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