mirror of https://github.com/k3s-io/k3s
118 lines
3.3 KiB
Go
118 lines
3.3 KiB
Go
// Copyright 2016 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ioutil
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import (
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"io"
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)
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var defaultBufferBytes = 128 * 1024
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// PageWriter implements the io.Writer interface so that writes will
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// either be in page chunks or from flushing.
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type PageWriter struct {
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w io.Writer
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// pageOffset tracks the page offset of the base of the buffer
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pageOffset int
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// pageBytes is the number of bytes per page
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pageBytes int
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// bufferedBytes counts the number of bytes pending for write in the buffer
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bufferedBytes int
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// buf holds the write buffer
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buf []byte
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// bufWatermarkBytes is the number of bytes the buffer can hold before it needs
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// to be flushed. It is less than len(buf) so there is space for slack writes
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// to bring the writer to page alignment.
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bufWatermarkBytes int
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}
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// NewPageWriter creates a new PageWriter. pageBytes is the number of bytes
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// to write per page. pageOffset is the starting offset of io.Writer.
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func NewPageWriter(w io.Writer, pageBytes, pageOffset int) *PageWriter {
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return &PageWriter{
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w: w,
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pageOffset: pageOffset,
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pageBytes: pageBytes,
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buf: make([]byte, defaultBufferBytes+pageBytes),
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bufWatermarkBytes: defaultBufferBytes,
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}
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}
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func (pw *PageWriter) Write(p []byte) (n int, err error) {
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if len(p)+pw.bufferedBytes <= pw.bufWatermarkBytes {
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// no overflow
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copy(pw.buf[pw.bufferedBytes:], p)
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pw.bufferedBytes += len(p)
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return len(p), nil
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}
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// complete the slack page in the buffer if unaligned
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slack := pw.pageBytes - ((pw.pageOffset + pw.bufferedBytes) % pw.pageBytes)
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if slack != pw.pageBytes {
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partial := slack > len(p)
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if partial {
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// not enough data to complete the slack page
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slack = len(p)
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}
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// special case: writing to slack page in buffer
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copy(pw.buf[pw.bufferedBytes:], p[:slack])
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pw.bufferedBytes += slack
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n = slack
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p = p[slack:]
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if partial {
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// avoid forcing an unaligned flush
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return n, nil
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}
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}
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// buffer contents are now page-aligned; clear out
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if err = pw.Flush(); err != nil {
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return n, err
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}
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// directly write all complete pages without copying
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if len(p) > pw.pageBytes {
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pages := len(p) / pw.pageBytes
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c, werr := pw.w.Write(p[:pages*pw.pageBytes])
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n += c
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if werr != nil {
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return n, werr
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}
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p = p[pages*pw.pageBytes:]
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}
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// write remaining tail to buffer
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c, werr := pw.Write(p)
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n += c
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return n, werr
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}
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// Flush flushes buffered data.
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func (pw *PageWriter) Flush() error {
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_, err := pw.flush()
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return err
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}
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// FlushN flushes buffered data and returns the number of written bytes.
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func (pw *PageWriter) FlushN() (int, error) {
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return pw.flush()
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}
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func (pw *PageWriter) flush() (int, error) {
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if pw.bufferedBytes == 0 {
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return 0, nil
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}
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n, err := pw.w.Write(pw.buf[:pw.bufferedBytes])
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pw.pageOffset = (pw.pageOffset + pw.bufferedBytes) % pw.pageBytes
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pw.bufferedBytes = 0
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return n, err
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}
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