1// Copyright 2009 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
5package strings
6
7import (
8 "errors"
9 "io"
10 "unicode/utf8"
11)
12
13// A Reader implements the io.Reader, io.ReaderAt, io.ByteReader, io.ByteScanner,
14// io.RuneReader, io.RuneScanner, io.Seeker, and io.WriterTo interfaces by reading
15// from a string.
16// The zero value for Reader operates like a Reader of an empty string.
17type Reader struct {
18 s string
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// string.
25func (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 string.
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.
36func (r *Reader) Size() int64 { return int64(len(r.s)) }
37
38// Read implements the io.Reader interface.
39func (r *Reader) Read(b []byte) (n int, err error) {
40 if r.i >= int64(len(r.s)) {
41 return 0, io.EOF
42 }
43 r.prevRune = -1
44 n = copy(b, r.s[r.i:])
45 r.i += int64(n)
46 return
47}
48
49// ReadAt implements the io.ReaderAt interface.
50func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
51 // cannot modify state - see io.ReaderAt
52 if off < 0 {
53 return 0, errors.New("strings.Reader.ReadAt: negative offset")
54 }
55 if off >= int64(len(r.s)) {
56 return 0, io.EOF
57 }
58 n = copy(b, r.s[off:])
59 if n < len(b) {
60 err = io.EOF
61 }
62 return
63}
64
65// ReadByte implements the io.ByteReader interface.
66func (r *Reader) ReadByte() (byte, 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 b, nil
74}
75
76// UnreadByte implements the io.ByteScanner interface.
77func (r *Reader) UnreadByte() error {
78 if r.i <= 0 {
79 return errors.New("strings.Reader.UnreadByte: at beginning of string")
80 }
81 r.prevRune = -1
82 r.i--
83 return nil
84}
85
86// ReadRune implements the io.RuneReader interface.
87func (r *Reader) ReadRune() (ch rune, size int, err error) {
88 if r.i >= int64(len(r.s)) {
89 r.prevRune = -1
90 return 0, 0, io.EOF
91 }
92 r.prevRune = int(r.i)
93 if c := r.s[r.i]; c < utf8.RuneSelf {
94 r.i++
95 return rune(c), 1, nil
96 }
97 ch, size = utf8.DecodeRuneInString(r.s[r.i:])
98 r.i += int64(size)
99 return
100}
101
102// UnreadRune implements the io.RuneScanner interface.
103func (r *Reader) UnreadRune() error {
104 if r.i <= 0 {
105 return errors.New("strings.Reader.UnreadRune: at beginning of string")
106 }
107 if r.prevRune < 0 {
108 return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
109 }
110 r.i = int64(r.prevRune)
111 r.prevRune = -1
112 return nil
113}
114
115// Seek implements the io.Seeker interface.
116func (r *Reader) Seek(offset int64, whence int) (int64, error) {
117 r.prevRune = -1
118 var abs int64
119 switch whence {
120 case io.SeekStart:
121 abs = offset
122 case io.SeekCurrent:
123 abs = r.i + offset
124 case io.SeekEnd:
125 abs = int64(len(r.s)) + offset
126 default:
127 return 0, errors.New("strings.Reader.Seek: invalid whence")
128 }
129 if abs < 0 {
130 return 0, errors.New("strings.Reader.Seek: negative position")
131 }
132 r.i = abs
133 return abs, nil
134}
135
136// WriteTo implements the io.WriterTo interface.
137func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
138 r.prevRune = -1
139 if r.i >= int64(len(r.s)) {
140 return 0, nil
141 }
142 s := r.s[r.i:]
143 m, err := io.WriteString(w, s)
144 if m > len(s) {
145 panic("strings.Reader.WriteTo: invalid WriteString count")
146 }
147 r.i += int64(m)
148 n = int64(m)
149 if m != len(s) && err == nil {
150 err = io.ErrShortWrite
151 }
152 return
153}
154
155// Reset resets the Reader to be reading from s.
156func (r *Reader) Reset(s string) { *r = Reader{s, 0, -1} }
157
158// NewReader returns a new Reader reading from s.
159// It is similar to bytes.NewBufferString but more efficient and read-only.
160func NewReader(s string) *Reader { return &Reader{s, 0, -1} }
