Avoid doing type switching in inner functions

The CPU profiler tells me that the encoder is spending a lot of time on
type switches.

1 files changed, 8 insertions, 1 deletions

diff --git a/internal/base64.go b/internal/base64.go
index 15adbf4..291a229 100644
--- a/internal/base64.go
+++ b/internal/base64.go
@@ -19,7 +19,10 @@ type base64Decoder struct {
 	bufLen int
 }
 
-func NewBase64Decoder(w io.Writer) io.WriteCloser {
+func NewBase64Decoder(w io.Writer) interface {
+	io.WriteCloser
+	RuneWriter
+} {
 	return &base64Decoder{
 		dst: w,
 	}
@@ -112,6 +115,10 @@ func (dec *base64Decoder) Write(dat []byte) (int, error) {
 	return len(dat), nil
 }
 
+func (dec *base64Decoder) WriteRune(r rune) (int, error) {
+	return WriteRune(dec, r)
+}
+
 func (dec *base64Decoder) Close() error {
 	if dec.bufLen == 0 {
 		return nil