docker-development-youtube-series/kubernetes/admissioncontrollers/introduction/sourcecode/main.go

package main

import (
  "net/http"
	"log"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/serializer"

	"os"
	"fmt"
	"path/filepath"
	"k8s.io/client-go/kubernetes"
	rest "k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	"k8s.io/client-go/util/homedir"

	"flag"
	"strconv"
	"io/ioutil"
	"k8s.io/api/admission/v1beta1"
	"errors"

	apiv1 "k8s.io/api/core/v1"
	"encoding/json"
)

var (
	universalDeserializer = serializer.NewCodecFactory(runtime.NewScheme()).UniversalDeserializer()
)

var parameters ServerParameters

type ServerParameters struct {
	port           int    // webhook server port
	certFile       string // path to the x509 certificate for https
	keyFile        string // path to the x509 private key matching `CertFile`
}

var config *rest.Config
var clientSet *kubernetes.Clientset

type patchOperation struct {
	Op    string      `json:"op"`
	Path  string      `json:"path"`
	Value interface{} `json:"value,omitempty"`
}


func main() {

	useKubeConfig := os.Getenv("USE_KUBECONFIG")
	kubeConfigFilePath := os.Getenv("KUBECONFIG")	

	flag.IntVar(&parameters.port, "port", 8443, "Webhook server port.")
  flag.StringVar(&parameters.certFile, "tlsCertFile", "/etc/webhook/certs/tls.crt", "File containing the x509 Certificate for HTTPS.")
  flag.StringVar(&parameters.keyFile, "tlsKeyFile", "/etc/webhook/certs/tls.key", "File containing the x509 private key to --tlsCertFile.")
  flag.Parse()

	if len(useKubeConfig) == 0 {
		// default to service account in cluster token
		c, err := rest.InClusterConfig()
		if err != nil {
			panic(err.Error())
		}
		config = c
	} else {
		//load from a kube config
		var kubeconfig string

		if kubeConfigFilePath == "" {
			if home := homedir.HomeDir(); home != "" {
				kubeconfig = filepath.Join(home, ".kube", "config")
			} 
		} else {
			kubeconfig = kubeConfigFilePath
		}

    fmt.Println("kubeconfig: " + kubeconfig)

		c, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
		if err != nil {
			panic(err.Error())
		}
		config = c
	}

	cs, err := kubernetes.NewForConfig(config)
  if err != nil {
    panic(err.Error())
  }
  clientSet = cs

	test()
  http.HandleFunc("/", HandleRoot)
	http.HandleFunc("/mutate", HandleMutate)

  log.Fatal(http.ListenAndServeTLS(":" + strconv.Itoa(parameters.port), parameters.certFile, parameters.keyFile, nil))
}

func HandleRoot(w http.ResponseWriter, r *http.Request){
	w.Write([]byte("HandleRoot!"))
}

func HandleMutate(w http.ResponseWriter, r *http.Request){
	
	 body, err := ioutil.ReadAll(r.Body)
	// err = ioutil.WriteFile("/tmp/request", body, 0644)
	if err != nil {
		panic(err.Error())
	}

	var admissionReviewReq v1beta1.AdmissionReview

	if _, _, err := universalDeserializer.Decode(body, nil, &admissionReviewReq); err != nil {
		w.WriteHeader(http.StatusBadRequest)
		fmt.Errorf("could not deserialize request: %v", err)
	} else if admissionReviewReq.Request == nil {
		w.WriteHeader(http.StatusBadRequest)
		errors.New("malformed admission review: request is nil")
	}

	fmt.Printf("Type: %v \t Event: %v \t Name: %v \n",
		admissionReviewReq.Request.Kind,
		admissionReviewReq.Request.Operation,
		admissionReviewReq.Request.Name,
	)

	var pod apiv1.Pod

	err = json.Unmarshal(admissionReviewReq.Request.Object.Raw, &pod)

	if err != nil {
  	fmt.Errorf("could not unmarshal pod on admission request: %v", err)
	}

	var patches []patchOperation
	
	labels := pod.ObjectMeta.Labels
	labels["example-webhook"] = "it-worked"

	patches = append(patches, patchOperation{
				Op:    "add",
				Path:  "/metadata/labels",
				Value: labels,
		})
	
	patchBytes, err := json.Marshal(patches)
	if err != nil {
		fmt.Errorf("could not marshal JSON patch: %v", err)
	}

	admissionReviewResponse := v1beta1.AdmissionReview{
		Response: &v1beta1.AdmissionResponse{
			UID: admissionReviewReq.Request.UID,
			Allowed: true,
		},
	}

	admissionReviewResponse.Response.Patch = patchBytes

	bytes, err := json.Marshal(&admissionReviewResponse)
	if err != nil {
		fmt.Errorf("marshaling response: %v", err)
	}

	w.Write(bytes)
}