libgo/go/strings/reader.go

   1 // Copyright 2009 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 strings
   6
   7 import (
   8         "errors"
   9         "io"
  10         "unicode/utf8"
  11 )
  12
  13 // A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo,
  14 // io.ByteScanner, and io.RuneScanner interfaces by reading
  15 // from a string.
  16 type Reader struct {
  17         s        string
  18         i        int64 // current reading index
  19         prevRune int   // index of previous rune; or < 0
  20 }
  21
  22 // Len returns the number of bytes of the unread portion of the
  23 // string.
  24 func (r *Reader) Len() int {
  25         if r.i >= int64(len(r.s)) {
  26                 return 0
  27         }
  28         return int(int64(len(r.s)) - r.i)
  29 }
  30
  31 // Size returns the original length of the underlying string.
  32 // Size is the number of bytes available for reading via ReadAt.
  33 // The returned value is always the same and is not affected by calls
  34 // to any other method.
  35 func (r *Reader) Size() int64 { return int64(len(r.s)) }
  36
  37 func (r *Reader) Read(b []byte) (n int, err error) {
  38         if len(b) == 0 {
  39                 return 0, nil
  40         }
  41         if r.i >= int64(len(r.s)) {
  42                 return 0, io.EOF
  43         }
  44         r.prevRune = -1
  45         n = copy(b, r.s[r.i:])
  46         r.i += int64(n)
  47         return
  48 }
  49
  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("strings.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 func (r *Reader) ReadByte() (b byte, err error) {
  66         r.prevRune = -1
  67         if r.i >= int64(len(r.s)) {
  68                 return 0, io.EOF
  69         }
  70         b = r.s[r.i]
  71         r.i++
  72         return
  73 }
  74
  75 func (r *Reader) UnreadByte() error {
  76         r.prevRune = -1
  77         if r.i <= 0 {
  78                 return errors.New("strings.Reader.UnreadByte: at beginning of string")
  79         }
  80         r.i--
  81         return nil
  82 }
  83
  84 func (r *Reader) ReadRune() (ch rune, size int, err error) {
  85         if r.i >= int64(len(r.s)) {
  86                 r.prevRune = -1
  87                 return 0, 0, io.EOF
  88         }
  89         r.prevRune = int(r.i)
  90         if c := r.s[r.i]; c < utf8.RuneSelf {
  91                 r.i++
  92                 return rune(c), 1, nil
  93         }
  94         ch, size = utf8.DecodeRuneInString(r.s[r.i:])
  95         r.i += int64(size)
  96         return
  97 }
  98
  99 func (r *Reader) UnreadRune() error {
 100         if r.prevRune < 0 {
 101                 return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
 102         }
 103         r.i = int64(r.prevRune)
 104         r.prevRune = -1
 105         return nil
 106 }
 107
 108 // Seek implements the io.Seeker interface.
 109 func (r *Reader) Seek(offset int64, whence int) (int64, error) {
 110         r.prevRune = -1
 111         var abs int64
 112         switch whence {
 113         case 0:
 114                 abs = offset
 115         case 1:
 116                 abs = int64(r.i) + offset
 117         case 2:
 118                 abs = int64(len(r.s)) + offset
 119         default:
 120                 return 0, errors.New("strings.Reader.Seek: invalid whence")
 121         }
 122         if abs < 0 {
 123                 return 0, errors.New("strings.Reader.Seek: negative position")
 124         }
 125         r.i = abs
 126         return abs, nil
 127 }
 128
 129 // WriteTo implements the io.WriterTo interface.
 130 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 131         r.prevRune = -1
 132         if r.i >= int64(len(r.s)) {
 133                 return 0, nil
 134         }
 135         s := r.s[r.i:]
 136         m, err := io.WriteString(w, s)
 137         if m > len(s) {
 138                 panic("strings.Reader.WriteTo: invalid WriteString count")
 139         }
 140         r.i += int64(m)
 141         n = int64(m)
 142         if m != len(s) && err == nil {
 143                 err = io.ErrShortWrite
 144         }
 145         return
 146 }
 147
 148 // NewReader returns a new Reader reading from s.
 149 // It is similar to bytes.NewBufferString but more efficient and read-only.
 150 func NewReader(s string) *Reader { return &Reader{s, 0, -1} }