kraken

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// Copyright (c) 2016-2019 Uber Technologies, Inc.
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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 rwutil
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import (
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	"bytes"
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	"fmt"
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	"io"
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	"github.com/aws/aws-sdk-go/aws"
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	"github.com/uber/kraken/utils/memsize"
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)
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type exceededCapError error
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// CappedBuffer is a buffer that returns errors if the buffer exceeds cap.
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type CappedBuffer struct {
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	capacity int64
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	buffer   *aws.WriteAtBuffer
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}
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// NewCappedBuffer creates a new CappedBuffer with the given capacity
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func NewCappedBuffer(capacity int) *CappedBuffer {
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	return &CappedBuffer{capacity: int64(capacity), buffer: aws.NewWriteAtBuffer([]byte{})}
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}
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// WriteAt writes the slice of bytes into CappedBuffer at given position
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func (b *CappedBuffer) WriteAt(p []byte, pos int64) (n int, err error) {
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	if pos+int64(len(p)) > b.capacity {
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		return 0, exceededCapError(
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			fmt.Errorf("buffer exceed max capacity %s", memsize.Format(uint64(b.capacity))))
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	}
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	return b.buffer.WriteAt(p, pos)
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}
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// DrainInto copies/drains/empties contents of CappedBuffer into dst
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func (b *CappedBuffer) DrainInto(dst io.Writer) error {
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	if _, err := io.Copy(dst, bytes.NewReader(b.buffer.Bytes())); err != nil {
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		return fmt.Errorf("drain buffer: %s", err)
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	}
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	return nil
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}
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