plugin-initialization.md

Plugin Initialization

The add command creates an initialization function for each added plugin in its directory.

// src/plugin-name/initialize.js
const plugin = require('plugin-name')

function initialize () {
  return {
    instance: plugin
  }
}

module.exports = initialize

You can update the return of the initialization to provide options to the plugin registration.

function initialize () {
  return {
    instance: plugin,
    options: {
      // option values
    }
  }
}

Customize Providers

The Koop provider specification allows adding transformation functions in the registration options.

For example, the before option can be used to customize the data request before the request is fired. The pre-processing function can be defined in the initialization function and assigned to the options object.

function initialize () {
  return {
    instance: plugin,
    options: {
      // This pre-processer rejects any requests with id 'xyz'.
      before: (request, callback) => {
        const { params: { id } } = request

        if (id === 'xyz') {
          const error = new Error('Forbidden')
          error.code = 403
          return callback(error)
        }

        callback()
      }
    }
  }
}

Similarily, the after option can be used to modify the response of the data request.

function initialize () {
  return {
    instance: plugin,
    options: {
      // This post-processer reprojects the returned data into WGS84.
      after: (request, geojson, callback) => {
        const fromSR = `spatial_reference_definition`

        try {
          const wgs84Data = reproject(fromSR, proj4.wgs84, geojson)
          callback(null, wg484Data)
        } catch (err) {
          callback(err)
        }
      }
    }
  }
}

You can better organize the code by moving the pre-processer and post-processer into their separate files. So the initialization file can look cleaner as

const rejectInvalidRequests = require('./reject-invalid-requests')
const reprojectResult = require('./reproject-result')

function initialize () {
  return {
    instance: plugin,
    options: {
      before: rejectInvalidRequests,
      after: reprojectResult
    }
  }
}

By having all initialization files and customization files in a dedicated directory for each plugin, you can make the plugin registration much simpler and significantly improve your project file structure.