/*
    * Copyright 2024 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.uring;
  
  
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.IoRegistration;
  import io.netty.channel.ServerChannel;
  import io.netty.channel.unix.Buffer;
  import io.netty.channel.unix.Errors;
  
  import java.net.SocketAddress;
  import java.nio.ByteBuffer;
  
  import static io.netty.channel.unix.Errors.ERRNO_EAGAIN_NEGATIVE;
  import static io.netty.channel.unix.Errors.ERRNO_EWOULDBLOCK_NEGATIVE;
  
  abstract class AbstractIoUringServerChannel extends AbstractIoUringChannel implements ServerChannel {
      private static final ChannelMetadata METADATA = new ChannelMetadata(false, 16);
  
      private static final class AcceptedAddressMemory {
          private final ByteBuffer acceptedAddressMemory;
          private final ByteBuffer acceptedAddressLengthMemory;
          private final long acceptedAddressMemoryAddress;
          private final long acceptedAddressLengthMemoryAddress;
  
          AcceptedAddressMemory() {
              acceptedAddressMemory = Buffer.allocateDirectWithNativeOrder(Native.SIZEOF_SOCKADDR_STORAGE);
              acceptedAddressMemoryAddress = Buffer.memoryAddress(acceptedAddressMemory);
              acceptedAddressLengthMemory = Buffer.allocateDirectWithNativeOrder(Long.BYTES);
              // Needs to be initialized to the size of acceptedAddressMemory.
              // See https://man7.org/linux/man-pages/man2/accept.2.html
              acceptedAddressLengthMemory.putLong(0, Native.SIZEOF_SOCKADDR_STORAGE);
              acceptedAddressLengthMemoryAddress = Buffer.memoryAddress(acceptedAddressLengthMemory);
          }
  
          void free() {
              Buffer.free(acceptedAddressMemory);
              Buffer.free(acceptedAddressLengthMemory);
          }
      }
      private final AcceptedAddressMemory acceptedAddressMemory;
      private long acceptId;
  
      protected AbstractIoUringServerChannel(LinuxSocket socket, boolean active) {
          super(null, socket, active);
  
          // We can only depend on the accepted address if multi-shot is not used.
          // From the manpage:
          //       The multishot variants allow an application to issue a single
          //       accept request, which will repeatedly trigger a CQE when a
          //       connection request comes in. Like other multishot type requests,
          //       the application should look at the CQE flags and see if
          //       IORING_CQE_F_MORE is set on completion as an indication of whether
          //       or not the accept request will generate further CQEs. Note that
          //       for the multishot variants, setting addr and addrlen may not make
          //       a lot of sense, as the same value would be used for every accepted
          //       connection. This means that the data written to addr may be
          //       overwritten by a new connection before the application has had
          //       time to process a past connection. If the application knows that a
          //       new connection cannot come in before a previous one has been
          //       processed, it may be used as expected.
          if (IoUring.isAcceptMultishotEnabled()) {
              acceptedAddressMemory = null;
          } else {
              acceptedAddressMemory = new AcceptedAddressMemory();
          }
      }
  
      @Override
      public final ChannelMetadata metadata() {
          return METADATA;
      }
  
      @Override
      protected final void doClose() throws Exception {
          super.doClose();
      }
  
      @Override
      protected final AbstractUringUnsafe newUnsafe() {
          return new UringServerChannelUnsafe();
     }
 
     @Override
     protected final void doWrite(ChannelOutboundBuffer in) {
         throw new UnsupportedOperationException();
     }
 
     @Override
     protected final void cancelOutstandingReads(IoRegistration registration, int numOutstandingReads) {
         if (acceptId != 0) {
             assert numOutstandingReads == 1 || numOutstandingReads == -1;
             IoUringIoOps ops = IoUringIoOps.newAsyncCancel((byte) 0, acceptId, Native.IORING_OP_ACCEPT);
             registration.submit(ops);
             acceptId = 0;
         } else {
             assert numOutstandingReads == 0 || numOutstandingReads == -1;
         }
     }
 
     @Override
     protected final void cancelOutstandingWrites(IoRegistration registration, int numOutstandingWrites) {
         assert numOutstandingWrites == 0;
     }
 
     abstract Channel newChildChannel(
             int fd, ByteBuffer acceptedAddressMemory) throws Exception;
 
     private final class UringServerChannelUnsafe extends AbstractIoUringChannel.AbstractUringUnsafe {
 
         @Override
         protected int scheduleWriteMultiple(ChannelOutboundBuffer in) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         protected int scheduleWriteSingle(Object msg) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         boolean writeComplete0(byte op, int res, int flags, short data, int outstanding) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         protected int scheduleRead0(boolean first, boolean socketIsEmpty) {
             assert acceptId == 0;
             final IoUringRecvByteAllocatorHandle allocHandle = recvBufAllocHandle();
             allocHandle.attemptedBytesRead(1);
 
             int fd = fd().intValue();
             IoRegistration registration = registration();
 
             final short ioPrio;
 
             final long acceptedAddressMemoryAddress;
             final long acceptedAddressLengthMemoryAddress;
             if (IoUring.isAcceptMultishotEnabled()) {
                 // Let's use multi-shot accept to reduce overhead.
                 ioPrio = Native.IORING_ACCEPT_MULTISHOT;
                 acceptedAddressMemoryAddress = 0;
                 acceptedAddressLengthMemoryAddress = 0;
             } else {
                 // Depending on if socketIsEmpty is true we will arm the poll upfront and skip the initial transfer
                 // attempt.
                 // See https://github.com/axboe/liburing/wiki/io_uring-and-networking-in-2023#socket-state
                 //
                 // Depending on if this is the first read or not we will use Native.IORING_ACCEPT_DONT_WAIT.
                 // The idea is that if the socket is blocking we can do the first read in a blocking fashion
                 // and so not need to also register POLLIN. As we can not 100 % sure if reads after the first will
                 // be possible directly we schedule these with Native.IORING_ACCEPT_DONT_WAIT. This allows us to still
                 // be able to signal the fireChannelReadComplete() in a timely manner and be consistent with other
                 // transports.
                 //
                 // IORING_ACCEPT_POLL_FIRST and IORING_ACCEPT_DONTWAIT were added in the same release.
                 // We need to check if its supported as otherwise providing these would result in an -EINVAL.
                 if (IoUring.isAcceptNoWaitSupported()) {
                     if (first) {
                         ioPrio = socketIsEmpty ? Native.IORING_ACCEPT_POLL_FIRST : 0;
                     } else {
                         ioPrio = Native.IORING_ACCEPT_DONTWAIT;
                     }
                 } else {
                     ioPrio = 0;
                 }
 
                 assert acceptedAddressMemory != null;
                 acceptedAddressMemoryAddress = acceptedAddressMemory.acceptedAddressMemoryAddress;
                 acceptedAddressLengthMemoryAddress = acceptedAddressMemory.acceptedAddressLengthMemoryAddress;
             }
 
             // See https://github.com/axboe/liburing/wiki/What's-new-with-io_uring-in-6.10#improvements-for-accept
             IoUringIoOps ops = IoUringIoOps.newAccept(fd, (byte) 0, 0, ioPrio,
                     acceptedAddressMemoryAddress, acceptedAddressLengthMemoryAddress, nextOpsId());
             acceptId = registration.submit(ops);
             if (acceptId == 0) {
                 return 0;
             }
             if ((ioPrio & Native.IORING_ACCEPT_MULTISHOT) != 0) {
                 // Let's return -1 to signal that we used multi-shot.
                 return -1;
             }
             return 1;
         }
 
         @Override
         protected void readComplete0(byte op, int res, int flags, short data, int outstanding) {
             if (res == Native.ERRNO_ECANCELED_NEGATIVE) {
                 acceptId = 0;
                 return;
             }
             boolean rearm = (flags & Native.IORING_CQE_F_MORE) == 0;
             if (rearm) {
                 // Only reset if we don't use multi-shot or we need to re-arm because the multi-shot was cancelled.
                 acceptId = 0;
             }
             final IoUringRecvByteAllocatorHandle allocHandle =
                     (IoUringRecvByteAllocatorHandle) unsafe()
                             .recvBufAllocHandle();
             final ChannelPipeline pipeline = pipeline();
             allocHandle.lastBytesRead(res);
 
             if (res >= 0) {
                 allocHandle.incMessagesRead(1);
                 final ByteBuffer acceptedAddressBuffer;
                 final long acceptedAddressLengthMemoryAddress;
                 if (acceptedAddressMemory == null) {
                     acceptedAddressBuffer = null;
                 } else {
                     acceptedAddressBuffer = acceptedAddressMemory.acceptedAddressMemory;
                 }
                 try {
                     Channel channel = newChildChannel(res, acceptedAddressBuffer);
                     pipeline.fireChannelRead(channel);
 
                     if (allocHandle.continueReading() &&
                             // If IORING_CQE_F_SOCK_NONEMPTY is supported we should check for it first before
                             // trying to schedule a read. If it's supported and not part of the flags we know for sure
                             // that the next read (which would be using Native.IORING_ACCEPT_DONTWAIT) will complete
                             // without be able to read any data. This is useless work and we can skip it.
                             //
                             // See https://github.com/axboe/liburing/wiki/What's-new-with-io_uring-in-6.10
                             !socketIsEmpty(flags)) {
                         if (rearm) {
                             // We only should schedule another read if we need to rearm.
                             // See https://github.com/axboe/liburing/wiki/io_uring-and-networking-in-2023#multi-shot
                             scheduleRead(false);
                         }
                     } else {
                         allocHandle.readComplete();
                         pipeline.fireChannelReadComplete();
                     }
                 } catch (Throwable cause) {
                     allocHandle.readComplete();
                     pipeline.fireChannelReadComplete();
                     pipeline.fireExceptionCaught(cause);
                 }
             } else {
                 allocHandle.readComplete();
                 pipeline.fireChannelReadComplete();
                 // Check if we did fail because there was nothing to accept atm.
                 if (res != ERRNO_EAGAIN_NEGATIVE && res != ERRNO_EWOULDBLOCK_NEGATIVE) {
                     // Something bad happened. Convert to an exception.
                     pipeline.fireExceptionCaught(Errors.newIOException("io_uring accept", res));
                 }
             }
         }
 
         @Override
         public void connect(final SocketAddress remoteAddress, final SocketAddress localAddress,
                             final ChannelPromise promise) {
             promise.setFailure(new UnsupportedOperationException());
         }
 
         @Override
         protected void freeResourcesNow(IoRegistration reg) {
             super.freeResourcesNow(reg);
             if (acceptedAddressMemory != null) {
                 acceptedAddressMemory.free();
             }
         }
     }
 
     @Override
     protected boolean socketIsEmpty(int flags) {
         // IORING_CQE_F_SOCK_NONEMPTY is used for accept since IORING_ACCEPT_DONTWAIT was added.
         // See https://github.com/axboe/liburing/wiki/What's-new-with-io_uring-in-6.10
         return IoUring.isAcceptNoWaitSupported() &&
                 IoUring.isCqeFSockNonEmptySupported() && (flags & Native.IORING_CQE_F_SOCK_NONEMPTY) == 0;
     }
 
     @Override
     boolean isPollInFirst() {
         return false;
     }
 }