1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
13 // A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo,
14 // io.ByteScanner, and io.RuneScanner interfaces by reading
18 i int // current reading index
19 prevRune int // index of previous rune; or < 0
22 // Len returns the number of bytes of the unread portion of the
24 func (r *Reader) Len() int {
31 func (r *Reader) Read(b []byte) (n int, err error) {
38 n = copy(b, r.s[r.i:])
44 func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
46 return 0, errors.New("strings: invalid offset")
48 if off >= int64(len(r.s)) {
51 n = copy(b, r.s[int(off):])
58 func (r *Reader) ReadByte() (b byte, err error) {
68 func (r *Reader) UnreadByte() error {
70 return errors.New("strings.Reader: at beginning of string")
77 func (r *Reader) ReadRune() (ch rune, size int, err error) {
82 if c := r.s[r.i]; c < utf8.RuneSelf {
84 return rune(c), 1, nil
86 ch, size = utf8.DecodeRuneInString(r.s[r.i:])
91 func (r *Reader) UnreadRune() error {
93 return errors.New("strings.Reader: previous operation was not ReadRune")
100 // Seek implements the io.Seeker interface.
101 func (r *Reader) Seek(offset int64, whence int) (int64, error) {
107 abs = int64(r.i) + offset
109 abs = int64(len(r.s)) + offset
111 return 0, errors.New("strings: invalid whence")
114 return 0, errors.New("strings: negative position")
117 return 0, errors.New("strings: position out of range")
123 // WriteTo implements the io.WriterTo interface.
124 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
130 m, err := io.WriteString(w, s)
132 panic("strings.Reader.WriteTo: invalid WriteString count")
136 if m != len(s) && err == nil {
137 err = io.ErrShortWrite
142 // NewReader returns a new Reader reading from s.
143 // It is similar to bytes.NewBufferString but more efficient and read-only.
144 func NewReader(s string) *Reader { return &Reader{s, 0, -1} }