wehub-resource-sync
94 lines
2.3 KiB
Go
94 lines
2.3 KiB
Go
// Copyright 2025 Dolthub, 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 file
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import (
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"github.com/edsrzf/mmap-go"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"os"
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"runtime"
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)
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const (
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uint64Size = 8
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uint32Size = 4
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)
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// MmapData holds both the page-aligned mapped region, and the actual requested data range
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type MmapData struct {
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data []byte
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originalData mmap.MMap
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}
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var mmapAlignment = int64(os.Getpagesize())
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func (m MmapData) GetUint64(offset uint64) uint64 {
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return binary.BigEndian.Uint64(m.data[offset : offset+uint64Size])
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}
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func (m MmapData) GetUint32(offset uint64) uint32 {
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return binary.BigEndian.Uint32(m.data[offset : offset+uint32Size])
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}
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func (m *MmapData) ReadAt(p []byte, off int64) (int, error) {
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if m.data == nil {
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return 0, errors.New("mmap: closed")
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}
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if off < 0 || int64(len(m.data)) < off {
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return 0, fmt.Errorf("mmap: invalid ReadAt offset %d", off)
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}
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n := copy(p, m.data[off:])
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if n < len(p) {
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return n, io.EOF
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}
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return n, nil
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}
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func Mmap(file *os.File, offset int64, length int) (reader *MmapData, err error) {
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// Align offset to page boundary
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alignedOffset := offset & ^(mmapAlignment - 1)
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adjustment := offset - alignedOffset
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adjustedLength := length + int(adjustment)
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// Map the region
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mappedData, err := mmap.MapRegion(file, adjustedLength, mmap.RDONLY, 0, alignedOffset)
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if err != nil {
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return &MmapData{}, err
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}
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// Return the adjusted slice starting at the actual offset
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reader = &MmapData{
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data: mappedData[adjustment : adjustment+int64(length)],
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originalData: mappedData,
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}
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runtime.SetFinalizer(reader, (*MmapData).Close)
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return reader, err
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}
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func (m *MmapData) Close() error {
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if m.data == nil {
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return nil
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}
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m.data = nil
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originalData := m.originalData
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m.originalData = nil
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return originalData.Unmap()
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}
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