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 // Size returns the original length of the underlying byte slice.
33 // Size is the number of bytes available for reading via ReadAt.
34 // The returned value is always the same and is not affected by calls
35 // to any other method.
36 func (r
*Reader
) Size() int64 { return int64(len(r
.s
)) }
38 func (r
*Reader
) Read(b
[]byte) (n
int, err error
) {
39 if r
.i
>= int64(len(r
.s
)) {
43 n
= copy(b
, r
.s
[r
.i
:])
48 func (r
*Reader
) ReadAt(b
[]byte, off
int64) (n
int, err error
) {
49 // cannot modify state - see io.ReaderAt
51 return 0, errors
.New("bytes.Reader.ReadAt: negative offset")
53 if off
>= int64(len(r
.s
)) {
56 n
= copy(b
, r
.s
[off
:])
63 func (r
*Reader
) ReadByte() (byte, error
) {
65 if r
.i
>= int64(len(r
.s
)) {
73 func (r
*Reader
) UnreadByte() error
{
76 return errors
.New("bytes.Reader.UnreadByte: at beginning of slice")
82 func (r
*Reader
) ReadRune() (ch rune
, size
int, err error
) {
83 if r
.i
>= int64(len(r
.s
)) {
88 if c
:= r
.s
[r
.i
]; c
< utf8
.RuneSelf
{
90 return rune(c
), 1, nil
92 ch
, size
= utf8
.DecodeRune(r
.s
[r
.i
:])
97 func (r
*Reader
) UnreadRune() error
{
99 return errors
.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
101 r
.i
= int64(r
.prevRune
)
106 // Seek implements the io.Seeker interface.
107 func (r
*Reader
) Seek(offset
int64, whence
int) (int64, error
) {
116 abs
= int64(len(r
.s
)) + offset
118 return 0, errors
.New("bytes.Reader.Seek: invalid whence")
121 return 0, errors
.New("bytes.Reader.Seek: negative position")
127 // WriteTo implements the io.WriterTo interface.
128 func (r
*Reader
) WriteTo(w io
.Writer
) (n
int64, err error
) {
130 if r
.i
>= int64(len(r
.s
)) {
136 panic("bytes.Reader.WriteTo: invalid Write count")
140 if m
!= len(b
) && err
== nil {
141 err
= io
.ErrShortWrite
146 // Reset resets the Reader to be reading from b.
147 func (r
*Reader
) Reset(b
[]byte) { *r
= Reader
{b
, 0, -1} }
149 // NewReader returns a new Reader reading from b.
150 func NewReader(b
[]byte) *Reader
{ return &Reader
{b
, 0, -1} }