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.
19 i
int64 // current reading index
20 prevRune
int // index of previous rune; or < 0
23 // Len returns the number of bytes of the unread portion of the
25 func (r
*Reader
) Len() int {
26 if r
.i
>= int64(len(r
.s
)) {
29 return int(int64(len(r
.s
)) - r
.i
)
32 func (r
*Reader
) Read(b
[]byte) (n
int, err error
) {
36 if r
.i
>= int64(len(r
.s
)) {
40 n
= copy(b
, r
.s
[r
.i
:])
45 func (r
*Reader
) ReadAt(b
[]byte, off
int64) (n
int, err error
) {
46 // cannot modify state - see io.ReaderAt
48 return 0, errors
.New("bytes.Reader.ReadAt: negative offset")
50 if off
>= int64(len(r
.s
)) {
53 n
= copy(b
, r
.s
[off
:])
60 func (r
*Reader
) ReadByte() (b
byte, err error
) {
62 if r
.i
>= int64(len(r
.s
)) {
70 func (r
*Reader
) UnreadByte() error
{
73 return errors
.New("bytes.Reader.UnreadByte: at beginning of slice")
79 func (r
*Reader
) ReadRune() (ch rune
, size
int, err error
) {
80 if r
.i
>= int64(len(r
.s
)) {
85 if c
:= r
.s
[r
.i
]; c
< utf8
.RuneSelf
{
87 return rune(c
), 1, nil
89 ch
, size
= utf8
.DecodeRune(r
.s
[r
.i
:])
94 func (r
*Reader
) UnreadRune() error
{
96 return errors
.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
98 r
.i
= int64(r
.prevRune
)
103 // Seek implements the io.Seeker interface.
104 func (r
*Reader
) Seek(offset
int64, whence
int) (int64, error
) {
111 abs
= int64(r
.i
) + offset
113 abs
= int64(len(r
.s
)) + offset
115 return 0, errors
.New("bytes.Reader.Seek: invalid whence")
118 return 0, errors
.New("bytes.Reader.Seek: negative position")
124 // WriteTo implements the io.WriterTo interface.
125 func (r
*Reader
) WriteTo(w io
.Writer
) (n
int64, err error
) {
127 if r
.i
>= int64(len(r
.s
)) {
133 panic("bytes.Reader.WriteTo: invalid Write count")
137 if m
!= len(b
) && err
== nil {
138 err
= io
.ErrShortWrite
143 // NewReader returns a new Reader reading from b.
144 func NewReader(b
[]byte) *Reader
{ return &Reader
{b
, 0, -1} }