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// Copyright 2009 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 strings
import (
"errors"
"io"
"unicode/utf8"
)
// A Reader implements the io.Reader, io.ByteScanner, and
// io.RuneScanner interfaces by reading from a string.
type Reader struct {
s string
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
// string.
func (r *Reader) Len() int {
return len(r.s) - r.i
}
func (r *Reader) Read(b []byte) (n int, err error) {
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) 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
}
// UnreadByte moves the reading position back by one byte.
// It is an error to call UnreadByte if nothing has been
// read yet.
func (r *Reader) UnreadByte() error {
if r.i <= 0 {
return errors.New("strings.Reader: at beginning of string")
}
r.i--
r.prevRune = -1
return nil
}
// ReadRune reads and returns the next UTF-8-encoded
// Unicode code point from the buffer.
// If no bytes are available, the error returned is io.EOF.
// If the bytes are an erroneous UTF-8 encoding, it
// consumes one byte and returns U+FFFD, 1.
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.DecodeRuneInString(r.s[r.i:])
r.i += size
return
}
// UnreadRune causes the next call to ReadRune to return the same rune
// as the previous call to ReadRune.
// The last method called on r must have been ReadRune.
func (r *Reader) UnreadRune() error {
if r.prevRune < 0 {
return errors.New("strings.Reader: previous operation was not ReadRune")
}
r.i = r.prevRune
r.prevRune = -1
return nil
}
// NewReader returns a new Reader reading from s.
// It is similar to bytes.NewBufferString but more efficient and read-only.
func NewReader(s string) *Reader { return &Reader{s, 0, -1} }
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