fix: optimize utility functions for CborReader

utils.go

@@ -23,7 +23,7 @@ const (
 // discard is a helper function to discard data from a reader, special-casing
 // the most common readers we encounter in this library for a significant
 // performance boost.
-func discard(br io.Reader, n int) error {
+func discard(br io.Reader, n int) (_err error) {
 	// If we're expecting no bytes, don't even try to read. Otherwise, we may read an EOF.
 	if n == 0 {
 		return nil
@@ -47,12 +47,45 @@ func discard(br io.Reader, n int) error {
 		}
 		_, err := r.Seek(int64(n), io.SeekCurrent)
 		return err
+	case *peeker:
+		// Discard the buffered byte, if any.
+		discarded := false
+
+		defer func() {
+			if discarded && _err == io.EOF {
+				_err = io.ErrUnexpectedEOF
+			}
+		}()
+
+		if r.peekState == peekUnread {
+			r.peekState = peekSet
+			n--
+			discarded = true
+		}
+		switch n {
+		case 0:
+			// Nothing else to read.
+			return nil
+		case 1:
+			// Only read one byte.
+		default:
+			// Read all but the last byte
+			err := discard(r.reader, n-1)
+			if err != nil {
+				return err
+			}
+			discarded = true
+		}
+		_, err := r.ReadByte()
+		return err
 	case *bufio.Reader:
 		discarded, err := r.Discard(n)
 		if discarded != 0 && discarded < n && err == io.EOF {
 			return io.ErrUnexpectedEOF
 		}
 		return err
+	case *CborReader:
+		return discard(r.r, n)
 	default:
 		discarded, err := io.CopyN(ioutil.Discard, br, int64(n))
 		if discarded != 0 && discarded < int64(n) && err == io.EOF {
@@ -246,6 +279,8 @@ func readByte(r io.Reader) (byte, error) {
 		return r.ReadByte()
 	case *peeker:
 		return r.ReadByte()
+	case *CborReader:
+		return r.ReadByte()
 	case io.ByteReader:
 		return r.ReadByte()
 	}
@@ -331,6 +366,8 @@ func readByteBuf(r io.Reader, scratch []byte) (byte, error) {
 		return r.ReadByte()
 	case *peeker:
 		return r.ReadByte()
+	case *CborReader:
+		return r.ReadByte()
 	case io.ByteReader:
 		return r.ReadByte()
 	}