Developing custom plugins

This document covers how to write a plugin binary using crane-lib. It requires:

Procedure

  1. Go to the development environment setup. (Optionally, an overview of the crane toolkit.)

  2. Create binary plugin for crane-lib as a simple Go program in the following format that will:

  • Read an input from stdin.
  • Call the Run function with the input object passed as unstructured.
  • Print the return value of Run function on stdout.
package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
	"github.com/konveyor/crane-lib/transform"
	"github.com/konveyor/crane-lib/transform/cli"
)

func main() {
	fields := []transform.OptionalFields{
		{
			FlagName: "my-flag",
			Help:     "What the flag does",
			Example:  "true",
		},
	}
	cli.RunAndExit(cli.NewCustomPlugin("MyCustomPlugin", "v1", fields, Run))
}

 func Run(request transform.PluginRequest) (transform.PluginResponse, error) {
	// plugin writers need to write custom code here.
	resp := transform.PluginResponse{
        Version:    string(transform.V1),
    }
	// prepare the response
	return resp, nil
}

The json is passed in using stdin is a transform.PluginRequest which consists of an inline unstructured object and an optional Extras map containing additional flags. Without any Extras the format is identical to the json output from a kubectl get -o json call.

When adding extra parameters, a map field “extras” is added at the top level (parallel to “apiVersion”, “kind”, etc.).

Version the plugin development output by passing in the JSOC object on stdin manually during development. For example, if the code above is compiled and run with the following json as input, the output will be {"version": "v1"}.

./my-plugin
{
   "apiVersion": "route.openshift.io/v1",
   "kind": "Route",
   "metadata": {
      "annotations": {
         "openshift.io/host.generated": "true"
      },
      "creationTimestamp": "2021-06-10T04:11:21Z",
      "managedFields": [
         {
            "apiVersion": "route.openshift.io/v1",
            "fieldsType": "FieldsV1",
            "fieldsV1": {
               "f:spec": {
                  "f:path": {},
                  "f:to": {
                     "f:kind": {},
                     "f:name": {},
                     "f:weight": {}
                  },
                  "f:wildcardPolicy": {}
               }
            },
            "manager": "oc",
            "operation": "Update",
            "time": "2021-06-10T04:11:21Z"
         },
         {
            "apiVersion": "route.openshift.io/v1",
            "fieldsType": "FieldsV1",
            "fieldsV1": {
               "f:status": {
                  "f:ingress": {}
               }
            },
            "manager": "openshift-router",
            "operation": "Update",
            "time": "2021-06-10T04:11:21Z"
         }
      ],
      "name": "mssql-app-route",
      "namespace": "mssql-persistent",
      "resourceVersion": "155816271",
      "selfLink": "/apis/route.openshift.io/v1/namespaces/mssql-persistent/routes/mssql-app-route",
      "uid": "42dca205-31bf-463d-b516-f84064523c2c"
   },
   "spec": {
      "host": "mssql-app-route-mssql-persistent.apps.cluster-alpatel-aux-tools-444.alpatel-aux-tools-444.mg.dog8code.com",
      "path": "/",
      "to": {
         "kind": "Service",
         "name": "mssql-app-service",
         "weight": 100
      },
      "wildcardPolicy": "None"
   },
   "status": {
      "ingress": [
         {
            "conditions": [
               {
                  "lastTransitionTime": "2021-06-10T04:11:21Z",
                  "status": "True",
                  "type": "Admitted"
               }
            ],
            "host": "mssql-app-route-mssql-persistent.apps.cluster-alpatel-aux-tools-444.alpatel-aux-tools-444.mg.dog8code.com",
            "routerCanonicalHostname": "apps.cluster-alpatel-aux-tools-444.alpatel-aux-tools-444.mg.dog8code.com",
            "routerName": "default",
            "wildcardPolicy": "None"
         }
      ]
   }
}

When the plugin is ready to be tested, put it in a directory and run with the crane cli command.

More accurate detail can be found [here] (https://github.com/konveyor/crane-lib/blob/main/transform/binary-plugin/README.md).

Source