Metadata Duplication

[novaugust]

Logster copies the Logger.metadata into its log message.
However, the standard for logging metadata through a backend is to configure that backend's metadata option, specifying which keys should be printed.
This means that with a correctly configured backend, like

config :logger, :console,
  format: "[$level] $levelpad $message $metadata",
  metadata: [:request_id, :trace_id, :span_id]

logs will be produced that have request_id, trace_id, and span_id logged twice: once in the message itself via Logster, and then again via the backend.

Example

[info]   state=set duration=... status=200 
params={...} path=... method=GET format=json-api controller=... action=show
span_id=1691184670686183571 trace_id=2439927720751528365 request_id=FZX--3x64qa8bTUAAFfx
request_id=FZX--3x64qa8bTUAAFfx trace_id=2439927720751528365 span_id=1691184670686183571 

I think the easiest fix for this would be to revert the work in #6 and update the readme or changelog with a small guide on how to configure a backend to include metadata (removing the responsibility from Logster)

[novaugust]

I should add, I'd be happy to do that work if it sounds good.

[pmenhart]

I am using a workaround with a custom formatter:
Since Elixir 1.7, the format/1 function can alternatively return a tuple {message, list_of_keywords}. Keywords are added to logger metadata. I format the message to my liking (e.g. Processed <method> <path> -> <status> (duration ms) <response_body_if error>).

format/1 can return all params as list_of_keywords (or exclude unwanted ones). Keywords are merged with metadata, i.e. any duplicates are eliminated.

However, I support your suggestion.
I am worried to break compatibility for existing users (if that's desirable). Instead of completely reverting #6, I propose to change Logster formatters to have 2 parameters: params and metadata.
Perhaps a new configuration option would tell whether to merge them together, or ignore metadata (defauting to "merge" for compatibility).

[novaugust]

I am worried to break compatibility for existing users

Luckily, there's semver! This is currently 0.10 after all =) The version they're using will still exist.

Anyone looking to upgrade will get the added benefit of correctly configuring their backends to include metadata in all their logs.

[navinpeiris]

That sounds excellent to me @novaugust, if you could send me a pull request with some info in the README like you suggested, I'll get the merged in and cut a release.

[navinpeiris]

Thanks @novaugust, this has been merged in and released with version 1.0.0