jldb/mdb/pfile/page.go

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