How to add custom data to the full model?

[cybardev]

I have:

• Pi Zero W system that plays an audio file
• Pi 3B+ Signal K server

I need to add the name of the played audio file to the Signal K full data model. What is the best way to achieve this?

I was considering:

• metadata
• notification
• custom source

The issue with the metadata and notification methods is that I need to make PUT requests to the server which requires authentication. I want it to "just work". So I thought maybe I can emulate an NMEA data source and add it to the server but I have no idea how to proceed with that.

Any suggestions or pointers would be greatly appreciated. Thanks.

[sbender9]

Metadata doesn't make sense. It is static.

And I guess a notification could work.

You should be sending a delta to the server over a websocket.

But that does require authentications. Which is really not that difficult.

There's no way to get data into the server without authenticating. Unless you turn security off.

[cybardev]

Would HTTP POST work with TCP then? If I set "Host" field to localhost, since I'll be sending the data from the same device.

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TCP 10110 is NMEA0183. I don’t think there is a way to communicate song name over that.

Acknowledged. Any suggestions to serve it as NMEA2000 data?

Context as to why I want this: Let's assume I'm making a speaker+SBC system that works underwater. I want it to plug into any NMEA2000-accepting network and say "Currently playing: test.flac" or so everytime it plays a new audio file. This is mainly for logging purposes. It would probably be easier to just use Signal K JSON data and toggle "Enable Logging", but I am required to make it work with non-Signal K (NMEA2k) systems as well.

[tkurki]

If you are required to do that then you probably know the NMEA2000 PGNs that you are supposed to send. Then you need to check if signalk-to-NMEA2000 supports them. If not you need to check if canboat(js) supports them. If yes then you can set up your own conversion of input to canboatjs compatible output, for example in Node-RED. If the PGN is not supported by canboat(js) you'lle need to figure out yourself what exactly you need to send.

All doable, but devil's in the details.

Related:

• Fusion audio control related PGNs at https://canboat.github.io/canboat/canboat.html
• Plugin to control Fusion audio https://github.com/sbender9/signalk-fusion-stereo

[cybardev]

@tkurki Thank you very much for all your help. I will look into these.

Meanwhile, I couldn't figure out how the POST would look like. Do you think you could give an example curl command (like what @sbender9 posted for #14) to send a delta to a newly created TCP port on localhost? I think I can infer the Python equivalent from that, but I'm somewhat lost on how to begin.

[tkurki]

You really should read up on communication protocols, to understand the relationship of POST, HTTP, TCP and UDP.

You can also find examples of sending Signal K over UDP with a bit of googling, but here goes from the command line:
echo '{"updates":[{"values":[{"path":"navigation.speedOverGround","value":3.14}]}]}' |nc -4u -w1 127.0.0.1 7778

[cybardev]

You really should read up on communication protocols, to understand the relationship of POST, HTTP, TCP and UDP.

Yes, I will definitely do that. Thank you for your suggestion. I apologize for bothering you with the small stuff.

Thank you very much for the netcat example. I will be back in office on Tuesday and will try it to see how it works. I'll mark your comment as answer afterwards, unless you feel like it's sufficient as is and can be closed already.

Thanks again for all your help, and thank you very much for your patience and time. Hope you have a nice weekend. 😊

[cybardev]

@tkurki Thank you very much for your example. I translated it to Python and it worked exactly as I needed.

Sample code for reference:

from socket import socket, AF_INET, SOCK_DGRAM

# create client-server connection
client = socket(AF_INET, SOCK_DGRAM)

# send delta to server
client.sendto(
    bytes('{"updates":[{"values":[{"path":"audio.filename","value":"test.flac"}]}]}', "utf-8"),
    ("localhost", 8375)
)

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Again I apologize for pestering you with such a small problem, but thanks to both of you for helping me out. Much appreciated. I hope you all have a wonderful day! 😊