72 lines
1.4 KiB
Go
72 lines
1.4 KiB
Go
package pfile
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import (
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"hash/crc32"
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"unsafe"
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"git.crumpington.com/public/jldb/lib/errs"
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)
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// ----------------------------------------------------------------------------
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const (
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pageSize = 512
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pageHeaderSize = 40
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pageDataSize = pageSize - pageHeaderSize
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pageTypeFree = 0
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pageTypeHead = 1
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pageTypeData = 2
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)
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var emptyPage = func() dataPage {
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p := newDataPage()
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h := p.Header()
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h.CRC = p.ComputeCRC()
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return p
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}()
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// ----------------------------------------------------------------------------
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type pageHeader struct {
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CRC uint32 // IEEE CRC-32 checksum.
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PageType uint32 // One of the PageType* constants.
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CollectionID uint64 //
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ItemID uint64
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DataSize uint64
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NextPage uint64
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}
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// ----------------------------------------------------------------------------
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type dataPage []byte
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func newDataPage() dataPage {
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p := dataPage(make([]byte, pageSize))
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return p
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}
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func (p dataPage) Header() *pageHeader {
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return (*pageHeader)(unsafe.Pointer(&p[0]))
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}
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func (p dataPage) ComputeCRC() uint32 {
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return crc32.ChecksumIEEE(p[4:])
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}
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func (p dataPage) Data() []byte {
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return p[pageHeaderSize:]
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}
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func (p dataPage) Write(data []byte) int {
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return copy(p[pageHeaderSize:], data)
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}
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func (p dataPage) Validate() error {
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header := p.Header()
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if header.CRC != p.ComputeCRC() {
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return errs.Corrupt.WithMsg("CRC mismatch on data page.")
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}
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return nil
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}
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