Logger: output as JSON

[josephjclark]

This PR enables the logger to output JSON objects rather than strings. So instead of logs like:

[CLI] i Loaded adaptor

You get logs like:

{ level: 'info', name: 'CLI', message: ['Loaded adaptor'] }

Objects are shown in-line rather than embedded as a string:

{ level: 'info', name: 'CLI', message: [{ data: {}, configuration: {} ] }

This is useless to the CLI, but dead handy for integration tests and Lightning as we can easily filter logs.

This also fixes #157, where deeply nested objects will be truncated. We now stringify all output objects, which has the added bonus of supporting circular structures. Note that properties with function values are ignored, which I think is appropriate.

[stuartc]

Great work here @josephjclark, it did take me a little while to get my head around the 'transparency' of this implementation.

I was trying to work out what the behaviour is when JSON logging is enabled and you log a string. But if my understanding is correct, the logger instance is created with a namespace already and when logging a string it emits JSON with the namespace attached right?

I'm happy to merge this but could you take a look at my comment around the logger using an env var vs the CLI explicitly being in charge of that (via a flag or env, either or)?

I can imagine some situations where your approach is useful down the line - but want to make sure I'm understanding your approach here.

[josephjclark]

Thanks Stu - let me sort out the env var thing, you're dead right about that

I was trying to work out what the behaviour is when JSON logging is enabled and you log a string

logger.log(`hello world`) // { level: 'info', message: 'hello world' }

the logger instance is created with a namespace already and when logging a string it emits JSON with the namespace attached right

💯

[josephjclark]

@stuartc All done!