client: WithTLSClientConfig: return early if no transport is set

tlsconfig.Client() does various things, including reading certs and
checking them. So we may as well return early if we're not gonna be
able to use the config.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/options.go

@@ -135,6 +135,10 @@ func WithScheme(scheme string) Opt {
 // WithTLSClientConfig applies a TLS config to the client transport.
 func WithTLSClientConfig(cacertPath, certPath, keyPath string) Opt {
 	return func(c *Client) error {
+		transport, ok := c.client.Transport.(*http.Transport)
+		if !ok {
+			return errors.Errorf("cannot apply tls config to transport: %T", c.client.Transport)
+		}
 		config, err := tlsconfig.Client(tlsconfig.Options{
 			CAFile:             cacertPath,
 			CertFile:           certPath,
@@ -144,11 +148,8 @@ func WithTLSClientConfig(cacertPath, certPath, keyPath string) Opt {
 		if err != nil {
 			return errors.Wrap(err, "failed to create tls config")
 		}
-		if transport, ok := c.client.Transport.(*http.Transport); ok {
-			transport.TLSClientConfig = config
-			return nil
-		}
-		return errors.Errorf("cannot apply tls config to transport: %T", c.client.Transport)
+		transport.TLSClientConfig = config
+		return nil
 	}
 }