github.com/uber/kraken@v0.1.4/utils/rwutil/cappedbuffer.go (about)

     1  // Copyright (c) 2016-2019 Uber Technologies, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  package rwutil
    15  
    16  import (
    17  	"bytes"
    18  	"fmt"
    19  	"io"
    20  
    21  	"github.com/aws/aws-sdk-go/aws"
    22  
    23  	"github.com/uber/kraken/utils/memsize"
    24  )
    25  
    26  type exceededCapError error
    27  
    28  // CappedBuffer is a buffer that returns errors if the buffer exceeds cap.
    29  type CappedBuffer struct {
    30  	capacity int64
    31  	buffer   *aws.WriteAtBuffer
    32  }
    33  
    34  // NewCappedBuffer creates a new CappedBuffer with the given capacity
    35  func NewCappedBuffer(capacity int) *CappedBuffer {
    36  	return &CappedBuffer{capacity: int64(capacity), buffer: aws.NewWriteAtBuffer([]byte{})}
    37  }
    38  
    39  // WriteAt writes the slice of bytes into CappedBuffer at given position
    40  func (b *CappedBuffer) WriteAt(p []byte, pos int64) (n int, err error) {
    41  	if pos+int64(len(p)) > b.capacity {
    42  		return 0, exceededCapError(
    43  			fmt.Errorf("buffer exceed max capacity %s", memsize.Format(uint64(b.capacity))))
    44  	}
    45  	return b.buffer.WriteAt(p, pos)
    46  }
    47  
    48  // DrainInto copies/drains/empties contents of CappedBuffer into dst
    49  func (b *CappedBuffer) DrainInto(dst io.Writer) error {
    50  	if _, err := io.Copy(dst, bytes.NewReader(b.buffer.Bytes())); err != nil {
    51  		return fmt.Errorf("drain buffer: %s", err)
    52  	}
    53  	return nil
    54  }