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.ByteReader, io.ByteScanner,
  14 // io.RuneReader, io.RuneScanner, io.Seeker, and io.WriterTo interfaces by reading
  15 // from a string.
  16 // The zero value for Reader operates like a Reader of an empty string.
  17 type Reader struct {
  18         s        string
  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 // string.
  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 string.
  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("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 // 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 implements the io.ByteScanner interface.
  77 func (r *Reader) UnreadByte() error {
  78         if r.i <= 0 {
  79                 return errors.New("strings.Reader.UnreadByte: at beginning of string")
  80         }
  81         r.prevRune = -1
  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.DecodeRuneInString(r.s[r.i:])
  98         r.i += int64(size)
  99         return
 100 }
 101
 102 // UnreadRune implements the io.RuneScanner interface.
 103 func (r *Reader) UnreadRune() error {
 104         if r.i <= 0 {
 105                 return errors.New("strings.Reader.UnreadRune: at beginning of string")
 106         }
 107         if r.prevRune < 0 {
 108                 return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
 109         }
 110         r.i = int64(r.prevRune)
 111         r.prevRune = -1
 112         return nil
 113 }
 114
 115 // Seek implements the io.Seeker interface.
 116 func (r *Reader) Seek(offset int64, whence int) (int64, error) {
 117         r.prevRune = -1
 118         var abs int64
 119         switch whence {
 120         case io.SeekStart:
 121                 abs = offset
 122         case io.SeekCurrent:
 123                 abs = r.i + offset
 124         case io.SeekEnd:
 125                 abs = int64(len(r.s)) + offset
 126         default:
 127                 return 0, errors.New("strings.Reader.Seek: invalid whence")
 128         }
 129         if abs < 0 {
 130                 return 0, errors.New("strings.Reader.Seek: negative position")
 131         }
 132         r.i = abs
 133         return abs, nil
 134 }
 135
 136 // WriteTo implements the io.WriterTo interface.
 137 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 138         r.prevRune = -1
 139         if r.i >= int64(len(r.s)) {
 140                 return 0, nil
 141         }
 142         s := r.s[r.i:]
 143         m, err := io.WriteString(w, s)
 144         if m > len(s) {
 145                 panic("strings.Reader.WriteTo: invalid WriteString count")
 146         }
 147         r.i += int64(m)
 148         n = int64(m)
 149         if m != len(s) && err == nil {
 150                 err = io.ErrShortWrite
 151         }
 152         return
 153 }
 154
 155 // Reset resets the Reader to be reading from s.
 156 func (r *Reader) Reset(s string) { *r = Reader{s, 0, -1} }
 157
 158 // NewReader returns a new Reader reading from s.
 159 // It is similar to bytes.NewBufferString but more efficient and read-only.
 160 func NewReader(s string) *Reader { return &Reader{s, 0, -1} }