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Source file src/bytes/reader.go

     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} }
   151	

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