// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/socket/tcp_socket_io_completion_port_win.h"

#include <functional>
#include <utility>

#include "base/dcheck_is_on.h"
#include "base/debug/crash_logging.h"
#include "base/memory/scoped_refptr.h"
#include "base/message_loop/message_pump_win.h"
#include "base/metrics/histogram_functions.h"
#include "base/notreached.h"
#include "base/numerics/checked_math.h"
#include "base/numerics/safe_conversions.h"
#include "base/rand_util.h"
#include "base/task/current_thread.h"
#include "base/threading/thread_checker.h"
#include "base/win/object_watcher.h"
#include "base/win/scoped_handle.h"
#include "net/base/io_buffer.h"
#include "net/base/net_errors.h"
#include "net/base/network_activity_monitor.h"
#include "net/log/net_log.h"
#include "net/socket/socket_net_log_params.h"

namespace net {

namespace {

// Outcome of setting FILE_SKIP_COMPLETION_PORT_ON_SUCCESS on a socket. Used in
// UMA histograms so should not be renumbered.
enum class SkipCompletionPortOnSuccessOutcome {
  kNotSupported,
  kSetFileCompletionNotificationModesFailed,
  kSuccess,
  kMaxValue = kSuccess
};

bool g_skip_completion_port_on_success_enabled = true;

// Returns true if all available transport protocols return Installable File
// System (IFS) handles. Returns false on error or if any available transport
// protocol doesn't return IFS handles. An IFS handle is required to use
// FILE_SKIP_COMPLETION_PORT_ON_SUCCESS. See
// https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-setfilecompletionnotificationmodes#:~:text=FILE_SKIP_COMPLETION_PORT_ON_SUCCESS
bool SkipCompletionPortOnSuccessIsSupported() {
  size_t info_count = 1;

  for (int num_attempts = 0; num_attempts < 3; ++num_attempts) {
    auto buffer = base::HeapArray<WSAPROTOCOL_INFOW>::Uninit(info_count);
    DWORD buffer_length =
        base::checked_cast<DWORD>(buffer.as_span().size_bytes());
    int result = ::WSAEnumProtocolsW(/*lpiProtocols=*/nullptr, buffer.data(),
                                     &buffer_length);
    if (result == SOCKET_ERROR) {
      if (::WSAGetLastError() == WSAENOBUFS) {
        // Insufficient buffer length: Try again with an updated `info_count`
        // computed from the requested `buffer_length`.
        info_count =
            base::CheckDiv(
                base::CheckAdd(buffer_length, sizeof(WSAPROTOCOL_INFOW) - 1),
                sizeof(WSAPROTOCOL_INFOW))
                .ValueOrDie();
        continue;
      }

      // Protocol retrieval error.
      return false;
    }

    // Return true iff all protocols return IFS handles.
    return std::ranges::all_of(
        buffer.subspan(0, result), [](const WSAPROTOCOL_INFOW& protocol_info) {
          return protocol_info.dwServiceFlags1 & XP1_IFS_HANDLES;
        });
  }

  // Too many protocol retrieval attempts failed due to insufficient buffer
  // length.
  return false;
}

// Returns true for 1/1000 calls, indicating if a subsampled histogram should be
// recorded.
bool ShouldRecordSubsampledHistogram() {
  // Not using `base::MetricsSubSampler` because it's not thread-safe sockets
  // could be used from multiple threads.
  static std::atomic<uint64_t> counter = base::RandUint64();
  // Relaxed memory order since there is no dependent memory access.
  uint64_t val = counter.fetch_add(1, std::memory_order_relaxed);
  return val % 1000 == 0;
}

class WSAEventHandleTraits {
 public:
  using Handle = WSAEVENT;

  WSAEventHandleTraits() = delete;
  WSAEventHandleTraits(const WSAEventHandleTraits&) = delete;
  WSAEventHandleTraits& operator=(const WSAEventHandleTraits&) = delete;

  static bool CloseHandle(Handle handle) {
    return ::WSACloseEvent(handle) != FALSE;
  }
  static bool IsHandleValid(Handle handle) {
    return handle != WSA_INVALID_EVENT;
  }
  static Handle NullHandle() { return WSA_INVALID_EVENT; }
};

// "Windows Sockets 2 event objects are system objects in Windows environments"
// so `base::win::VerifierTraits` verifier can be used.
// Source:
// https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsacreateevent
#if DCHECK_IS_ON()
using VerifierTraits = base::win::VerifierTraits;
#else
using VerifierTraits = base::win::DummyVerifierTraits;
#endif
using ScopedWSAEventHandle =
    base::win::GenericScopedHandle<WSAEventHandleTraits, VerifierTraits>;

}  // namespace

class TcpSocketIoCompletionPortWin::CoreImpl
    : public TCPSocketWin::Core,
      public base::win::ObjectWatcher::Delegate,
      public base::MessagePumpForIO::IOHandler {
 public:
  // Context for an overlapped I/O operation.
  struct IOContext : public base::MessagePumpForIO::IOContext {
    using CompletionMethod =
        int (TcpSocketIoCompletionPortWin::*)(DWORD bytes_transferred,
                                              DWORD error,
                                              scoped_refptr<IOBuffer> buffer,
                                              int buffer_length);

    explicit IOContext(scoped_refptr<CoreImpl> core);

    // Keeps the `CoreImpl` alive until the operation is complete. Required to
    // handle `base::MessagePumpForIO::IOHandler::OnIOCompleted`.
    const scoped_refptr<CoreImpl> core_keep_alive;

    // Buffer used for the operation, or null if the operation was ReadIfReady.
    scoped_refptr<IOBuffer> buffer;
    int buffer_length = 0;

    // Method to call upon completion of the operation. The return value is
    // passed to `completion_callback`.
    CompletionMethod completion_method = nullptr;

    // External callback to invoke upon completion of the operation.
    // Note: This callback is cleared if the context belongs to an outstanding
    // ReadIfReady() call which has since been cancelled.
    // See TcpSocketIoCompletionPortWin::CancelReadIfReady().
    CompletionOnceCallback completion_callback;
  };

  explicit CoreImpl(TcpSocketIoCompletionPortWin* socket);

  CoreImpl(const CoreImpl&) = delete;
  CoreImpl& operator=(const CoreImpl&) = delete;

  // TCPSocketWin::Core:
  void Detach() override;
  HANDLE GetConnectEvent() override;
  void WatchForConnect() override;

  // Sets a weak reference to the pending ReadIfReady IO context. There is an
  // assumption that we will only have one outstanding ReadIfReady request at
  // any given time.
  void set_pending_read_if_ready_io_context(
      IOContext* read_if_ready_io_context) {
    CHECK(!pending_read_if_ready_io_context_);
    pending_read_if_ready_io_context_ = read_if_ready_io_context;
  }

  // Returns the pending ReadIfReady IO context if any. Please note that this
  // releases the weak reference for the IOContext held by this instance.
  IOContext* take_pending_read_if_ready_io_context() {
    return pending_read_if_ready_io_context_.ExtractAsDangling();
  }
  // Returns true if we have a pending read IO context.
  bool has_pending_read_if_ready_io_context() const {
    return pending_read_if_ready_io_context_ != nullptr;
  }

 private:
  ~CoreImpl() override;

  // base::win::ObjectWatcher::Delegate:
  void OnObjectSignaled(HANDLE object) override;

  // base::MessagePumpForIO::IOHandler:
  void OnIOCompleted(base::MessagePumpForIO::IOContext* context,
                     DWORD bytes_transferred,
                     DWORD error) override;

  // Stops watching and closes the connect event, if valid.
  void StopWatchingAndCloseConnectEvent();

  // Owning socket.
  raw_ptr<TcpSocketIoCompletionPortWin> socket_;

  // Event to watch for connect completion.
  ScopedWSAEventHandle connect_event_;

  // Watcher for `connect_event_`.
  base::win::ObjectWatcher connect_watcher_;

  // Weak reference to the last initiated pending ReadIfReady IO context if any.
  // There is an assumption that we will only have one outstanding Read request
  // at any given time.
  raw_ptr<IOContext> pending_read_if_ready_io_context_ = nullptr;
};

TcpSocketIoCompletionPortWin::DisableSkipCompletionPortOnSuccessForTesting::
    DisableSkipCompletionPortOnSuccessForTesting() {
  CHECK(g_skip_completion_port_on_success_enabled);
  g_skip_completion_port_on_success_enabled = false;
}

TcpSocketIoCompletionPortWin::DisableSkipCompletionPortOnSuccessForTesting::
    ~DisableSkipCompletionPortOnSuccessForTesting() {
  CHECK(!g_skip_completion_port_on_success_enabled);
  g_skip_completion_port_on_success_enabled = true;
}

TcpSocketIoCompletionPortWin::TcpSocketIoCompletionPortWin(
    std::unique_ptr<SocketPerformanceWatcher> socket_performance_watcher,
    NetLog* net_log,
    const NetLogSource& source)
    : TCPSocketWin(std::move(socket_performance_watcher), net_log, source) {}

TcpSocketIoCompletionPortWin::TcpSocketIoCompletionPortWin(
    std::unique_ptr<SocketPerformanceWatcher> socket_performance_watcher,
    NetLogWithSource net_log_source)
    : TCPSocketWin(std::move(socket_performance_watcher), net_log_source) {}

TcpSocketIoCompletionPortWin::~TcpSocketIoCompletionPortWin() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  Close();
}

int TcpSocketIoCompletionPortWin::Read(IOBuffer* buf,
                                       int buf_len,
                                       CompletionOnceCallback callback) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  return HandleReadRequest(buf, buf_len, std::move(callback),
                           /*allow_zero_byte_overlapped_read=*/false);
}

int TcpSocketIoCompletionPortWin::ReadIfReady(IOBuffer* buf,
                                              int buf_len,
                                              CompletionOnceCallback callback) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  return HandleReadRequest(buf, buf_len, std::move(callback),
                           /*allow_zero_byte_overlapped_read=*/true);
}

int TcpSocketIoCompletionPortWin::CancelReadIfReady() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  CoreImpl& core = GetCoreImpl();

  // Only ReadIfReady() operations can be cancelled.
  CoreImpl::IOContext* pending_read_if_ready_io_context =
      core.take_pending_read_if_ready_io_context();

  CHECK(pending_read_if_ready_io_context);

  DVLOG(2) << "CancelReadIfReady(). Read operation pending completion";
  pending_read_if_ready_io_context->completion_callback.Reset();
  return net::OK;
}

int TcpSocketIoCompletionPortWin::Write(
    IOBuffer* buf,
    int buf_len,
    CompletionOnceCallback callback,
    const NetworkTrafficAnnotationTag& traffic_annotation) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  if (!EnsureOverlappedIOInitialized()) {
    return net::ERR_FAILED;
  }

  CoreImpl& core = GetCoreImpl();

  WSABUF write_buffer;
  write_buffer.len = buf_len;
  write_buffer.buf = buf->data();
  DWORD bytes_sent = 0;
  auto context = std::make_unique<CoreImpl::IOContext>(&core);

  const int rv =
      ::WSASend(socket_, &write_buffer, /*dwBufferCount=*/1, &bytes_sent,
                /*dwFlags=*/0, context->GetOverlapped(),
                /*lpCompletionRoutine=*/nullptr);

  // "Citations" below are from
  // https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsasend

  if (rv == 0) {
    // When "the send operation has completed immediately, WSASend returns zero"
    // and "completion routine will have already been scheduled", unless the
    // option to skip completion port on success is set.

    if (skip_completion_port_on_success_) {
      // Free `context` here since it will no longer be accessed.
      context.reset();
    } else {
      // Release `context` so that `OnIOCompleted()` can take ownership, but
      // don't set any member since completion is already handled.
      context.release();
    }

    return DidCompleteWrite(bytes_sent, ERROR_SUCCESS, buf, buf_len);
  }

  CHECK_EQ(rv, SOCKET_ERROR);
  const int wsa_error = ::WSAGetLastError();
  if (wsa_error == WSA_IO_PENDING) {
    // "The error code WSA_IO_PENDING indicates that the overlapped operation
    // has been successfully initiated and that completion will be indicated at
    // a later time." Set members of `context` for proper completion handling
    // and release it so that `OnIOCompleted()` can take ownership.
    context->buffer = buf;
    context->buffer_length = buf_len;
    context->completion_callback = std::move(callback);
    context->completion_method =
        &TcpSocketIoCompletionPortWin::DidCompleteWrite;
    context.release();

    return ERR_IO_PENDING;
  }

  // "Any other error code [than WSA_IO_PENDING] indicates that [...] no
  // completion indication will occur", so free `context` here.
  context.reset();

  int net_error = MapSystemError(wsa_error);
  NetLogSocketError(net_log_, NetLogEventType::SOCKET_WRITE_ERROR, net_error,
                    wsa_error);
  return net_error;
}

scoped_refptr<TCPSocketWin::Core> TcpSocketIoCompletionPortWin::CreateCore() {
  return base::MakeRefCounted<CoreImpl>(this);
}

bool TcpSocketIoCompletionPortWin::HasPendingRead() const {
  return num_pending_reads_ != 0;
}

void TcpSocketIoCompletionPortWin::OnClosed() {}

bool TcpSocketIoCompletionPortWin::EnsureOverlappedIOInitialized() {
  CHECK_NE(socket_, INVALID_SOCKET);
  if (registered_as_io_handler_) {
    return true;
  }

  // Register the `CoreImpl` as an I/O handler for the socket.
  CoreImpl& core = GetCoreImpl();
  registered_as_io_handler_ = base::CurrentIOThread::Get()->RegisterIOHandler(
      reinterpret_cast<HANDLE>(socket_), &core);
  if (!registered_as_io_handler_) {
    return false;
  }

  // Activate an option to skip the completion port when an operation completes
  // immediately.
  static const bool skip_completion_port_on_success_is_supported =
      SkipCompletionPortOnSuccessIsSupported();
  if (g_skip_completion_port_on_success_enabled &&
      skip_completion_port_on_success_is_supported) {
    BOOL result = ::SetFileCompletionNotificationModes(
        reinterpret_cast<HANDLE>(socket_),
        FILE_SKIP_COMPLETION_PORT_ON_SUCCESS);
    skip_completion_port_on_success_ = (result != 0);
  }

  // Report the outcome of activating an option to skip the completion port when
  // an operation completes immediately to UMA. Subsampled for efficiency.
  if (ShouldRecordSubsampledHistogram()) {
    SkipCompletionPortOnSuccessOutcome outcome;
    if (skip_completion_port_on_success_) {
      outcome = SkipCompletionPortOnSuccessOutcome::kSuccess;
    } else if (skip_completion_port_on_success_is_supported) {
      outcome = SkipCompletionPortOnSuccessOutcome::
          kSetFileCompletionNotificationModesFailed;
    } else {
      outcome = SkipCompletionPortOnSuccessOutcome::kNotSupported;
    }

    base::UmaHistogramEnumeration(
        "Net.Socket.SkipCompletionPortOnSuccessOutcome", outcome);
  }

  return true;
}

int TcpSocketIoCompletionPortWin::DidCompleteRead(
    DWORD bytes_transferred,
    DWORD error,
    scoped_refptr<IOBuffer> buffer,
    int buffer_length) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  // We can clear out the pending ReadIfReady IO context here as
  // the ReadIfReady operation has completed.
  GetCoreImpl().take_pending_read_if_ready_io_context();

  CHECK_GT(num_pending_reads_, 0);
  --num_pending_reads_;

  if (error == ERROR_SUCCESS) {
    if (buffer) {
      // `bytes_transferred` should be <= `buffer_length` so cast should
      // succeed.
      const int rv = base::checked_cast<int>(bytes_transferred);
      net_log_.AddByteTransferEvent(NetLogEventType::SOCKET_BYTES_RECEIVED, rv,
                                    buffer->data());
      activity_monitor::IncrementBytesReceived(rv);
      return rv;
    }  // else: asynchronous ReadIfReady completed.
    return OK;
  }

  const int rv = MapSystemError(error);
  CHECK_NE(rv, ERR_IO_PENDING);
  NetLogSocketError(net_log_, NetLogEventType::SOCKET_READ_ERROR, rv, error);
  return rv;
}

int TcpSocketIoCompletionPortWin::DidCompleteWrite(
    DWORD bytes_transferred,
    DWORD error,
    scoped_refptr<IOBuffer> buffer,
    int buffer_length) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  if (error == ERROR_SUCCESS) {
    // `bytes_transferred` should be <= `buffer_length` so cast should succeed.
    const int rv = base::checked_cast<int>(bytes_transferred);
    if (rv > buffer_length) {
      // It seems that some winsock interceptors report that more was written
      // than was available. Treat this as an error.  https://crbug.com/27870
      LOG(ERROR) << "Detected broken LSP: Asked to write " << buffer_length
                 << " bytes, but " << rv << " bytes reported.";
      return ERR_WINSOCK_UNEXPECTED_WRITTEN_BYTES;
    }

    net_log_.AddByteTransferEvent(NetLogEventType::SOCKET_BYTES_SENT, rv,
                                  buffer->data());
    return rv;
  }

  const int rv = MapSystemError(error);
  CHECK_NE(rv, ERR_IO_PENDING);
  NetLogSocketError(net_log_, NetLogEventType::SOCKET_WRITE_ERROR, rv, error);
  return rv;
}

int TcpSocketIoCompletionPortWin::HandleReadRequest(
    IOBuffer* buffer,
    int buf_len,
    CompletionOnceCallback callback,
    bool allow_zero_byte_overlapped_read) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  CHECK_NE(socket_, INVALID_SOCKET);

  if (!EnsureOverlappedIOInitialized()) {
    return net::ERR_FAILED;
  }

  CoreImpl& core = GetCoreImpl();
  CHECK(!core.has_pending_read_if_ready_io_context());

  WSABUF read_buffer{.len = static_cast<ULONG>(buf_len), .buf = buffer->data()};
  DWORD flags = 0;
  DWORD bytes_read = 0;

  std::unique_ptr<CoreImpl::IOContext> context;
  if (!allow_zero_byte_overlapped_read) {
    context = std::make_unique<CoreImpl::IOContext>(&core);
  }

  auto handle_immediate_completion = [&](DWORD bytes_transferred, DWORD error) {
    if (skip_completion_port_on_success_) {
      // Free `context` here since it will no longer be accessed.
      context.reset();
    } else {
      // Release `context` so that `OnIOCompleted()` can take ownership, but
      // don't set any member since completion is already handled.
      context.release();
    }
    ++num_pending_reads_;
    return DidCompleteRead(bytes_transferred, error, buffer, buf_len);
  };

  // Perform a read. The presence of an OVERLAPPED structure depends on
  // whether zero-byte overlapped reads are allowed (for ReadIfReady).
  auto rv = ::WSARecv(
      socket_, &read_buffer, /*dwBufferCount=*/1, &bytes_read, &flags,
      allow_zero_byte_overlapped_read ? nullptr : context->GetOverlapped(),
      nullptr);

  // "Citations" below are from
  // https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsarecv

  if (rv == 0) {
    // When "the receive operation has completed immediately, WSARecv returns
    // zero" and "completion routine will have already been scheduled", unless
    // the option to skip completion port on success is set.
    return handle_immediate_completion(bytes_read, ERROR_SUCCESS);
  }

  int wsa_error = ::WSAGetLastError();

  if (allow_zero_byte_overlapped_read) {
    context = std::make_unique<CoreImpl::IOContext>(&core);
    // Clear the buffer and retry with an overlapped zero-byte read. The
    // expectation here is that this WSARecv call will complete later and
    // we will receive a notification about data being available in the
    // completion callback. See CoreImpl::OnIOCompleted(). The return
    // value from WSARecv here in that case will be WSA_IO_PENDING.
    read_buffer = {};
    rv = ::WSARecv(socket_, &read_buffer, /*dwBufferCount=*/1, &bytes_read,
                   &flags, context->GetOverlapped(), nullptr);
    if (rv == 0) {
      // Immediate completion for zero-byte read. The contract for ReadIfReady
      // explicitly states that on synchronous completion we need to return
      // bytes read or 0 for EOF. As we passed in a 0 byte buffer, WSARecv
      // returns 0 and bytes_read is also set to 0. If we return 0, the
      // callers assume it is EOF and propagate failures like ERR_EMPTY_RESPONSE
      // etc.
      //
      // We need to issue another non overlapped WSARecv here with the passed
      // in buffer which should hopefully complete synchronously. If it fails
      // we need to propagate the error upstream.
      read_buffer.len = buf_len;
      read_buffer.buf = buffer->data();
      rv = ::WSARecv(socket_, &read_buffer, /*dwBufferCount=*/1, &bytes_read,
                     &flags, nullptr, nullptr);
      if (rv == 0) {
        return handle_immediate_completion(bytes_read, ERROR_SUCCESS);
      }

      wsa_error = ::WSAGetLastError();

      SCOPED_CRASH_KEY_NUMBER("TcpSocketIOCP", "ReadIfReadyError", wsa_error);

      NOTREACHED() << "ReadIfReady(). Synchronous WSARecv on socket failed "
                   << "with error: " << wsa_error
                   << " after zero byte overlapped WSARecv reported data.";
    } else {
      wsa_error = ::WSAGetLastError();
    }
  }

  if (wsa_error == WSA_IO_PENDING) {
    // "The error code WSA_IO_PENDING indicates that the overlapped operation
    // has been successfully initiated and that completion will be indicated at
    // a later time." Set members of `context` for proper completion handling
    // and release it so that `OnIOCompleted()` can take ownership.
    context->completion_callback = std::move(callback);
    context->completion_method = &TcpSocketIoCompletionPortWin::DidCompleteRead;
    if (!allow_zero_byte_overlapped_read) {
      // Hold a reference to the caller buffer if they called Read().
      context->buffer = buffer;
      context->buffer_length = buf_len;
    } else {
      // Hold a weak reference to the IOContext created for the ReadIfReady()
      // operation in case this operation is cancelled later.
      // See TcpSocketIoCompletionPortWin::CancelReadIfReady().
      core.set_pending_read_if_ready_io_context(context.get());
    }
    context.release();

    ++num_pending_reads_;
    return ERR_IO_PENDING;
  }

  // "Any other error code [than WSA_IO_PENDING] indicates that [...] no
  // completion indication will occur", so free `context` here.
  context.reset();

  int net_error = MapSystemError(wsa_error);
  NetLogSocketError(net_log_, NetLogEventType::SOCKET_READ_ERROR, net_error,
                    wsa_error);
  return net_error;
}

TcpSocketIoCompletionPortWin::CoreImpl&
TcpSocketIoCompletionPortWin::GetCoreImpl() {
  return CHECK_DEREF(static_cast<CoreImpl*>(core_.get()));
}

TcpSocketIoCompletionPortWin::CoreImpl::IOContext::IOContext(
    scoped_refptr<CoreImpl> core)
    : core_keep_alive(std::move(core)) {}

TcpSocketIoCompletionPortWin::CoreImpl::CoreImpl(
    TcpSocketIoCompletionPortWin* socket)
    : base::MessagePumpForIO::IOHandler(FROM_HERE), socket_(socket) {}

void TcpSocketIoCompletionPortWin::CoreImpl::Detach() {
  StopWatchingAndCloseConnectEvent();

  // It is not possible to stop ongoing read or write operations. Clear
  // `socket_` so that the completion handler doesn't invoke completion methods.
  socket_ = nullptr;
  pending_read_if_ready_io_context_ = nullptr;
}

HANDLE TcpSocketIoCompletionPortWin::CoreImpl::GetConnectEvent() {
  if (!connect_event_.IsValid()) {
    // Lazy-initialize the event.
    connect_event_.Set(::WSACreateEvent());
    ::WSAEventSelect(socket_->socket_, connect_event_.get(), FD_CONNECT);
  }
  return connect_event_.get();
}

void TcpSocketIoCompletionPortWin::CoreImpl::WatchForConnect() {
  CHECK(connect_event_.IsValid());
  connect_watcher_.StartWatchingOnce(connect_event_.get(), this);
}

TcpSocketIoCompletionPortWin::CoreImpl::~CoreImpl() {
  CHECK(!socket_);
}

void TcpSocketIoCompletionPortWin::CoreImpl::OnObjectSignaled(HANDLE object) {
  CHECK_EQ(object, connect_event_.get());
  CHECK(socket_);
  CHECK(!!socket_->connect_callback_);

  // Stop watching and close the event since it's no longer needed.
  StopWatchingAndCloseConnectEvent();

  socket_->DidCompleteConnect();
}

void TcpSocketIoCompletionPortWin::CoreImpl::OnIOCompleted(
    base::MessagePumpForIO::IOContext* context,
    DWORD bytes_transferred,
    DWORD error) {
  // Take ownership of `context`, which was released in `Read` or `Write`. The
  // cast is safe because all overlapped I/O operations handled by this are
  // issued with the OVERLAPPED member of an `IOContext` object.
  std::unique_ptr<IOContext> derived_context(static_cast<IOContext*>(context));

  if (socket_ && derived_context->completion_method) {
    const int rv = std::invoke(
        derived_context->completion_method, socket_, bytes_transferred, error,
        std::move(derived_context->buffer), derived_context->buffer_length);
    // The completion callback is cleared when an outstanding ReadIfReady is
    // cancelled. See TcpSocketIoCompletionPortWin::CancelReadIfReady().
    if (derived_context->completion_callback) {
      std::move(derived_context->completion_callback).Run(rv);
    }
  }
}

void TcpSocketIoCompletionPortWin::CoreImpl::
    StopWatchingAndCloseConnectEvent() {
  if (connect_event_.IsValid()) {
    connect_watcher_.StopWatching();
    connect_event_.Close();
  }
}

}  // namespace net