1 // Copyright 2012 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.WriterTo, io.Seeker,
14 // io.ByteScanner, and io.RuneScanner interfaces by reading from
16 // Unlike a Buffer, a Reader is read-only and supports seeking.
17 // The zero value for Reader operates like a Reader of an empty slice.
20 i int64 // current reading index
21 prevRune int // index of previous rune; or < 0
24 // Len returns the number of bytes of the unread portion of the
26 func (r *Reader) Len() int {
27 if r.i >= int64(len(r.s)) {
30 return int(int64(len(r.s)) - r.i)
33 // Size returns the original length of the underlying byte slice.
34 // Size is the number of bytes available for reading via ReadAt.
35 // The returned value is always the same and is not affected by calls
36 // to any other method.
37 func (r *Reader) Size() int64 { return int64(len(r.s)) }
39 // Read implements the io.Reader interface.
40 func (r *Reader) Read(b []byte) (n int, err error) {
41 if r.i >= int64(len(r.s)) {
45 n = copy(b, r.s[r.i:])
50 // ReadAt implements the io.ReaderAt interface.
51 func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
52 // cannot modify state - see io.ReaderAt
54 return 0, errors.New("bytes.Reader.ReadAt: negative offset")
56 if off >= int64(len(r.s)) {
59 n = copy(b, r.s[off:])
66 // ReadByte implements the io.ByteReader interface.
67 func (r *Reader) ReadByte() (byte, error) {
69 if r.i >= int64(len(r.s)) {
77 // UnreadByte complements ReadByte in implementing the io.ByteScanner interface.
78 func (r *Reader) UnreadByte() error {
80 return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
87 // ReadRune implements the io.RuneReader interface.
88 func (r *Reader) ReadRune() (ch rune, size int, err error) {
89 if r.i >= int64(len(r.s)) {
94 if c := r.s[r.i]; c < utf8.RuneSelf {
96 return rune(c), 1, nil
98 ch, size = utf8.DecodeRune(r.s[r.i:])
103 // UnreadRune complements ReadRune in implementing the io.RuneScanner interface.
104 func (r *Reader) UnreadRune() error {
106 return errors.New("bytes.Reader.UnreadRune: at beginning of slice")
109 return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
111 r.i = int64(r.prevRune)
116 // Seek implements the io.Seeker interface.
117 func (r *Reader) Seek(offset int64, whence int) (int64, error) {
126 abs = int64(len(r.s)) + offset
128 return 0, errors.New("bytes.Reader.Seek: invalid whence")
131 return 0, errors.New("bytes.Reader.Seek: negative position")
137 // WriteTo implements the io.WriterTo interface.
138 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
140 if r.i >= int64(len(r.s)) {
146 panic("bytes.Reader.WriteTo: invalid Write count")
150 if m != len(b) && err == nil {
151 err = io.ErrShortWrite
156 // Reset resets the Reader to be reading from b.
157 func (r *Reader) Reset(b []byte) { *r = Reader{b, 0, -1} }
159 // NewReader returns a new Reader reading from b.
160 func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }