@dandi/core/logging

Dandi’s splits the responsibilities of logging into two primary parts:

• Logger is the primary interface that developers will interact with - implementations of Logger are used to generate the log entries themselves, and can draw in contextual metadata about where they are called from. An app will have a single Logger instance. If no provider for Logger is available, the app will use NoopLogger by default.

• LogListener implementations receive the log data generated by the Logger. What they do with that data depends on the implementation - ConsoleLogListener, for example, formats the log data and sends it to the program’s console output. Other implementations could store the data locally, or transmit it to a remote API. An app may use any number of LogListener implementations simultaneously.

By default, this pattern is implemented using an RxJS Subject. The Subject instance is defined using the LogStream injection token. The Logger instance calls next() on the LogStream for each log entry. LogListener instances subscribe to the LogStream as an Observable.

Note: The DI system in @dandi/core uses Logger internally, which is why Logger is part of the root @dandi/core package and not @dandi/core/logging.

Implementations

Logger

ContexualLogger

• Package: @dandi/core/logging
• Module: LoggingModule in @dandi/core/logging
• Includes a reference the consuming service in the logging data

// main.ts
import { DandiApplication } from '@dandi/core'
import { LoggingModule } from '@dandi/core/logging' // includes ContextualLogger

const container = new DandiApplication({
  providers: [
    LoggingModule,
    /* other providers */
  ]
})

// my-service.ts
import { Inject, Injectable, Logger } from '@dandi/core'

@Injectable()
export class MyService {
  constructor(@Inject(Logger) private logger: Logger) {
    this.logger.debug('Constructed!')
  }
}

In the above example, when the instances are created, the ContextualLogger instance uses the InjectionContext token provided by the Dandi DI system to receive a reference to the instance of MyService that caused it to be created. It then includes that reference when creating log entries like the call to debug().

NoopLogger

• Package: @dandi/core
• Module: n/a - used as a fallback by @dandi/core
• As the name suggests, NoopLogger does not generate log entries

When no Logger implementation is configured, NoopLogger is used by default.

ConsoleLogListener

• Package: @dandi/core/logging
• Module: n/a
• Outputs formatted log data to the environment’s console

Include ConsoleLogListener by calling the use method on LoggingModule.

import { DandiApplication } from '@dandi/core'
import { ConsoleLogListener, LoggingModule } from '@dandi/core/logging'

const container = new DandiApplication({
  providers: [
    LoggingModule.use(ConsoleLogListener),
    /* other providers */
  ]
})

Formatting

ConsoleLogListener can be customized to format the log data as desired.

TODO

API Documentation

TODO

Logger

TODO