| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package strings |
| |
| import ( |
| "errors" |
| "io" |
| "unicode/utf8" |
| ) |
| |
| // A Reader implements the io.Reader, io.ReaderAt, io.ByteReader, io.ByteScanner, |
| // io.RuneReader, io.RuneScanner, io.Seeker, and io.WriterTo interfaces by reading |
| // from a string. |
| // The zero value for Reader operates like a Reader of an empty string. |
| type Reader struct { |
| s string |
| i int64 // current reading index |
| prevRune int // index of previous rune; or < 0 |
| } |
| |
| // Len returns the number of bytes of the unread portion of the |
| // string. |
| func (r *Reader) Len() int { |
| if r.i >= int64(len(r.s)) { |
| return 0 |
| } |
| return int(int64(len(r.s)) - r.i) |
| } |
| |
| // Size returns the original length of the underlying string. |
| // Size is the number of bytes available for reading via ReadAt. |
| // The returned value is always the same and is not affected by calls |
| // to any other method. |
| func (r *Reader) Size() int64 { return int64(len(r.s)) } |
| |
| // Read implements the io.Reader interface. |
| func (r *Reader) Read(b []byte) (n int, err error) { |
| if r.i >= int64(len(r.s)) { |
| return 0, io.EOF |
| } |
| r.prevRune = -1 |
| n = copy(b, r.s[r.i:]) |
| r.i += int64(n) |
| return |
| } |
| |
| // ReadAt implements the io.ReaderAt interface. |
| func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) { |
| // cannot modify state - see io.ReaderAt |
| if off < 0 { |
| return 0, errors.New("strings.Reader.ReadAt: negative offset") |
| } |
| if off >= int64(len(r.s)) { |
| return 0, io.EOF |
| } |
| n = copy(b, r.s[off:]) |
| if n < len(b) { |
| err = io.EOF |
| } |
| return |
| } |
| |
| // ReadByte implements the io.ByteReader interface. |
| func (r *Reader) ReadByte() (byte, error) { |
| r.prevRune = -1 |
| if r.i >= int64(len(r.s)) { |
| return 0, io.EOF |
| } |
| b := r.s[r.i] |
| r.i++ |
| return b, nil |
| } |
| |
| // UnreadByte implements the io.ByteScanner interface. |
| func (r *Reader) UnreadByte() error { |
| if r.i <= 0 { |
| return errors.New("strings.Reader.UnreadByte: at beginning of string") |
| } |
| r.prevRune = -1 |
| r.i-- |
| return nil |
| } |
| |
| // ReadRune implements the io.RuneReader interface. |
| func (r *Reader) ReadRune() (ch rune, size int, err error) { |
| if r.i >= int64(len(r.s)) { |
| r.prevRune = -1 |
| return 0, 0, io.EOF |
| } |
| r.prevRune = int(r.i) |
| if c := r.s[r.i]; c < utf8.RuneSelf { |
| r.i++ |
| return rune(c), 1, nil |
| } |
| ch, size = utf8.DecodeRuneInString(r.s[r.i:]) |
| r.i += int64(size) |
| return |
| } |
| |
| // UnreadRune implements the io.RuneScanner interface. |
| func (r *Reader) UnreadRune() error { |
| if r.i <= 0 { |
| return errors.New("strings.Reader.UnreadRune: at beginning of string") |
| } |
| if r.prevRune < 0 { |
| return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune") |
| } |
| r.i = int64(r.prevRune) |
| r.prevRune = -1 |
| return nil |
| } |
| |
| // Seek implements the io.Seeker interface. |
| func (r *Reader) Seek(offset int64, whence int) (int64, error) { |
| r.prevRune = -1 |
| var abs int64 |
| switch whence { |
| case io.SeekStart: |
| abs = offset |
| case io.SeekCurrent: |
| abs = r.i + offset |
| case io.SeekEnd: |
| abs = int64(len(r.s)) + offset |
| default: |
| return 0, errors.New("strings.Reader.Seek: invalid whence") |
| } |
| if abs < 0 { |
| return 0, errors.New("strings.Reader.Seek: negative position") |
| } |
| r.i = abs |
| return abs, nil |
| } |
| |
| // WriteTo implements the io.WriterTo interface. |
| func (r *Reader) WriteTo(w io.Writer) (n int64, err error) { |
| r.prevRune = -1 |
| if r.i >= int64(len(r.s)) { |
| return 0, nil |
| } |
| s := r.s[r.i:] |
| m, err := io.WriteString(w, s) |
| if m > len(s) { |
| panic("strings.Reader.WriteTo: invalid WriteString count") |
| } |
| r.i += int64(m) |
| n = int64(m) |
| if m != len(s) && err == nil { |
| err = io.ErrShortWrite |
| } |
| return |
| } |
| |
| // Reset resets the Reader to be reading from s. |
| func (r *Reader) Reset(s string) { *r = Reader{s, 0, -1} } |
| |
| // NewReader returns a new Reader reading from s. |
| // It is similar to bytes.NewBufferString but more efficient and non-writable. |
| func NewReader(s string) *Reader { return &Reader{s, 0, -1} } |