145 lines
3.0 KiB
Go
145 lines
3.0 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package strings
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import (
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"errors"
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"io"
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"unicode/utf8"
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)
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// A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo,
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// io.ByteScanner, and io.RuneScanner interfaces by reading
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// from a string.
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type Reader struct {
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s string
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i int64 // current reading index
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prevRune int // index of previous rune; or < 0
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}
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// Len returns the number of bytes of the unread portion of the
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// string.
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func (r *Reader) Len() int {
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if r.i >= int64(len(r.s)) {
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return 0
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}
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return int(int64(len(r.s)) - r.i)
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}
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func (r *Reader) Read(b []byte) (n int, err error) {
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if len(b) == 0 {
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return 0, nil
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}
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if r.i >= int64(len(r.s)) {
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return 0, io.EOF
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}
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r.prevRune = -1
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n = copy(b, r.s[r.i:])
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r.i += int64(n)
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return
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}
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func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
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// cannot modify state - see io.ReaderAt
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if off < 0 {
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return 0, errors.New("strings.Reader.ReadAt: negative offset")
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}
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if off >= int64(len(r.s)) {
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return 0, io.EOF
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}
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n = copy(b, r.s[off:])
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if n < len(b) {
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err = io.EOF
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}
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return
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}
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func (r *Reader) ReadByte() (b byte, err error) {
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r.prevRune = -1
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if r.i >= int64(len(r.s)) {
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return 0, io.EOF
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}
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b = r.s[r.i]
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r.i++
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return
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}
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func (r *Reader) UnreadByte() error {
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r.prevRune = -1
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if r.i <= 0 {
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return errors.New("strings.Reader.UnreadByte: at beginning of string")
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}
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r.i--
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return nil
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}
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func (r *Reader) ReadRune() (ch rune, size int, err error) {
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if r.i >= int64(len(r.s)) {
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r.prevRune = -1
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return 0, 0, io.EOF
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}
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r.prevRune = int(r.i)
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if c := r.s[r.i]; c < utf8.RuneSelf {
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r.i++
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return rune(c), 1, nil
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}
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ch, size = utf8.DecodeRuneInString(r.s[r.i:])
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r.i += int64(size)
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return
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}
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func (r *Reader) UnreadRune() error {
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if r.prevRune < 0 {
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return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
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}
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r.i = int64(r.prevRune)
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r.prevRune = -1
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return nil
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}
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// Seek implements the io.Seeker interface.
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func (r *Reader) Seek(offset int64, whence int) (int64, error) {
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r.prevRune = -1
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var abs int64
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switch whence {
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case 0:
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abs = offset
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case 1:
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abs = int64(r.i) + offset
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case 2:
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abs = int64(len(r.s)) + offset
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default:
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return 0, errors.New("strings.Reader.Seek: invalid whence")
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}
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if abs < 0 {
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return 0, errors.New("strings.Reader.Seek: negative position")
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}
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r.i = abs
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return abs, nil
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}
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// WriteTo implements the io.WriterTo interface.
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func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
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r.prevRune = -1
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if r.i >= int64(len(r.s)) {
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return 0, nil
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}
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s := r.s[r.i:]
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m, err := io.WriteString(w, s)
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if m > len(s) {
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panic("strings.Reader.WriteTo: invalid WriteString count")
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}
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r.i += int64(m)
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n = int64(m)
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if m != len(s) && err == nil {
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err = io.ErrShortWrite
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}
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return
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}
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// NewReader returns a new Reader reading from s.
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// It is similar to bytes.NewBufferString but more efficient and read-only.
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func NewReader(s string) *Reader { return &Reader{s, 0, -1} }
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