🌱 Add certwatcher callback

pkg/certwatcher/certwatcher.go

@@ -44,6 +44,9 @@ type CertWatcher struct {
 
 	certPath string
 	keyPath  string
+
+	// callback is a function to be invoked when the certificate changes.
+	callback func(tls.Certificate)
 }
 
 // New returns a new CertWatcher watching the given certificate and key.
@@ -68,6 +71,17 @@ func New(certPath, keyPath string) (*CertWatcher, error) {
 	return cw, nil
 }
 
+// RegisterCallback registers a callback to be invoked when the certificate changes.
+func (cw *CertWatcher) RegisterCallback(callback func(tls.Certificate)) {
+	cw.Lock()
+	defer cw.Unlock()
+	// If the current certificate is not nil, invoke the callback immediately.
+	if cw.currentCert != nil {
+		callback(*cw.currentCert)
+	}
+	cw.callback = callback
+}
+
 // GetCertificate fetches the currently loaded certificate, which may be nil.
 func (cw *CertWatcher) GetCertificate(_ *tls.ClientHelloInfo) (*tls.Certificate, error) {
 	cw.RLock()
@@ -146,6 +160,14 @@ func (cw *CertWatcher) ReadCertificate() error {
 
 	log.Info("Updated current TLS certificate")
 
+	// If a callback is registered, invoke it with the new certificate.
+	cw.RLock()
+	defer cw.RUnlock()
+	if cw.callback != nil {
+		go func() {
+			cw.callback(cert)
+		}()
+	}
 	return nil
 }
 

pkg/certwatcher/certwatcher_test.go

@@ -20,13 +20,15 @@ import (
 	"context"
 	"crypto/rand"
 	"crypto/rsa"
+	"crypto/tls"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/pem"
 	"fmt"
 	"math/big"
 	"net"
 	"os"
+	"sync/atomic"
 	"time"
 
 	. "github.com/onsi/ginkgo/v2"
@@ -97,6 +99,11 @@ var _ = Describe("CertWatcher", func() {
 
 		It("should reload currentCert when changed", func() {
 			doneCh := startWatcher()
+			called := atomic.Int64{}
+			watcher.RegisterCallback(func(crt tls.Certificate) {
+				called.Add(1)
+				Expect(crt.Certificate).ToNot(BeEmpty())
+			})
 
 			firstcert, _ := watcher.GetCertificate(nil)
 
@@ -111,6 +118,7 @@ var _ = Describe("CertWatcher", func() {
 
 			ctxCancel()
 			Eventually(doneCh, "4s").Should(BeClosed())
+			Expect(called.Load()).To(BeNumerically(">=", 1))
 		})
 
 		Context("prometheus metric read_certificate_total", func() {