blob: e97a6c5ad759ec13a62ef3cde9dbdcb109962c63 [file] [log] [blame]
//
// Copyright 2015 Google, Inc.
//
// 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.
//
#define LOG_TAG "bt_gatts"
#include "gatt_server_old.h"
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <base/bind.h>
#include <algorithm>
#include <array>
#include <condition_variable>
#include <map>
#include <memory>
#include <mutex>
#include <set>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <hardware/bluetooth.h>
#include <hardware/bt_gatt.h>
#include "service/hal/bluetooth_interface.h"
#include "service/logging_helpers.h"
#include "osi/include/log.h"
#include "osi/include/osi.h"
namespace {
const size_t kMaxGattAttributeSize = 512;
std::vector<btgatt_db_element_t> pending_svc_decl;
std::unordered_set<int> blob_index;
// TODO(icoolidge): Support multiple instances
// TODO(armansito): Remove this variable. No point of having this if
// each bluetooth::gatt::Server instance already keeps a pointer to the
// ServerInternals that is associated with it (which is much cleaner). It looks
// like this variable exists because the btif callbacks don't allow the
// upper-layer to pass user data to them. We could:
//
// 1. Fix the btif callbacks so that some sort of continuation can be
// attached to a callback. This might be a long shot since the callback
// interface doesn't allow more than one caller to register its own callbacks
// (which might be what we want though, since this would make the API more
// flexible).
//
// 2. Allow creation of Server objects using a factory method that returns
// the result asynchronously in a base::Callback. The RegisterServerCallback
// provides an |app_uuid|, which can be used to store callback structures in
// a map and lazily instantiate the Server and invoke the correct callback.
// This is a general pattern that we should use throughout the daemon, since
// all operations can timeout or fail and this is best reported in an
// asynchronous base::Callback.
//
static bluetooth::gatt::ServerInternals* g_internal = nullptr;
enum { kPipeReadEnd = 0, kPipeWriteEnd = 1, kPipeNumEnds = 2 };
} // namespace
void DoNothing(uint8_t p) {}
namespace bluetooth {
namespace gatt {
struct Characteristic {
Uuid uuid;
int blob_section;
std::vector<uint8_t> blob;
// Support synchronized blob updates by latching under mutex.
std::vector<uint8_t> next_blob;
bool next_blob_pending;
bool notify;
};
struct ServerInternals {
ServerInternals();
~ServerInternals();
int Initialize();
bt_status_t AddCharacteristic(const Uuid& uuid, uint8_t properties,
uint16_t permissions);
// This maps API attribute Uuids to BlueDroid handles.
std::map<Uuid, int> uuid_to_attribute;
// The attribute cache, indexed by BlueDroid handles.
std::unordered_map<int, Characteristic> characteristics;
// Associate a control attribute with its value attribute.
std::unordered_map<int, int> controlled_blobs;
ScanResults scan_results;
Uuid last_write;
const btgatt_interface_t* gatt;
int server_if;
int client_if;
int service_handle;
std::set<int> connections;
std::mutex lock;
std::condition_variable api_synchronize;
int pipefd[kPipeNumEnds];
};
} // namespace gatt
} // namespace bluetooth
namespace {
/** Callback invoked in response to register_server */
void RegisterServerCallback(int status, int server_if,
const bluetooth::Uuid& app_uuid) {
LOG_INFO(LOG_TAG, "%s: status:%d server_if:%d app_uuid:%p", __func__, status,
server_if, &app_uuid);
g_internal->server_if = server_if;
pending_svc_decl.push_back(
{.type = BTGATT_DB_PRIMARY_SERVICE, .uuid = app_uuid});
}
void ServiceAddedCallback(int status, int server_if,
std::vector<btgatt_db_element_t> service) {
LOG_INFO(LOG_TAG, "%s: status:%d server_if:%d count:%zu svc_handle:%d",
__func__, status, server_if, service.size(),
service[0].attribute_handle);
std::lock_guard<std::mutex> lock(g_internal->lock);
g_internal->server_if = server_if;
g_internal->service_handle = service[0].attribute_handle;
uint16_t prev_char_handle = 0;
uint16_t prev_char_properties = 0;
for (size_t i = 1; i < service.size(); i++) {
const btgatt_db_element_t& el = service[i];
if (el.type == BTGATT_DB_DESCRIPTOR) {
LOG_INFO(LOG_TAG, "%s: descr_handle:%d", __func__, el.attribute_handle);
} else if (el.type == BTGATT_DB_CHARACTERISTIC) {
bluetooth::Uuid id(el.uuid);
uint16_t char_handle = el.attribute_handle;
LOG_INFO(LOG_TAG, "%s: char_handle:%d", __func__, char_handle);
g_internal->uuid_to_attribute[id] = char_handle;
g_internal->characteristics[char_handle].uuid = id;
g_internal->characteristics[char_handle].blob_section = 0;
// If the added characteristic is blob
if (blob_index.find(i) != blob_index.end()) {
// Finally, associate the control attribute with the value attribute.
// Also, initialize the control attribute to a readable zero.
const uint16_t control_attribute = char_handle;
const uint16_t blob_attribute = prev_char_handle;
g_internal->controlled_blobs[control_attribute] = blob_attribute;
g_internal->characteristics[blob_attribute].notify =
prev_char_properties & bluetooth::gatt::kPropertyNotify;
bluetooth::gatt::Characteristic& ctrl =
g_internal->characteristics[control_attribute];
ctrl.next_blob.clear();
ctrl.next_blob.push_back(0);
ctrl.next_blob_pending = true;
ctrl.blob_section = 0;
ctrl.notify = false;
}
prev_char_handle = char_handle;
prev_char_properties = el.properties;
}
}
pending_svc_decl.clear();
blob_index.clear();
// The Uuid provided here is unimportant, and is only used to satisfy
// BlueDroid.
// It must be different than any other registered Uuid.
bluetooth::Uuid client_id = bluetooth::Uuid::GetRandom();
bt_status_t btstat = g_internal->gatt->client->register_client(client_id);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "%s: Failed to register client", __func__);
}
}
void RequestReadCallback(int conn_id, int trans_id, const RawAddress& bda,
int attr_handle, int attribute_offset_octets,
bool is_long) {
std::lock_guard<std::mutex> lock(g_internal->lock);
bluetooth::gatt::Characteristic& ch =
g_internal->characteristics[attr_handle];
// Latch next_blob to blob on a 'fresh' read.
if (ch.next_blob_pending && attribute_offset_octets == 0 &&
ch.blob_section == 0) {
std::swap(ch.blob, ch.next_blob);
ch.next_blob_pending = false;
}
const size_t blob_offset_octets =
std::min(ch.blob.size(), ch.blob_section * kMaxGattAttributeSize);
const size_t blob_remaining = ch.blob.size() - blob_offset_octets;
const size_t attribute_size = std::min(kMaxGattAttributeSize, blob_remaining);
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG,
"%s: connection:%d (%s) reading attr:%d attribute_offset_octets:%d "
"blob_section:%u (is_long:%u)",
__func__, conn_id, addr.c_str(), attr_handle,
attribute_offset_octets, ch.blob_section, is_long);
btgatt_response_t response;
response.attr_value.len = 0;
if (attribute_offset_octets < static_cast<int>(attribute_size)) {
std::copy(ch.blob.begin() + blob_offset_octets + attribute_offset_octets,
ch.blob.begin() + blob_offset_octets + attribute_size,
response.attr_value.value);
response.attr_value.len = attribute_size - attribute_offset_octets;
}
response.attr_value.handle = attr_handle;
response.attr_value.offset = attribute_offset_octets;
response.attr_value.auth_req = 0;
g_internal->gatt->server->send_response(conn_id, trans_id, 0, response);
}
void RequestWriteCallback(int conn_id, int trans_id, const RawAddress& bda,
int attr_handle, int attribute_offset, bool need_rsp,
bool is_prep, std::vector<uint8_t> value) {
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG,
"%s: connection:%d (%s:trans:%d) write attr:%d attribute_offset:%d "
"length:%zu "
"need_resp:%u is_prep:%u",
__func__, conn_id, addr.c_str(), trans_id, attr_handle,
attribute_offset, value.size(), need_rsp, is_prep);
std::lock_guard<std::mutex> lock(g_internal->lock);
bluetooth::gatt::Characteristic& ch =
g_internal->characteristics[attr_handle];
ch.blob.resize(attribute_offset + value.size());
std::copy(value.begin(), value.end(), ch.blob.begin() + attribute_offset);
auto target_blob = g_internal->controlled_blobs.find(attr_handle);
// If this is a control attribute, adjust offset of the target blob.
if (target_blob != g_internal->controlled_blobs.end() &&
ch.blob.size() == 1u) {
g_internal->characteristics[target_blob->second].blob_section = ch.blob[0];
LOG_INFO(LOG_TAG, "%s: updating attribute %d blob_section to %u", __func__,
target_blob->second, ch.blob[0]);
} else if (!is_prep) {
// This is a single frame characteristic write.
// Notify upwards because we're done now.
const bluetooth::Uuid::UUID128Bit& attr_uuid = ch.uuid.To128BitBE();
ssize_t status;
OSI_NO_INTR(status = write(g_internal->pipefd[kPipeWriteEnd],
attr_uuid.data(), attr_uuid.size()));
if (-1 == status)
LOG_ERROR(LOG_TAG, "%s: write failed: %s", __func__, strerror(errno));
} else {
// This is a multi-frame characteristic write.
// Wait for an 'RequestExecWriteCallback' to notify completion.
g_internal->last_write = ch.uuid;
}
// Respond only if needed.
if (!need_rsp) return;
btgatt_response_t response;
response.attr_value.handle = attr_handle;
response.attr_value.offset = attribute_offset;
response.attr_value.len = value.size();
response.attr_value.auth_req = 0;
// Provide written data back to sender for the response.
// Remote stacks use this to validate the success of the write.
std::copy(value.begin(), value.end(), response.attr_value.value);
g_internal->gatt->server->send_response(conn_id, trans_id, 0, response);
}
void RequestExecWriteCallback(int conn_id, int trans_id, const RawAddress& bda,
int exec_write) {
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG, "%s: connection:%d (%s:trans:%d) exec_write:%d", __func__,
conn_id, addr.c_str(), trans_id, exec_write);
// This 'response' data is unused for ExecWriteResponses.
// It is only used to pass BlueDroid argument validation.
btgatt_response_t response = {};
g_internal->gatt->server->send_response(conn_id, trans_id, 0, response);
if (!exec_write) return;
std::lock_guard<std::mutex> lock(g_internal->lock);
// Communicate the attribute Uuid as notification of a write update.
const bluetooth::Uuid::UUID128Bit uuid = g_internal->last_write.To128BitBE();
ssize_t status;
OSI_NO_INTR(status = write(g_internal->pipefd[kPipeWriteEnd], uuid.data(),
uuid.size()));
if (-1 == status)
LOG_ERROR(LOG_TAG, "%s: write failed: %s", __func__, strerror(errno));
}
void ConnectionCallback(int conn_id, int server_if, int connected,
const RawAddress& bda) {
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG, "%s: connection:%d server_if:%d connected:%d addr:%s",
__func__, conn_id, server_if, connected, addr.c_str());
if (connected == 1) {
g_internal->connections.insert(conn_id);
} else if (connected == 0) {
g_internal->connections.erase(conn_id);
}
}
void EnableAdvertisingCallback(uint8_t status) {
LOG_INFO(LOG_TAG, "%s: status:%d", __func__, status);
// This terminates a Start call.
std::lock_guard<std::mutex> lock(g_internal->lock);
g_internal->api_synchronize.notify_one();
}
void RegisterClientCallback(int status, int client_if,
const bluetooth::Uuid& app_uuid) {
LOG_INFO(LOG_TAG, "%s: status:%d client_if:%d uuid[0]:%s", __func__, status,
client_if, app_uuid.ToString().c_str());
g_internal->client_if = client_if;
// Setup our advertisement. This has no callback.
g_internal->gatt->advertiser->SetData(0 /* std_inst */, false,
{/*TODO: put inverval 2,2 here*/},
base::Bind(&DoNothing));
g_internal->gatt->advertiser->Enable(
0 /* std_inst */, true, base::Bind(&EnableAdvertisingCallback),
0 /* no duration */, 0 /* no maxExtAdvEvent*/, base::Bind(&DoNothing));
}
void ServiceStoppedCallback(int status, int server_if, int srvc_handle) {
LOG_INFO(LOG_TAG, "%s: status:%d server_if:%d srvc_handle:%d", __func__,
status, server_if, srvc_handle);
// This terminates a Stop call.
// TODO(icoolidge): make this symmetric with start
std::lock_guard<std::mutex> lock(g_internal->lock);
g_internal->api_synchronize.notify_one();
}
void ScanResultCallback(uint16_t ble_evt_type, uint8_t addr_type,
RawAddress* bda, uint8_t ble_primary_phy,
uint8_t ble_secondary_phy, uint8_t ble_advertising_sid,
int8_t ble_tx_power, int8_t rssi,
uint16_t ble_periodic_adv_int,
std::vector<uint8_t> adv_data) {
std::string addr(BtAddrString(bda));
std::lock_guard<std::mutex> lock(g_internal->lock);
g_internal->scan_results[addr] = rssi;
}
void ClientConnectCallback(int conn_id, int status, int client_if,
const RawAddress& bda) {
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG, "%s: conn_id:%d status:%d client_if:%d %s", __func__,
conn_id, status, client_if, addr.c_str());
}
void ClientDisconnectCallback(int conn_id, int status, int client_if,
const RawAddress& bda) {
std::string addr(BtAddrString(&bda));
LOG_INFO(LOG_TAG, "%s: conn_id:%d status:%d client_if:%d %s", __func__,
conn_id, status, client_if, addr.c_str());
}
void IndicationSentCallback(UNUSED_ATTR int conn_id, UNUSED_ATTR int status) {
// TODO(icoolidge): what to do
}
void ResponseConfirmationCallback(UNUSED_ATTR int status,
UNUSED_ATTR int handle) {
// TODO(icoolidge): what to do
}
const btgatt_server_callbacks_t gatt_server_callbacks = {
RegisterServerCallback,
ConnectionCallback,
ServiceAddedCallback,
ServiceStoppedCallback,
nullptr, /* service_deleted_cb */
RequestReadCallback,
RequestReadCallback,
RequestWriteCallback,
RequestWriteCallback,
RequestExecWriteCallback,
ResponseConfirmationCallback,
IndicationSentCallback,
nullptr, /* congestion_cb*/
nullptr, /* mtu_changed_cb */
nullptr, /* phy_update_cb */
nullptr, /* conn_update_cb */
};
// TODO(eisenbach): Refactor GATT interface to not require servers
// to refer to the client interface.
const btgatt_client_callbacks_t gatt_client_callbacks = {
RegisterClientCallback,
ClientConnectCallback,
ClientDisconnectCallback,
nullptr, /* search_complete_cb; */
nullptr, /* register_for_notification_cb; */
nullptr, /* notify_cb; */
nullptr, /* read_characteristic_cb; */
nullptr, /* write_characteristic_cb; */
nullptr, /* read_descriptor_cb; */
nullptr, /* write_descriptor_cb; */
nullptr, /* execute_write_cb; */
nullptr, /* read_remote_rssi_cb; */
nullptr, /* configure_mtu_cb; */
nullptr, /* congestion_cb; */
nullptr, /* get_gatt_db_cb; */
nullptr, /* services_removed_cb */
nullptr, /* services_added_cb */
nullptr, /* phy_update_cb */
nullptr, /* conn_update_cb */
};
const btgatt_scanner_callbacks_t gatt_scanner_callbacks = {
ScanResultCallback,
nullptr, /* batchscan_reports_cb; */
nullptr, /* batchscan_threshold_cb; */
nullptr, /* track_adv_event_cb; */
};
const btgatt_callbacks_t gatt_callbacks = {
/** Set to sizeof(btgatt_callbacks_t) */
sizeof(btgatt_callbacks_t),
/** GATT Client callbacks */
&gatt_client_callbacks,
/** GATT Server callbacks */
&gatt_server_callbacks,
/** GATT Server callbacks */
&gatt_scanner_callbacks,
};
} // namespace
namespace bluetooth {
namespace gatt {
int ServerInternals::Initialize() {
// Get the interface to the GATT profile.
const bt_interface_t* bt_iface =
hal::BluetoothInterface::Get()->GetHALInterface();
gatt = reinterpret_cast<const btgatt_interface_t*>(
bt_iface->get_profile_interface(BT_PROFILE_GATT_ID));
if (!gatt) {
LOG_ERROR(LOG_TAG, "Error getting GATT interface");
return -1;
}
bt_status_t btstat = gatt->init(&gatt_callbacks);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to initialize gatt interface");
return -1;
}
int status = pipe(pipefd);
if (status == -1) {
LOG_ERROR(LOG_TAG, "pipe creation failed: %s", strerror(errno));
return -1;
}
return 0;
}
bt_status_t ServerInternals::AddCharacteristic(const Uuid& uuid,
uint8_t properties,
uint16_t permissions) {
pending_svc_decl.push_back({.type = BTGATT_DB_CHARACTERISTIC,
.uuid = uuid,
.properties = properties,
.permissions = permissions});
return BT_STATUS_SUCCESS;
}
ServerInternals::ServerInternals()
: gatt(nullptr),
server_if(0),
client_if(0),
service_handle(0),
pipefd{INVALID_FD, INVALID_FD} {}
ServerInternals::~ServerInternals() {
if (pipefd[0] != INVALID_FD) close(pipefd[0]);
if (pipefd[1] != INVALID_FD) close(pipefd[1]);
gatt->server->delete_service(server_if, service_handle);
gatt->server->unregister_server(server_if);
gatt->client->unregister_client(client_if);
}
Server::Server() : internal_(nullptr) {}
Server::~Server() {}
bool Server::Initialize(const Uuid& service_id, int* gatt_pipe) {
internal_.reset(new ServerInternals);
if (!internal_) {
LOG_ERROR(LOG_TAG, "Error creating internals");
return false;
}
g_internal = internal_.get();
std::unique_lock<std::mutex> lock(internal_->lock);
int status = internal_->Initialize();
if (status) {
LOG_ERROR(LOG_TAG, "Error initializing internals");
return false;
}
bt_status_t btstat = internal_->gatt->server->register_server(service_id);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to register server");
return false;
}
internal_->api_synchronize.wait(lock);
// TODO(icoolidge): Better error handling.
if (internal_->server_if == 0) {
LOG_ERROR(LOG_TAG, "Initialization of server failed");
return false;
}
*gatt_pipe = internal_->pipefd[kPipeReadEnd];
LOG_INFO(LOG_TAG, "Server Initialize succeeded");
return true;
}
bool Server::SetAdvertisement(const std::vector<Uuid>& ids,
const std::vector<uint8_t>& service_data,
const std::vector<uint8_t>& manufacturer_data,
bool transmit_name) {
// std::vector<uint8_t> id_data;
// const auto& mutable_manufacturer_data = manufacturer_data;
// const auto& mutable_service_data = service_data;
// for (const Uuid &id : ids) {
// const auto le_id = id.To128BitLE();
// id_data.insert(id_data.end(), le_id.begin(), le_id.end());
// }
std::lock_guard<std::mutex> lock(internal_->lock);
// Setup our advertisement. This has no callback.
internal_->gatt->advertiser->SetData(0, false, /* beacon, not scan response */
{}, base::Bind(&DoNothing));
// transmit_name, /* name */
// 2, 2, interval
// mutable_manufacturer_data,
// mutable_service_data,
// id_data);
return true;
}
bool Server::SetScanResponse(const std::vector<Uuid>& ids,
const std::vector<uint8_t>& service_data,
const std::vector<uint8_t>& manufacturer_data,
bool transmit_name) {
// std::vector<uint8_t> id_data;
// const auto& mutable_manufacturer_data = manufacturer_data;
// const auto& mutable_service_data = service_data;
// for (const Uuid &id : ids) {
// const auto le_id = id.To128BitLE();
// id_data.insert(id_data.end(), le_id.begin(), le_id.end());
// }
std::lock_guard<std::mutex> lock(internal_->lock);
// Setup our advertisement. This has no callback.
internal_->gatt->advertiser->SetData(0, true, /* scan response */
{}, base::Bind(&DoNothing));
// transmit_name, /* name */
// false, /* no txpower */
// 2, 2, interval
// 0, /* appearance */
// mutable_manufacturer_data,
// mutable_service_data,
// id_data);
return true;
}
bool Server::AddCharacteristic(const Uuid& id, int properties,
int permissions) {
std::unique_lock<std::mutex> lock(internal_->lock);
bt_status_t btstat =
internal_->AddCharacteristic(id, properties, permissions);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to add characteristic to service: 0x%04x",
internal_->service_handle);
return false;
}
internal_->api_synchronize.wait(lock);
const int handle = internal_->uuid_to_attribute[id];
internal_->characteristics[handle].notify = properties & kPropertyNotify;
return true;
}
bool Server::AddBlob(const Uuid& id, const Uuid& control_id, int properties,
int permissions) {
std::unique_lock<std::mutex> lock(internal_->lock);
// First, add the primary attribute (characteristic value)
bt_status_t btstat =
internal_->AddCharacteristic(id, properties, permissions);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to set scan response data");
return false;
}
// Next, add the secondary attribute (blob control).
// Control attributes have fixed permissions/properties.
// Remember position at which blob was added.
blob_index.insert(pending_svc_decl.size());
btstat =
internal_->AddCharacteristic(control_id, kPropertyRead | kPropertyWrite,
kPermissionRead | kPermissionWrite);
return true;
}
bool Server::Start() {
std::unique_lock<std::mutex> lock(internal_->lock);
bt_status_t btstat = internal_->gatt->server->add_service(
internal_->server_if, pending_svc_decl);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to start service with handle: 0x%04x",
internal_->service_handle);
return false;
}
internal_->api_synchronize.wait(lock);
return true;
}
bool Server::Stop() {
std::unique_lock<std::mutex> lock(internal_->lock);
bt_status_t btstat = internal_->gatt->server->stop_service(
internal_->server_if, internal_->service_handle);
if (btstat != BT_STATUS_SUCCESS) {
LOG_ERROR(LOG_TAG, "Failed to stop service with handle: 0x%04x",
internal_->service_handle);
return false;
}
internal_->api_synchronize.wait(lock);
return true;
}
bool Server::ScanEnable() {
internal_->gatt->scanner->Scan(true);
return true;
}
bool Server::ScanDisable() {
internal_->gatt->scanner->Scan(false);
return true;
}
bool Server::GetScanResults(ScanResults* results) {
std::lock_guard<std::mutex> lock(internal_->lock);
*results = internal_->scan_results;
return true;
}
bool Server::SetCharacteristicValue(const Uuid& id,
const std::vector<uint8_t>& value) {
std::lock_guard<std::mutex> lock(internal_->lock);
const int attribute_id = internal_->uuid_to_attribute[id];
Characteristic& ch = internal_->characteristics[attribute_id];
ch.next_blob = value;
ch.next_blob_pending = true;
if (!ch.notify) return true;
for (auto connection : internal_->connections) {
internal_->gatt->server->send_indication(internal_->server_if, attribute_id,
connection, true, {0});
}
return true;
}
bool Server::GetCharacteristicValue(const Uuid& id,
std::vector<uint8_t>* value) {
std::lock_guard<std::mutex> lock(internal_->lock);
const int attribute_id = internal_->uuid_to_attribute[id];
*value = internal_->characteristics[attribute_id].blob;
return true;
}
} // namespace gatt
} // namespace bluetooth