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segment_reader.go
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/
segment_reader.go
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// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package xio
import (
"io"
"github.com/m3db/m3/src/dbnode/ts"
"github.com/m3db/m3/src/x/pool"
)
type segmentReader struct {
segment ts.Segment
lazyHead []byte
lazyTail []byte
si int
pool SegmentReaderPool
}
// NewSegmentReader creates a new segment reader along with a specified segment.
func NewSegmentReader(segment ts.Segment) SegmentReader {
return &segmentReader{segment: segment}
}
func (sr *segmentReader) Clone(
pool pool.CheckedBytesPool,
) (SegmentReader, error) {
return NewSegmentReader(sr.segment.Clone(pool)), nil
}
func (sr *segmentReader) Read(b []byte) (int, error) {
if len(b) == 0 {
return 0, nil
}
if b := sr.segment.Head; b != nil && len(sr.lazyHead) == 0 {
sr.lazyHead = b.Bytes()
}
if b := sr.segment.Tail; b != nil && len(sr.lazyTail) == 0 {
sr.lazyTail = b.Bytes()
}
nh, nt := len(sr.lazyHead), len(sr.lazyTail)
if sr.si >= nh+nt {
return 0, io.EOF
}
n := 0
if sr.si < nh {
nRead := copy(b, sr.lazyHead[sr.si:])
sr.si += nRead
n += nRead
if n == len(b) {
return n, nil
}
}
if sr.si < nh+nt {
nRead := copy(b[n:], sr.lazyTail[sr.si-nh:])
sr.si += nRead
n += nRead
}
if n == 0 {
return 0, io.EOF
}
return n, nil
}
func (sr *segmentReader) Segment() (ts.Segment, error) {
return sr.segment, nil
}
func (sr *segmentReader) Reset(segment ts.Segment) {
sr.segment = segment
sr.si = 0
sr.lazyHead = sr.lazyHead[:0]
sr.lazyTail = sr.lazyTail[:0]
}
func (sr *segmentReader) Finalize() {
sr.segment.Finalize()
sr.lazyHead = nil
sr.lazyTail = nil
if pool := sr.pool; pool != nil {
pool.Put(sr)
}
}