BLE: Introduce GenericGattClient and platform abstraction over ATT/GATT.

This changes introduce a platform adaptation over ATT/GATT that can be implemented by porter.
Unlike the GattClient interface, the ATT/GATT adaptation is simple, follow closely the Bluetooth specification and won't change over time.
Implementation of the GattClient interface is realized by the class GenericGattClient which accept in input a pal::GattClient.

This change will also free design space once adopted by partners, addition to the GattClient interface won't require partner support.

Author: pan-

features/FEATURE_BLE/ble/generic/GenericGattClient.h

@@ -0,0 +1,154 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017-2017 ARM Limited
+ *
+ * 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 MBED_BLE_GENERIC_GATT_CLIENT
+#define MBED_BLE_GENERIC_GATT_CLIENT
+
+#include <algorithm>
+#include "ble/GattClient.h"
+#include "ble/pal/PalGattClient.h"
+
+// IMPORTANT: private header. Not part of the public interface.
+
+namespace ble {
+namespace generic {
+
+// forward declarations
+struct procedure_control_block_t;
+struct discovery_control_block_t;
+struct read_control_block_t;
+struct write_control_block_t;
+struct descriptor_discovery_control_block_t;
+
+/**
+ * Generic implementation of the GattClient.
+ * It requires a pal::GattClient injected at construction site.
+ * @important: Not part of the public interface of BLE API.
+ */
+class GenericGattClient : public GattClient {
+
+    // give access to control block classes
+    friend struct procedure_control_block_t;
+    friend struct discovery_control_block_t;
+    friend struct read_control_block_t;
+    friend struct write_control_block_t;
+    friend struct descriptor_discovery_control_block_t;
+
+public:
+    /**
+     * Create a GenericGattClient from a pal::GattClient
+     */
+    GenericGattClient(pal::GattClient* pal_client);
+
+    /**
+     * @see GattClient::launchServiceDiscovery
+     */
+    virtual ble_error_t launchServiceDiscovery(
+        Gap::Handle_t connection_handle,
+        ServiceDiscovery::ServiceCallback_t service_callback,
+        ServiceDiscovery::CharacteristicCallback_t characteristic_callback,
+        const UUID& matching_service_uuid,
+        const UUID& matching_characteristic_uuid
+    );
+
+	/**
+	 * @see GattClient::isServiceDiscoveryActive
+	 */
+    virtual bool isServiceDiscoveryActive() const;
+
+	/**
+	 * @see GattClient::terminateServiceDiscovery
+	 */
+    virtual void terminateServiceDiscovery();
+
+	/**
+	 * @see GattClient::read
+	 */
+    virtual ble_error_t read(
+        Gap::Handle_t connection_handle,
+        GattAttribute::Handle_t attribute_handle,
+        uint16_t offset
+    ) const;
+
+	/**
+	 * @see GattClient::write
+	 */
+    virtual ble_error_t write(
+        GattClient::WriteOp_t cmd,
+        Gap::Handle_t connection_handle,
+        GattAttribute::Handle_t attribute_handle,
+        size_t length,
+        const uint8_t* value
+    ) const;
+
+	/**
+	 * @see GattClient::onServiceDiscoveryTermination
+	 */
+    virtual void onServiceDiscoveryTermination(
+        ServiceDiscovery::TerminationCallback_t callback
+    );
+
+	/**
+	 * @see GattClient::discoverCharacteristicDescriptors
+	 */
+    virtual ble_error_t discoverCharacteristicDescriptors(
+        const DiscoveredCharacteristic& characteristic,
+        const CharacteristicDescriptorDiscovery::DiscoveryCallback_t& discoveryCallback,
+        const CharacteristicDescriptorDiscovery::TerminationCallback_t& terminationCallback
+    );
+
+	/**
+	 * @see GattClient::isCharacteristicDescriptorDiscoveryActive
+	 */
+    virtual bool isCharacteristicDescriptorDiscoveryActive(
+        const DiscoveredCharacteristic& characteristic
+    ) const;
+
+	/**
+	 * @see GattClient::terminateCharacteristicDescriptorDiscovery
+	 */
+    virtual void terminateCharacteristicDescriptorDiscovery(
+        const DiscoveredCharacteristic& characteristic
+    );
+
+	/**
+	 * @see GattClient::reset
+	 */
+    virtual ble_error_t reset(void);
+
+private:
+    procedure_control_block_t* get_control_block(Gap::Handle_t connection);
+    const procedure_control_block_t* get_control_block(Gap::Handle_t connection) const;
+    void insert_control_block(procedure_control_block_t* cb) const;
+    void remove_control_block(procedure_control_block_t* cb) const;
+
+    void on_termination(Gap::Handle_t connection_handle);
+    void on_server_message_received(connection_handle_t, const pal::AttServerMessage&);
+    void on_server_response(connection_handle_t, const pal::AttServerMessage&);
+    void on_server_event(connection_handle_t, const pal::AttServerMessage&);
+    void on_transaction_timeout(connection_handle_t);
+
+    uint16_t get_mtu(Gap::Handle_t connection) const;
+
+    pal::GattClient* const _pal_client;
+    ServiceDiscovery::TerminationCallback_t _termination_callback;
+    mutable procedure_control_block_t* control_blocks;
+};
+
+}
+}
+
+#endif /* MBED_BLE_GENERIC_GATT_CLIENT */