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. 4 5 package bytes 6 7 import ( 8 "errors" 9 "io" 10 "unicode/utf8" 11 ) 12 13 // A Reader implements the io.Reader, io.ReaderAt, io.WriterTo, io.Seeker, 14 // io.ByteScanner, and io.RuneScanner interfaces by reading from 15 // a byte slice. 16 // Unlike a Buffer, a Reader is read-only and supports seeking. 17 type Reader struct { 18 s []byte 19 i int64 // current reading index 20 prevRune int // index of previous rune; or < 0 21 } 22 23 // Len returns the number of bytes of the unread portion of the 24 // slice. 25 func (r *Reader) Len() int { 26 if r.i >= int64(len(r.s)) { 27 return 0 28 } 29 return int(int64(len(r.s)) - r.i) 30 } 31 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)) } 37 38 // Read implements the io.Reader interface. 39 func (r *Reader) Read(b []byte) (n int, err error) { 40 if r.i >= int64(len(r.s)) { 41 return 0, io.EOF 42 } 43 r.prevRune = -1 44 n = copy(b, r.s[r.i:]) 45 r.i += int64(n) 46 return 47 } 48 49 // ReadAt implements the io.ReaderAt interface. 50 func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) { 51 // cannot modify state - see io.ReaderAt 52 if off < 0 { 53 return 0, errors.New("bytes.Reader.ReadAt: negative offset") 54 } 55 if off >= int64(len(r.s)) { 56 return 0, io.EOF 57 } 58 n = copy(b, r.s[off:]) 59 if n < len(b) { 60 err = io.EOF 61 } 62 return 63 } 64 65 // ReadByte implements the io.ByteReader interface. 66 func (r *Reader) ReadByte() (byte, error) { 67 r.prevRune = -1 68 if r.i >= int64(len(r.s)) { 69 return 0, io.EOF 70 } 71 b := r.s[r.i] 72 r.i++ 73 return b, nil 74 } 75 76 // UnreadByte complements ReadByte in implementing the io.ByteScanner interface. 77 func (r *Reader) UnreadByte() error { 78 r.prevRune = -1 79 if r.i <= 0 { 80 return errors.New("bytes.Reader.UnreadByte: at beginning of slice") 81 } 82 r.i-- 83 return nil 84 } 85 86 // ReadRune implements the io.RuneReader interface. 87 func (r *Reader) ReadRune() (ch rune, size int, err error) { 88 if r.i >= int64(len(r.s)) { 89 r.prevRune = -1 90 return 0, 0, io.EOF 91 } 92 r.prevRune = int(r.i) 93 if c := r.s[r.i]; c < utf8.RuneSelf { 94 r.i++ 95 return rune(c), 1, nil 96 } 97 ch, size = utf8.DecodeRune(r.s[r.i:]) 98 r.i += int64(size) 99 return 100 } 101 102 // UnreadRune complements ReadRune in implementing the io.RuneScanner interface. 103 func (r *Reader) UnreadRune() error { 104 if r.prevRune < 0 { 105 return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune") 106 } 107 r.i = int64(r.prevRune) 108 r.prevRune = -1 109 return nil 110 } 111 112 // Seek implements the io.Seeker interface. 113 func (r *Reader) Seek(offset int64, whence int) (int64, error) { 114 r.prevRune = -1 115 var abs int64 116 switch whence { 117 case io.SeekStart: 118 abs = offset 119 case io.SeekCurrent: 120 abs = r.i + offset 121 case io.SeekEnd: 122 abs = int64(len(r.s)) + offset 123 default: 124 return 0, errors.New("bytes.Reader.Seek: invalid whence") 125 } 126 if abs < 0 { 127 return 0, errors.New("bytes.Reader.Seek: negative position") 128 } 129 r.i = abs 130 return abs, nil 131 } 132 133 // WriteTo implements the io.WriterTo interface. 134 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) { 135 r.prevRune = -1 136 if r.i >= int64(len(r.s)) { 137 return 0, nil 138 } 139 b := r.s[r.i:] 140 m, err := w.Write(b) 141 if m > len(b) { 142 panic("bytes.Reader.WriteTo: invalid Write count") 143 } 144 r.i += int64(m) 145 n = int64(m) 146 if m != len(b) && err == nil { 147 err = io.ErrShortWrite 148 } 149 return 150 } 151 152 // Reset resets the Reader to be reading from b. 153 func (r *Reader) Reset(b []byte) { *r = Reader{b, 0, -1} } 154 155 // NewReader returns a new Reader reading from b. 156 func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} } 157
