Discussing the article: "Developing an MQTT client for Metatrader 5: a TDD approach — Part 5"
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Check out the new article: Developing an MQTT client for Metatrader 5: a TDD approach — Part 5.
This article is the fifth part of a series describing our development steps of a native MQL5 client for the MQTT 5.0 protocol. In this part we describe the structure of PUBLISH packets, how we are setting their Publish Flags, encoding Topic Name(s) strings, and setting Packet Identifier(s) when required.
MQTT is a pub/sub message sharing protocol. So we can expect that its core is on PUBLISH and SUBSCRIBE packets. All other packet types exist to get on them.
Besides being able to write PUBLISH packets, we must also be able to read them, since the messages our Client will receive from other Clients are PUBLISH packets too. That is because the delivery protocol is symmetric.
PUBLISH packets have a different fixed header with Publish Flags and a variable header with a required Topic Name encoded as UFT-8 string, and a required Packet Identifier (if QoS > 0). Besides that, it can eventually use almost all the properties and user properties introduced in MQTT 5.0, including those properties related to the Request/Response interaction mode.
In this article, we will see the structure of its headers and how we are testing and implementing the Publish Flags, the Topic Name(s), and the Packet Identifier(s).
Author: Jocimar Lopes