text: /* mbed Microcontroller Library
   * Copyright (c) 2006-2020 ARM Limited
   *
   * SPDX-License-Identifier: Apache-2.0
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #ifndef BLE_PAL_ATTCLIENT_H_
  #define BLE_PAL_ATTCLIENT_H_
  
  #include "platform/Callback.h"
  
  #include "ble/common/UUID.h"
  #include "ble/common/BLETypes.h"
  #include "ble/common/blecommon.h"
  #include "AttServerMessage.h"
  
  namespace ble {
  
  /**
   * Send attribute protocol requests to an ATT server. It also handle reception
   * of ATT response and server indication/notification.
   *
   * Every request send and response or response event received is for a specified
   * connection.
   *
   * @warning This class should not be used outside mbed BLE, availability is not
   * guaranteed for all ports.
   *
   * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F
   */
  class PalAttClient  {
  public:
      /**
       * Initialization of the instance. An implementation can use this function
       * to initialise the subsystems needed to realize the ATT operations of this
       * interface.
       *
       * This function has to be called before any other operations.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       */
      virtual ble_error_t initialize() = 0;
  
      /**
       * Termination of the instance. An implementation can use this function
       * to release the subsystems initialised  to realise the ATT operations of
       * this interface.
       *
       * After a call to this function, initialise should be called again to
       * allow usage of the interface.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       */
      virtual ble_error_t terminate() = 0;
  
      /**
       * Send an exchange MTU request which negotiate the size of the MTU used by
       * the connection.
       *
       * First the client send to the server the maximum rx mtu that it can receive
       * then the client reply with the maximum rx mtu it can receive.
       *
       * The mtu choosen for the connection is the minimum of the client Rx mtu
       * and server Rx mtu values.
       *
       * If an error occured then the mtu used remains the default value.
       *
       * @param connection The handle of the connection to send this request to.
       *
       * @return BLE_ERROR_NONE if the request has been succesfully sent or the
       * appropriate error otherwise.
       *
       * @see ble::AttExchangeMTUResponse The type of response received from
       * the  server
       * @see ble::AttErrorResponse::REQUEST_NOT_SUPPORTED The error code
       * returned by the server in case of error.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.2.1
       */
      virtual ble_error_t exchange_mtu_request(connection_handle_t connection) = 0;
  
      /**
       * Acquire the size of the mtu for a given connection.
       *
       * @param connection The handle of the connection for which the the MTU size
       * should be acquired.
       *
       * @param mtu_size Output parameter which will contain the MTU size.
       *
       * @return BLE_ERROR_NONE if the MTU size has been acquired or the
       * appropriate error otherwise.
       */
      virtual ble_error_t get_mtu_size(
          connection_handle_t connection_handle,
          uint16_t& mtu_size
      ) = 0;
  
      /**
       * Send a find information request to a server in order to obtain the
       * mapping of attribute handles with their associated types.
       *
       * The server will reply with a ble::AttFindInformationResponse
       * containing at least one [attribute handle, attribute type] pair. If the
       * last handle in the response is not equal to the end handle of the finding
       * range then this request can be issued again with an updated range (begin
       * equal to last handle received + 1) to discover the remaining attributes.
       *
       * To discover the whole ATT server, the first find information request
       * should have a discovery range of [0x0001 - 0xFFFF].
       *
       * The server can send a ble::AttErrorResponse with the code
       * ble::AttErrorResponse::ATTRIBUTE_NOT_FOUND if no attributes have
       * been found in the range specified. The attribute handle in the response
       * is then equal to the first handle of the discovery range.
       *
       * If the range is malformed the server will reply a
       * ble::AttErrorResponse with the error code ble::INVALID_HANDLE.
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param discovery_range The attribute range where handle-type informations
       * should be discovered.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.3.1
       */
      virtual ble_error_t find_information_request(
          connection_handle_t connection_handle,
          attribute_handle_range_t discovery_range
      ) = 0;
  
      /**
       * Send a Find By Type Value Request which retrieve the handles of attributes
       * that have known 16-bit UUID attribute type and known attribute value.
       *
       * The server should reply with a ble::AttFindByTypeValueResponse
       * containing the handle (or handle range in case of grouping attributes) of
       * the attribute found.
       *
       * If not all attributes can be contained in the response it is necessary to
       * send again this request with an updated range to continue the discovery.
       *
       * The server can send a ble::AttErrorResponse with the code
       * ble::AttErrorResponse::ATTRIBUTE_NOT_FOUND if no attributes have
       * been found in the range specified. The attribute handle in the response
       * is then equal to the first handle of the discovery range.
       *
       * If the range is malformed the server will reply a
       * ble::AttErrorResponse with the error code ble::INVALID_HANDLE.
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param discovery_range The handle range where attributes with type and
       * value are searched.
       * @param type The type of attribute to find (it is a 16 bit UUID).
       * @param value The value of the attributes to found.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.3.3
       */
      virtual ble_error_t find_by_type_value_request(
          connection_handle_t connection_handle,
          attribute_handle_range_t discovery_range,
          uint16_t type,
          const Span<const uint8_t>& value
      ) = 0;
  
      /**
       * Send a Read By Type Request used to obtain the values of attributes where
       * the attribute type is known but the handle is not known.
       *
       * If attributes with the type requested are present in the range, the server
       * should reply with a ble::AttReadByTypeResponse. If the response does
       * not cover the full range, the request should be sent again with an updated
       * range.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::ATTRIBUTE_NOT_FOUND: If there is no
       *     attributes matching type in the range.
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the range is
       *     invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption.
       *   - ble::AttErrorResponse::READ_NOT_PERMITTED: If the attribute
       *     value cannot be read.
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param read_range The handle range where attributes with the given type
       * should be read.
       * @param type The type of attributes to read.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.4.1
       */
      virtual ble_error_t read_by_type_request(
          connection_handle_t connection_handle,
          attribute_handle_range_t read_range,
          const UUID& type
      ) = 0;
  
      /**
       * Send a Read Request to read the value of an attribute in the server.
       *
       * In case of success, the server will reply with a ble::AttReadResponse.
       * containing the value of the attribute. If the length of the value in the
       * response is equal to (mtu - 1) then the remaining part of the value can
       * be obtained by a read_blob_request.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the attribute handle
       *     is invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption.
       *   - ble::AttErrorResponse::READ_NOT_PERMITTED: If the attribute
       *     value cannot be read.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle The handle of the attribute to read.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or the
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.4.3
       */
      virtual ble_error_t read_request(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle
      ) = 0;
  
      /**
       * Send a read blob request to a server to read a part of the value of an
       * attribute at a given offset.
       *
       * In case of success, the server will reply with a ble::AttReadBlobResponse
       * containing the value read. If the value of the attribute starting at the
       * offset requested is longer than (mtu - 1) octets then only the first
       * (mtu - 1) octets will be present in the response.
       * The remaining octets can be acquired by another Read Blob Request with an
       * updated index.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the attribute handle
       *     is invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption.
       *   - ble::AttErrorResponse::READ_NOT_PERMITTED: If the attribute
       *     value cannot be read.
       *   - ble::AttErrorResponse::INVALID_OFFSET: If the offset is greater
       *     than the attribute length.
       *   - ble::AttErrorResponse::ATTRIBUTE_NOT_LONG: If the attribute
       *     value has a length that is less than or equal to (mtu - 1).
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle The handle of the attribute to read.
       * @param offset The offset of the first octet to read.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.4.5
       */
      virtual ble_error_t read_blob_request(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle,
          uint16_t offset
      ) = 0;
  
      /**
       * Send a read multiple request to the server. It is used to read two or more
       * attributes values at once.
       *
       * In case of success, the server will reply with a
       * ble::AttReadMultipleResponse containing the concatenation of the
       * values read. Given that values are concatained, all attributes values
       * should be of fixed size except for the last one. The concatained value
       * is also truncated to (mtu - 1) if it doesn't fit in the response.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If any of the attribute
       *     handle is invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient to read any of the attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient to read any of the attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size to read any of the
       *     attributes.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption required to read any of the attributes.
       *   - ble::AttErrorResponse::READ_NOT_PERMITTED: If any of the
       *     attributes value cannot be read.
       * The first attribute causing the error is reporter in the handle_in_error
       * field in the error response.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handles Set of attribute handles to read.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.4.7
       */
      virtual ble_error_t read_multiple_request(
          connection_handle_t connection_handle,
          const Span<const attribute_handle_t>& attribute_handles
      ) = 0;
  
      /**
       * Send a read by group type request to the server. It is used to get
       * informations about grouping attribute of a given type on a server.
       *
       * The server will reply with a ble::ReadByGroupTypeResponse containing
       * informations about the grouping attribute found. Informations are:
       *    - handle of the grouping attribute.
       *    - last handle of the group .
       *    - attribute value.
       *
       * If the last handle received is not the last handle of the discovery range
       * then it is necessary to send another request with a discovery range
       * updated to: [last handle + 1 : end].
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the range of handle
       *     provided is invalid.
       *   - ble::AttErrorResponse::UNSUPPORTED_GROUP_TYPE: if the group type
       *     is not a supported grouping attribute.
       *   - ble::AttErrorResponse::ATTRIBUTE_NOT_FOUND: If no attribute with
       *     the given type exists within the range provided.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient to read the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient to read the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size to read the requested
       *     attributes.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption required to read the requested attributes.
       *   - ble::AttErrorResponse::READ_NOT_PERMITTED: If any of the
       *     attributes value cannot be read.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param read_range Range where this request apply.
       * @param group_type Type of the grouping attribute to find and read.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.4.9
       */
      virtual ble_error_t read_by_group_type_request(
          connection_handle_t connection_handle,
          attribute_handle_range_t read_range,
          const UUID& group_type
      ) = 0;
  
      /**
       * Send a write request to the server to write the value of an attribute.
       *
       * In case of success, the server will reply with a
       * ble::AttWriteResponse to acknowledge that the write operation went
       * well.
       *
       * If the attribute value has a variable length, then the attribute value
       * shall be truncated or lengthened to match the length of the value in the
       * request.
       *
       * If the attribute value has a fixed length and the Attribute Value parameter length
       * is less than or equal to the length of the attribute value, the octets of the
       * attribute value parameter length shall be written; all other octets in this attribute
       * value shall be unchanged.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the handle to write is
       *     invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient to write the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient to write the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size to write the requested
       *     attributes.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption required to write the requested attributes.
       *   - ble::AttErrorResponse::WRITE_NOT_PERMITTED: If the attribute
       *     value cannot be written due to permission.
       *   - ble::AttErrorResponse::INVALID_ATTRIBUTE_VALUE_LENGTH: If the
       *     value to write exceeds the maximum valid length or of the attribute
       *     value; whether the attribute has a variable length value or a fixed
       *     length value.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle Handle of the attribute to write.
       * @param value Value to write. It can't be longer than (mtu - 3).
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.5.1
       */
      virtual ble_error_t write_request(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle,
          const Span<const uint8_t>& value
      ) = 0;
  
      /**
       * Send a write command to the server. A write command is similar to a write
       * request except that it won't receive any response from the server
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle Handle of the attribute to write.
       * @param value Value to write. It can't be longer than (mtu - 3).
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.5.3
       */
      virtual ble_error_t write_command(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle,
          const Span<const uint8_t>& value
      ) = 0;
  
      /**
       * Send a signed write command to the server. Behaviour is similar to a write
       * command except that 12 bytes of the mtu are reserved for the authentication
       * signature.
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle Handle of the attribute to write.
       * @param value Value to write. It can't be longer than (mtu - 15).
       *
       * @note the authentication signature to send with this request is
       * computed by the implementation following the rules defined in BLUETOOTH
       * SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.3.1.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.5.4
       */
      virtual ble_error_t signed_write_command(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle,
          const Span<const uint8_t>& value
      ) = 0;
  
      /**
       * The Prepare Write Request is used to request the server to prepare to
       * write the value of an attribute. The client can send multiple prepare
       * write request which will be put in a queue until the client send an
       * Execute Write Request which will execute sequentially the write request
       * in the queue.
       *
       * In case of success the server will respond with a
       * ble::AttPrepareWriteResponse containing the values (attribute handle,
       * offset and value) present in the write request.
       *
       * If a prepare write request is rejected by the server, the state queue of
       * the prepare write request queue remains unaltered.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_HANDLE: If the handle to write is
       *     invalid.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHENTICATION: If the client
       *     security is not sufficient to write the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_AUTHORIZATION: If the client
       *     authorization is not sufficient to write the requested attribute.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION_KEY_SIZE: If the
       *     client has an insufficient encryption key size to write the requested
       *     attributes.
       *   - ble::AttErrorResponse::INSUFFICIENT_ENCRYPTION: If the client
       *     has not enabled encryption required to write the requested attributes.
       *   - ble::AttErrorResponse::WRITE_NOT_PERMITTED: If the attribute
       *     value cannot be written due to permission.
       *   - ble::PREPARE_QUEUE_FULL: If the queue of prepare write request
       *     is full.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param attribute_handle The handle of the attribute to be written.
       * @param offset The offset of the first octet to be written.
       * @param value The value of the attribute to be written. It can't be longer
       * than (mtu - 5).
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.6.1
       *
       */
      virtual ble_error_t prepare_write_request(
          connection_handle_t connection_handle,
          attribute_handle_t attribute_handle,
          uint16_t offset,
          const Span<const uint8_t>& value
      ) = 0;
  
      /**
       * Send an Execute Write Request to the server. This request will instruct
       * the server to execute or cancel the prepare write requests currently held
       * in the prepare queue from this client.
       *
       * If the execute parameter is set to true, the server should execute the
       * request held in the queue. If the parameter is equal to false then the
       * server should cancel the requests in the queue.
       *
       * In case of success, the server will respond with a
       * ble::AttExecuteWriteResponse indicating that the request was correctly
       * handled.
       *
       * In case of error, the server will send a ble::AttErrorResponse. The
       * error code depends on the situation:
       *   - ble::AttErrorResponse::INVALID_OFFSET: If the value offset is
       *     greater than the current length of the attribute to write.
       *   - ble::AttErrorResponse::INVALID_ATTRIBUTE_VALUE_LENGTH: If the
       *     length of the value write exceeds the length of the attribute value
       *     about to be written.
       * Higher layer can also set an application error code (0x80 - 0x9F).
       *
       * The error response will contains the attribute handle which as caused the
       * error and the remaining of the prepare queue is discarded. The state of
       * the attributes that were to be written from the prepare queue is not
       * defined in this case.
       *
       * @param connection_handle The handle of the connection to send this
       * request to.
       * @param execute Boolean indicating if the prepare queue should be executed
       * or cleared.
       *
       * @return BLE_ERROR_NONE if the request has been successfully sent or an
       * appropriate error otherwise.
       *
       * @note see BLUETOOTH SPECIFICATION Version 5.0 | Vol 3, Part F Section 3.4.6.3
       */
      virtual ble_error_t execute_write_request(
          connection_handle_t connection_handle,
          bool execute
      ) = 0;
  
      /**
       * Register a callback which will handle messages from the server.
       *
       * @param cb The callback object which will handle messages from the server.
       * It accept two parameters in input: The handle of the connection where the
       * message was received and the message received. Real type of the message
       * can be obtained from its opcode.
       */
      virtual void when_server_message_received(
          mbed::Callback<void(connection_handle_t, const AttServerMessage&)> cb
      ) = 0;
  
      /**
       * Register a callback handling transaction timeout.
       *
       * @param cb The callback handling timeout of a transaction. It accepts as
       * a parameter the connection handle involved in the timeout.
       *
       * @note No more attribute protocol requests, commands, indication or
       * notification shall be sent over a connection implied in a transaction
       * timeout. To send a new ATT message, the conenction should be
       * reestablished.
       */
      virtual void when_transaction_timeout(
           mbed::Callback<void(connection_handle_t)> cb
       ) = 0;
  };
  
  } // namespace ble
  
  #endif /* BLE_PAL_ATTCLIENT_H_ */
  