QBluetoothSocket Class

The QBluetoothSocket class enables connection to a Bluetooth device running a bluetooth server. More...

Header:	#include <QBluetoothSocket>
qmake:	QT += bluetooth
Since:	Qt 5.2
Inherits:	QIODevice

This class was introduced in Qt 5.2.

• List of all members, including inherited members

Public Types

enum	SocketError { UnknownSocketError, NoSocketError, HostNotFoundError, ServiceNotFoundError, NetworkError, …, RemoteHostClosedError }
enum	SocketState { UnconnectedState, ServiceLookupState, ConnectingState, ConnectedState, BoundState, …, ListeningState }

Public Functions

	QBluetoothSocket(QObject *parent = nullptr)
	QBluetoothSocket(QBluetoothServiceInfo::Protocol socketType, QObject *parent = nullptr)
virtual	~QBluetoothSocket()
void	abort()
void	connectToService(const QBluetoothServiceInfo &service, QIODevice::OpenMode openMode = ReadWrite)
void	connectToService(const QBluetoothAddress &address, const QBluetoothUuid &uuid, QIODevice::OpenMode openMode = ReadWrite)
void	connectToService(const QBluetoothAddress &address, quint16 port, QIODevice::OpenMode openMode = ReadWrite)
void	disconnectFromService()
QBluetoothSocket::SocketError	error() const
QString	errorString() const
QBluetoothAddress	localAddress() const
QString	localName() const
quint16	localPort() const
QBluetoothAddress	peerAddress() const
QString	peerName() const
quint16	peerPort() const
QBluetooth::SecurityFlags	preferredSecurityFlags() const
void	setPreferredSecurityFlags(QBluetooth::SecurityFlags flags)
bool	setSocketDescriptor(int socketDescriptor, QBluetoothServiceInfo::Protocol socketType, QBluetoothSocket::SocketState socketState = ConnectedState, QIODevice::OpenMode openMode = ReadWrite)
int	socketDescriptor() const
QBluetoothServiceInfo::Protocol	socketType() const
QBluetoothSocket::SocketState	state() const

Reimplemented Public Functions

virtual qint64	bytesAvailable() const override
virtual qint64	bytesToWrite() const override
virtual bool	canReadLine() const override
virtual void	close() override
virtual bool	isSequential() const override

Signals

void	connected()
void	disconnected()
void	error(QBluetoothSocket::SocketError error)
void	stateChanged(QBluetoothSocket::SocketState state)

Protected Functions

void	doDeviceDiscovery(const QBluetoothServiceInfo &service, QIODevice::OpenMode openMode)
void	setSocketError(QBluetoothSocket::SocketError error_)
void	setSocketState(QBluetoothSocket::SocketState state)

Reimplemented Protected Functions

virtual qint64	readData(char *data, qint64 maxSize) override
virtual qint64	writeData(const char *data, qint64 maxSize) override

Detailed Description

QBluetoothSocket supports two socket types, L2CAP and RFCOMM.

L2CAP is a low level datagram-oriented Bluetooth socket. Android does not support L2CAP for socket connections.

RFCOMM is a reliable, stream-oriented socket. RFCOMM sockets emulate an RS-232 serial port.

To create a connection to a Bluetooth service, create a socket of the appropriate type and call connectToService() passing the Bluetooth address and port number. QBluetoothSocket will emit the connected() signal when the connection is established.

If the Protocol is not supported on a platform, calling connectToService() will emit a UnsupportedProtocolError error.

Note: QBluetoothSocket does not support synchronous read and write operations. Functions such as waitForReadyRead() and waitForBytesWritten() are not implemented. I/O operations should be performed using readyRead(), read() and write().

On iOS, this class cannot be used because the platform does not expose an API which may permit access to QBluetoothSocket related features.

Member Type Documentation

enum QBluetoothSocket::SocketError

This enum describes Bluetooth socket error types.

Constant	Value	Description
QBluetoothSocket::UnknownSocketError	QAbstractSocket::UnknownSocketError	An unknown error has occurred.
QBluetoothSocket::NoSocketError	-2	No error. Used for testing.
QBluetoothSocket::HostNotFoundError	QAbstractSocket::HostNotFoundError	Could not find the remote host.
QBluetoothSocket::ServiceNotFoundError	QAbstractSocket::SocketAddressNotAvailableError	Could not find the service UUID on remote host.
QBluetoothSocket::NetworkError	QAbstractSocket::NetworkError	Attempt to read or write from socket returned an error
QBluetoothSocket::UnsupportedProtocolError	8	The Protocol is not supported on this platform.
QBluetoothSocket::OperationError	QAbstractSocket::OperationError	An operation was attempted while the socket was in a state that did not permit it.
QBluetoothSocket::RemoteHostClosedError	QAbstractSocket::RemoteHostClosedError	The remote host closed the connection. This value was introduced by Qt 5.10.

enum QBluetoothSocket::SocketState

This enum describes the state of the Bluetooth socket.

Constant	Value	Description
QBluetoothSocket::UnconnectedState	QAbstractSocket::UnconnectedState	Socket is not connected.
QBluetoothSocket::ServiceLookupState	QAbstractSocket::HostLookupState	Socket is querying connection parameters.
QBluetoothSocket::ConnectingState	QAbstractSocket::ConnectingState	Socket is attempting to connect to a device.
QBluetoothSocket::ConnectedState	QAbstractSocket::ConnectedState	Socket is connected to a device.
QBluetoothSocket::BoundState	QAbstractSocket::BoundState	Socket is bound to a local address and port.
QBluetoothSocket::ClosingState	QAbstractSocket::ClosingState	Socket is connected and will be closed once all pending data is written to the socket.
QBluetoothSocket::ListeningState	QAbstractSocket::ListeningState	Socket is listening for incoming connections.

Member Function Documentation

QBluetoothSocket::QBluetoothSocket(QObject *parent = nullptr)

Constructs a Bluetooth socket with parent.

QBluetoothSocket::QBluetoothSocket(QBluetoothServiceInfo::Protocol socketType, QObject *parent = nullptr)

Constructs a Bluetooth socket of socketType type, with parent.

[signal] void QBluetoothSocket::connected()

This signal is emitted when a connection is established.

See also QBluetoothSocket::ConnectedState and stateChanged().

[signal] void QBluetoothSocket::disconnected()

This signal is emitted when the socket is disconnected.

See also QBluetoothSocket::UnconnectedState and stateChanged().

[signal] void QBluetoothSocket::error(QBluetoothSocket::SocketError error)

This signal is emitted when an error occurs.

Note: Signal error is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

connect(bluetoothSocket, QOverload<QBluetoothSocket::SocketError>::of(&QBluetoothSocket::error),
    [=](QBluetoothSocket::SocketError error){ /* ... */ });

See also error().

[signal] void QBluetoothSocket::stateChanged(QBluetoothSocket::SocketState state)

This signal is emitted when the socket state changes to state.

See also connected(), disconnected(), state(), and QBluetoothSocket::SocketState.

[virtual] QBluetoothSocket::~QBluetoothSocket()

Destroys the Bluetooth socket.

void QBluetoothSocket::abort()

Aborts the current connection and resets the socket. Unlike disconnectFromService(), this function immediately closes the socket, discarding any pending data in the write buffer.

Note: On Android, aborting the socket requires asynchronous interaction with Android threads. Therefore the associated disconnected() and stateChanged() signals are delayed until the threads have finished the closure.

See also disconnectFromService() and close().

[override virtual] qint64 QBluetoothSocket::bytesAvailable() const

Reimplements: QIODevice::bytesAvailable() const.

Returns the number of incoming bytes that are waiting to be read.

See also bytesToWrite() and read().

[override virtual] qint64 QBluetoothSocket::bytesToWrite() const

Reimplements: QIODevice::bytesToWrite() const.

Returns the number of bytes that are waiting to be written. The bytes are written when control goes back to the event loop.

[override virtual] bool QBluetoothSocket::canReadLine() const

Reimplements: QIODevice::canReadLine() const.

Returns true if you can read at least one line from the device

[override virtual] void QBluetoothSocket::close()

Reimplements: QIODevice::close().

Disconnects the socket's connection with the device.

Note: On Android, closing the socket requires asynchronous interaction with Android threads. Therefore the associated disconnected() and stateChanged() signals are delayed until the threads have finished the closure.

void QBluetoothSocket::connectToService(const QBluetoothServiceInfo &service, QIODevice::OpenMode openMode = ReadWrite)

Attempts to connect to the service described by service.

The socket is opened in the given openMode. The socketType() is ignored if service specifies a differing QBluetoothServiceInfo::socketProtocol().

The socket first enters ConnectingState and attempts to connect to the device providing service. If a connection is established, QBluetoothSocket enters ConnectedState and emits connected().

At any point, the socket can emit error() to signal that an error occurred.

Note that most platforms require a pairing prior to connecting to the remote device. Otherwise the connection process may fail.

On Android, only RFCOMM connections are possible. This function ignores any socket protocol indicator and assumes RFCOMM.

See also state() and disconnectFromService().

void QBluetoothSocket::connectToService(const QBluetoothAddress &address, const QBluetoothUuid &uuid, QIODevice::OpenMode openMode = ReadWrite)

Attempts to make a connection to the service identified by uuid on the device with address address.

The socket is opened in the given openMode.

For BlueZ, the socket first enters the ServiceLookupState and queries the connection parameters for uuid. If the service parameters are successfully retrieved the socket enters ConnectingState, and attempts to connect to address. If a connection is established, QBluetoothSocket enters ConnectedState and emits connected().

On Android, the service connection can directly be established using the UUID of the remote service. Therefore the platform does not require the ServiceLookupState and socketType() is always set to QBluetoothServiceInfo::RfcommProtocol.

At any point, the socket can emit error() to signal that an error occurred.

Note that most platforms require a pairing prior to connecting to the remote device. Otherwise the connection process may fail.

See also state() and disconnectFromService().

void QBluetoothSocket::connectToService(const QBluetoothAddress &address, quint16 port, QIODevice::OpenMode openMode = ReadWrite)

Attempts to make a connection with address on the given port.

The socket is opened in the given openMode.

The socket first enters ConnectingState, and attempts to connect to address. If a connection is established, QBluetoothSocket enters ConnectedState and emits connected().

At any point, the socket can emit error() to signal that an error occurred.

On Android and BlueZ (version 5.46 or above), a connection to a service can not be established using a port. Calling this function will emit a ServiceNotFoundError.

Note that most platforms require a pairing prior to connecting to the remote device. Otherwise the connection process may fail.

See also state() and disconnectFromService().

void QBluetoothSocket::disconnectFromService()

Attempts to close the socket. If there is pending data waiting to be written QBluetoothSocket will enter ClosingState and wait until all data has been written. Eventually, it will enter UnconnectedState and emit the disconnected() signal.

See also connectToService().

[protected] void QBluetoothSocket::doDeviceDiscovery(const QBluetoothServiceInfo &service, QIODevice::OpenMode openMode)

Start device discovery for service and open the socket with openMode. If the socket is created with a service uuid device address, use service discovery to find the port number to connect to.

QBluetoothSocket::SocketError QBluetoothSocket::error() const

Returns the last error.

QString QBluetoothSocket::errorString() const

Returns a user displayable text string for the error.

[override virtual] bool QBluetoothSocket::isSequential() const

Reimplements: QIODevice::isSequential() const.

QBluetoothAddress QBluetoothSocket::localAddress() const

Returns the address of the local device.

Although some platforms may differ the socket must generally be connected to guarantee the return of a valid address. In particular, this is true when dealing with platforms that support multiple local Bluetooth adapters.

QString QBluetoothSocket::localName() const

Returns the name of the local device.

Although some platforms may differ the socket must generally be connected to guarantee the return of a valid name. In particular, this is true when dealing with platforms that support multiple local Bluetooth adapters.

quint16 QBluetoothSocket::localPort() const

Returns the port number of the local socket if available, otherwise returns 0. Although some platforms may differ the socket must generally be connected to guarantee the return of a valid port number.

On Android and macOS, this feature is not supported and returns 0.

QBluetoothAddress QBluetoothSocket::peerAddress() const

Returns the address of the peer device.

QString QBluetoothSocket::peerName() const

Returns the name of the peer device.

quint16 QBluetoothSocket::peerPort() const

Return the port number of the peer socket if available, otherwise returns 0. On Android, this feature is not supported.

QBluetooth::SecurityFlags QBluetoothSocket::preferredSecurityFlags() const

Returns the security parameters used for the initial connection attempt.

The security parameters may be renegotiated between the two parties during or after the connection has been established. If such a change happens it is not reflected in the value of this flag.

On macOS, this flag is always set to QBluetooth::Secure.

This function was introduced in Qt 5.6.

See also setPreferredSecurityFlags().

[override virtual protected] qint64 QBluetoothSocket::readData(char *data, qint64 maxSize)

Reimplements: QIODevice::readData(char *data, qint64 maxSize).

void QBluetoothSocket::setPreferredSecurityFlags(QBluetooth::SecurityFlags flags)

Sets the preferred security parameter for the connection attempt to flags. This value is incorporated when calling connectToService(). Therefore it is required to reconnect to change this parameter for an existing connection.

On Bluez this property is set to QBluetooth::Authorization by default.

On macOS, this value is ignored as the platform does not permit access to the security parameter of the socket. By default the platform prefers secure/encrypted connections though and therefore this function always returns QBluetooth::Secure.

Android only supports two levels of security (secure and non-secure). If this flag is set to QBluetooth::NoSecurity the socket object will not employ any authentication or encryption. Any other security flag combination will trigger a secure Bluetooth connection. This flag is set to QBluetooth::Secure by default.

Note: A secure connection requires a pairing between the two devices. On some platforms, the pairing is automatically initiated during the establishment of the connection. Other platforms require the application to manually trigger the pairing before attempting to connect.

This function was introduced in Qt 5.6.

See also preferredSecurityFlags().

bool QBluetoothSocket::setSocketDescriptor(int socketDescriptor, QBluetoothServiceInfo::Protocol socketType, QBluetoothSocket::SocketState socketState = ConnectedState, QIODevice::OpenMode openMode = ReadWrite)

Set the socket to use socketDescriptor with a type of socketType, which is in state, socketState, and mode, openMode.

Returns true on success

See also socketDescriptor().

[protected] void QBluetoothSocket::setSocketError(QBluetoothSocket::SocketError error_)

Sets the type of error that last occurred to error_.

[protected] void QBluetoothSocket::setSocketState(QBluetoothSocket::SocketState state)

Sets the socket state to state.

int QBluetoothSocket::socketDescriptor() const

Returns the platform-specific socket descriptor, if available. This function returns -1 if the descriptor is not available or an error has occurred.

See also setSocketDescriptor().

QBluetoothServiceInfo::Protocol QBluetoothSocket::socketType() const

Returns the socket type. The socket automatically adjusts to the protocol offered by the remote service.

Android only support RFCOMM based sockets.

QBluetoothSocket::SocketState QBluetoothSocket::state() const

Returns the current state of the socket.

[override virtual protected] qint64 QBluetoothSocket::writeData(const char *data, qint64 maxSize)

Reimplements: QIODevice::writeData(const char *data, qint64 maxSize).