Improve UVariantLen

common/rw/varint.go

@@ -0,0 +1,77 @@
+package rw
+
+import (
+	"encoding/binary"
+	"io"
+
+	"github.com/sagernet/sing/common"
+)
+
+type stubByteReader struct {
+	io.Reader
+}
+
+func (r stubByteReader) ReadByte() (byte, error) {
+	return ReadByte(r.Reader)
+}
+
+func ToByteReader(reader io.Reader) io.ByteReader {
+	if byteReader, ok := reader.(io.ByteReader); ok {
+		return byteReader
+	}
+	return &stubByteReader{reader}
+}
+
+func ReadUVariant(reader io.Reader) (uint64, error) {
+	return binary.ReadUvarint(ToByteReader(reader))
+}
+
+func UVariantLen(x uint64) int {
+	switch {
+	case x < 1<<(7*1):
+		return 1
+	case x < 1<<(7*2):
+		return 2
+	case x < 1<<(7*3):
+		return 3
+	case x < 1<<(7*4):
+		return 4
+	case x < 1<<(7*5):
+		return 5
+	case x < 1<<(7*6):
+		return 6
+	case x < 1<<(7*7):
+		return 7
+	case x < 1<<(7*8):
+		return 8
+	case x < 1<<(7*9):
+		return 9
+	default:
+		return 10
+	}
+}
+
+func WriteUVariant(writer io.Writer, value uint64) error {
+	var b [8]byte
+	return common.Error(writer.Write(b[:binary.PutUvarint(b[:], value)]))
+}
+
+func WriteVString(writer io.Writer, value string) error {
+	err := WriteUVariant(writer, uint64(len(value)))
+	if err != nil {
+		return err
+	}
+	return WriteString(writer, value)
+}
+
+func ReadVString(reader io.Reader) (string, error) {
+	length, err := binary.ReadUvarint(ToByteReader(reader))
+	if err != nil {
+		return "", err
+	}
+	value, err := ReadBytes(reader, int(length))
+	if err != nil {
+		return "", err
+	}
+	return string(value), nil
+}