add update check

Author: spowelljr

Makefile

@@ -6,7 +6,7 @@ ARCH=$(if $(findstring amd64, $(GOARCH)),x86_64,$(GOARCH))
 KO_VERSION=0.11.2
 
 build: ## Build the gcp-auth-webhook binary
-	CGO_ENABLED=0 GOOS=linux go build -o out/gcp-auth-webhook server.go
+	CGO_ENABLED=0 GOOS=linux go build -ldflags="-X 'main.Version=$(VERSION)'" -o out/gcp-auth-webhook server.go
 
 .PHONY: image
 image: ## Create and push multiarch manifest and images

go.mod

@@ -3,6 +3,7 @@ module github.com/GoogleContainerTools/gcp-auth-webhook
 go 1.18
 
 require (
+	github.com/blang/semver/v4 v4.0.0
 	k8s.io/api v0.24.1
 	k8s.io/apimachinery v0.24.1
 )

go.sum

@@ -5,6 +5,8 @@ github.com/PuerkitoBio/purell v1.1.1/go.mod h1:c11w/QuzBsJSee3cPx9rAFu61PvFxuPbt
 github.com/PuerkitoBio/urlesc v0.0.0-20170810143723-de5bf2ad4578/go.mod h1:uGdkoq3SwY9Y+13GIhn11/XLaGBb4BfwItxLd5jeuXE=
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5/go.mod h1:wHh0iHkYZB8zMSxRWpUBQtwG5a7fFgvEO+odwuTv2gs=
 github.com/asaskevich/govalidator v0.0.0-20190424111038-f61b66f89f4a/go.mod h1:lB+ZfQJz7igIIfQNfa7Ml4HSf2uFQQRzpGGRXenZAgY=
+github.com/blang/semver/v4 v4.0.0 h1:1PFHFE6yCCTv8C1TeyNNarDzntLi7wMI5i/pzqYIsAM=
+github.com/blang/semver/v4 v4.0.0/go.mod h1:IbckMUScFkM3pff0VJDNKRiT6TG/YpiHIM2yvyW5YoQ=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=

server.go

@@ -22,6 +22,7 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/blang/semver/v4"
 	admissionv1 "k8s.io/api/admission/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -36,6 +37,7 @@ var (
 	runtimeScheme = runtime.NewScheme()
 	codecs        = serializer.NewCodecFactory(runtimeScheme)
 	deserializer  = codecs.UniversalDeserializer()
+	Version       string
 )
 
 var projectAliases = []string{
@@ -309,9 +311,49 @@ func needsEnvVar(c corev1.Container, name string) bool {
 	return true
 }
 
+func updateCheck() error {
+	type release struct {
+		Name string `json:"name"`
+	}
+
+	var releases []release
+
+	resp, err := http.Get("https://storage.googleapis.com/minikube-gcp-auth/releases.json")
+	if err != nil {
+		return fmt.Errorf("failed to get releases file: %v", err)
+	}
+	defer resp.Body.Close()
+	if err := json.NewDecoder(resp.Body).Decode(&releases); err != nil {
+		return fmt.Errorf("failed to decode releases file: %v", err)
+	}
+	if len(releases) == 0 {
+		return fmt.Errorf("no releases found in releases file")
+	}
+
+	currVersion, err := semver.ParseTolerant(Version)
+	if err != nil {
+		return fmt.Errorf("unable to parse current version: %v", err)
+	}
+	name := releases[0].Name
+	latestVersion, err := semver.ParseTolerant(name)
+	if err != nil {
+		return fmt.Errorf("unable to parse latest version: %v", err)
+	}
+
+	if currVersion.LT(latestVersion) {
+		log.Printf("gcp-auth-webhook %s is available!", name)
+	}
+
+	return nil
+}
+
 func main() {
 	log.Print("GCP Auth Webhook started!")
 
+	if err := updateCheck(); err != nil {
+		log.Println(err)
+	}
+
 	mux := http.NewServeMux()
 
 	mux.HandleFunc("/mutate", mutateHandler)