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Just let me log

This package exposes a DvelopLogger-class which is initialized with a level and 1-n Providers. See Concepts for more information.

Initialize a logger

const logger = new DvelopLogger({
  level: "info",// logs info and above
  providers: [
    // Providers define a logging scheme. Currently only OTEL is supported.
    otelProviderFactory({
      appName: "acme-myapp",
      appVersion: "1.0.0",
      instanceId: "0",

      // Transports define where to logging statements are send. Multiple transports can be used.
      transports: [
        consoleTransportFactory(), // logs to console
        fileTransportFactory("./logs.txt") // logs to file 'logs.txt'
      ]
    })
  ],
});

Supported LogLevels are debug, info and error, represented by exposed methods.

Start Logging

The minimal logstatement defines a level and a string to log. The OTEL-Provider transforms the information.

logger.debug({}, "Hello World!");
/**
 * {
 *   "time":"2022-07-07T11:06:34.105Z",
 *   "sev":9,
 *   "body":"Hello World!",
 *   "res":{
 *     "svc":{
 *       "name":"acme-myapp",
 *       "ver":"1.0.0"
 *       "inst": "0"
 *     }
 *   },
 *   "vis":1
 * }
 */

For each method the first argument is a DvelopContext-object and the second argument a DvelopLogEvent-object.

try {
  convinceLeonidasThatThisIsMadness();
} catch (error: any) {

  logger.error({
    systemBaseUri: "https://sparta.d-velop.cloud",
    tenantId: "T8r3cWM4JII"
  }, {
    name: "MissionFailedLogger",
    message: "Apparently this is Sparta",
    error: error,
    customAttributes: {
      learnings: "Don't stand near a well"
    }
  });
}
/**
 * {
 *   "time":"479BCT11:11:11.111Z",
 *   "sev":17,
 *   "name":"MissionFailedLogger",
 *   "body":"Apparently this is Sparta",
 *   "tn":"T8r3cWM4JII",
 *   "res":{
 *     "svc":{
 *       "name":"acme-myapp",
 *       "ver":"1.0.0",
 *       "inst": "0"
 *     }
 *   },
 *   "attr":{
 *     "learnings":"Don't stand near a well",
 *     "exception":{
 *       "message":"THIS IS SPARTA",
 *       "type":"RoundHouseKickError",
 *       "stacktrace":"..."
 *     }
 *   },
 *   "vis":1
 * }
 */

Concepts

In this package logging is divided over three layers

1. Transports
2. Providers
3. Logger

Transports

Transports are responsible for transporting a log-event. Transports are agnostic about the form of the log event.

export type TransportFn = (event: any) => Promise<void>;

There are currently two default transports supported:

import { TransportFn, consoleTransportFactory, fileTransportFactory } from "@dvelop-sdk/logging";

const consoleTransport: TransportFn = consoleTransportFactory();
await consoleTransport("Hello World!"); // log "Hello World" to console in Node.js and Browsers

const fileTransport: TransportFn = fileTransportFactory("./logs.txt");
await fileTransport("Hello World!"); // log "Hello World" to logs.txt

You can easily implement your own Transport-Function:

async function myTransport(event: any): Promise<void> {
  // jump through hoops
}

Providers

Providers are able to work with the DvelopLogEvent-Type. The do transformation and may support any Transport-Functions, a subset or none (e.g a Syslog-Provider could have a UDP Transport to Port 514 baked in).

export type ProviderFn = (context: DvelopContext, event: DvelopLogEvent, level: DvelopLogLevel) => Promise<void>;

One default Provider is supported:

import { ProviderFn, otelProviderFactory } from "@dvelop-sdk/logging";

const otel: ProviderFn =  otelProviderFactory({
  appName: "acme-myapp",
  appVersion: "1.0.0",
  instanceId: "0",
  transports: [ consoleTransport, fileTransport, myTransport ]
});

D.velop default is to log in a JSON-Format derived from the Open Telemetry Standard. The otelProviderFactory creates a ProviderFn that is responsable for according transformations (e.g. map level "info" to OTELs numeric severity of 9).

You can easily implement your own Provider-Function:

// do a fixed provider
async function myProvider(context: DvelopContext, event: DvelopLogEvent, level: DvelopLogLevel): Promise<void> {
  // jump through hoops
}

// or have some init
async function myProviderFactory(howMuchIsTheFish: number): ProviderFn {
  return (context: DvelopContext, event: DvelopLogEvent, level: DvelopLogLevel) => Promise<void> {
    // jump through hoops
  }
}

// or even support generic TransportFunctions
async function myProviderFactory(transports: TransportFn[]): ProviderFn {
  return (context: DvelopContext, event: DvelopLogEvent, level: DvelopLogLevel) => Promise<void> {
    const formattedEvent: any = {} // jump through hoops
    transports.forEach(t => t(formattedEvent));
  }
}

Logger

Finally we have that can log something. The DvelopLogger accepts a level (everything above is logged) and 1-n provider-functions.

const logger = new DvelopLogger({
  level: "info",
  providers: [
    otelProviderFactory({
      appName: "acme-myapp",
      appVersion: "1.0.0",
      instanceId: "0",
      transports: [
        consoleTransportFactory(),
        fileTransportFactory("./logs.txt")
      ]
    })
  ],
});