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Generic Attribute Profile (GATT)

The GATT layer manages a service database and provide APIs for service registration and attribute declaration.

Services can be registered using bt_gatt_service_register() API which takes a bt_gatt_service structure that describes the attributes included in the service. The helper macro BT_GATT_SERVICE() can be used to declare a service.

Attributes can be declared using the bt_gatt_attr struct or using one of the helper macros:

BT_GATT_PRIMARY_SERVICE

Declares a Primary Service.

BT_GATT_SECONDARY_SERVICE

Declares a Secondary Service.

BT_GATT_INCLUDE_SERVICE

Declares a Include Service.

BT_GATT_CHARACTERISTIC

Declares a Characteristic.

BT_GATT_DESCRIPTOR

Declares a Descriptor.

BT_GATT_ATTRIBUTE

Declares a Generic Attribute.

BT_GATT_CCC

Declares a Client Characteristic Configuration.

BT_GATT_CEP

Declares a Characteristic Extended Properties.

BT_GATT_CUD

Declares a Characteristic User Description.

Each attribute contains a uuid, which describes their type, a read callback, a write callback and a set of permissions. The read and write callbacks are not invoked if the attribute’s permissions do not allow the respective operation.

Note

GATT does not support 32-bit UUIDs. All 32-bit UUIDs should be converted to 128-bit UUIDs when included in ATT PDUs.

Note

The read and write callbacks for attributes are called directly from the RX thread, so it is not advisable to block for long periods within them.

The bt_gatt_notify() API,can be used to notify changes in attribute values, or bt_gatt_notify_cb() can be used to pass a callback that is invoked when it is known exactly when the data has been transmitted over the air. Indications are supported by bt_gatt_indicate() API.

Client procedures can be enabled using the configuration option`CONFIG_BT_GATT_CLIENT`

The discovery process can be initiated using the bt_gatt_discover() API which takes the bt_gatt_discover_params struct which describes the type of discovery. The parameters also serves as a filter when setting the uuid field only attributes that match the specified field, while setting it to NULL allows for the discovery of all attributes.

Note

Caching discovered attributes is not supported.

Read procedures are supported by bt_gatt_read() API which takes the bt_gatt_read_params struct as parameters. More attributes can be set in parameter 1, although setting multiple handles requires the CONFIG_BT_GATT_READ_MULTIPLE

Write procedures are supported by bt_gatt_write() API and takes bt_gatt_write_params struct as parameters. In case the write operation don’t require a response bt_gatt_write_without_response() or bt_gatt_write_without_response_cb() APIs can be used, with the later working similarly to bt_gatt_notify_cb().

Subscriptions to notifications and indications can be initiated with using the bt_gatt_subscribe() API which takes bt_gatt_subscribe_params as parameters. Multiple subscriptions to the same attribute are supported , so multiple notify callbacks can be triggered for the same attribute.Subscriptions can be removed with using the bt_gatt_unsubscribe() API.

Note

When removing a subscription, the notify callback is called with the data set to NULL.

API Reference

group bt_gatt

Generic Attribute Profile (GATT)

Defines

BT_GATT_ERR(_att_err)

Construct error return value for attribute read and write callbacks.

Parameters:

  • _att_err – ATT error code

Returns:

Appropriate error code for the attribute callbacks.

BT_GATT_CHRC_BROADCAST

Characteristic broadcast property.

Characteristic Properties Bit field values

If set, permits broadcasts of the Characteristic Value using Server Characteristic Configuration Descriptor.

BT_GATT_CHRC_READ

Characteristic read property.

If set, permits reads of the Characteristic Value.

BT_GATT_CHRC_WRITE_WITHOUT_RESP

Characteristic write without response property.

If set, permits write of the Characteristic Value without response.

BT_GATT_CHRC_WRITE

Characteristic write with response property.

If set, permits write of the Characteristic Value with response.

BT_GATT_CHRC_NOTIFY

Characteristic notify property.

If set, permits notifications of a Characteristic Value without acknowledgment.

BT_GATT_CHRC_INDICATE

Characteristic indicate property.

If set, permits indications of a Characteristic Value with acknowledgment.

BT_GATT_CHRC_AUTH

Characteristic Authenticated Signed Writes property.

If set, permits signed writes to the Characteristic Value.

BT_GATT_CHRC_EXT_PROP

Characteristic Extended Properties property.

If set, additional characteristic properties are defined in the Characteristic Extended Properties Descriptor.

BT_GATT_CEP_RELIABLE_WRITE

Characteristic Extended Properties Bit field values

BT_GATT_CEP_WRITABLE_AUX
BT_GATT_CCC_NOTIFY

Client Characteristic Configuration Notification.

Client Characteristic Configuration Values

If set, changes to Characteristic Value shall be notified.

BT_GATT_CCC_INDICATE

Client Characteristic Configuration Indication.

If set, changes to Characteristic Value shall be indicated.

BT_GATT_SCC_BROADCAST

Server Characteristic Configuration Broadcast.

Server Characteristic Configuration Values

If set, the characteristic value shall be broadcast in the advertising data when the server is advertising.

Typedefs

typedef ssize_t (*bt_gatt_attr_read_func_t)(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Attribute read callback.

The callback can also be used locally to read the contents of the attribute in which case no connection will be set.

Param conn:

The connection that is requesting to read

Param attr:

The attribute that’s being read

Param buf:

Buffer to place the read result in

Param len:

Length of data to read

Param offset:

Offset to start reading from

Return:

Number of bytes read, or in case of an error BT_GATT_ERR() with a specific BT_ATT_ERR_* error code.

typedef ssize_t (*bt_gatt_attr_write_func_t)(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *buf, uint16_t len, uint16_t offset, uint8_t flags)

Attribute write callback.

Param conn:

The connection that is requesting to write

Param attr:

The attribute that’s being written

Param buf:

Buffer with the data to write

Param len:

Number of bytes in the buffer

Param offset:

Offset to start writing from

Param flags:

Flags (BT_GATT_WRITE_FLAG_*)

Return:

Number of bytes written, or in case of an error BT_GATT_ERR() with a specific BT_ATT_ERR_* error code.

Enums

enum bt_gatt_perm

GATT attribute permission bit field values

Values:

enumerator BT_GATT_PERM_NONE

No operations supported, e.g. for notify-only

enumerator BT_GATT_PERM_READ

Attribute read permission.

enumerator BT_GATT_PERM_WRITE

Attribute write permission.

enumerator BT_GATT_PERM_READ_ENCRYPT

Attribute read permission with encryption.

If set, requires encryption for read access.

enumerator BT_GATT_PERM_WRITE_ENCRYPT

Attribute write permission with encryption.

If set, requires encryption for write access.

enumerator BT_GATT_PERM_READ_AUTHEN

Attribute read permission with authentication.

If set, requires encryption using authenticated link-key for read access.

enumerator BT_GATT_PERM_WRITE_AUTHEN

Attribute write permission with authentication.

If set, requires encryption using authenticated link-key for write access.

enumerator BT_GATT_PERM_PREPARE_WRITE

Attribute prepare write permission.

If set, allows prepare writes with use of BT_GATT_WRITE_FLAG_PREPARE passed to write callback.

enumerator BT_GATT_PERM_READ_LESC

Attribute read permission with LE Secure Connection encryption.

If set, requires that LE Secure Connections is used for read access.

enumerator BT_GATT_PERM_WRITE_LESC

Attribute write permission with LE Secure Connection encryption.

If set, requires that LE Secure Connections is used for write access.

enum bt_gatt_write_flag

GATT attribute write flags

Values:

enumerator BT_GATT_WRITE_FLAG_PREPARE

Attribute prepare write flag.

If set, write callback should only check if the device is authorized but no data shall be written.

enumerator BT_GATT_WRITE_FLAG_CMD

Attribute write command flag.

If set, indicates that write operation is a command (Write without response) which doesn’t generate any response.

enumerator BT_GATT_WRITE_FLAG_EXECUTE

Attribute write execute flag.

If set, indicates that write operation is a execute, which indicates the end of a long write, and will come after 1 or more BT_GATT_WRITE_FLAG_PREPARE.

struct bt_gatt_attr

GATT Attribute structure.

struct bt_gatt_service_static

GATT Service structure.

struct bt_gatt_service

GATT Service structure.

struct bt_gatt_service_val

Service Attribute Value.

struct bt_gatt_include

Include Attribute Value.

struct bt_gatt_cb

GATT callback structure.

struct bt_gatt_chrc

Characteristic Attribute Value.

struct bt_gatt_cep

Characteristic Extended Properties Attribute Value.

struct bt_gatt_ccc

Client Characteristic Configuration Attribute Value

struct bt_gatt_scc

Server Characteristic Configuration Attribute Value

struct bt_gatt_cpf

GATT Characteristic Presentation Format Attribute Value.

GATT Server

group bt_gatt_server

Defines

BT_GATT_SERVICE_DEFINE(_name, ...)

Statically define and register a service.

Helper macro to statically define and register a service.

Parameters:

  • _name – Service name.

BT_GATT_SERVICE_INSTANCE_DEFINE(_name, _instances, _instance_num, _attrs_def)

Statically define service structure array.

Helper macro to statically define service structure array. Each element of the array is linked to the service attribute array which is also defined in this scope using _attrs_def macro.

Parameters:

  • _name – Name of service structure array.

  • _instances – Array of instances to pass as user context to the attribute callbacks.

  • _instance_num – Number of elements in instance array.

  • _attrs_def – Macro provided by the user that defines attribute array for the service. This macro should accept single parameter which is the instance context.

BT_GATT_SERVICE(_attrs)

Service Structure Declaration Macro.

Helper macro to declare a service structure.

Parameters:

  • _attrs – Service attributes.

BT_GATT_PRIMARY_SERVICE(_service)

Primary Service Declaration Macro.

Helper macro to declare a primary service attribute.

Parameters:

  • _service – Service attribute value.

BT_GATT_SECONDARY_SERVICE(_service)

Secondary Service Declaration Macro.

Helper macro to declare a secondary service attribute.

Note

A secondary service is only intended to be included from a primary service or another secondary service or other higher layer specification.

Parameters:

  • _service – Service attribute value.

BT_GATT_INCLUDE_SERVICE(_service_incl)

Include Service Declaration Macro.

Helper macro to declare database internal include service attribute.

Parameters:

  • _service_incl – the first service attribute of service to include

BT_GATT_CHRC_INIT(_uuid, _handle, _props)
BT_GATT_CHARACTERISTIC(_uuid, _props, _perm, _read, _write, _user_data)

Characteristic and Value Declaration Macro.

Helper macro to declare a characteristic attribute along with its attribute value.

Parameters:

  • _uuid – Characteristic attribute uuid.

  • _props – Characteristic attribute properties, a bitmap of BT_GATT_CHRC_* macros.

  • _perm – Characteristic Attribute access permissions, a bitmap of bt_gatt_perm values.

  • _read – Characteristic Attribute read callback ( bt_gatt_attr_read_func_t).

  • _write – Characteristic Attribute write callback ( bt_gatt_attr_write_func_t).

  • _user_data – Characteristic Attribute user data.

BT_GATT_CCC_MAX
BT_GATT_CCC_INITIALIZER(_changed, _write, _match)

Initialize Client Characteristic Configuration Declaration Macro.

Helper macro to initialize a Managed CCC attribute value.

Parameters:

  • _changed – Configuration changed callback.

  • _write – Configuration write callback.

  • _match – Configuration match callback.

BT_GATT_CCC_MANAGED(_ccc, _perm)

Managed Client Characteristic Configuration Declaration Macro.

Helper macro to declare a Managed CCC attribute.

Parameters:

  • _ccc – CCC attribute user data, shall point to a _bt_gatt_ccc.

  • _perm – CCC access permissions, a bitmap of bt_gatt_perm values.

BT_GATT_CCC(_changed, _perm)

Client Characteristic Configuration Declaration Macro.

Helper macro to declare a CCC attribute.

Parameters:

  • _changed – Configuration changed callback.

  • _perm – CCC access permissions, a bitmap of bt_gatt_perm values.

BT_GATT_CEP(_value)

Characteristic Extended Properties Declaration Macro.

Helper macro to declare a CEP attribute.

Parameters:
BT_GATT_CUD(_value, _perm)

Characteristic User Format Descriptor Declaration Macro.

Helper macro to declare a CUD attribute.

Parameters:

  • _value – User description NULL-terminated C string.

  • _perm – Descriptor attribute access permissions, a bitmap of bt_gatt_perm values.

BT_GATT_CPF(_value)

Characteristic Presentation Format Descriptor Declaration Macro.

Helper macro to declare a CPF attribute.

Parameters:
BT_GATT_DESCRIPTOR(_uuid, _perm, _read, _write, _user_data)

Descriptor Declaration Macro.

Helper macro to declare a descriptor attribute.

Parameters:

  • _uuid – Descriptor attribute uuid.

  • _perm – Descriptor attribute access permissions, a bitmap of bt_gatt_perm values.

  • _read – Descriptor attribute read callback ( bt_gatt_attr_read_func_t).

  • _write – Descriptor attribute write callback ( bt_gatt_attr_write_func_t).

  • _user_data – Descriptor attribute user data.

BT_GATT_ATTRIBUTE(_uuid, _perm, _read, _write, _user_data)

Attribute Declaration Macro.

Helper macro to declare an attribute.

Parameters:

  • _uuid – Attribute uuid.

  • _perm – Attribute access permissions, a bitmap of bt_gatt_perm values.

  • _read – Attribute read callback ( bt_gatt_attr_read_func_t).

  • _write – Attribute write callback ( bt_gatt_attr_write_func_t).

  • _user_data – Attribute user data.

Typedefs

typedef uint8_t (*bt_gatt_attr_func_t)(const struct bt_gatt_attr *attr, uint16_t handle, void *user_data)

Attribute iterator callback.

Param attr:

Attribute found.

Param handle:

Attribute handle found.

Param user_data:

Data given.

Return:

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return:

BT_GATT_ITER_STOP to stop.

typedef void (*bt_gatt_complete_func_t)(struct bt_conn *conn, void *user_data)

Notification complete result callback.

Param conn:

Connection object.

Param user_data:

Data passed in by the user.

typedef void (*bt_gatt_indicate_func_t)(struct bt_conn *conn, struct bt_gatt_indicate_params *params, uint8_t err)

Indication complete result callback.

Param conn:

Connection object.

Param params:

Indication params object.

Param err:

ATT error code

typedef void (*bt_gatt_indicate_params_destroy_t)(struct bt_gatt_indicate_params *params)

Enums

enum bt_gatt_iter_status

Values:

enumerator BT_GATT_ITER_STOP
enumerator BT_GATT_ITER_CONTINUE

Functions

void bt_gatt_cb_register(struct bt_gatt_cb *cb)

Register GATT callbacks.

Register callbacks to monitor the state of GATT.

Parameters:

cb – Callback struct.

int bt_gatt_service_register(struct bt_gatt_service *svc)

Register GATT service.

Register GATT service. Applications can make use of macros such as BT_GATT_PRIMARY_SERVICE, BT_GATT_CHARACTERISTIC, BT_GATT_DESCRIPTOR, etc.

When using CONFIG_BT_SETTINGS then all services that should have bond configuration loaded, i.e. CCC values, must be registered before calling settings_load.

When using CONFIG_BT_GATT_CACHING and CONFIG_BT_SETTINGS then all services that should be included in the GATT Database Hash calculation should be added before calling settings_load. All services registered after settings_load will trigger a new database hash calculation and a new hash stored.

There are two situations where this function can be called: either before `bt_init()` has been called, or after `settings_load()` has been called. Registering a service in the middle is not supported and will return an error.

Parameters:

svc – Service containing the available attributes

Returns:

0 in case of success or negative value in case of error.

Returns:

-EAGAIN if `bt_init()` has been called but `settings_load()` hasn’t yet.

int bt_gatt_service_unregister(struct bt_gatt_service *svc)

Unregister GATT service.

Parameters:

svc – Service to be unregistered.

Returns:

0 in case of success or negative value in case of error.

bool bt_gatt_service_is_registered(const struct bt_gatt_service *svc)

Check if GATT service is registered.

Parameters:

svc – Service to be checked.

Returns:

true if registered or false if not register.

void bt_gatt_foreach_attr_type(uint16_t start_handle, uint16_t end_handle, const struct bt_uuid *uuid, const void *attr_data, uint16_t num_matches, bt_gatt_attr_func_t func, void *user_data)

Attribute iterator by type.

Iterate attributes in the given range matching given UUID and/or data.

Parameters:

  • start_handle – Start handle.

  • end_handle – End handle.

  • uuid – UUID to match, passing NULL skips UUID matching.

  • attr_data – Attribute data to match, passing NULL skips data matching.

  • num_matches – Number matches, passing 0 makes it unlimited.

  • func – Callback function.

  • user_data – Data to pass to the callback.

static inline void bt_gatt_foreach_attr(uint16_t start_handle, uint16_t end_handle, bt_gatt_attr_func_t func, void *user_data)

Attribute iterator.

Iterate attributes in the given range.

Parameters:

  • start_handle – Start handle.

  • end_handle – End handle.

  • func – Callback function.

  • user_data – Data to pass to the callback.

struct bt_gatt_attr *bt_gatt_attr_next(const struct bt_gatt_attr *attr)

Iterate to the next attribute.

Iterate to the next attribute following a given attribute.

Parameters:

attr – Current Attribute.

Returns:

The next attribute or NULL if it cannot be found.

struct bt_gatt_attr *bt_gatt_find_by_uuid(const struct bt_gatt_attr *attr, uint16_t attr_count, const struct bt_uuid *uuid)

Find Attribute by UUID.

Find the attribute with the matching UUID. To limit the search to a service set the attr to the service attributes and the attr_count to the service attribute count .

Parameters:

  • attr – Pointer to an attribute that serves as the starting point for the search of a match for the UUID. Passing NULL will search the entire range.

  • attr_count – The number of attributes from the starting point to search for a match for the UUID. Set to 0 to search until the end.

  • uuid – UUID to match.

uint16_t bt_gatt_attr_get_handle(const struct bt_gatt_attr *attr)

Get Attribute handle.

Parameters:

attr – Attribute object.

Returns:

Handle of the corresponding attribute or zero if the attribute could not be found.

uint16_t bt_gatt_attr_value_handle(const struct bt_gatt_attr *attr)

Get the handle of the characteristic value descriptor.

Note

The user_data of the attribute must of type bt_gatt_chrc.

Parameters:

attr – A Characteristic Attribute.

Returns:

the handle of the corresponding Characteristic Value. The value will be zero (the invalid handle) if attr was not a characteristic attribute.

ssize_t bt_gatt_attr_read(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t buf_len, uint16_t offset, const void *value, uint16_t value_len)

Generic Read Attribute value helper.

Read attribute value from local database storing the result into buffer.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value.

  • buf_len – Buffer length.

  • offset – Start offset.

  • value – Attribute value.

  • value_len – Length of the attribute value.

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_service(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Service Attribute helper.

Read service attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_uuid.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_included(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Include Attribute helper.

Read include service attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_include.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_chrc(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Attribute helper.

Read characteristic attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_chrc.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_ccc(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Client Characteristic Configuration Attribute helper.

Read CCC attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a _bt_gatt_ccc.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_write_ccc(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *buf, uint16_t len, uint16_t offset, uint8_t flags)

Write Client Characteristic Configuration Attribute helper.

Write value in the buffer into CCC attribute.

Note

Only use this with attributes which user_data is a _bt_gatt_ccc.

Parameters:

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

  • flags – Write flags.

Returns:

number of bytes written in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_cep(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Extended Properties Attribute helper.

Read CEP attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_cep.

Parameters:

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_cud(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic User Description Descriptor Attribute helper.

Read CUD attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a NULL-terminated C string.

Parameters:

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns:

number of bytes read in case of success or negative values in case of error.

ssize_t bt_gatt_attr_read_cpf(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Presentation format Descriptor Attribute helper.

Read CPF attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_pf.

Parameters:

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns:

number of bytes read in case of success or negative values in case of error.

int bt_gatt_notify_cb(struct bt_conn *conn, struct bt_gatt_notify_params *params)

Notify attribute value change.

This function works in the same way as bt_gatt_notify. With the addition that after sending the notification the callback function will be called.

The callback is run from System Workqueue context. When called from the System Workqueue context this API will not wait for resources for the callback but instead return an error. The number of pending callbacks can be increased with the CONFIG_BT_CONN_TX_MAX option.

Alternatively it is possible to notify by UUID by setting it on the parameters, when using this method the attribute if provided is used as the start range when looking up for possible matches.

Parameters:

  • conn – Connection object.

  • params – Notification parameters.

Returns:

0 in case of success or negative value in case of error.

int bt_gatt_notify_multiple(struct bt_conn *conn, uint16_t num_params, struct bt_gatt_notify_params params[])

Send multiple notifications in a single PDU.

The GATT Server will send a single ATT_MULTIPLE_HANDLE_VALUE_NTF PDU containing all the notifications passed to this API.

All `params` must have the same `func` and `user_data` (due to implementation limitation). But `func(user_data)` will be invoked for each parameter.

As this API may block to wait for Bluetooth Host resources, it is not recommended to call it from a cooperative thread or a Bluetooth callback.

The peer’s GATT Client must write to this device’s Client Supported Features attribute and set the bit for Multiple Handle Value Notifications before this API can be used.

Only use this API to force the use of the ATT_MULTIPLE_HANDLE_VALUE_NTF PDU. For standard applications, `bt_gatt_notify_cb` is preferred, as it will use this PDU if supported and automatically fallback to ATT_HANDLE_VALUE_NTF when not supported by the peer.

This API has an additional limitation: it only accepts valid attribute references and not UUIDs like `bt_gatt_notify` and `bt_gatt_notify_cb`.

Parameters:

  • conn – Target client. Notifying all connected clients by passing `NULL` is not yet supported, please use `bt_gatt_notify` instead.

  • num_params – Element count of `params` array. Has to be greater than 1.

  • params – Array of notification parameters. It is okay to free this after calling this function.

Return values:

  • 0 – Success. The PDU is queued for sending.

  • -EINVAL –

    • One of the attribute handles is invalid.

    • Only one parameter was passed. This API expects 2 or more.

    • Not all `func` were equal or not all `user_data` were equal.

    • One of the characteristics is not notifiable.

    • An UUID was passed in one of the parameters.

  • -ERANGE –

    • The notifications cannot all fit in a single ATT_MULTIPLE_HANDLE_VALUE_NTF.

    • They exceed the MTU of all open ATT bearers.

  • -EPERM – The connection has a lower security level than required by one of the attributes.

  • -EOPNOTSUPP – The peer hasn’t yet communicated that it supports this PDU type.

static inline int bt_gatt_notify(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *data, uint16_t len)

Notify attribute value change.

Send notification of attribute value change, if connection is NULL notify all peer that have notification enabled via CCC otherwise do a direct notification only the given connection.

The attribute object on the parameters can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC.

Parameters:

  • conn – Connection object.

  • attr – Characteristic or Characteristic Value attribute.

  • data – Pointer to Attribute data.

  • len – Attribute value length.

Returns:

0 in case of success or negative value in case of error.

static inline int bt_gatt_notify_uuid(struct bt_conn *conn, const struct bt_uuid *uuid, const struct bt_gatt_attr *attr, const void *data, uint16_t len)

Notify attribute value change by UUID.

Send notification of attribute value change, if connection is NULL notify all peer that have notification enabled via CCC otherwise do a direct notification only on the given connection.

The attribute object is the starting point for the search of the UUID.

Parameters:

  • conn – Connection object.

  • uuid – The UUID. If the server contains multiple services with the same UUID, then the first occurrence, starting from the attr given, is used.

  • attr – Pointer to an attribute that serves as the starting point for the search of a match for the UUID.

  • data – Pointer to Attribute data.

  • len – Attribute value length.

Returns:

0 in case of success or negative value in case of error.

int bt_gatt_indicate(struct bt_conn *conn, struct bt_gatt_indicate_params *params)

Indicate attribute value change.

Send an indication of attribute value change. if connection is NULL indicate all peer that have notification enabled via CCC otherwise do a direct indication only the given connection.

The attribute object on the parameters can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC.

Alternatively it is possible to indicate by UUID by setting it on the parameters, when using this method the attribute if provided is used as the start range when looking up for possible matches.

Note

This procedure is asynchronous therefore the parameters need to remains valid while it is active. The procedure is active until the destroy callback is run.

Parameters:

  • conn – Connection object.

  • params – Indicate parameters.

Returns:

0 in case of success or negative value in case of error.

bool bt_gatt_is_subscribed(struct bt_conn *conn, const struct bt_gatt_attr *attr, uint16_t ccc_type)

Check if connection have subscribed to attribute.

Check if connection has subscribed to attribute value change.

The attribute object can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC, or the Client Characteristic Configuration Descriptor (CCCD) which is created by BT_GATT_CCC.

Parameters:

  • conn – Connection object.

  • attr – Attribute object.

  • ccc_type – The subscription type, BT_GATT_CCC_NOTIFY and/or BT_GATT_CCC_INDICATE.

Returns:

true if the attribute object has been subscribed.

uint16_t bt_gatt_get_mtu(struct bt_conn *conn)

Get ATT MTU for a connection.

Get negotiated ATT connection MTU, note that this does not equal the largest amount of attribute data that can be transferred within a single packet.

Parameters:

conn – Connection object.

Returns:

MTU in bytes

struct bt_gatt_ccc_cfg

GATT CCC configuration entry.

struct bt_gatt_notify_params
struct bt_gatt_indicate_params

GATT Indicate Value parameters.

GATT Client

group bt_gatt_client

Typedefs

typedef uint8_t (*bt_gatt_discover_func_t)(struct bt_conn *conn, const struct bt_gatt_attr *attr, struct bt_gatt_discover_params *params)

Discover attribute callback function.

If discovery procedure has completed this callback will be called with attr set to NULL. This will not happen if procedure was stopped by returning BT_GATT_ITER_STOP.

The attribute object as well as its UUID and value objects are temporary and must be copied to in order to cache its information. Only the following fields of the attribute contains valid information:

  • uuid UUID representing the type of attribute.

  • handle Handle in the remote database.

  • user_data The value of the attribute, if the discovery type maps to an ATT operation that provides this information. NULL otherwise. See below.

The effective type of attr->user_data is determined by params. Note that the fields params->type and params->uuid are left unchanged by the discovery procedure.

params->type | params->uuid | Type of attr->user_data ————————————-|————————-|————————— BT_GATT_DISCOVER_PRIMARY | any | bt_gatt_service_val BT_GATT_DISCOVER_SECONDARY | any | bt_gatt_service_val BT_GATT_DISCOVER_INCLUDE | any | bt_gatt_include BT_GATT_DISCOVER_CHARACTERISTIC | any | bt_gatt_chrc BT_GATT_DISCOVER_STD_CHAR_DESC | BT_UUID_GATT_CEP | bt_gatt_cep BT_GATT_DISCOVER_STD_CHAR_DESC | BT_UUID_GATT_CCC | bt_gatt_ccc BT_GATT_DISCOVER_STD_CHAR_DESC | BT_UUID_GATT_SCC | bt_gatt_scc BT_GATT_DISCOVER_STD_CHAR_DESC | BT_UUID_GATT_CPF | bt_gatt_cpf BT_GATT_DISCOVER_DESCRIPTOR | any | NULL BT_GATT_DISCOVER_ATTRIBUTE | any | NULL

Also consider if using read-by-type instead of discovery is more convenient. See bt_gatt_read with bt_gatt_read_params::handle_count set to 0.

Param conn:

Connection object.

Param attr:

Attribute found, or NULL if not found.

Param params:

Discovery parameters given.

Return:

BT_GATT_ITER_CONTINUE to continue discovery procedure.

Return:

BT_GATT_ITER_STOP to stop discovery procedure.

typedef uint8_t (*bt_gatt_read_func_t)(struct bt_conn *conn, uint8_t err, struct bt_gatt_read_params *params, const void *data, uint16_t length)

Read callback function.

When reading using by_uuid, `params->start_handle` is the attribute handle for this `data` item.

Param conn:

Connection object.

Param err:

ATT error code.

Param params:

Read parameters used.

Param data:

Attribute value data. NULL means read has completed.

Param length:

Attribute value length.

Return:

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return:

BT_GATT_ITER_STOP to stop.

typedef void (*bt_gatt_write_func_t)(struct bt_conn *conn, uint8_t err, struct bt_gatt_write_params *params)

Write callback function.

Param conn:

Connection object.

Param err:

ATT error code.

Param params:

Write parameters used.

typedef uint8_t (*bt_gatt_notify_func_t)(struct bt_conn *conn, struct bt_gatt_subscribe_params *params, const void *data, uint16_t length)

Notification callback function.

In the case of an empty notification, the data pointer will be non-NULL while the length will be 0, which is due to the special case where a data NULL pointer means unsubscribed.

Param conn:

Connection object. May be NULL, indicating that the peer is being unpaired

Param params:

Subscription parameters.

Param data:

Attribute value data. If NULL then subscription was removed.

Param length:

Attribute value length.

Return:

BT_GATT_ITER_CONTINUE to continue receiving value notifications. BT_GATT_ITER_STOP to unsubscribe from value notifications.

typedef void (*bt_gatt_subscribe_func_t)(struct bt_conn *conn, uint8_t err, struct bt_gatt_subscribe_params *params)

Subscription callback function.

Param conn:

Connection object.

Param err:

ATT error code.

Param params:

Subscription parameters used.

Enums

enum bt_gatt_discover_type

GATT Discover types

Values:

enumerator BT_GATT_DISCOVER_PRIMARY

Discover Primary Services.

enumerator BT_GATT_DISCOVER_SECONDARY

Discover Secondary Services.

enumerator BT_GATT_DISCOVER_INCLUDE

Discover Included Services.

enumerator BT_GATT_DISCOVER_CHARACTERISTIC

Discover Characteristic Values.

Discover Characteristic Value and its properties.

enumerator BT_GATT_DISCOVER_DESCRIPTOR

Discover Descriptors.

Discover Attributes which are not services or characteristics.

Note

The use of this type of discover is not recommended for discovering in ranges across multiple services/characteristics as it may incur in extra round trips.

enumerator BT_GATT_DISCOVER_ATTRIBUTE

Discover Attributes.

Discover Attributes of any type.

Note

The use of this type of discover is not recommended for discovering in ranges across multiple services/characteristics as it may incur in more round trips.

enumerator BT_GATT_DISCOVER_STD_CHAR_DESC

Discover standard characteristic descriptor values.

Discover standard characteristic descriptor values and their properties. Supported descriptors:

  • Characteristic Extended Properties

  • Client Characteristic Configuration

  • Server Characteristic Configuration

  • Characteristic Presentation Format

enum bt_gatt_subscribe_flag

Subscription flags

Values:

enumerator BT_GATT_SUBSCRIBE_FLAG_VOLATILE

Persistence flag.

If set, indicates that the subscription is not saved on the GATT server side. Therefore, upon disconnection, the subscription will be automatically removed from the client’s subscriptions list and when the client reconnects, it will have to issue a new subscription.

enumerator BT_GATT_SUBSCRIBE_FLAG_NO_RESUB

No resubscribe flag.

By default when BT_GATT_SUBSCRIBE_FLAG_VOLATILE is unset, the subscription will be automatically renewed when the client reconnects, as a workaround for GATT servers that do not persist subscriptions.

This flag will disable the automatic resubscription. It is useful if the application layer knows that the GATT server remembers subscriptions from previous connections and wants to avoid renewing the subscriptions.

enumerator BT_GATT_SUBSCRIBE_FLAG_WRITE_PENDING

Write pending flag.

If set, indicates write operation is pending waiting remote end to respond.

Note

Internal use only.

enumerator BT_GATT_SUBSCRIBE_FLAG_SENT

Sent flag.

If set, indicates that a subscription request (CCC write) has already been sent in the active connection.

Used to avoid sending subscription requests multiple times when the CONFIG_BT_GATT_AUTO_RESUBSCRIBE quirk is enabled.

Note

Internal use only.

enumerator BT_GATT_SUBSCRIBE_NUM_FLAGS

Functions

int bt_gatt_exchange_mtu(struct bt_conn *conn, struct bt_gatt_exchange_params *params)

Exchange MTU.

This client procedure can be used to set the MTU to the maximum possible size the buffers can hold.

The Response comes in callback params->func. The callback is run from the context specified by ‘config BT_RECV_CONTEXT’. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Note

Shall only be used once per connection.

Parameters:

  • conn – Connection object.

  • params – Exchange MTU parameters.

Return values:

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

  • -EALREADY – The MTU exchange procedure has been already performed.

int bt_gatt_discover(struct bt_conn *conn, struct bt_gatt_discover_params *params)

GATT Discover function.

This procedure is used by a client to discover attributes on a server.

Primary Service Discovery: Procedure allows to discover primary services either by Discover All Primary Services or Discover Primary Services by Service UUID. Include Service Discovery: Procedure allows to discover all Include Services within specified range. Characteristic Discovery: Procedure allows to discover all characteristics within specified handle range as well as discover characteristics with specified UUID. Descriptors Discovery: Procedure allows to discover all characteristic descriptors within specified range.

For each attribute found the callback is called which can then decide whether to continue discovering or stop.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback where iter `attr` is `NULL` or callback will return `BT_GATT_ITER_STOP`.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters:

  • conn – Connection object.

  • params – Discover parameters.

Return values:

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

int bt_gatt_read(struct bt_conn *conn, struct bt_gatt_read_params *params)

Read Attribute Value by handle.

This procedure read the attribute value and return it to the callback.

When reading attributes by UUID the callback can be called multiple times depending on how many instances of given the UUID exists with the start_handle being updated for each instance.

If an instance does contain a long value which cannot be read entirely the caller will need to read the remaining data separately using the handle and offset.

The Response comes in callback params->func. The callback is run from the context specified by ‘config BT_RECV_CONTEXT’. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters:

  • conn – Connection object.

  • params – Read parameters.

Return values:

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

int bt_gatt_write(struct bt_conn *conn, struct bt_gatt_write_params *params)

Write Attribute Value by handle.

The Response comes in callback params->func. The callback is run from the context specified by ‘config BT_RECV_CONTEXT’. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from Bluetooth event context. When called from Bluetooth context, this function will instead instead return `-ENOMEM` if it would block to avoid a deadlock.

Parameters:

  • conn – Connection object.

  • params – Write parameters.

Return values:

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside Bluetooth event context to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

int bt_gatt_write_without_response_cb(struct bt_conn *conn, uint16_t handle, const void *data, uint16_t length, bool sign, bt_gatt_complete_func_t func, void *user_data)

Write Attribute Value by handle without response with callback.

This function works in the same way as bt_gatt_write_without_response. With the addition that after sending the write the callback function will be called.

The callback is run from System Workqueue context. When called from the System Workqueue context this API will not wait for resources for the callback but instead return an error. The number of pending callbacks can be increased with the CONFIG_BT_CONN_TX_MAX option.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Note

By using a callback it also disable the internal flow control which would prevent sending multiple commands without waiting for their transmissions to complete, so if that is required the caller shall not submit more data until the callback is called.

Parameters:

  • conn – Connection object.

  • handle – Attribute handle.

  • data – Data to be written.

  • length – Data length.

  • sign – Whether to sign data

  • func – Transmission complete callback.

  • user_data – User data to be passed back to callback.

Return values:

  • 0 – Successfully queued request.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

static inline int bt_gatt_write_without_response(struct bt_conn *conn, uint16_t handle, const void *data, uint16_t length, bool sign)

Write Attribute Value by handle without response.

This procedure write the attribute value without requiring an acknowledgment that the write was successfully performed

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters:

  • conn – Connection object.

  • handle – Attribute handle.

  • data – Data to be written.

  • length – Data length.

  • sign – Whether to sign data

Return values:

  • 0 – Successfully queued request.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

int bt_gatt_subscribe(struct bt_conn *conn, struct bt_gatt_subscribe_params *params)

Subscribe Attribute Value Notification.

This procedure subscribe to value notification using the Client Characteristic Configuration handle. If notification received subscribe value callback is called to return notified value. One may then decide whether to unsubscribe directly from this callback. Notification callback with NULL data will not be called if subscription was removed by this method.

The Response comes in callback params->subscribe. The callback is run from the context specified by ‘config BT_RECV_CONTEXT’. The Notification callback params->notify is also called from the BT RX thread.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Note

Notifications are asynchronous therefore the params must remain valid while subscribed and cannot be reused for additional subscriptions whilst active.

Parameters:

  • conn – Connection object.

  • params – Subscribe parameters.

Return values:

  • 0 – Successfully queued request. Will call params->write on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

int bt_gatt_resubscribe(uint8_t id, const bt_addr_le_t *peer, struct bt_gatt_subscribe_params *params)

Resubscribe Attribute Value Notification subscription.

Resubscribe to Attribute Value Notification when already subscribed from a previous connection. The GATT server will remember subscription from previous connections when bonded, so resubscribing can be done without performing a new subscribe procedure after a power cycle.

Note

Notifications are asynchronous therefore the parameters need to remain valid while subscribed.

Parameters:

  • id – Local identity (in most cases BT_ID_DEFAULT).

  • peer – Remote address.

  • params – Subscribe parameters.

Returns:

0 in case of success or negative value in case of error.

int bt_gatt_unsubscribe(struct bt_conn *conn, struct bt_gatt_subscribe_params *params)

Unsubscribe Attribute Value Notification.

This procedure unsubscribe to value notification using the Client Characteristic Configuration handle. Notification callback with NULL data will be called if subscription was removed by this call, until then the parameters cannot be reused.

The Response comes in callback params->func. The callback is run from the BT RX thread.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters:

  • conn – Connection object.

  • params – Subscribe parameters.

Return values:

  • 0 – Successfully queued request. Will call params->write on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT.

void bt_gatt_cancel(struct bt_conn *conn, void *params)

Try to cancel the first pending request identified by params.

This function does not release params for reuse. The usual callbacks for the request still apply. A successful cancel simulates a BT_ATT_ERR_UNLIKELY response from the server.

This function can cancel the following request functions:

Parameters:

  • conn – The connection the request was issued on.

  • params – The address `params` used in the request function call.

struct bt_gatt_exchange_params

GATT Exchange MTU parameters.

struct bt_gatt_discover_params

GATT Discover Attributes parameters.

struct bt_gatt_read_params

GATT Read parameters.

struct bt_gatt_write_params

GATT Write parameters.

struct bt_gatt_subscribe_params

GATT Subscribe parameters.