moat-link 0.2.29

Message exchange between MoaT instances

Moat-Link is a library that distributes messages between several possible back-ends, channel arrangements or encodings.

The associated server links these backends into one coherent system, provide message history, documentation, and whatnot.

Rationale

Often, services have differing ideas how to encode “their” messages. For instance, Home Assistant likes JSON, except for boolean content which is encoded as “ON” and “OFF”. On the other hand, encodings like msgpack or CBOR replace the overhead of textual analysis and repeated division by ten with typed binary data.

MoaT-KV supported this usecase via its own MQTT server, which is based on hbmqtt. Unfortunately hbmqtt is unsupported, high-overhead, and doesn’t support MQTT 5. MoaT-KV adds its own overhead and doesn’t support non-retained messages.

Structure

MoaT-Link consists of a couple of related services.

Server

The main server records messages in its history, affords redundancy, can re-supply the MQTT server with retained state, and so on.

Translator

Translators send and receive messages from other channels or topics.

For instance, Home Assistant’s default of device state/cmd/control in one single hierarchy doesn’t always mesh well with other systems’ ideas.

Errors

MoaT-Link supports error handling and recovery.

Web view

Last but not least, we want a HTML front-end for introspection and debugging.

Message Encoding

MoaT-Link supports various encodings, most notably CBOR and msgpack. Its native default is CBOR because, unlike msgpack, CBOR’s extensions are simply normal (but tagged) data structures and thus are introspectable.