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// Copyright 2015 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package wal
import (
"encoding/binary"
"hash"
"io"
"os"
"sync"
"github.com/coreos/etcd/pkg/crc"
"github.com/coreos/etcd/pkg/ioutil"
"github.com/coreos/etcd/wal/walpb"
)
// walPageBytes is the alignment for flushing records to the backing Writer.
// It should be a multiple of the minimum sector size so that WAL can safely
// distinguish between torn writes and ordinary data corruption.
const walPageBytes = 8 * minSectorSize
type encoder struct {
mu sync.Mutex
bw *ioutil.PageWriter
crc hash.Hash32
buf []byte
uint64buf []byte
}
func newEncoder(w io.Writer, prevCrc uint32, pageOffset int) *encoder {
return &encoder{
bw: ioutil.NewPageWriter(w, walPageBytes, pageOffset),
crc: crc.New(prevCrc, crcTable),
// 1MB buffer
buf: make([]byte, 1024*1024),
uint64buf: make([]byte, 8),
}
}
// newFileEncoder creates a new encoder with current file offset for the page writer.
func newFileEncoder(f *os.File, prevCrc uint32) (*encoder, error) {
offset, err := f.Seek(0, io.SeekCurrent)
if err != nil {
return nil, err
}
return newEncoder(f, prevCrc, int(offset)), nil
}
func (e *encoder) encode(rec *walpb.Record) error {
e.mu.Lock()
defer e.mu.Unlock()
e.crc.Write(rec.Data)
rec.Crc = e.crc.Sum32()
var (
data []byte
err error
n int
)
if rec.Size() > len(e.buf) {
data, err = rec.Marshal()
if err != nil {
return err
}
} else {
n, err = rec.MarshalTo(e.buf)
if err != nil {
return err
}
data = e.buf[:n]
}
lenField, padBytes := encodeFrameSize(len(data))
if err = writeUint64(e.bw, lenField, e.uint64buf); err != nil {
return err
}
if padBytes != 0 {
data = append(data, make([]byte, padBytes)...)
}
_, err = e.bw.Write(data)
return err
}
func encodeFrameSize(dataBytes int) (lenField uint64, padBytes int) {
lenField = uint64(dataBytes)
// force 8 byte alignment so length never gets a torn write
padBytes = (8 - (dataBytes % 8)) % 8
if padBytes != 0 {
lenField |= uint64(0x80|padBytes) << 56
}
return lenField, padBytes
}
func (e *encoder) flush() error {
e.mu.Lock()
defer e.mu.Unlock()
return e.bw.Flush()
}
func writeUint64(w io.Writer, n uint64, buf []byte) error {
// http://golang.org/src/encoding/binary/binary.go
binary.LittleEndian.PutUint64(buf, n)
_, err := w.Write(buf)
return err
}
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