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71 lines
2.2 KiB
71 lines
2.2 KiB
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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