github.com/tidwall/go@v0.0.0-20170415222209-6694a6888b7d/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 r.i >= int64(len(r.s)) {
    40  		return 0, io.EOF
    41  	}
    42  	r.prevRune = -1
    43  	n = copy(b, r.s[r.i:])
    44  	r.i += int64(n)
    45  	return
    46  }
    47  
    48  func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
    49  	// cannot modify state - see io.ReaderAt
    50  	if off < 0 {
    51  		return 0, errors.New("bytes.Reader.ReadAt: negative offset")
    52  	}
    53  	if off >= int64(len(r.s)) {
    54  		return 0, io.EOF
    55  	}
    56  	n = copy(b, r.s[off:])
    57  	if n < len(b) {
    58  		err = io.EOF
    59  	}
    60  	return
    61  }
    62  
    63  func (r *Reader) ReadByte() (byte, error) {
    64  	r.prevRune = -1
    65  	if r.i >= int64(len(r.s)) {
    66  		return 0, io.EOF
    67  	}
    68  	b := r.s[r.i]
    69  	r.i++
    70  	return b, nil
    71  }
    72  
    73  func (r *Reader) UnreadByte() error {
    74  	r.prevRune = -1
    75  	if r.i <= 0 {
    76  		return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
    77  	}
    78  	r.i--
    79  	return nil
    80  }
    81  
    82  func (r *Reader) ReadRune() (ch rune, size int, err error) {
    83  	if r.i >= int64(len(r.s)) {
    84  		r.prevRune = -1
    85  		return 0, 0, io.EOF
    86  	}
    87  	r.prevRune = int(r.i)
    88  	if c := r.s[r.i]; c < utf8.RuneSelf {
    89  		r.i++
    90  		return rune(c), 1, nil
    91  	}
    92  	ch, size = utf8.DecodeRune(r.s[r.i:])
    93  	r.i += int64(size)
    94  	return
    95  }
    96  
    97  func (r *Reader) UnreadRune() error {
    98  	if r.prevRune < 0 {
    99  		return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
   100  	}
   101  	r.i = int64(r.prevRune)
   102  	r.prevRune = -1
   103  	return nil
   104  }
   105  
   106  // Seek implements the io.Seeker interface.
   107  func (r *Reader) Seek(offset int64, whence int) (int64, error) {
   108  	r.prevRune = -1
   109  	var abs int64
   110  	switch whence {
   111  	case io.SeekStart:
   112  		abs = offset
   113  	case io.SeekCurrent:
   114  		abs = r.i + offset
   115  	case io.SeekEnd:
   116  		abs = int64(len(r.s)) + offset
   117  	default:
   118  		return 0, errors.New("bytes.Reader.Seek: invalid whence")
   119  	}
   120  	if abs < 0 {
   121  		return 0, errors.New("bytes.Reader.Seek: negative position")
   122  	}
   123  	r.i = abs
   124  	return abs, nil
   125  }
   126  
   127  // WriteTo implements the io.WriterTo interface.
   128  func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
   129  	r.prevRune = -1
   130  	if r.i >= int64(len(r.s)) {
   131  		return 0, nil
   132  	}
   133  	b := r.s[r.i:]
   134  	m, err := w.Write(b)
   135  	if m > len(b) {
   136  		panic("bytes.Reader.WriteTo: invalid Write count")
   137  	}
   138  	r.i += int64(m)
   139  	n = int64(m)
   140  	if m != len(b) && err == nil {
   141  		err = io.ErrShortWrite
   142  	}
   143  	return
   144  }
   145  
   146  // Reset resets the Reader to be reading from b.
   147  func (r *Reader) Reset(b []byte) { *r = Reader{b, 0, -1} }
   148  
   149  // NewReader returns a new Reader reading from b.
   150  func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }