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147 lines
2.8 KiB
147 lines
2.8 KiB
// Copyright 2015, Joe Tsai. 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.md file.
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package prefix
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import (
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"bytes"
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"io"
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"strings"
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)
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// For some of the common Readers, we wrap and extend them to satisfy the
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// compress.BufferedReader interface to improve performance.
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type buffer struct {
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*bytes.Buffer
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}
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type bytesReader struct {
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*bytes.Reader
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pos int64
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buf []byte
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arr [512]byte
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}
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type stringReader struct {
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*strings.Reader
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pos int64
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buf []byte
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arr [512]byte
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}
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func (r *buffer) Buffered() int {
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return r.Len()
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}
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func (r *buffer) Peek(n int) ([]byte, error) {
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b := r.Bytes()
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if len(b) < n {
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return b, io.EOF
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}
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return b[:n], nil
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}
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func (r *buffer) Discard(n int) (int, error) {
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b := r.Next(n)
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if len(b) < n {
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return len(b), io.EOF
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}
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return n, nil
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}
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func (r *bytesReader) Buffered() int {
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r.update()
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if r.Len() > len(r.buf) {
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return len(r.buf)
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}
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return r.Len()
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}
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func (r *bytesReader) Peek(n int) ([]byte, error) {
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if n > len(r.arr) {
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return nil, io.ErrShortBuffer
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}
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// Return sub-slice of local buffer if possible.
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r.update()
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if len(r.buf) >= n {
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return r.buf[:n], nil
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}
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// Fill entire local buffer, and return appropriate sub-slice.
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cnt, err := r.ReadAt(r.arr[:], r.pos)
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r.buf = r.arr[:cnt]
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if cnt < n {
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return r.arr[:cnt], err
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}
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return r.arr[:n], nil
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}
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func (r *bytesReader) Discard(n int) (int, error) {
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var err error
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if n > r.Len() {
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n, err = r.Len(), io.EOF
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}
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r.Seek(int64(n), io.SeekCurrent)
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return n, err
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}
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// update reslices the internal buffer to be consistent with the read offset.
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func (r *bytesReader) update() {
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pos, _ := r.Seek(0, io.SeekCurrent)
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if off := pos - r.pos; off >= 0 && off < int64(len(r.buf)) {
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r.buf, r.pos = r.buf[off:], pos
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} else {
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r.buf, r.pos = nil, pos
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}
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}
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func (r *stringReader) Buffered() int {
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r.update()
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if r.Len() > len(r.buf) {
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return len(r.buf)
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}
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return r.Len()
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}
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func (r *stringReader) Peek(n int) ([]byte, error) {
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if n > len(r.arr) {
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return nil, io.ErrShortBuffer
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}
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// Return sub-slice of local buffer if possible.
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r.update()
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if len(r.buf) >= n {
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return r.buf[:n], nil
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}
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// Fill entire local buffer, and return appropriate sub-slice.
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cnt, err := r.ReadAt(r.arr[:], r.pos)
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r.buf = r.arr[:cnt]
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if cnt < n {
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return r.arr[:cnt], err
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}
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return r.arr[:n], nil
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}
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func (r *stringReader) Discard(n int) (int, error) {
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var err error
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if n > r.Len() {
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n, err = r.Len(), io.EOF
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}
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r.Seek(int64(n), io.SeekCurrent)
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return n, err
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}
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// update reslices the internal buffer to be consistent with the read offset.
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func (r *stringReader) update() {
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pos, _ := r.Seek(0, io.SeekCurrent)
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if off := pos - r.pos; off >= 0 && off < int64(len(r.buf)) {
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r.buf, r.pos = r.buf[off:], pos
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} else {
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r.buf, r.pos = nil, pos
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}
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}
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