MQTT streaming client implementation

[viacheslauK]

Brief

• MQTT openDAQ streaming client module;
• Example applications;
• Reworking MQTT client wrapper (PAHO wrapper);
• Improving MQTT openDAQ streaming server module;
• Tests for client and server MQTT modules;
• Tests for MQTT client wrapper;

Description

• Implementation of MQTT openDAQ streaming client module allows to receive and parse MQTT messages which adhere to a strict message structure. It allows discovering of MQTT openDAQ devices and communication with them.
• The example applications demonstrate a typical approach to working with openDAQ MQTT modules.
• MQTT client wrapper reworking changed the architecture of wrapper classes, removed unused functional and duplication of code. The previous approach with separate publisher and subscriber class was redesigned into single client class.
• New tests for client and server MQTT modules.
• New tests for MQTT client wrapper allow to test communication with a MQTT brocker and messaging between clients.

[NikolaiShipilov]

Shortlist of things to be addressed before merge:

• broken boost dependencies - since source code uses some boost functionality #include <boost/...> - the corresponding dependencies should be explicitly set within CMake
  * add dependencies required for tests with CMake
• pthread linkage missing within example and test apps