PicoRuby aims to bring Ruby into the world of microcontrollers, where severe memory and execution constraints make practical networking difficult. In this talk, I present a real-world implementation of a practical MQTT client on PicoRuby with mruby/c, built on top of picoruby-net.

Unlike CRuby, mruby/c provides no threads and very restricted memory. Implementing MQTT in this environment required careful design of polling-based progress, buffer management, connection lifecycle handling, and the boundary between Ruby and native code, while preserving a Ruby-like programming model.

This session explores what it actually takes to implement a non-trivial network protocol in Ruby under extreme constraints. It shows how far Ruby can realistically be pushed toward bare-metal environments and where it must adapt.