binary_plugin

How to develop a plugin binary

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

1. Go development environment setup
2. Optionally, an overview of the crane toolkit

The binary plugin for crane-lib is meant to be a simple Go program in the following format:

package main

import (
	"fmt"

	jsonpatch "github.com/evanphx/json-patch"
	"github.com/konveyor/crane-lib/transform"
	"github.com/konveyor/crane-lib/transform/cli"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
)

func main() {
	u, err := cli.Unstructured(cli.ObjectReaderOrDie())
	if err != nil {
		cli.WriterErrorAndExit(fmt.Errorf("error getting unstructured object: %#v", err))
	}

	cli.RunAndExit(cli.NewCustomPlugin("OpenshiftCustomPlugin", Run), u)
}

func Run(u *unstructured.Unstructured) (transform.PluginResponse, error) {
	// plugin writers need to write custome code here.
    resp := transform.PluginResponse{}
    // prepare the response
    return resp, nil
}

All it does is read an input from stdin, calls the Run function with the input object passed as unstructured and prints the return value of Run function on stdout.

During the development of the plugin, one can iterate by passing in the JSON object on stdin manually. For example, if the above code is compiled and run, this will be the output

./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"
         }
      ]
   }
}
{}

Note: the json object was entered from console, and the response was {}

From here, one can iterate over the plugin development. Once the plugin is ready to be tested, it can be put in a directory and run with the crane cli command.