                 // Lazy unset to make sure we don't prematurely unset it while scheduling a new task.
                 FINISH_READ_FUTURE_UPDATER.compareAndSet(peer, peerFinishReadFuture, null);
             }
         }
         // We should only set readInProgress to false if there is any data that was read as otherwise we may miss to
         // forward data later on.
         if (peer.readInProgress && !peer.inboundBuffer.isEmpty()) {
             peer.readInProgress = false;
             peer.readInbound();
         }
     }
 
     private class LocalUnsafe extends AbstractUnsafe implements LocalIoHandle {
 
         private final Runnable shutdownHook = this::closeNow;
 
         @Override
         public void close() {
             close(voidPromise());
         }
 
         @Override
         public void handle(IoRegistration registration, IoEvent event) {
             // NOOP
         }
 
         @Override
         public void registered() {
             // Check if both peer and parent are non-null because this channel was created by a LocalServerChannel.
             // This is needed as a peer may not be null also if a LocalChannel was connected before and
             // deregistered / registered later again.
             //
             // See https://github.com/netty/netty/issues/2400
             //
             // Store the peer in a local variable as it may be set to null if doClose() is called.
             // See https://github.com/netty/netty/issues/2144
             final LocalChannel peer = LocalChannel.this.peer;
             if (peer != null && parent() != null) {
                 // Set our state before the peer's, so the peer sees this channel as active once it is connected.
                 State oldState = state;
                 state = State.CONNECTED;
 
                 // Move the peer from BOUND to CONNECTED atomically, as it may be closed concurrently on its own
                 // event loop. If this channel was connected before and is registered again, the peer is CONNECTED
                 // already.
                 if (STATE_UPDATER.compareAndSet(peer, State.BOUND, State.CONNECTED) ||
                         peer.state == State.CONNECTED) {
                     peer.remoteAddress = parent().localAddress();
 
                     // Always call peer.eventLoop().execute() even if peer.eventLoop().inEventLoop() is true.
                     // This ensures that if both channels are on the same event loop, the peer's channelActive
                     // event is triggered *after* this channel's channelRegistered event, so that this channel's
                     // pipeline is fully initialized by ChannelInitializer before any channelRead events.
                     peer.eventLoop().execute(new Runnable() {
                         @Override
                         public void run() {
                             ChannelPromise promise = peer.connectPromise;
 
                             // Only trigger fireChannelActive() if the promise was not null and was not completed
                             // yet. connectPromise may be set to null if doClose() was called in the meantime.
                             if (promise != null && promise.trySuccess()) {
                                 peer.pipeline().fireChannelActive();
                             }
                         }
                     });
                 } else {
                     // The peer was closed before this channel was registered, so it never uses this channel.
                     // Close this channel once the registration is complete.
                     LocalChannel.this.peer = null;
                     state = oldState;
                     eventLoop().execute(this::closeNow);
                 }
             }
             EventLoop loop = eventLoop();
             if (!(loop instanceof IoEventLoop) && loop instanceof SingleThreadEventExecutor) {
                 ((SingleThreadEventExecutor) eventLoop()).addShutdownHook(shutdownHook);
             }
         }
 
         @Override
         public void unregistered() {
             EventLoop loop = eventLoop();
             if (!(loop instanceof IoEventLoop) && loop instanceof SingleThreadEventExecutor) {
                 ((SingleThreadEventExecutor) eventLoop()).removeShutdownHook(shutdownHook);
             }
         }
 
         @Override
         public void closeNow() {
             close(voidPromise());
         }
 
         @Override
         public void connect(final SocketAddress remoteAddress,
                 SocketAddress localAddress, final ChannelPromise promise) {
             if (!promise.setUncancellable() || !ensureOpen(promise)) {
                 return;
             }
 
             if (state == State.CONNECTED) {
                 Exception cause = new AlreadyConnectedException();
                 safeSetFailure(promise, cause);
                 return;
             }
 
             if (connectPromise != null) {
                 throw new ConnectionPendingException();
             }
 
             connectPromise = promise;
 
             if (state != State.BOUND) {
                 // Not bound yet and no localAddress specified - get one.
                 if (localAddress == null) {
                     localAddress = new LocalAddress(LocalChannel.this);
                 }
             }
 
             if (localAddress != null) {
                 try {
                     doBind(localAddress);
                 } catch (Throwable t) {
                     safeSetFailure(promise, t);
                     close(voidPromise());
                     return;
                 }
             }
 
             Channel boundChannel = LocalChannelRegistry.get(remoteAddress);
             if (!(boundChannel instanceof LocalServerChannel)) {
                 Exception cause = new ConnectException("connection refused: " + remoteAddress);
                 safeSetFailure(promise, cause);
                 close(voidPromise());
                 return;
             }
 
             LocalServerChannel serverChannel = (LocalServerChannel) boundChannel;
             peer = serverChannel.serve(LocalChannel.this);
         }
     }
 }