[Ovmsdev] Server V3 topic prefix, stability and encryption

[Jakob Löw]

Hey,

I've seen some changes pushed to the repo regarding the v3 server. I
did some development on that too and found it to be very unstable,
often crashing after start (when transmitting all metrics) or when the
NetUp was called before any interface was up. Both issues were
connected to race conditions. I opened two pull requests to fix them
[0], [1].
The first one also introduces a new configuration option to set a
custom prefix for the MQTT topic. OVMS metric names seem to use a sort
of namespacing using dots, like m.freeram or v.e.on. Replacing dots in
metric names by slashes in MQTT topics, makes the OVMS follow MQTT
namespacing rules (m/freeram and v/e/on).

One thing currently missing with the Server V3 is encryption. Mongoose
supports SSL so enabling it would be easy, but the problem is the
certificate management. We could allow users to load certs onto the
module, however this is something unexperienced users wouldnt do.
Another option is to ship the OVMS with a list of common root certs,
like many browsers do. The certs shipped with firefox are ~500KB and
can be easily obtained e.g. from the debian repos [2]. This could then
also be used by the server v2 to replace the outdated RC4 encryption.

- Jakob

[0] https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pu
ll/137
[1] https://github.com/openvehicles/mongoose/pull/1
[2] https://packages.debian.org/stretch/ca-certificates
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