52 lines
1.6 KiB
Go
52 lines
1.6 KiB
Go
package contentenc
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// intraBlock identifies a part of a file block
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type intraBlock struct {
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BlockNo uint64 // Block number in file
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Skip uint64 // Offset into block plaintext
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Length uint64 // Length of data from this block
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fs *ContentEnc
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}
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// isPartial - is the block partial? This means we have to do read-modify-write.
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func (ib *intraBlock) IsPartial() bool {
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if ib.Skip > 0 || ib.Length < ib.fs.plainBS {
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return true
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}
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return false
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}
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// CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
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// (complete block)
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func (ib *intraBlock) CiphertextRange() (offset uint64, length uint64) {
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return ib.fs.BlockNoToCipherOff(ib.BlockNo), ib.fs.cipherBS
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}
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// PlaintextRange - get byte range in plaintext corresponding to BlockNo
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// (complete block)
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func (ib *intraBlock) PlaintextRange() (offset uint64, length uint64) {
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return ib.fs.BlockNoToPlainOff(ib.BlockNo), ib.fs.plainBS
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}
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// CropBlock - crop a potentially larger plaintext block down to the relevant part
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func (ib *intraBlock) CropBlock(d []byte) []byte {
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lenHave := len(d)
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lenWant := int(ib.Skip + ib.Length)
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if lenHave < lenWant {
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return d[ib.Skip:lenHave]
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}
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return d[ib.Skip:lenWant]
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}
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// Ciphertext range corresponding to the sum of all "blocks" (complete blocks)
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func (ib *intraBlock) JointCiphertextRange(blocks []intraBlock) (offset uint64, length uint64) {
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firstBlock := blocks[0]
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lastBlock := blocks[len(blocks)-1]
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offset = ib.fs.BlockNoToCipherOff(firstBlock.BlockNo)
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offsetLast := ib.fs.BlockNoToCipherOff(lastBlock.BlockNo)
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length = offsetLast + ib.fs.cipherBS - offset
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return offset, length
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}
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