{"id":996,"date":"2022-05-22T02:47:37","date_gmt":"2022-05-22T06:47:37","guid":{"rendered":"https:\/\/jausoft.com\/blog\/?p=996"},"modified":"2022-05-22T22:39:43","modified_gmt":"2022-05-23T02:39:43","slug":"direct-bt-bluetooth-server-and-client-programming-in-cpp-and-java_pt1","status":"publish","type":"post","link":"https:\/\/jausoft.com\/blog\/2022\/05\/22\/direct-bt-bluetooth-server-and-client-programming-in-cpp-and-java_pt1\/","title":{"rendered":"Direct-BT, Bluetooth Server and Client Programming in C++ and Java (Part 1)"},"content":{"rendered":"

This is the first article covering Direct-BT<\/em><\/a>\u00a0 using version 2.7.1 and may give you a little introduction into this project.<\/p>\n

See Direct-BT C++ Implementation Details (Part 1)<\/a> for some insight view.<\/p>\n

Overview<\/h2>\n

Direct-BT<\/em><\/a> provides direct Bluetooth LE and BREDR<\/a> programming, offering robust high-performance support for embedded & desktop with zero overhead via C++ and Java.<\/p>\n

It supports a fully event driven workflow from adapter management, device discovery to GATT programming, using its platform agnostic HCI, L2CAP, SMP and GATT protocol implementation.<\/p>\n

Multiple Bluetooth adapter are handled, as well as multiple concurrent connections per adapter.<\/p>\n

Peripheral server device programming is supported as well as the central client, which is also used for Java<\/a> and C++ self unit testing<\/a> across two or more Bluetooth adapter.<\/p>\n

LE legacy pairing<\/em> as well as SMP LE Secure Connections <\/em>is fully supported.<\/p>\n

Only BREDR support is currently incomplete and not yet usable, even though the API has been prepared.<\/p>\n

Direct-BT’s API and implementation<\/a> closely follows and references the official Bluetooth Specification<\/a>.<\/p>\n

Direct-BT has been used successfully in a medical trial, as well as in a connected medical device application<\/a>.<\/p>\n

The Jau C++ and Java support library<\/a> has been extracted to encapsulate its generic use-cases and some of its artifacts are discussed here in the implementation section.<\/p>\n

Repeater, a Bluetooth LE Proxy \/ Forwarder<\/h2>\n

The provided dbt_repeater<\/a> application allows to connect between a Bluetooth client and server to analyze their protocol.<\/p>\n

In detail, dbt_repeater<\/em> connects to a given peripheral-server device and thereafter advertises itself using same advertising and scan-response properties except the device-name to a given central-client.
\nAfter the central-client connected to dbt_repeater<\/em>, all GATT requests are forwarded to the given peripheral-server and their replies are sent back.
\nHence repeater requires two Bluetooth LE adapter to simultaneously maintain its client & server connection.<\/p>\n

Besides (GATT) protocol analysis of 3rd party devices, dbt_repeater<\/em> is also useful to extend peripheral-server device’s range. A third application of this idea, using TCP\/IP forwarding in-between a split-repeater is under investigation. The latter would surely be a limitless range extender as well as ensuring operation without radio interference.<\/p>\n

Direct-BT Origins<\/h2>\n

Direct-BT<\/em> development started around April 2020, initially as an alternative TinyB<\/em> Java-API implementation.<\/p>\n

The work was motivated due to strict performance, discovery- and connection timing requirements, as well as being able to handle multiple devices concurrently using a real-time event driven low-overhead architecture.<\/p>\n

Zafena’s POC-Workstation<\/a> was originally implemented using TinyB<\/em> and hence the D-Bus layer to the BlueZ<\/em> client library.<\/p>\n

Real time knowledge when devices are discovered and connected were not available and cloaked<\/em> by the caching mechanism. Advertising package details were not exposed.<\/p>\n

Connections attempts often took up to 10 seconds to be completed. Detailed information from the Bluetooth<\/em> layer were inaccessible including detailed error states.<\/p>\n

Fine grained control about discovery and connection parameter were not exposed by the D-Bus API and hence TinyB<\/em>.<\/p>\n

In January 2020 we tried to remedy certain aspects to meet our goals, but concluded to require direct Bluetooth<\/em> control via the BlueZ<\/em>\/Linux<\/em> kernel implementation.<\/p>\n

Direct-BT<\/em> was born.<\/p>\n

We then implemented data types for<\/p>\n