libgo/go/bytes/reader.go

   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} }