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

     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  func (r *Reader) Read(b []byte) (n int, err error) {
    39  	if len(b) == 0 {
    40  		return 0, nil
    41  	}
    42  	if r.i >= int64(len(r.s)) {
    43  		return 0, io.EOF
    44  	}
    45  	r.prevRune = -1
    46  	n = copy(b, r.s[r.i:])
    47  	r.i += int64(n)
    48  	return
    49  }
    50  
    51  func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
    52  	// cannot modify state - see io.ReaderAt
    53  	if off < 0 {
    54  		return 0, errors.New("bytes.Reader.ReadAt: negative offset")
    55  	}
    56  	if off >= int64(len(r.s)) {
    57  		return 0, io.EOF
    58  	}
    59  	n = copy(b, r.s[off:])
    60  	if n < len(b) {
    61  		err = io.EOF
    62  	}
    63  	return
    64  }
    65  
    66  func (r *Reader) ReadByte() (b byte, err 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
    74  }
    75  
    76  func (r *Reader) UnreadByte() error {
    77  	r.prevRune = -1
    78  	if r.i <= 0 {
    79  		return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
    80  	}
    81  	r.i--
    82  	return nil
    83  }
    84  
    85  func (r *Reader) ReadRune() (ch rune, size int, err error) {
    86  	if r.i >= int64(len(r.s)) {
    87  		r.prevRune = -1
    88  		return 0, 0, io.EOF
    89  	}
    90  	r.prevRune = int(r.i)
    91  	if c := r.s[r.i]; c < utf8.RuneSelf {
    92  		r.i++
    93  		return rune(c), 1, nil
    94  	}
    95  	ch, size = utf8.DecodeRune(r.s[r.i:])
    96  	r.i += int64(size)
    97  	return
    98  }
    99  
   100  func (r *Reader) UnreadRune() error {
   101  	if r.prevRune < 0 {
   102  		return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
   103  	}
   104  	r.i = int64(r.prevRune)
   105  	r.prevRune = -1
   106  	return nil
   107  }
   108  
   109  // Seek implements the io.Seeker interface.
   110  func (r *Reader) Seek(offset int64, whence int) (int64, error) {
   111  	r.prevRune = -1
   112  	var abs int64
   113  	switch whence {
   114  	case 0:
   115  		abs = offset
   116  	case 1:
   117  		abs = int64(r.i) + offset
   118  	case 2:
   119  		abs = int64(len(r.s)) + offset
   120  	default:
   121  		return 0, errors.New("bytes.Reader.Seek: invalid whence")
   122  	}
   123  	if abs < 0 {
   124  		return 0, errors.New("bytes.Reader.Seek: negative position")
   125  	}
   126  	r.i = abs
   127  	return abs, nil
   128  }
   129  
   130  // WriteTo implements the io.WriterTo interface.
   131  func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
   132  	r.prevRune = -1
   133  	if r.i >= int64(len(r.s)) {
   134  		return 0, nil
   135  	}
   136  	b := r.s[r.i:]
   137  	m, err := w.Write(b)
   138  	if m > len(b) {
   139  		panic("bytes.Reader.WriteTo: invalid Write count")
   140  	}
   141  	r.i += int64(m)
   142  	n = int64(m)
   143  	if m != len(b) && err == nil {
   144  		err = io.ErrShortWrite
   145  	}
   146  	return
   147  }
   148  
   149  // NewReader returns a new Reader reading from b.
   150  func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }