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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bytes
import (
"errors"
"io"
"unicode/utf8"
)
// A Reader implements the io.Reader, io.ReaderAt, io.Seeker,
// io.ByteScanner, and io.RuneScanner interfaces by reading from
// a byte slice.
// Unlike a Buffer, a Reader is read-only and supports seeking.
type Reader struct {
s []byte
i int // current reading index
prevRune int // index of previous rune; or < 0
}
// Len returns the number of bytes of the unread portion of the
// slice.
func (r *Reader) Len() int {
if r.i >= len(r.s) {
return 0
}
return len(r.s) - r.i
}
func (r *Reader) Read(b []byte) (n int, err error) {
if len(b) == 0 {
return 0, nil
}
if r.i >= len(r.s) {
return 0, io.EOF
}
n = copy(b, r.s[r.i:])
r.i += n
r.prevRune = -1
return
}
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
if off < 0 {
return 0, errors.New("bytes: invalid offset")
}
if off >= int64(len(r.s)) {
return 0, io.EOF
}
n = copy(b, r.s[int(off):])
if n < len(b) {
err = io.EOF
}
return
}
func (r *Reader) ReadByte() (b byte, err error) {
if r.i >= len(r.s) {
return 0, io.EOF
}
b = r.s[r.i]
r.i++
r.prevRune = -1
return
}
func (r *Reader) UnreadByte() error {
if r.i <= 0 {
return errors.New("bytes.Reader: at beginning of slice")
}
r.i--
r.prevRune = -1
return nil
}
func (r *Reader) ReadRune() (ch rune, size int, err error) {
if r.i >= len(r.s) {
return 0, 0, io.EOF
}
r.prevRune = r.i
if c := r.s[r.i]; c < utf8.RuneSelf {
r.i++
return rune(c), 1, nil
}
ch, size = utf8.DecodeRune(r.s[r.i:])
r.i += size
return
}
func (r *Reader) UnreadRune() error {
if r.prevRune < 0 {
return errors.New("bytes.Reader: previous operation was not ReadRune")
}
r.i = r.prevRune
r.prevRune = -1
return nil
}
// Seek implements the io.Seeker interface.
func (r *Reader) Seek(offset int64, whence int) (int64, error) {
var abs int64
switch whence {
case 0:
abs = offset
case 1:
abs = int64(r.i) + offset
case 2:
abs = int64(len(r.s)) + offset
default:
return 0, errors.New("bytes: invalid whence")
}
if abs < 0 {
return 0, errors.New("bytes: negative position")
}
if abs >= 1<<31 {
return 0, errors.New("bytes: position out of range")
}
r.i = int(abs)
return abs, nil
}
// NewReader returns a new Reader reading from b.
func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }
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