Set comments to exported methods of mailgun backend

backend/mailgun/mailgun.go

@@ -21,10 +21,12 @@ type Backend struct {
 	publicKey  string
 }
 
+// User type
 type User struct {
 	mailgunClient mg.Mailgun
 }
 
+// NewBackend returns new instance of backend
 func NewBackend(domain, privateKey, publicKey string) (smtp.Backend, error) {
 	if domain == "" || privateKey == "" || publicKey == "" {
 		return nil, fmt.Errorf("domain, privateKey, publicKey must not be empty")
@@ -37,18 +39,23 @@ func NewBackend(domain, privateKey, publicKey string) (smtp.Backend, error) {
 	}, nil
 }
 
+// Login is used to authenticate the user
+// In relay there's no need for that at the moment
 func (b *Backend) Login(username, password string) (smtp.User, error) {
 	return &User{
 		mailgunClient: mg.NewMailgun(b.Domain, b.privateKey, b.publicKey),
 	}, nil
 }
 
+// AnonymousLogin returns anonymouse user object
 func (b *Backend) AnonymousLogin() (smtp.User, error) {
 	return &User{
 		mailgunClient: mg.NewMailgun(b.Domain, b.privateKey, b.publicKey),
 	}, nil
 }
 
+// Send will send email synchronously via Mailgun service
+// TODO: Send messages via queue
 func (u *User) Send(from string, to []string, r io.Reader) error {
 	m, err := mail.ReadMessage(r)
 	if err != nil {
@@ -71,6 +78,8 @@ func (u *User) Send(from string, to []string, r io.Reader) error {
 	return nil
 }
 
+// Logout is calle after all operations are complete within the session
+// Here in relay there's no need to implement anything special for that
 func (u *User) Logout() error {
 	return nil
 }