72 lines
2.2 KiB
Go
72 lines
2.2 KiB
Go
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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 is the block number in the file
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BlockNo uint64
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// Skip is an offset into the block payload
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// In forward mode: block plaintext
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// In reverse mode: offset into block ciphertext. Takes the header into
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// account.
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Skip uint64
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// Length of payload data in this block
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// In forward mode: length of the plaintext
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// In reverse mode: length of the ciphertext. Takes header and trailer into
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// account.
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Length uint64
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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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// BlockCipherOff returns the ciphertext offset corresponding to BlockNo
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func (ib *IntraBlock) BlockCipherOff() (offset uint64) {
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return ib.fs.BlockNoToCipherOff(ib.BlockNo)
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}
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// BlockPlainOff returns the plaintext offset corresponding to BlockNo
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func (ib *IntraBlock) BlockPlainOff() (offset uint64) {
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return ib.fs.BlockNoToPlainOff(ib.BlockNo)
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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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// JointCiphertextRange is the ciphertext range corresponding to the sum of all
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// "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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// JointPlaintextRange is the plaintext range corresponding to the sum of all
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// "blocks" (complete blocks)
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func JointPlaintextRange(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 = firstBlock.BlockPlainOff()
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length = lastBlock.BlockPlainOff() + lastBlock.fs.PlainBS() - offset
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return offset, length
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}
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