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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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.
//go:build !windows
// +build !windows
package file
import (
"io"
"github.com/apache/arrow-go/v18/parquet"
"golang.org/x/exp/mmap"
"golang.org/x/xerrors"
)
func mmapOpen(filename string) (parquet.ReaderAtSeeker, error) {
rdr, err := mmap.Open(filename)
if err != nil {
return nil, err
}
return &mmapAdapter{rdr, 0}, nil
}
// an adapter for mmap'd files
type mmapAdapter struct {
*mmap.ReaderAt
pos int64
}
func (m *mmapAdapter) Close() error {
return m.ReaderAt.Close()
}
func (m *mmapAdapter) ReadAt(p []byte, off int64) (int, error) {
return m.ReaderAt.ReadAt(p, off)
}
func (m *mmapAdapter) Read(p []byte) (n int, err error) {
n, err = m.ReaderAt.ReadAt(p, m.pos)
m.pos += int64(n)
return
}
func (m *mmapAdapter) Seek(offset int64, whence int) (int64, error) {
newPos, offs := int64(0), offset
switch whence {
case io.SeekStart:
newPos = offs
case io.SeekCurrent:
newPos = m.pos + offs
case io.SeekEnd:
newPos = int64(m.ReaderAt.Len()) + offs
}
if newPos < 0 {
return 0, xerrors.New("negative result pos")
}
if newPos > int64(m.ReaderAt.Len()) {
return 0, xerrors.New("new position exceeds size of file")
}
m.pos = newPos
return newPos, nil
}
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