Direct-BT LE and BREDR Library

Original document location.

Git Repository

This project's canonical repositories is hosted on Gothel Software.

Goals

This project aims to create a clean, modern and easy to use API for Bluetooth LE and BREDR, fully accessible through C++, Java and other languages.

Overview

Direct-BT provides direct Bluetooth LE and BREDR programming, offering robust high-performance support for embedded & desktop with zero overhead via C++ and Java.

You will find a detailed overview of Direct-BT (C++) and the same in the Java API.

Direct-BT supports a fully event driven workflow from adapter management via device discovery to GATT programming. using its platform agnostic HCI, L2CAP, SMP and GATT client-side protocol implementation.

AdapterStatusListener allows listening to adapter changes and device discovery and BTGattCharListener to GATT indications and notifications.

Direct-BT may be utilized via its C++ API or via its Java API.

Direct-BT is exposed via the following native libraries

• libdirect_bt.so for the core C++ implementation.
• libjavadirect_bt.so for the Java binding.

Direct-BT is C++17 conform and shall upgrade towards C++20 when widely available on all target platforms.

Some more elaboration on the implementation and its status

The host-side of HCI, L2CAP etc is usually implemented within the OS, e.g. Linux/BlueZ Kernel. These layers communicate with the actual BT controller and the user application, acting as the middleman.

Direct-BT offers packet types and handler facilities for HCI, L2CAP, SMP, ATT-PDU and GATT (as well to Linux/BlueZ-Mngr) to communicate with these universal host-side Bluetooth layers and hence to reach-out to devices.

Currently only the master/client mode is supported to work with LE BT devices.

LE Secure Connections and LE legacy pairing is supported, exposing BTSecurityLevel and SMPIOCapability setup per connection and providing automatic security mode negotiation.

BLE slave peripheral and GATT server support is underway.

BREDR support is planned and prepared for.

To support other platforms than Linux/BlueZ, we will have to

• move specified HCI host features used in DBTManager to HCIHandler, SMPHandler,.. - and -
• add specialization for each new platform using their non-platform-agnostic features.

Supported Platforms

The following platforms are tested and hence supported

Debian 10 Buster (GNU/Linux)

• amd64 (validated, Generic)
• arm64 (validated, Raspberry Pi 3+ and 4)
• arm32 (validated, Raspberry Pi 3+ and 4)

Debian 11 Bullseye (GNU/Linux)

• amd64 (validated, Generic)
• arm64 (should work, Raspberry Pi 3+ and 4)
• arm32 (should work, Raspberry Pi 3+ and 4)

The following Bluetooth Adapter were tested

• Bluetooth 4.0
  • Intel Bluemoon Bluetooth Adapter
  • CSR Bluetooth Adapter (CSR8510,..)
  • Raspberry Pi Bluetooth Adapter (BCM43455 on 3+, 4)
• Bluetooth 5.0
  • Intel AX200 Bluetooth 5.0 (Wi-Fi 6 802.11ax (2.4Gbps) + BT 5.0)
  • Realtek Bluetooth 5.0 (RTK_BT_5.0)

Using <em>Direct-BT</em> Applications

System Preparations

Since Direct-BT is not using a 3rd party Bluetooth client library or daemon/service, they should be disabled to allow operation without any interference. To disable the BlueZ D-Bus userspace daemon bluetoothd via systemd, you may use the following commands.

systemctl stop bluetooth
systemctl disable bluetooth
systemctl mask bluetooth

Required Permissions for <em>Direct-BT</em> Applications

Since Direct-BT requires root permissions to certain Bluetooth network device facilities, non-root user require to be granted such permissions.

For GNU/Linux, there permissions are called capabilities. The following capabilites are required

• CAP_NET_RAW (Raw HCI access)
• CAP_NET_ADMIN (Additional raw HCI access plus (re-)setting the adapter etc)

On Debian 11 we can use package libcap2-bin, version 1:2.44-1, which provides the binaries /sbin/setcap and /sbin/getcap. It depends on package libcap2, version >= 1:2.33. If using earlier setcap binaries, your mileage may vary (YMMV).

Launch as <tt>root</tt>

In case your platform lacks support for mentioned setcap, you may need to execute your application as root using sudo, e.g.:

LD_LIBRARY_PATH=`pwd`/dist-amd64/lib sudo dist-amd64/bin/dbt_scanner10

Launch as <tt>user</tt> using <tt>setcap</tt>

To launch your Direct-BT application as a user, you may set the required capabilities before launch via setcap

sudo setcap 'cap_net_raw,cap_net_admin+eip' dist-amd64/bin/dbt_scanner10
LD_LIBRARY_PATH=`pwd`/dist-amd64/lib dist-amd64/bin/dbt_scanner10

Launch as <tt>user</tt> via <tt>capsh</tt>

Alternatively one can set the required capabilities of a Direct-BT application and launch it as a user via capsh.

sudo /sbin/capsh --caps="cap_net_raw,cap_net_admin+eip cap_setpcap,cap_setuid,cap_setgid+ep" \
   --keep=1 --user=$USER --addamb=cap_net_raw,cap_net_admin+eip \
   -- -c "YOUR FANCY direct_bt STUFF"

Notable here is that capsh needs to be invoked by root to hand over the capabilities and to pass over the cap_net_raw,cap_net_admin+eip via –addamb=... it also needs cap_setpcap,cap_setuid,cap_setgid+ep beforehand.

Launch Examples

The capsh method (default), setcap and root method is being utilized in

• scripts/run-dbt_scanner10.sh
• scripts/run-java-scanner10.sh

See Examples below ...

Programming with <em>Direct-BT</em>

API

Exposed API closely follows and references the Bluetooth Specification.

API Documentation

Up to date API documentation can be found:

• API Overview (C++) and the same in the Java API.
• C++ API Doc.
• Java API Doc.
• jaulib Standalone C++ API Doc.

A guide for getting started with Direct-BT on C++ and Java may follow up.

Java Specifics

org.direct_bt.BTFactory provides a factory to instantiate the initial root org.direct_bt.BTManager, using the Direct-BT implementation.

Examples

Direct-BT C++ examples are available, dbt_scanner10.cpp demonstrates the event driven and multithreading workflow.

Direct-BT Java examples are availble, DBTScanner10.java demonstrates the event driven and multithreading workflow - matching dbt_scanner10.cpp.

Building <em>Direct-BT</em>

The project requires CMake 3.13+ for building and a Java JDK >= 11.

This project also uses the Jau Library as a git submodule, which has been extracted earlier from this project to better encapsulation and allow general use.

Direct-BT does not require GLib/GIO nor shall the BlueZ userspace service bluetoothd be active for best experience.

To disable the bluetoothd service using systemd:

systemctl stop bluetooth
systemctl disable bluetooth
systemctl mask bluetooth

Installing build dependencies on Debian (10 or 11):

apt install git
apt install build-essential g++ gcc libc-dev libpthread-stubs0-dev 
apt install libunwind8 libunwind-dev
apt install openjdk-11-jdk openjdk-11-jre junit4
apt install cmake cmake-extras extra-cmake-modules pkg-config
apt install doxygen graphviz

For a generic build use:

CPU_COUNT=`getconf _NPROCESSORS_ONLN`
git clone --recurse-submodules git://jausoft.com/srv/scm/direct_bt.git
cd direct_bt
mkdir build
cd build
cmake -DBUILDJAVA=ON -DBUILDEXAMPLES=ON -DBUILD_TESTING=ON ..
make -j $CPU_COUNT install test doc

The install target of the last command will create the include/ and lib/ directories with a copy of the headers and library objects respectively in your build location. Note that doing an out-of-source build may cause issues when rebuilding later on.

Our cmake configure has a number of options, cmake-gui or ccmake can show you all the options. The interesting ones are detailed below:

Changing install path from /usr/local to /usr

-DCMAKE_INSTALL_PREFIX=/usr

Building debug build:

-DDEBUG=ON

Disable stripping native lib even in non debug build:

-DUSE_STRIP=OFF

Override default javac debug arguments source,lines:

-DJAVAC_DEBUG_ARGS="source,lines,vars"
 
-DJAVAC_DEBUG_ARGS="none"

Building debug and instrumentation (sanitizer) build:

-DDEBUG=ON -DINSTRUMENTATION=ON

Using clang instead of gcc:

-DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang++

Cross-compiling on a different system:

-DCMAKE_CXX_FLAGS:STRING=-m32 -march=i586
-DCMAKE_C_FLAGS:STRING=-m32 -march=i586

To build Java bindings:

-DBUILDJAVA=ON

To build examples:

-DBUILDEXAMPLES=ON

To build documentation run:

make doc

Build Status

Will be updated

Support & Sponsorship

Direct-BT is the new implementation as provided by Gothel Software and Zafena ICT.

If you like to utilize Direct-BT in a commercial setting, please contact Gothel Software to setup a potential support contract.

Common issues

If you have any issues, please go through the Troubleshooting Guide.

If the solution is not there, please search for an existing issue in our Bugzilla DB, please contact us for a new bugzilla account via email to Sven Gothel sgoth.nosp@m.el@j.nosp@m.ausof.nosp@m.t.co.nosp@m.m.

Contributing to <em>Direct-BT</em>

You shall agree to Developer Certificate of Origin and Sign-off your code, using a real name and e-mail address.

Please check the Contribution document for more details.

Historical Notes

<em>TinyB</em> Removal since version 2.3

Starting with version 2.3, the previously refactored TinyB has been removed completely.

Motivation was lack of detailed Bluetooth support, inclusive increasing diversion with Direct-BT. Furthermore, work is underway for BLE slave peripheral and GATT server support and its mapping to BlueZ D-Bus is questionable and would be resource intensive.

Changes

2.3.0 Direct-BT Maturity (Bluetooth LE)

• TODO

2.3.00

• Removal of TinyB

2.2.14

• Bluetooth 5.0 Support
  • Using HCI extended scanning and connecting if supported (old API may not work on new adapter)
  • Parsing and translating extended and enhanced event types, etc
  • TODO: User selection of LE_2M and L2_CODED, ... ???

2.2.13

• Revised API: BTGattChar::addCharListener(..) in C++ and Java for a more intuitive use.
• Fix EUI48Sub::scanEUI48Sub(..): Fail on missing expected colon, i.e. after each two digits
• Fix JNIAdapterStatusListener::deviceConnected(..): NewObject(.., deviceClazzCtor, ..) used wrong argument order

2.2.11

• Fix EUI48 unit test and refine on application permissions for launching applications
• Make BTDeviceRegistry and BTSecurityRegistry universal
• Move BTDeviceRegistry and BTSecurityRegistry to direct_bt library (from examples)
• EUI48Sub: Complement with hash_code(), clear(), indexOf(), contains(), ...
• SMPKeyBin: Tighten constraints, readAndApply(..) must validate minSecLevel.
• BTAdapter::mgmtEvDeviceFoundHCI(..): Clarify code path, covering name change via AD EIR.
• Passthrough all paramter BTAdapter::startDiscovery(..) -> HCIHandler::le_set_scan_param(..): Add le_scan_active and filter_policy. Active scanning is used to gather device name in discovery mode (AD EIR).
• Add -dbt_debug argument for AD EIR direct_bt.debug.hci.scan_ad_eir and parse EIR GAPFlags
• Fix BTGattHandler: Gather all Descriptors from all Characteristics (only queried 1st Char.)
• SMPKeyBin's base filename compatibility with FAT32 Long Filename (LFN)

2.2.5

• Complete SMPKeyBin user API: Convenient static 'one shot' entries + support no-encryption case
• Fix leaked AdapterStatusListener
• Fixed HCIHandler and l2cap related issues
• Unified free function to_string(..) and member toString()
• Tested key regeneration use-case: Pairing failure (bad key), key removal and auto security negotiation.
• Adding SMPKeyBin file removal support.
• Tested negative passkey/boolean input, requested via auto security negotiation.
• Using negative passkey response via setPairingPasskey(passkey = 0) for performance.

2.2.4

• Providing full featured SMPKeyBin for LTK, CSRK and secure connection param setup persistence and upload.
• Added Auto Security mode, negotiating the security setup with any device.
• Bugfixes in HCIHandler and ACL/SMP packet processing.
• Enhanced robusteness of underlying C++ API and implementation.

2.2.00

• Kicked off junit testing for Java implementation
• Adding direct_bt-fat.jar (fat jar) bootstrapping its contained native libraries using merged-in jaulib.
• Java API renaming, incl package: org.tinyb to org.direct_bt.
• Completing SMP/Security implementation (WIP)
• Replaced std::vector and jau::cow_vector with jau::darray and jau::cow_darray

2.1.33

• Added AdapterStatusListener callback methods devicePairingState(..) and deviceReady(..), supporting security/pairing.
• Added support for LE Secure Connections and LE legacy pairing utilizing SMP and BlueZ/Kernel features.
• Exposing BTSecurityLevel and SMPIOCapability for connection oriented security setup on BlueZ/Kernel, see DBTDevice and BluetoothDevice.
• Covering SMP over L2CAP messaging via SMPPDUMsg types and retrieval via HCI/ACL/L2CAP on BlueZ/Kernel

2.1.30

• Use read lock-free jau::cow_vector for all callback-lists, avoiding locks in callback iteration
• Passed GCC all warnings, compile clean
• Passed GCC sanitizer runtime checks
• Using extracted Jau C++ Support Library, enhanced encapsulation
• Passed valgrind's memcheck, helgrind and drd validating no memory leak nor data race or deadlock using dbt_scanner10
• Added native de-mangled backtrace support using libunwind and and abi::__cxa_demangle
• Reaching robust implementation state of Direct-BT, including recovery from L2CAP transmission breakdown on Raspberry Pi.
• Resolved race conditions on rapid device discovery and connect, using one thread per device.
• API documentation with examples
• Tested on GNU/Linux x86_64, arm32 and arm64 with native and Java examples.
• Tested on Bluetooth Adapter: Intel, CSR and Raspberry Pi
• Almost removed non-standard Linux/BlueZ-Mngr kernel dependency using the universal HCI protocol, remaining portion configures the adapter.

2.0.0

• Java D-Bus implementation details of package 'tinyb' moved to tinyb.dbus.
• The tinyb.jar jar file has been renamed to tinyb2.jar, avoiding conflicts.
• General interfaces matching the original implementation and following BlueZ API were created in package org.tinyb.
• Class org.tinyb.BluetoothFactory provides a factory to instantiate the initial root org.tinyb.BluetoothManager, either using the original D-Bus implementation or an alternative implementation.
• C++ namespace and implementation kept unchanged.

0.5.0

• Added notifications API
• Capitalized RSSI and UUID properly in Java
• Added JNI Helper classes for managing lifetime of JNIEnv and Global Refences

0.4.0

• Added asynchronous methods for discovering BluetoothObjects