Source file src/pkg/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.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        int // 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 >= len(r.s) {
    27			return 0
    28		}
    29		return 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 >= len(r.s) {
    37			return 0, io.EOF
    38		}
    39		n = copy(b, r.s[r.i:])
    40		r.i += n
    41		r.prevRune = -1
    42		return
    43	}
    44	
    45	func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
    46		if off < 0 {
    47			return 0, errors.New("bytes: invalid offset")
    48		}
    49		if off >= int64(len(r.s)) {
    50			return 0, io.EOF
    51		}
    52		n = copy(b, r.s[int(off):])
    53		if n < len(b) {
    54			err = io.EOF
    55		}
    56		return
    57	}
    58	
    59	func (r *Reader) ReadByte() (b byte, err error) {
    60		if r.i >= len(r.s) {
    61			return 0, io.EOF
    62		}
    63		b = r.s[r.i]
    64		r.i++
    65		r.prevRune = -1
    66		return
    67	}
    68	
    69	func (r *Reader) UnreadByte() error {
    70		if r.i <= 0 {
    71			return errors.New("bytes.Reader: at beginning of slice")
    72		}
    73		r.i--
    74		r.prevRune = -1
    75		return nil
    76	}
    77	
    78	func (r *Reader) ReadRune() (ch rune, size int, err error) {
    79		if r.i >= len(r.s) {
    80			return 0, 0, io.EOF
    81		}
    82		r.prevRune = r.i
    83		if c := r.s[r.i]; c < utf8.RuneSelf {
    84			r.i++
    85			return rune(c), 1, nil
    86		}
    87		ch, size = utf8.DecodeRune(r.s[r.i:])
    88		r.i += size
    89		return
    90	}
    91	
    92	func (r *Reader) UnreadRune() error {
    93		if r.prevRune < 0 {
    94			return errors.New("bytes.Reader: previous operation was not ReadRune")
    95		}
    96		r.i = r.prevRune
    97		r.prevRune = -1
    98		return nil
    99	}
   100	
   101	// Seek implements the io.Seeker interface.
   102	func (r *Reader) Seek(offset int64, whence int) (int64, error) {
   103		var abs int64
   104		switch whence {
   105		case 0:
   106			abs = offset
   107		case 1:
   108			abs = int64(r.i) + offset
   109		case 2:
   110			abs = int64(len(r.s)) + offset
   111		default:
   112			return 0, errors.New("bytes: invalid whence")
   113		}
   114		if abs < 0 {
   115			return 0, errors.New("bytes: negative position")
   116		}
   117		if abs >= 1<<31 {
   118			return 0, errors.New("bytes: position out of range")
   119		}
   120		r.i = int(abs)
   121		return abs, nil
   122	}
   123	
   124	// NewReader returns a new Reader reading from b.
   125	func NewReader(b []byte) *Reader { return &Reader{b, 0, -1} }