Context Items

Much of the power of Klogging is in the way you can include context information in log events.

Base Context

You can specify items to add to every Klogging log event in your application. Examples might be application name or a build identifier.

Specify them using the Context object, for example:

const val APP_NAME_KEY = "appName"
const val APP_NAME = "analysis-service"
const val BUILD_NUMBER_KEY = "buildNumber"
const val BUILD_NUMBER_ENV = "BUILD_NUMBER"

Context.addBaseContext(
    APP_NAME_KEY to APP_NAME,
    BUILD_NUMBER_KEY to System.getenv(BUILD_NUMBER_ENV),
)

Log events include those values, for example:

{
  "@t": "2022-06-16T08:52:12.064882Z",
  "@l": "INFO",
  "@mt": "Execution time {elapsedMs} ms",
  "host": "09b4396db8ae",
  "appName": "analysis-service",
  "buildNumber": "2.4.0-d22d0dd",
  "logger": "com.wodgeworks.analysis.RunTimer",
  "elapsedMs": "73",
  "run": "a6f72c37-7e2f-4d69-a73f-7f493cb04d1d",
  "context": "DefaultDispatcher-worker-3"
}

From other coroutine context elements

Klogging can include information from other coroutine context elements.

As an example, if your application is using Project Reactor, you can store information in a Reactor Context and wrap that in a coroutine ReactorContext.

Configure Klogging to use all the values from the Reactor context in log events (EventItems is a convenient type alias for Map<String, Any?>):

import io.klogging.config.Context
import io.klogging.events.EventItems
import kotlinx.coroutines.reactor.ReactorContext

val reactorExtractor: (ReactorContext) -> EventItems = { ctx ->
    // TBC
}

Context.addContextItemExtractor(ReactorContext, reactorExtractor)

Any log events emitted within the scope of the Reactor context will include items returned by the reactorExtractor() function from that context.