// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.io;

/// A TCP socket using TLS and SSL.
///
/// A secure socket may be used as either a [Stream] or an [IOSink].
abstract class SecureSocket implements Socket {
  external factory SecureSocket._(RawSecureSocket rawSocket);

  /// Constructs a new secure client socket and connects it to the given
  /// [host] on port [port].
  ///
  /// The returned Future will complete with a
  /// [SecureSocket] that is connected and ready for subscription.
  ///
  /// The certificate provided by the server is checked
  /// using the trusted certificates set in the SecurityContext object.
  /// The default SecurityContext object contains a built-in set of trusted
  /// root certificates for well-known certificate authorities.
  ///
  /// [onBadCertificate] is an optional handler for unverifiable certificates.
  /// The handler receives the [X509Certificate], and can inspect it and
  /// decide (or let the user decide) whether to accept
  /// the connection or not.  The handler should return true
  /// to continue the [SecureSocket] connection.
  ///
  /// [supportedProtocols] is an optional list of protocols (in decreasing
  /// order of preference) to use during the ALPN protocol negotiation with the
  /// server.  Example values are "http/1.1" or "h2".  The selected protocol
  /// can be obtained via [SecureSocket.selectedProtocol].
  ///
  /// The argument [timeout] is used to specify the maximum allowed time to wait
  /// for a connection to be established. If [timeout] is longer than the system
  /// level timeout duration, a timeout may occur sooner than specified in
  /// [timeout]. On timeout, a [SocketException] is thrown and all ongoing
  /// connection attempts to [host] are cancelled.
  static Future<SecureSocket> connect(host, int port,
      {SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols,
      Duration? timeout}) {
    return RawSecureSocket.connect(host, port,
            context: context,
            onBadCertificate: onBadCertificate,
            supportedProtocols: supportedProtocols,
            timeout: timeout)
        .then((rawSocket) => new SecureSocket._(rawSocket));
  }

  /// Like [connect], but returns a [Future] that completes with a
  /// [ConnectionTask] that can be cancelled if the [SecureSocket] is no
  /// longer needed.
  static Future<ConnectionTask<SecureSocket>> startConnect(host, int port,
      {SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols}) {
    return RawSecureSocket.startConnect(host, port,
            context: context,
            onBadCertificate: onBadCertificate,
            supportedProtocols: supportedProtocols)
        .then((rawState) {
      Future<SecureSocket> socket =
          rawState.socket.then((rawSocket) => new SecureSocket._(rawSocket));
      return new ConnectionTask<SecureSocket>._(socket, rawState._onCancel);
    });
  }

  /// Initiates TLS on an existing connection.
  ///
  /// Takes an already connected [socket] and starts client side TLS
  /// handshake to make the communication secure. When the returned
  /// future completes the [SecureSocket] has completed the TLS
  /// handshake. Using this function requires that the other end of the
  /// connection is prepared for TLS handshake.
  ///
  /// If the [socket] already has a subscription, this subscription
  /// will no longer receive and events. In most cases calling
  /// [StreamSubscription.pause] on this subscription before
  /// starting TLS handshake is the right thing to do.
  ///
  /// The given [socket] is closed and may not be used anymore.
  ///
  /// If the [host] argument is passed it will be used as the host name
  /// for the TLS handshake. If [host] is not passed the host name from
  /// the [socket] will be used. The [host] can be either a [String] or
  /// an [InternetAddress].
  ///
  /// [supportedProtocols] is an optional list of protocols (in decreasing
  /// order of preference) to use during the ALPN protocol negotiation with the
  /// server.  Example values are "http/1.1" or "h2".  The selected protocol
  /// can be obtained via [SecureSocket.selectedProtocol].
  ///
  /// Calling this function will _not_ cause a DNS host lookup. If the
  /// [host] passed is a [String], the [InternetAddress] for the
  /// resulting [SecureSocket] will have the passed in [host] as its
  /// host value and the internet address of the already connected
  /// socket as its address value.
  ///
  /// See [connect] for more information on the arguments.
  static Future<SecureSocket> secure(Socket socket,
      {host,
      SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      @Since("2.6") List<String>? supportedProtocols}) {
    return ((socket as dynamic /*_Socket*/)._detachRaw() as Future)
        .then<RawSecureSocket>((detachedRaw) {
      return RawSecureSocket.secure(detachedRaw[0] as RawSocket,
          subscription: detachedRaw[1] as StreamSubscription<RawSocketEvent>?,
          host: host,
          context: context,
          onBadCertificate: onBadCertificate,
          supportedProtocols: supportedProtocols);
    }).then<SecureSocket>((raw) => new SecureSocket._(raw));
  }

  /// Initiates TLS on an existing server connection.
  ///
  /// Takes an already connected [socket] and starts server side TLS
  /// handshake to make the communication secure. When the returned
  /// future completes the [SecureSocket] has completed the TLS
  /// handshake. Using this function requires that the other end of the
  /// connection is going to start the TLS handshake.
  ///
  /// If the [socket] already has a subscription, this subscription
  /// will no longer receive and events. In most cases calling
  /// [StreamSubscription.pause] on this subscription
  /// before starting TLS handshake is the right thing to do.
  ///
  /// If some of the data of the TLS handshake has already been read
  /// from the socket this data can be passed in the [bufferedData]
  /// parameter. This data will be processed before any other data
  /// available on the socket.
  ///
  /// See [SecureServerSocket.bind] for more information on the
  /// arguments.
  static Future<SecureSocket> secureServer(
      Socket socket, SecurityContext? context,
      {List<int>? bufferedData,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false,
      List<String>? supportedProtocols}) {
    return ((socket as dynamic /*_Socket*/)._detachRaw() as Future)
        .then<RawSecureSocket>((detachedRaw) {
      return RawSecureSocket.secureServer(detachedRaw[0] as RawSocket, context,
          subscription: detachedRaw[1] as StreamSubscription<RawSocketEvent>?,
          bufferedData: bufferedData,
          requestClientCertificate: requestClientCertificate,
          requireClientCertificate: requireClientCertificate,
          supportedProtocols: supportedProtocols);
    }).then<SecureSocket>((raw) => new SecureSocket._(raw));
  }

  /// The peer certificate for a connected SecureSocket.
  ///
  /// If this [SecureSocket] is the server end of a secure socket connection,
  /// [peerCertificate] will return the client certificate, or `null` if no
  /// client certificate was received.  If this socket is the client end,
  /// [peerCertificate] will return the server's certificate.
  X509Certificate? get peerCertificate;

  /// The protocol which was selected during ALPN protocol negotiation.
  ///
  /// Returns `null` if one of the peers does not have support for ALPN, did not
  /// specify a list of supported ALPN protocols or there was no common
  /// protocol between client and server.
  String? get selectedProtocol;

  /// Renegotiates an existing secure connection.
  ///
  /// Renews the session keys and possibly changes the connection properties.
  ///
  /// This repeats the SSL or TLS handshake, with options that allow clearing
  /// the session cache and requesting a client certificate.
  void renegotiate(
      {bool useSessionCache = true,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false});
}

/// `RawSecureSocket` provides a secure (SSL or TLS) network connection.
///
/// Client connections to a server are provided by calling
/// RawSecureSocket.connect.  A secure server, created with
/// [RawSecureServerSocket], also returns `RawSecureSocket` objects representing
/// the server end of a secure connection.
/// The certificate provided by the server is checked
/// using the trusted certificates set in the [SecurityContext] object.
/// The default [SecurityContext] object contains a built-in set of trusted
/// root certificates for well-known certificate authorities.
abstract class RawSecureSocket implements RawSocket {
  /// Constructs a new secure client socket and connect it to the given
  /// host on the given port.
  ///
  /// The returned [Future] is completed with the
  /// [RawSecureSocket] when it is connected and ready for subscription.
  ///
  /// The certificate provided by the server is checked using the trusted
  /// certificates set in the SecurityContext object If a certificate and key are
  /// set on the client, using [SecurityContext.useCertificateChain] and
  /// [SecurityContext.usePrivateKey], and the server asks for a client
  /// certificate, then that client certificate is sent to the server.
  ///
  /// [onBadCertificate] is an optional handler for unverifiable certificates.
  /// The handler receives the [X509Certificate], and can inspect it and
  /// decide (or let the user decide) whether to accept
  /// the connection or not.  The handler should return true
  /// to continue the [RawSecureSocket] connection.
  ///
  /// [supportedProtocols] is an optional list of protocols (in decreasing
  /// order of preference) to use during the ALPN protocol negotiation with the
  /// server.  Example values are "http/1.1" or "h2".  The selected protocol
  /// can be obtained via [RawSecureSocket.selectedProtocol].
  static Future<RawSecureSocket> connect(host, int port,
      {SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols,
      Duration? timeout}) {
    _RawSecureSocket._verifyFields(host, port, false, false);
    return RawSocket.connect(host, port, timeout: timeout).then((socket) {
      return secure(socket,
          context: context,
          onBadCertificate: onBadCertificate,
          supportedProtocols: supportedProtocols);
    });
  }

  /// Like [connect], but returns a [Future] that completes with a
  /// [ConnectionTask] that can be cancelled if the [RawSecureSocket] is no
  /// longer needed.
  static Future<ConnectionTask<RawSecureSocket>> startConnect(host, int port,
      {SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols}) {
    return RawSocket.startConnect(host, port)
        .then((ConnectionTask<RawSocket> rawState) {
      Future<RawSecureSocket> socket = rawState.socket.then((rawSocket) {
        return secure(rawSocket,
            context: context,
            onBadCertificate: onBadCertificate,
            supportedProtocols: supportedProtocols);
      });
      return new ConnectionTask<RawSecureSocket>._(socket, rawState._onCancel);
    });
  }

  /// Initiates TLS on an existing connection.
  ///
  /// Takes an already connected [socket] and starts client side TLS
  /// handshake to make the communication secure. When the returned
  /// future completes the [RawSecureSocket] has completed the TLS
  /// handshake. Using this function requires that the other end of the
  /// connection is prepared for TLS handshake.
  ///
  /// If the [socket] already has a subscription, pass the existing
  /// subscription in the [subscription] parameter. The [secure]
  /// operation will take over the subscription by replacing the
  /// handlers with it own secure processing. The caller must not touch
  /// this subscription anymore. Passing a paused subscription is an
  /// error.
  ///
  /// If the [host] argument is passed it will be used as the host name
  /// for the TLS handshake. If [host] is not passed the host name from
  /// the [socket] will be used. The [host] can be either a [String] or
  /// an [InternetAddress].
  ///
  /// [supportedProtocols] is an optional list of protocols (in decreasing
  /// order of preference) to use during the ALPN protocol negotiation with the
  /// server.  Example values are "http/1.1" or "h2".  The selected protocol
  /// can be obtained via [SecureSocket.selectedProtocol].
  ///
  /// Calling this function will _not_ cause a DNS host lookup. If the
  /// [host] passed is a [String] the [InternetAddress] for the
  /// resulting [SecureSocket] will have this passed in [host] as its
  /// host value and the internet address of the already connected
  /// socket as its address value.
  ///
  /// See [connect] for more information on the arguments.
  static Future<RawSecureSocket> secure(RawSocket socket,
      {StreamSubscription<RawSocketEvent>? subscription,
      host,
      SecurityContext? context,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols}) {
    socket.readEventsEnabled = false;
    socket.writeEventsEnabled = false;
    return _RawSecureSocket.connect(
        host != null ? host : socket.address.host, socket.port, false, socket,
        subscription: subscription,
        context: context,
        onBadCertificate: onBadCertificate,
        supportedProtocols: supportedProtocols);
  }

  /// Initiates TLS on an existing server connection.
  ///
  /// Takes an already connected [socket] and starts server side TLS
  /// handshake to make the communication secure. When the returned
  /// future completes the [RawSecureSocket] has completed the TLS
  /// handshake. Using this function requires that the other end of the
  /// connection is going to start the TLS handshake.
  ///
  /// If the [socket] already has a subscription, pass the existing
  /// subscription in the [subscription] parameter. The [secureServer]
  /// operation will take over the subscription by replacing the
  /// handlers with it own secure processing. The caller must not touch
  /// this subscription anymore. Passing a paused subscription is an
  /// error.
  ///
  /// If some of the data of the TLS handshake has already been read
  /// from the socket this data can be passed in the [bufferedData]
  /// parameter. This data will be processed before any other data
  /// available on the socket.
  ///
  /// See [RawSecureServerSocket.bind] for more information on the
  /// arguments.
  static Future<RawSecureSocket> secureServer(
      RawSocket socket, SecurityContext? context,
      {StreamSubscription<RawSocketEvent>? subscription,
      List<int>? bufferedData,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false,
      List<String>? supportedProtocols}) {
    socket.readEventsEnabled = false;
    socket.writeEventsEnabled = false;
    return _RawSecureSocket.connect(
        socket.address, socket.remotePort, true, socket,
        context: context,
        subscription: subscription,
        bufferedData: bufferedData,
        requestClientCertificate: requestClientCertificate,
        requireClientCertificate: requireClientCertificate,
        supportedProtocols: supportedProtocols);
  }

  /// Renegotiate an existing secure connection, renewing the session keys
  /// and possibly changing the connection properties.
  ///
  /// This repeats the SSL or TLS handshake, with options that allow clearing
  /// the session cache and requesting a client certificate.
  void renegotiate(
      {bool useSessionCache = true,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false});

  /// Get the peer certificate for a connected RawSecureSocket.  If this
  /// RawSecureSocket is the server end of a secure socket connection,
  /// [peerCertificate] will return the client certificate, or null, if no
  /// client certificate was received.  If it is the client end,
  /// [peerCertificate] will return the server's certificate.
  X509Certificate? get peerCertificate;

  /// The protocol which was selected during protocol negotiation.
  ///
  /// Returns null if one of the peers does not have support for ALPN, did not
  /// specify a list of supported ALPN protocols or there was no common
  /// protocol between client and server.
  String? get selectedProtocol;
}

/// X509Certificate represents an SSL certificate, with accessors to
/// get the fields of the certificate.
@pragma("vm:entry-point")
abstract class X509Certificate {
  @pragma("vm:entry-point")
  external factory X509Certificate._();

  /// The DER encoded bytes of the certificate.
  Uint8List get der;

  /// The PEM encoded String of the certificate.
  String get pem;

  /// The SHA1 hash of the certificate.
  Uint8List get sha1;

  String get subject;
  String get issuer;
  DateTime get startValidity;
  DateTime get endValidity;
}

class _FilterStatus {
  bool progress = false; // The filter read or wrote data to the buffers.
  bool readEmpty = true; // The read buffers and decryption filter are empty.
  bool writeEmpty = true; // The write buffers and encryption filter are empty.
  // These are set if a buffer changes state from empty or full.
  bool readPlaintextNoLongerEmpty = false;
  bool writePlaintextNoLongerFull = false;
  bool readEncryptedNoLongerFull = false;
  bool writeEncryptedNoLongerEmpty = false;

  _FilterStatus();
}

class _RawSecureSocket extends Stream<RawSocketEvent>
    implements RawSecureSocket {
  // Status states
  static const int handshakeStatus = 201;
  static const int connectedStatus = 202;
  static const int closedStatus = 203;

  // Buffer identifiers.
  // These must agree with those in the native C++ implementation.
  static const int readPlaintextId = 0;
  static const int writePlaintextId = 1;
  static const int readEncryptedId = 2;
  static const int writeEncryptedId = 3;
  static const int bufferCount = 4;

  // Is a buffer identifier for an encrypted buffer?
  static bool _isBufferEncrypted(int identifier) =>
      identifier >= readEncryptedId;

  final RawSocket _socket;
  final Completer<_RawSecureSocket> _handshakeComplete =
      new Completer<_RawSecureSocket>();
  final _controller = new StreamController<RawSocketEvent>(sync: true);
  late final StreamSubscription<RawSocketEvent> _socketSubscription;
  List<int>? _bufferedData;
  int _bufferedDataIndex = 0;
  final InternetAddress address;
  final bool isServer;
  final SecurityContext context;
  final bool requestClientCertificate;
  final bool requireClientCertificate;
  final bool Function(X509Certificate certificate)? onBadCertificate;

  var _status = handshakeStatus;
  bool _writeEventsEnabled = true;
  bool _readEventsEnabled = true;
  int _pauseCount = 0;
  bool _pendingReadEvent = false;
  bool _socketClosedRead = false; // The network socket is closed for reading.
  bool _socketClosedWrite = false; // The network socket is closed for writing.
  bool _closedRead = false; // The secure socket has fired an onClosed event.
  bool _closedWrite = false; // The secure socket has been closed for writing.
  // The network socket is gone.
  Completer<RawSecureSocket> _closeCompleter = new Completer<RawSecureSocket>();
  _FilterStatus _filterStatus = new _FilterStatus();
  bool _connectPending = true;
  bool _filterPending = false;
  bool _filterActive = false;

  _SecureFilter? _secureFilter = new _SecureFilter._();
  String? _selectedProtocol;

  static Future<_RawSecureSocket> connect(
      dynamic /*String|InternetAddress*/ host,
      int requestedPort,
      bool isServer,
      RawSocket socket,
      {SecurityContext? context,
      StreamSubscription<RawSocketEvent>? subscription,
      List<int>? bufferedData,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false,
      bool onBadCertificate(X509Certificate certificate)?,
      List<String>? supportedProtocols}) {
    _verifyFields(host, requestedPort, requestClientCertificate,
        requireClientCertificate);
    if (host is InternetAddress) host = host.host;
    InternetAddress address = socket.address;
    if (host != null) {
      address = InternetAddress._cloneWithNewHost(address, host);
    }
    return new _RawSecureSocket(
            address,
            requestedPort,
            isServer,
            context ?? SecurityContext.defaultContext,
            socket,
            subscription,
            bufferedData,
            requestClientCertificate,
            requireClientCertificate,
            onBadCertificate,
            supportedProtocols)
        ._handshakeComplete
        .future;
  }

  _RawSecureSocket(
      this.address,
      int requestedPort,
      this.isServer,
      this.context,
      this._socket,
      StreamSubscription<RawSocketEvent>? subscription,
      this._bufferedData,
      this.requestClientCertificate,
      this.requireClientCertificate,
      this.onBadCertificate,
      List<String>? supportedProtocols) {
    _controller
      ..onListen = _onSubscriptionStateChange
      ..onPause = _onPauseStateChange
      ..onResume = _onPauseStateChange
      ..onCancel = _onSubscriptionStateChange;
    // Throw an ArgumentError if any field is invalid.  After this, all
    // errors will be reported through the future or the stream.
    final secureFilter = _secureFilter!;
    secureFilter.init();
    secureFilter
        .registerHandshakeCompleteCallback(_secureHandshakeCompleteHandler);
    if (onBadCertificate != null) {
      secureFilter.registerBadCertificateCallback(_onBadCertificateWrapper);
    }
    _socket.readEventsEnabled = true;
    _socket.writeEventsEnabled = false;
    if (subscription == null) {
      // If a current subscription is provided use this otherwise
      // create a new one.
      _socketSubscription = _socket.listen(_eventDispatcher,
          onError: _reportError, onDone: _doneHandler);
    } else {
      _socketSubscription = subscription;
      if (_socketSubscription.isPaused) {
        _socket.close();
        throw new ArgumentError("Subscription passed to TLS upgrade is paused");
      }
      // If we are upgrading a socket that is already closed for read,
      // report an error as if we received readClosed during the handshake.
      dynamic s = _socket; // Cast to dynamic to avoid warning.
      if (s._socket.closedReadEventSent) {
        _eventDispatcher(RawSocketEvent.readClosed);
      }
      _socketSubscription
        ..onData(_eventDispatcher)
        ..onError(_reportError)
        ..onDone(_doneHandler);
    }
    try {
      var encodedProtocols =
          SecurityContext._protocolsToLengthEncoding(supportedProtocols);
      secureFilter.connect(
          address.host,
          context,
          isServer,
          requestClientCertificate || requireClientCertificate,
          requireClientCertificate,
          encodedProtocols);
      _secureHandshake();
    } catch (e, s) {
      _reportError(e, s);
    }
  }

  StreamSubscription<RawSocketEvent> listen(void onData(RawSocketEvent data)?,
      {Function? onError, void onDone()?, bool? cancelOnError}) {
    _sendWriteEvent();
    return _controller.stream.listen(onData,
        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
  }

  static void _verifyFields(host, int requestedPort,
      bool requestClientCertificate, bool requireClientCertificate) {
    if (host is! String && host is! InternetAddress) {
      throw new ArgumentError("host is not a String or an InternetAddress");
    }
    // TODO(40614): Remove once non-nullability is sound.
    ArgumentError.checkNotNull(requestedPort, "requestedPort");
    if (requestedPort < 0 || requestedPort > 65535) {
      throw ArgumentError("requestedPort is not in the range 0..65535");
    }
    // TODO(40614): Remove once non-nullability is sound.
    ArgumentError.checkNotNull(
        requestClientCertificate, "requestClientCertificate");
    ArgumentError.checkNotNull(
        requireClientCertificate, "requireClientCertificate");
  }

  int get port => _socket.port;

  InternetAddress get remoteAddress => _socket.remoteAddress;

  int get remotePort => _socket.remotePort;

  void set _owner(owner) {
    (_socket as dynamic)._owner = owner;
  }

  int available() {
    return _status != connectedStatus
        ? 0
        : _secureFilter!.buffers![readPlaintextId].length;
  }

  Future<RawSecureSocket> close() {
    shutdown(SocketDirection.both);
    return _closeCompleter.future;
  }

  void _completeCloseCompleter([RawSocket? dummy]) {
    if (!_closeCompleter.isCompleted) _closeCompleter.complete(this);
  }

  void _close() {
    _closedWrite = true;
    _closedRead = true;
    _socket.close().then(_completeCloseCompleter);
    _socketClosedWrite = true;
    _socketClosedRead = true;
    if (!_filterActive && _secureFilter != null) {
      _secureFilter!.destroy();
      _secureFilter = null;
    }
    if (_socketSubscription != null) {
      _socketSubscription.cancel();
    }
    _controller.close();
    _status = closedStatus;
  }

  void shutdown(SocketDirection direction) {
    if (direction == SocketDirection.send ||
        direction == SocketDirection.both) {
      _closedWrite = true;
      if (_filterStatus.writeEmpty) {
        _socket.shutdown(SocketDirection.send);
        _socketClosedWrite = true;
        if (_closedRead) {
          _close();
        }
      }
    }
    if (direction == SocketDirection.receive ||
        direction == SocketDirection.both) {
      _closedRead = true;
      _socketClosedRead = true;
      _socket.shutdown(SocketDirection.receive);
      if (_socketClosedWrite) {
        _close();
      }
    }
  }

  bool get writeEventsEnabled => _writeEventsEnabled;

  void set writeEventsEnabled(bool value) {
    _writeEventsEnabled = value;
    if (value) {
      Timer.run(() => _sendWriteEvent());
    }
  }

  bool get readEventsEnabled => _readEventsEnabled;

  void set readEventsEnabled(bool value) {
    _readEventsEnabled = value;
    _scheduleReadEvent();
  }

  Uint8List? read([int? length]) {
    if (length != null && length < 0) {
      throw new ArgumentError(
          "Invalid length parameter in SecureSocket.read (length: $length)");
    }
    if (_closedRead) {
      throw new SocketException("Reading from a closed socket");
    }
    if (_status != connectedStatus) {
      return null;
    }
    var result = _secureFilter!.buffers![readPlaintextId].read(length);
    _scheduleFilter();
    return result;
  }

  SocketMessage? readMessage([int? count]) {
    throw UnsupportedError("Message-passing not supported by secure sockets");
  }

  static int _fixOffset(int? offset) => offset ?? 0;

  // Write the data to the socket, and schedule the filter to encrypt it.
  int write(List<int> data, [int offset = 0, int? bytes]) {
    if (bytes != null && bytes < 0) {
      throw new ArgumentError(
          "Invalid bytes parameter in SecureSocket.read (bytes: $bytes)");
    }
    // TODO(40614): Remove once non-nullability is sound.
    offset = _fixOffset(offset);
    if (offset < 0) {
      throw new ArgumentError(
          "Invalid offset parameter in SecureSocket.read (offset: $offset)");
    }
    if (_closedWrite) {
      _controller.addError(new SocketException("Writing to a closed socket"));
      return 0;
    }
    if (_status != connectedStatus) return 0;
    bytes ??= data.length - offset;

    int written =
        _secureFilter!.buffers![writePlaintextId].write(data, offset, bytes);
    if (written > 0) {
      _filterStatus.writeEmpty = false;
    }
    _scheduleFilter();
    return written;
  }

  int sendMessage(List<SocketControlMessage> controlMessages, List<int> data,
      [int offset = 0, int? count]) {
    throw UnsupportedError("Message-passing not supported by secure sockets");
  }

  X509Certificate? get peerCertificate => _secureFilter!.peerCertificate;

  String? get selectedProtocol => _selectedProtocol;

  bool _onBadCertificateWrapper(X509Certificate certificate) {
    if (onBadCertificate == null) return false;
    return onBadCertificate!(certificate);
  }

  bool setOption(SocketOption option, bool enabled) {
    return _socket.setOption(option, enabled);
  }

  Uint8List getRawOption(RawSocketOption option) {
    return _socket.getRawOption(option);
  }

  void setRawOption(RawSocketOption option) {
    _socket.setRawOption(option);
  }

  void _eventDispatcher(RawSocketEvent event) {
    try {
      if (event == RawSocketEvent.read) {
        _readHandler();
      } else if (event == RawSocketEvent.write) {
        _writeHandler();
      } else if (event == RawSocketEvent.readClosed) {
        _closeHandler();
      }
    } catch (e, stackTrace) {
      _reportError(e, stackTrace);
    }
  }

  void _readHandler() {
    _readSocket();
    _scheduleFilter();
  }

  void _writeHandler() {
    _writeSocket();
    _scheduleFilter();
  }

  void _doneHandler() {
    if (_filterStatus.readEmpty) {
      _close();
    }
  }

  void _reportError(e, [StackTrace? stackTrace]) {
    if (_status == closedStatus) {
      return;
    } else if (_connectPending) {
      // _connectPending is true until the handshake has completed, and the
      // _handshakeComplete future returned from SecureSocket.connect has
      // completed.  Before this point, we must complete it with an error.
      _handshakeComplete.completeError(e, stackTrace);
    } else {
      _controller.addError(e, stackTrace);
    }
    _close();
  }

  void _closeHandler() async {
    if (_status == connectedStatus) {
      if (_closedRead) return;
      _socketClosedRead = true;
      if (_filterStatus.readEmpty) {
        _closedRead = true;
        _controller.add(RawSocketEvent.readClosed);
        if (_socketClosedWrite) {
          _close();
        }
      } else {
        await _scheduleFilter();
      }
    } else if (_status == handshakeStatus) {
      _socketClosedRead = true;
      if (_filterStatus.readEmpty) {
        _reportError(
            new HandshakeException('Connection terminated during handshake'),
            null);
      } else {
        await _secureHandshake();
      }
    }
  }

  Future<void> _secureHandshake() async {
    try {
      bool needRetryHandshake = await _secureFilter!.handshake();
      if (needRetryHandshake) {
        // Some certificates have been evaluated, need to retry handshake.
        await _secureHandshake();
      } else {
        _filterStatus.writeEmpty = false;
        _readSocket();
        _writeSocket();
        await _scheduleFilter();
      }
    } catch (e, stackTrace) {
      _reportError(e, stackTrace);
    }
  }

  void renegotiate(
      {bool useSessionCache = true,
      bool requestClientCertificate = false,
      bool requireClientCertificate = false}) {
    if (_status != connectedStatus) {
      throw new HandshakeException(
          "Called renegotiate on a non-connected socket");
    }
    _secureFilter!.renegotiate(
        useSessionCache, requestClientCertificate, requireClientCertificate);
    _status = handshakeStatus;
    _filterStatus.writeEmpty = false;
    _scheduleFilter();
  }

  void _secureHandshakeCompleteHandler() {
    _status = connectedStatus;
    if (_connectPending) {
      _connectPending = false;
      try {
        _selectedProtocol = _secureFilter!.selectedProtocol();
        // We don't want user code to run synchronously in this callback.
        Timer.run(() => _handshakeComplete.complete(this));
      } catch (error, stack) {
        _handshakeComplete.completeError(error, stack);
      }
    }
  }

  void _onPauseStateChange() {
    if (_controller.isPaused) {
      _pauseCount++;
    } else {
      _pauseCount--;
      if (_pauseCount == 0) {
        _scheduleReadEvent();
        _sendWriteEvent(); // Can send event synchronously.
      }
    }

    if (!_socketClosedRead || !_socketClosedWrite) {
      if (_controller.isPaused) {
        _socketSubscription.pause();
      } else {
        _socketSubscription.resume();
      }
    }
  }

  void _onSubscriptionStateChange() {
    if (_controller.hasListener) {
      // TODO(ajohnsen): Do something here?
    }
  }

  Future<void> _scheduleFilter() {
    _filterPending = true;
    return _tryFilter();
  }

  Future<void> _tryFilter() async {
    try {
      while (true) {
        if (_status == closedStatus) {
          return;
        }
        if (!_filterPending || _filterActive) {
          return;
        }
        _filterActive = true;
        _filterPending = false;

        _filterStatus = await _pushAllFilterStages();
        _filterActive = false;
        if (_status == closedStatus) {
          _secureFilter!.destroy();
          _secureFilter = null;
          return;
        }
        _socket.readEventsEnabled = true;
        if (_filterStatus.writeEmpty && _closedWrite && !_socketClosedWrite) {
          // Checks for and handles all cases of partially closed sockets.
          shutdown(SocketDirection.send);
          if (_status == closedStatus) {
            return;
          }
        }
        if (_filterStatus.readEmpty && _socketClosedRead && !_closedRead) {
          if (_status == handshakeStatus) {
            _secureFilter!.handshake();
            if (_status == handshakeStatus) {
              throw new HandshakeException(
                  'Connection terminated during handshake');
            }
          }
          _closeHandler();
        }
        if (_status == closedStatus) {
          return;
        }
        if (_filterStatus.progress) {
          _filterPending = true;
          if (_filterStatus.writeEncryptedNoLongerEmpty) {
            _writeSocket();
          }
          if (_filterStatus.writePlaintextNoLongerFull) {
            _sendWriteEvent();
          }
          if (_filterStatus.readEncryptedNoLongerFull) {
            _readSocket();
          }
          if (_filterStatus.readPlaintextNoLongerEmpty) {
            _scheduleReadEvent();
          }
          if (_status == handshakeStatus) {
            await _secureHandshake();
          }
        }
      }
    } catch (e, st) {
      _reportError(e, st);
    }
  }

  List<int>? _readSocketOrBufferedData(int bytes) {
    final bufferedData = _bufferedData;
    if (bufferedData != null) {
      if (bytes > bufferedData.length - _bufferedDataIndex) {
        bytes = bufferedData.length - _bufferedDataIndex;
      }
      var result =
          bufferedData.sublist(_bufferedDataIndex, _bufferedDataIndex + bytes);
      _bufferedDataIndex += bytes;
      if (bufferedData.length == _bufferedDataIndex) {
        _bufferedData = null;
      }
      return result;
    } else if (!_socketClosedRead) {
      return _socket.read(bytes);
    } else {
      return null;
    }
  }

  void _readSocket() {
    if (_status == closedStatus) return;
    var buffer = _secureFilter!.buffers![readEncryptedId];
    if (buffer.writeFromSource(_readSocketOrBufferedData) > 0) {
      _filterStatus.readEmpty = false;
    } else {
      _socket.readEventsEnabled = false;
    }
  }

  void _writeSocket() {
    if (_socketClosedWrite) return;
    var buffer = _secureFilter!.buffers![writeEncryptedId];
    if (buffer.readToSocket(_socket)) {
      // Returns true if blocked
      _socket.writeEventsEnabled = true;
    }
  }

  // If a read event should be sent, add it to the controller.
  _scheduleReadEvent() {
    if (!_pendingReadEvent &&
        _readEventsEnabled &&
        _pauseCount == 0 &&
        _secureFilter != null &&
        !_secureFilter!.buffers![readPlaintextId].isEmpty) {
      _pendingReadEvent = true;
      Timer.run(_sendReadEvent);
    }
  }

  _sendReadEvent() {
    _pendingReadEvent = false;
    if (_status != closedStatus &&
        _readEventsEnabled &&
        _pauseCount == 0 &&
        _secureFilter != null &&
        !_secureFilter!.buffers![readPlaintextId].isEmpty) {
      _controller.add(RawSocketEvent.read);
      _scheduleReadEvent();
    }
  }

  // If a write event should be sent, add it to the controller.
  _sendWriteEvent() {
    if (!_closedWrite &&
        _writeEventsEnabled &&
        _pauseCount == 0 &&
        _secureFilter != null &&
        _secureFilter!.buffers![writePlaintextId].free > 0) {
      _writeEventsEnabled = false;
      _controller.add(RawSocketEvent.write);
    }
  }

  Future<_FilterStatus> _pushAllFilterStages() async {
    bool wasInHandshake = _status != connectedStatus;
    List args = new List<dynamic>.filled(2 + bufferCount * 2, null);
    args[0] = _secureFilter!._pointer();
    args[1] = wasInHandshake;
    var bufs = _secureFilter!.buffers!;
    for (var i = 0; i < bufferCount; ++i) {
      args[2 * i + 2] = bufs[i].start;
      args[2 * i + 3] = bufs[i].end;
    }

    var response =
        await _IOService._dispatch(_IOService.sslProcessFilter, args);
    if (response.length == 2) {
      if (wasInHandshake) {
        // If we're in handshake, throw a handshake error.
        _reportError(
            new HandshakeException('${response[1]} error ${response[0]}'),
            null);
      } else {
        // If we're connected, throw a TLS error.
        _reportError(
            new TlsException('${response[1]} error ${response[0]}'), null);
      }
    }
    int start(int index) => response[2 * index];
    int end(int index) => response[2 * index + 1];

    _FilterStatus status = new _FilterStatus();
    // Compute writeEmpty as "write plaintext buffer and write encrypted
    // buffer were empty when we started and are empty now".
    status.writeEmpty = bufs[writePlaintextId].isEmpty &&
        start(writeEncryptedId) == end(writeEncryptedId);
    // If we were in handshake when this started, _writeEmpty may be false
    // because the handshake wrote data after we checked.
    if (wasInHandshake) status.writeEmpty = false;

    // Compute readEmpty as "both read buffers were empty when we started
    // and are empty now".
    status.readEmpty = bufs[readEncryptedId].isEmpty &&
        start(readPlaintextId) == end(readPlaintextId);

    _ExternalBuffer buffer = bufs[writePlaintextId];
    int new_start = start(writePlaintextId);
    if (new_start != buffer.start) {
      status.progress = true;
      if (buffer.free == 0) {
        status.writePlaintextNoLongerFull = true;
      }
      buffer.start = new_start;
    }
    buffer = bufs[readEncryptedId];
    new_start = start(readEncryptedId);
    if (new_start != buffer.start) {
      status.progress = true;
      if (buffer.free == 0) {
        status.readEncryptedNoLongerFull = true;
      }
      buffer.start = new_start;
    }
    buffer = bufs[writeEncryptedId];
    int new_end = end(writeEncryptedId);
    if (new_end != buffer.end) {
      status.progress = true;
      if (buffer.length == 0) {
        status.writeEncryptedNoLongerEmpty = true;
      }
      buffer.end = new_end;
    }
    buffer = bufs[readPlaintextId];
    new_end = end(readPlaintextId);
    if (new_end != buffer.end) {
      status.progress = true;
      if (buffer.length == 0) {
        status.readPlaintextNoLongerEmpty = true;
      }
      buffer.end = new_end;
    }
    return status;
  }
}

/// A circular buffer backed by an external byte array.  Accessed from
/// both C++ and Dart code in an unsynchronized way, with one reading
/// and one writing.  All updates to start and end are done by Dart code.
class _ExternalBuffer {
  // This will be an ExternalByteArray, backed by C allocated data.
  @pragma("vm:entry-point", "set")
  List<int>? data;

  @pragma("vm:entry-point")
  int start;

  @pragma("vm:entry-point")
  int end;

  final int size;

  _ExternalBuffer(int size)
      : size = size,
        start = size ~/ 2,
        end = size ~/ 2;

  void advanceStart(int bytes) {
    assert(start > end || start + bytes <= end);
    start += bytes;
    if (start >= size) {
      start -= size;
      assert(start <= end);
      assert(start < size);
    }
  }

  void advanceEnd(int bytes) {
    assert(start <= end || start > end + bytes);
    end += bytes;
    if (end >= size) {
      end -= size;
      assert(end < start);
      assert(end < size);
    }
  }

  bool get isEmpty => end == start;

  int get length => start > end ? size + end - start : end - start;

  int get linearLength => start > end ? size - start : end - start;

  int get free => start > end ? start - end - 1 : size + start - end - 1;

  int get linearFree {
    if (start > end) return start - end - 1;
    if (start == 0) return size - end - 1;
    return size - end;
  }

  Uint8List? read(int? bytes) {
    if (bytes == null) {
      bytes = length;
    } else {
      bytes = min(bytes, length);
    }
    if (bytes == 0) return null;
    Uint8List result = new Uint8List(bytes);
    int bytesRead = 0;
    // Loop over zero, one, or two linear data ranges.
    while (bytesRead < bytes) {
      int toRead = min(bytes - bytesRead, linearLength);
      result.setRange(bytesRead, bytesRead + toRead, data!, start);
      advanceStart(toRead);
      bytesRead += toRead;
    }
    return result;
  }

  int write(List<int> inputData, int offset, int bytes) {
    if (bytes > free) {
      bytes = free;
    }
    int written = 0;
    int toWrite = min(bytes, linearFree);
    // Loop over zero, one, or two linear data ranges.
    while (toWrite > 0) {
      data!.setRange(end, end + toWrite, inputData, offset);
      advanceEnd(toWrite);
      offset += toWrite;
      written += toWrite;
      toWrite = min(bytes - written, linearFree);
    }
    return written;
  }

  int writeFromSource(List<int>? getData(int requested)) {
    int written = 0;
    int toWrite = linearFree;
    // Loop over zero, one, or two linear data ranges.
    while (toWrite > 0) {
      // Source returns at most toWrite bytes, and it returns null when empty.
      var inputData = getData(toWrite);
      if (inputData == null || inputData.length == 0) break;
      var len = inputData.length;
      data!.setRange(end, end + len, inputData);
      advanceEnd(len);
      written += len;
      toWrite = linearFree;
    }
    return written;
  }

  bool readToSocket(RawSocket socket) {
    // Loop over zero, one, or two linear data ranges.
    while (true) {
      var toWrite = linearLength;
      if (toWrite == 0) return false;
      int bytes = socket.write(data!, start, toWrite);
      advanceStart(bytes);
      if (bytes < toWrite) {
        // The socket has blocked while we have data to write.
        return true;
      }
    }
  }
}

abstract class _SecureFilter {
  external factory _SecureFilter._();

  void connect(
      String hostName,
      SecurityContext context,
      bool isServer,
      bool requestClientCertificate,
      bool requireClientCertificate,
      Uint8List protocols);
  void destroy();
  Future<bool> handshake();
  String? selectedProtocol();
  void rehandshake();
  void renegotiate(bool useSessionCache, bool requestClientCertificate,
      bool requireClientCertificate);
  void init();
  X509Certificate? get peerCertificate;
  int processBuffer(int bufferIndex);
  void registerBadCertificateCallback(Function callback);
  void registerHandshakeCompleteCallback(Function handshakeCompleteHandler);

  // This call may cause a reference counted pointer in the native
  // implementation to be retained. It should only be called when the resulting
  // value is passed to the IO service through a call to dispatch().
  int _pointer();

  List<_ExternalBuffer>? get buffers;
}

/// A secure networking exception caused by a failure in the
/// TLS/SSL protocol.
class TlsException implements IOException {
  final String type;
  final String message;
  final OSError? osError;

  @pragma("vm:entry-point")
  const TlsException([String message = "", OSError? osError])
      : this._("TlsException", message, osError);

  const TlsException._(this.type, this.message, this.osError);

  String toString() {
    StringBuffer sb = new StringBuffer();
    sb.write(type);
    if (message.isNotEmpty) {
      sb.write(": $message");
      if (osError != null) {
        sb.write(" ($osError)");
      }
    } else if (osError != null) {
      sb.write(": $osError");
    }
    return sb.toString();
  }
}

/// An exception that happens in the handshake phase of establishing
/// a secure network connection.
@pragma("vm:entry-point")
class HandshakeException extends TlsException {
  @pragma("vm:entry-point")
  const HandshakeException([String message = "", OSError? osError])
      : super._("HandshakeException", message, osError);
}

/// An exception that happens in the handshake phase of establishing
/// a secure network connection, when looking up or verifying a
/// certificate.
class CertificateException extends TlsException {
  @pragma("vm:entry-point")
  const CertificateException([String message = "", OSError? osError])
      : super._("CertificateException", message, osError);
}