Adapt to production MQTT protocol

[johanstokking]

See https://github.com/TheThingsNetwork/ttn/tree/refactor/mqtt

[FokkeZB]

@johanstokking, @htdvisser may I have your input on these changes for node-ttn to work with production?

Changes in the message formats:

• downlink
  • payload > payload_raw
  • no more ttl
• uplink
  • fields > payload_fields
  • payload > payload_raw
  • Include full metadata array, not just first object in array
  • Inject Dev EUI as dev_eui instead of devEUI, like MQTT does in activations
• activation
  • Pass on full message instead of just devEUI, which also means this is now dev_eui.

Changes in the broker address

• If staging.thethingsnetwork.org is give, enable legacy flag so the library continuous to work with those message formats
• If we will have a default production broker, make that constructor argument optional.
• Allow the user to just give the region and compose the broker URL in the constructor.

Other improvements while we're at it:

• connect
  • Pass along connack argument?
• end
  • Send along the optional force and cb options?

[htdvisser]

The URLs for the Load Balancers of our datacenters are currently as follows:

• eu.thethings.network
• us-west.thethings.network
• brazil.thethings.network
• se-asia.thethings.network

We might want to create additional CNAMES for mqtt/router/broker/handler, but maybe the plain URLs are more clear?

[FokkeZB]

Thanks @htdvisser, I'd suggest that the Client constructor will accept:

• 'eu.thethings.network', 'app id', 'app key'
• 'eu', 'app id', 'app key': when the first arg doesn't contain a . it will add .thethings.network
• 'app id', 'app key': when the first arg is skipped it defaults to eu.thethings.network

We just need to be sure that the we never introduce something like us.west but always stick to dashes, just like Amazon does.

[htdvisser]

I think defaulting to eu (last bullet) is a bad idea. Applications can only be registered with one handler, and therefore messages will only arrive on one MQTT broker. Users should explicitly pass the region.

[FokkeZB]

Clear, thx!

[FokkeZB]

As part of the refactor I've simplified the API

https://github.com/TheThingsNetwork/node-ttn/blob/refactor/src/example.js

• Client(broker, appEUI, accessKey) > Client(region, appId, accessKey)
• uplink -> message
• downlink() -> send()

For discussion on standardising on a simple API for SDKs:

https://docs.google.com/document/d/1nk6_Tty1WZ3RCl0hOVspLq6h87ZrQQiL2OjFguNdK7s/edit?usp=sharing