CoAP server with Rack interface

I'm working on a CoAP [0] server with a Rack interface for my diploma

Your feedback would be very valuable for me although it is not clear, I
manage to make many changes based on it before handing in the thesis. I
compiled a quick README and hope it suffices as a starting point for
testing the server. Maybe it is just interesting, the Rack interface is
used in another protocol context.
Some more info on CoAP from RFC7252:
The Constrained Application Protocol (CoAP) is a specialized web
transfer protocol for use with constrained nodes and constrained
(e.g., low-power, lossy) networks. The protocol is designed for machine-
to-machine (M2M) applications such as smart energy and building
CoAP provides a request/response interaction model between
application endpoints, supports built-in discovery of services and
resources, and includes key concepts of the Web such as URIs and
Internet media types. CoAP is designed to easily interface with HTTP
for integration with the Web while meeting specialized requirements
such as multicast support, very low overhead, and simplicity for
constrained environments.
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