fix:add graceful shutdown to courier handler (#296)

Courier would not stop with the provided Background handler.
This changes the methods of Courier so that the graceful package can be
used in the same way as the http endpoints can be used.

Closes #295

cmd/daemon/serve.go

@@ -1,7 +1,6 @@
 package daemon
 
 import (
-	stdctx "context"
 	"net/http"
 	"strings"
 	"sync"
@@ -165,9 +164,10 @@ func sqa(cmd *cobra.Command, d driver.Driver) *metricsx.Service {
 func bgTasks(d driver.Driver, wg *sync.WaitGroup, cmd *cobra.Command, args []string) {
 	defer wg.Done()
 
-	if err := d.Registry().Courier().Work(stdctx.Background()); err != nil {
+	if err := graceful.Graceful(d.Registry().Courier().Work, d.Registry().Courier().Shutdown); err != nil {
 		d.Logger().WithError(err).Fatalf("Failed to run courier worker.")
 	}
+	d.Logger().Println("courier worker was shutdown gracefully")
 }
 
 func ServeAll(d driver.Driver) func(cmd *cobra.Command, args []string) {

courier/courier.go

@@ -27,6 +27,9 @@ type (
 		dialer *gomail.Dialer
 		d      smtpDependencies
 		c      configuration.Provider
+		// graceful shutdown handling
+		ctx      context.Context
+		shutdown context.CancelFunc
 	}
 	Provider interface {
 		Courier() *Courier
@@ -38,9 +41,12 @@ func NewSMTP(d smtpDependencies, c configuration.Provider) *Courier {
 	sslSkipVerify, _ := strconv.ParseBool(uri.Query().Get("skip_ssl_verify"))
 	password, _ := uri.User.Password()
 	port, _ := strconv.ParseInt(uri.Port(), 10, 64)
+	ctx, cancel := context.WithCancel(context.Background())
 	return &Courier{
-		d: d,
-		c: c,
+		d:        d,
+		c:        c,
+		ctx:      ctx,
+		shutdown: cancel,
 		dialer: &gomail.Dialer{
 			Host:     uri.Hostname(),
 			Port:     int(port),
@@ -82,20 +88,28 @@ func (m *Courier) QueueEmail(ctx context.Context, t EmailTemplate) (uuid.UUID, e
 	return message.ID, nil
 }
 
-func (m *Courier) Work(ctx context.Context) error {
+func (m *Courier) Work() error {
 	errChan := make(chan error)
 	defer close(errChan)
 
-	go m.watchMessages(ctx, errChan)
+	go m.watchMessages(m.ctx, errChan)
 
 	select {
-	case <-ctx.Done():
-		return ctx.Err()
+	case <-m.ctx.Done():
+		if m.ctx.Err() == context.Canceled {
+			return nil
+		}
+		return m.ctx.Err()
 	case err := <-errChan:
 		return err
 	}
 }
 
+func (m *Courier) Shutdown(ctx context.Context) error {
+	m.shutdown()
+	return nil
+}
+
 func (m *Courier) watchMessages(ctx context.Context, errChan chan error) {
 	for {
 		if err := backoff.Retry(func() error {

courier/courier_test.go

@@ -104,7 +104,7 @@ func TestSMTP(t *testing.T) {
 	c := reg.Courier()
 
 	go func() {
-		require.NoError(t, c.Work(context.Background()))
+		require.NoError(t, c.Work())
 	}()
 
 	t.Run("case=queue messages", func(t *testing.T) {