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writer.go
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writer.go
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// Copyright 2015 The LUCI 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 recordio
import (
"bytes"
"encoding/binary"
"io"
)
func writeFrameHeader(w io.Writer, frameSize uint64) (int, error) {
sizeBuf := make([]byte, binary.MaxVarintLen64)
return w.Write(sizeBuf[:binary.PutUvarint(sizeBuf, frameSize)])
}
// WriteFrame writes a single frame to an io.Writer.
func WriteFrame(w io.Writer, frame []byte) (int, error) {
count, err := writeFrameHeader(w, uint64(len(frame)))
if err != nil {
return count, err
}
amount, err := w.Write(frame)
count += amount
if err != nil {
return count, err
}
return count, nil
}
// Writer implements the io.Writer interface. Data written to the Writer is
// translated into a series of frames. Each frame is spearated by a call to
// Flush.
//
// Frame boundaries are created by calling Flush. Flush will always write a
// frame, even if the frame's data size is zero.
//
// Data written over consecutive Write calls belongs to the same frame. It is
// buffered until a frame boundary is created via Flush().
type Writer interface {
io.Writer
// Flush writes the buffered frame
Flush() error
// Reset clears the writer state and attaches it to a new inner Writer
// instance.
Reset(io.Writer)
}
// writer implements the Writer interface by wrapping an io.Writer.
type writer struct {
inner io.Writer
buf bytes.Buffer
}
// NewWriter creates a new Writer instance that data as frames to an underlying
// io.Writer.
func NewWriter(w io.Writer) Writer {
return &writer{
inner: w,
}
}
func (w *writer) Write(data []byte) (int, error) {
return w.buf.Write(data)
}
func (w *writer) Flush() error {
_, err := WriteFrame(w.inner, w.buf.Bytes())
if err != nil {
return err
}
w.buf.Reset()
return nil
}
func (w *writer) Reset(inner io.Writer) {
w.inner = inner
w.buf.Reset()
}