path: root/doc/gatt-api.txt

BlueZ D-Bus GATT API description
********************************

GATT local and remote services share the same high-level D-Bus API. Local
refers to GATT based service exported by a BlueZ plugin or an external
application. Remote refers to GATT services exported by the peer.

BlueZ acts as a proxy, translating ATT operations to D-Bus method calls and
Properties (or the opposite). Support for D-Bus Object Manager is mandatory for
external services to allow seamless GATT declarations (Service, Characteristic
and Descriptors) discovery. Each GATT service tree is required to export a D-Bus
Object Manager at its root that is solely responsible for the objects that
belong to that service.

Releasing a registered GATT service is not defined yet. Any API extension
should avoid breaking the defined API, and if possible keep an unified GATT
remote and local services representation.

Service hierarchy
=================

GATT remote and local service representation. Object path for local services
is freely definable.

External applications implementing local services must register the services
using GattManager1 registration method and must implement the methods and
properties defined in GattService1 interface.

Service		org.bluez
Interface	org.bluez.GattService1
Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX

Properties	string UUID [read-only]

			128-bit service UUID.

		boolean Primary [read-only]

			Indicates whether or not this GATT service is a
			primary service. If false, the service is secondary.

		object Device [read-only, optional]

			Object path of the Bluetooth device the service
			belongs to. Only present on services from remote
			devices.

		array{object} Includes [read-only, optional]

			Array of object paths representing the included
			services of this service.

		uint16 Handle [read-write, optional] (Server Only)

			Service handle. When available in the server it
			would attempt to use to allocate into the database
			which may fail, to auto allocate the value 0x0000
			shall be used which will cause the allocated handle to
			be set once registered.


Characteristic hierarchy
========================

For local GATT defined services, the object paths need to follow the service
path hierarchy and are freely definable.

Service		org.bluez
Interface	org.bluez.GattCharacteristic1
Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY

Methods		array{byte} ReadValue(dict options)

			Issues a request to read the value of the
			characteristic and returns the value if the
			operation was successful.

			Possible options: "offset": uint16 offset
					  "mtu": Exchanged MTU (Server only)
					  "device": Object Device (Server only)

			Possible Errors: org.bluez.Error.Failed(string ecode)
					 org.bluez.Error.InProgress
					 org.bluez.Error.NotPermitted
					 org.bluez.Error.NotAuthorized
					 org.bluez.Error.InvalidOffset
					 org.bluez.Error.NotSupported

			Possible Error Code: string 0x80 - 0x9f

		void WriteValue(array{byte} value, dict options)

			Issues a request to write the value of the
			characteristic.

			Possible options: "offset": Start offset
					  "type": string
						Possible values:
						"command": Write without
						response
						"request": Write with response
						"reliable": Reliable Write
					  "mtu": Exchanged MTU (Server only)
					  "device": Device path (Server only)
					  "link": Link type (Server only)
					  "prepare-authorize": True if prepare
							       authorization
							       request

			Possible Errors: org.bluez.Error.Failed(string ecode)
					 org.bluez.Error.InProgress
					 org.bluez.Error.NotPermitted
					 org.bluez.Error.InvalidValueLength
					 org.bluez.Error.NotAuthorized
					 org.bluez.Error.NotSupported

			Possible Error Code: string 0x80 - 0x9f

		fd, uint16 AcquireWrite(dict options) [optional]

			Acquire file descriptor and MTU for writing. Only
			sockets are supported. Usage of WriteValue will be
			locked causing it to return NotPermitted error.

			For server the MTU returned shall be equal or smaller
			than the negotiated MTU.

			For client it only works with characteristic that has
			WriteAcquired property which relies on
			write-without-response Flag.

			To release the lock the client shall close the file
			descriptor, a HUP is generated in case the device
			is disconnected.

			Note: the MTU can only be negotiated once and is
			symmetric therefore this method may be delayed in
			order to have the exchange MTU completed, because of
			that the file descriptor is closed during
			reconnections as the MTU has to be renegotiated.

			Possible options: "device": Object Device (Server only)
					  "mtu": Exchanged MTU (Server only)
					  "link": Link type (Server only)

			Possible Errors: org.bluez.Error.Failed
					 org.bluez.Error.NotSupported

		fd, uint16 AcquireNotify(dict options) [optional]

			Acquire file descriptor and MTU for notify. Only
			sockets are support. Usage of StartNotify will be locked
			causing it to return NotPermitted error.

			For server the MTU returned shall be equal or smaller
			than the negotiated MTU.

			Only works with characteristic that has NotifyAcquired
			which relies on notify Flag and no other client have
			called StartNotify.

			Notification are enabled during this procedure so
			StartNotify shall not be called, any notification
			will be dispatched via file descriptor therefore the
			Value property is not affected during the time where
			notify has been acquired.

			To release the lock the client shall close the file
			descriptor, a HUP is generated in case the device
			is disconnected.

			Note: the MTU can only be negotiated once and is
			symmetric therefore this method may be delayed in
			order to have the exchange MTU completed, because of
			that the file descriptor is closed during
			reconnections as the MTU has to be renegotiated.

			Possible options: "device": Object Device (Server only)
					  "mtu": Exchanged MTU (Server only)
					  "link": Link type (Server only)

			Possible Errors: org.bluez.Error.Failed
					 org.bluez.Error.NotSupported

		void StartNotify()

			Starts a notification session from this characteristic
			if it supports value notifications or indications.

			Possible Errors: org.bluez.Error.Failed
					 org.bluez.Error.NotPermitted
					 org.bluez.Error.InProgress
					 org.bluez.Error.NotConnected
					 org.bluez.Error.NotSupported

		void StopNotify()

			This method will cancel any previous StartNotify
			transaction. Note that notifications from a
			characteristic are shared between sessions thus
			calling StopNotify will release a single session.

			Possible Errors: org.bluez.Error.Failed

		void Confirm() [optional] (Server only)

			This method doesn't expect a reply so it is just a
			confirmation that value was received.

			Possible Errors: org.bluez.Error.Failed

Properties	string UUID [read-only]

			128-bit characteristic UUID.

		object Service [read-only]

			Object path of the GATT service the characteristic
			belongs to.

		array{byte} Value [read-only, optional]

			The cached value of the characteristic. This property
			gets updated only after a successful read request and
			when a notification or indication is received, upon
			which a PropertiesChanged signal will be emitted.

		boolean WriteAcquired [read-only, optional]

			True, if this characteristic has been acquired by any
			client using AcquireWrite.

			For client properties is ommited in case
			'write-without-response' flag is not set.

			For server the presence of this property indicates
			that AcquireWrite is supported.

		boolean NotifyAcquired [read-only, optional]

			True, if this characteristic has been acquired by any
			client using AcquireNotify.

			For client this properties is ommited in case 'notify'
			flag is not set.

			For server the presence of this property indicates
			that AcquireNotify is supported.

		boolean Notifying [read-only, optional]

			True, if notifications or indications on this
			characteristic are currently enabled.

		array{string} Flags [read-only]

			Defines how the characteristic value can be used. See
			Core spec "Table 3.5: Characteristic Properties bit
			field", and "Table 3.8: Characteristic Extended
			Properties bit field".

			The "x-notify" and "x-indicate" flags restrict access
			to notifications and indications by imposing write
			restrictions on a characteristic's client
			characteristic configuration descriptor.

			Allowed values:

				"broadcast"
				"read"
				"write-without-response"
				"write"
				"notify"
				"indicate"
				"authenticated-signed-writes"
				"extended-properties"
				"reliable-write"
				"writable-auxiliaries"
				"encrypt-read"
				"encrypt-write"
				"encrypt-notify" (Server only)
				"encrypt-indicate" (Server only)
				"encrypt-authenticated-read"
				"encrypt-authenticated-write"
				"encrypt-authenticated-notify" (Server only)
				"encrypt-authenticated-indicate" (Server only)
				"secure-read" (Server only)
				"secure-write" (Server only)
				"secure-notify" (Server only)
				"secure-indicate" (Server only)
				"authorize"

		uint16 Handle [read-write, optional] (Server Only)

			Characteristic handle. When available in the server it
			would attempt to use to allocate into the database
			which may fail, to auto allocate the value 0x0000
			shall be used which will cause the allocated handle to
			be set once registered.

		uint16 MTU [read-only]

			Characteristic MTU, this is valid both for ReadValue
			and WriteValue but either method can use long
			procedures when supported.

Characteristic Descriptors hierarchy
====================================

Local or remote GATT characteristic descriptors hierarchy.

Service		org.bluez
Interface	org.bluez.GattDescriptor1
Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY/descriptorZZZ

Methods		array{byte} ReadValue(dict flags)

			Issues a request to read the value of the
			characteristic and returns the value if the
			operation was successful.

			Possible options: "offset": Start offset
					  "device": Device path (Server only)
					  "link": Link type (Server only)

			Possible Errors: org.bluez.Error.Failed
					 org.bluez.Error.InProgress
					 org.bluez.Error.NotPermitted
					 org.bluez.Error.NotAuthorized
					 org.bluez.Error.NotSupported

		void WriteValue(array{byte} value, dict flags)

			Issues a request to write the value of the
			characteristic.

			Possible options: "offset": Start offset
					  "device": Device path (Server only)
					  "link": Link type (Server only)
					  "prepare-authorize": boolean Is prepare
							       authorization
							       request

			Possible Errors: org.bluez.Error.Failed
					 org.bluez.Error.InProgress
					 org.bluez.Error.NotPermitted
					 org.bluez.Error.InvalidValueLength
					 org.bluez.Error.NotAuthorized
					 org.bluez.Error.NotSupported

Properties	string UUID [read-only]

			128-bit descriptor UUID.

		object Characteristic [read-only]

			Object path of the GATT characteristic the descriptor
			belongs to.

		array{byte} Value [read-only, optional]

			The cached value of the descriptor. This property
			gets updated only after a successful read request, upon
			which a PropertiesChanged signal will be emitted.

		array{string} Flags [read-only]

			Defines how the descriptor value can be used.

			Possible values:

				"read"
				"write"
				"encrypt-read"
				"encrypt-write"
				"encrypt-authenticated-read"
				"encrypt-authenticated-write"
				"secure-read" (Server Only)
				"secure-write" (Server Only)
				"authorize"

		uint16 Handle [read-write, optional] (Server Only)

			Characteristic handle. When available in the server it
			would attempt to use to allocate into the database
			which may fail, to auto allocate the value 0x0000
			shall be used which will cause the allocated handle to
			be set once registered.

GATT Profile hierarchy
=====================

Local profile (GATT client) instance. By registering this type of object
an application effectively indicates support for a specific GATT profile
and requests automatic connections to be established to devices
supporting it.

Service		<application dependent>
Interface	org.bluez.GattProfile1
Object path	<application dependent>

Methods		void Release()

			This method gets called when the service daemon
			unregisters the profile. The profile can use it to
			do cleanup tasks. There is no need to unregister the
			profile, because when this method gets called it has
			already been unregistered.

Properties	array{string} UUIDs [read-only]

			128-bit GATT service UUIDs to auto connect.


GATT Manager hierarchy
======================

GATT Manager allows external applications to register GATT services and
profiles.

Registering a profile allows applications to subscribe to *remote* services.
These must implement the GattProfile1 interface defined above.

Registering a service allows applications to publish a *local* GATT service,
which then becomes available to remote devices. A GATT service is represented by
a D-Bus object hierarchy where the root node corresponds to a service and the
child nodes represent characteristics and descriptors that belong to that
service. Each node must implement one of GattService1, GattCharacteristic1,
or GattDescriptor1 interfaces described above, based on the attribute it
represents. Each node must also implement the standard D-Bus Properties
interface to expose their properties. These objects collectively represent a
GATT service definition.

To make service registration simple, BlueZ requires that all objects that belong
to a GATT service be grouped under a D-Bus Object Manager that solely manages
the objects of that service. Hence, the standard DBus.ObjectManager interface
must be available on the root service path. An example application hierarchy
containing two separate GATT services may look like this:

-> /com/example
  |   - org.freedesktop.DBus.ObjectManager
  |
  -> /com/example/service0
  | |   - org.freedesktop.DBus.Properties
  | |   - org.bluez.GattService1
  | |
  | -> /com/example/service0/char0
  | |     - org.freedesktop.DBus.Properties
  | |     - org.bluez.GattCharacteristic1
  | |
  | -> /com/example/service0/char1
  |   |   - org.freedesktop.DBus.Properties
  |   |   - org.bluez.GattCharacteristic1
  |   |
  |   -> /com/example/service0/char1/desc0
  |       - org.freedesktop.DBus.Properties
  |       - org.bluez.GattDescriptor1
  |
  -> /com/example/service1
    |   - org.freedesktop.DBus.Properties
    |   - org.bluez.GattService1
    |
    -> /com/example/service1/char0
        - org.freedesktop.DBus.Properties
        - org.bluez.GattCharacteristic1

When a service is registered, BlueZ will automatically obtain information about
all objects using the service's Object Manager. Once a service has been
registered, the objects of a service should not be removed. If BlueZ receives an
InterfacesRemoved signal from a service's Object Manager, it will immediately
unregister the service. Similarly, if the application disconnects from the bus,
all of its registered services will be automatically unregistered.
InterfacesAdded signals will be ignored.

Examples:
	- Client
		test/example-gatt-client
		client/bluetoothctl
	- Server
		test/example-gatt-server
		tools/gatt-service


Service		org.bluez
Interface	org.bluez.GattManager1
Object path	[variable prefix]/{hci0,hci1,...}

Methods		void RegisterApplication(object application, dict options)

			Registers a local GATT services hierarchy as described
			above (GATT Server) and/or GATT profiles (GATT Client).

			The application object path together with the D-Bus
			system bus connection ID define the identification of
			the application registering a GATT based
			service or profile.

			Possible errors: org.bluez.Error.InvalidArguments
					 org.bluez.Error.AlreadyExists

		void UnregisterApplication(object application)

			This unregisters the services that has been
			previously registered. The object path parameter
			must match the same value that has been used
			on registration.

			Possible errors: org.bluez.Error.InvalidArguments
					 org.bluez.Error.DoesNotExist