Create Subscriber

In order to create a new Subscriber, there are some things that you need to keep in mind.

Coming out from the way the stream works, the minimum requirements for a new Subscriber are the following:

• Be a constructor, accepting settings {Object} parameter
• Contain a handle function, that accepts a message {Object}

A simple example of a new Subscriber:

ES6 syntax:

class CustomSubscriber {
   constructor(settings) {
      this.settings = settings || {};
   }

   handle(message) {
      // logic
   }
}

module.exports = CustomSubscriber;

Constructor parameters explanation

settings contains config parameters of the stream

Message structure

The message object contains the following set of properties:

message.payload:

{
    level: {'silly'|'verbose'|'debug'|'info'|'warn'|'error'},
    text: {string},
    meta: {
      instanceId: {string},
      notify: {true}, // by default,
      stack: {string}, // in case error was given to log,
      ... (other metadata provided in runtime)
    },
    error: {Error} // in case message was an error
 }

message.logLevels

message.logLevels is an ES6 Map, containing - entries of the log levels.

silly -> 0
verbose -> 1
debug -> 2
info -> 3
warn -> 4
error -> 5

Message object also exposes the following function:

message.getPrefix(settings {Object}, delimiter {string})

This function returns a prefix for the message based on settings and / or env variables.

By default, a delimiter is :

Additional features

If you want to allow user to pre-configure your subscriber, instead of exposing a class:

module.exports = CustomSubscriber;

expose the wrapper function:

const logtify = require('logtify');
const streamBuffer = logtify.streamBuffer;
const { stream } = logtify();

module.exports = (configs) => {
   // some logic, validation, etc
   const subscriberData = {
    class: CustomSubscriber,
    config: configs
   };

   streamBuffer.addSubscriber(subscriberData);
   const mergedConfigs = Object.assign({}, configs, stream.settings);
   stream.subscribe(new CustomSubscriber(mergedConfigs));

   return subscriberData;
}

This way the stream will take the given configs, merged with the original stream's settings and pass it to the constructor of a class during the subscriber initialization.

Exposing an adapter

expose the wrapper function:

const logtify = require('logtify');
const streamBuffer = logtify.streamBuffer;
const { stream } = logtify();

module.exports = (configs) => {
   // some logic, validation, etc
   const subscriberData = {
    class: CustomSubscriber,
    config: configs,
    adapter: {
      name: 'unicorn',
      class: CustomAdapter
    }
   };

   streamBuffer.addSubscriber(subscriberData);
   const mergedConfigs = Object.assign({}, configs, stream.settings);
   stream.subscribe(new CustomSubscriber(mergedConfigs));
   stream.bindAdapter('unicorn', new CustomAdapter(stream, mergedConfigs));
   return subscriberData;
}

After this point, when a user uses your subscriber with a stream, he the adapter will be automatically initialized and will be then accessible via:

const { unicorn } = require('logtify')(...);

Presets

Stream may get some presets as part of the settings. You can create yours and process them within your particular subscriber:

class CustomSubscriber {
   constructor(settings) {
      if (settings.presets) {
         this.presets = settings.presets; // {Array} of strings
      }
   }
}

References:

Create Adapter