github.com/ccccaoqing/test@v0.0.0-20220510085219-3985d23445c0/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  func (r *Reader) Read(b []byte) (n int, err error) {
    33  	if len(b) == 0 {
    34  		return 0, nil
    35  	}
    36  	if r.i >= int64(len(r.s)) {
    37  		return 0, io.EOF
    38  	}
    39  	r.prevRune = -1
    40  	n = copy(b, r.s[r.i:])
    41  	r.i += int64(n)
    42  	return
    43  }
    44  
    45  func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
    46  	// cannot modify state - see io.ReaderAt
    47  	if off < 0 {
    48  		return 0, errors.New("bytes.Reader.ReadAt: negative offset")
    49  	}
    50  	if off >= int64(len(r.s)) {
    51  		return 0, io.EOF
    52  	}
    53  	n = copy(b, r.s[off:])
    54  	if n < len(b) {
    55  		err = io.EOF
    56  	}
    57  	return
    58  }
    59  
    60  func (r *Reader) ReadByte() (b byte, err error) {
    61  	r.prevRune = -1
    62  	if r.i >= int64(len(r.s)) {
    63  		return 0, io.EOF
    64  	}
    65  	b = r.s[r.i]
    66  	r.i++
    67  	return
    68  }
    69  
    70  func (r *Reader) UnreadByte() error {
    71  	r.prevRune = -1
    72  	if r.i <= 0 {
    73  		return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
    74  	}
    75  	r.i--
    76  	return nil
    77  }
    78  
    79  func (r *Reader) ReadRune() (ch rune, size int, err error) {
    80  	if r.i >= int64(len(r.s)) {
    81  		r.prevRune = -1
    82  		return 0, 0, io.EOF
    83  	}
    84  	r.prevRune = int(r.i)
    85  	if c := r.s[r.i]; c < utf8.RuneSelf {
    86  		r.i++
    87  		return rune(c), 1, nil
    88  	}
    89  	ch, size = utf8.DecodeRune(r.s[r.i:])
    90  	r.i += int64(size)
    91  	return
    92  }
    93  
    94  func (r *Reader) UnreadRune() error {
    95  	if r.prevRune < 0 {
    96  		return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
    97  	}
    98  	r.i = int64(r.prevRune)
    99  	r.prevRune = -1
   100  	return nil
   101  }
   102  
   103  // Seek implements the io.Seeker interface.
   104  func (r *Reader) Seek(offset int64, whence int) (int64, error) {
   105  	r.prevRune = -1
   106  	var abs int64
   107  	switch whence {
   108  	case 0:
   109  		abs = offset
   110  	case 1:
   111  		abs = int64(r.i) + offset
   112  	case 2:
   113  		abs = int64(len(r.s)) + offset
   114  	default:
   115  		return 0, errors.New("bytes.Reader.Seek: invalid whence")
   116  	}
   117  	if abs < 0 {
   118  		return 0, errors.New("bytes.Reader.Seek: negative position")
   119  	}
   120  	r.i = abs
   121  	return abs, nil
   122  }
   123  
   124  // WriteTo implements the io.WriterTo interface.
   125  func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
   126  	r.prevRune = -1
   127  	if r.i >= int64(len(r.s)) {
   128  		return 0, nil
   129  	}
   130  	b := r.s[r.i:]
   131  	m, err := w.Write(b)
   132  	if m > len(b) {
   133  		panic("bytes.Reader.WriteTo: invalid Write count")
   134  	}
   135  	r.i += int64(m)
   136  	n = int64(m)
   137  	if m != len(b) && err == nil {
   138  		err = io.ErrShortWrite
   139  	}
   140  	return
   141  }
   142  
   143  // NewReader returns a new Reader reading from b.
   144  func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }