Even though a lot of Qt use cases are about creating user interfaces, Qt provides a diverse set of middle-layer APIs for non-GUI functionality. One of the younger middle-layer APIs in Qt is Qt Bluetooth. From its first release in Qt 5.2 onwards, it has grown and improved in every Qt release.
In light of the forthcoming Qt 5.5 release, I'd like to tell you a bit more about the current status of Qt Bluetooth. It started out as a solution to interact with Bluetooth devices on Linux using Bluez 4.x. At the time, the supported feature set focused on classic Bluetooth development. It targeted the type of profiles and capabilities most commonly encountered by applications:
Local Device Control
Device & Service Discovery
Serial Port Profile for Server & Client
Over time, the number of supported platforms was significantly expanded to cover Android (Qt 5.3), Bluez 5 (Qt 5.4) & OS X (Qt 5.5). Unfortunately, there are no API's which would permit the implementation of the above features on iOS too.
One of the more recent feature additions is related to Bluetooth Low Energy and Internet of Things. What started as a Technology Preview in Qt 5.4 for Linux quickly became a very important subset of the Qt Bluetooth APIs. The recent explosion of available wearables, health and environment sensors requires Qt to be able to interact with such Bluetooth Smart enabled devices. Qt 5.5 takes this development into account and provides Bluetooth Low Energy support on all existing Qt Bluetooth platforms. In addition, Bluetooth Low Energy on iOS was added too.
Well, what's missing? I guess my personal list is rather long and some of those items are less visible. Hopefully, we can close the gap towards the last major platform which is not yet supported. A WinRT port is being planned for Qt 5.6. On the Low Energy side of things, Qt Bluetooth should be able to run on Bluetooth Low Energy devices which offer their services to other devices (server role). Better scanning and advertising features, to interact for example with devices adhering to the iBeacon standard, are desirable too.
For the interested mind, the semi-official roadmap for the missing features is QTBUG-31674. I am interested in your feedback. Either drop a comment here or directly in Jira.