github.com/mdempsky/go@v0.0.0-20151201204031-5dd372bd1e70/src/strings/reader.go (about)

     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} }