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package contentenc
// IntraBlock identifies a part of a file block
type IntraBlock struct {
// BlockNo is the block number in the file
BlockNo uint64
// Skip is an offset into the block payload
// In forward mode: block plaintext
// In reverse mode: offset into block ciphertext. Takes the header into
// account.
Skip uint64
// Length of payload data in this block
// In forward mode: length of the plaintext
// In reverse mode: length of the ciphertext. Takes header and trailer into
// account.
Length uint64
fs *ContentEnc
}
// IsPartial - is the block partial? This means we have to do read-modify-write.
func (ib *IntraBlock) IsPartial() bool {
if ib.Skip > 0 || ib.Length < ib.fs.plainBS {
return true
}
return false
}
// BlockCipherOff returns the ciphertext offset corresponding to BlockNo
func (ib *IntraBlock) BlockCipherOff() (offset uint64) {
return ib.fs.BlockNoToCipherOff(ib.BlockNo)
}
// BlockPlainOff returns the plaintext offset corresponding to BlockNo
func (ib *IntraBlock) BlockPlainOff() (offset uint64) {
return ib.fs.BlockNoToPlainOff(ib.BlockNo)
}
// CropBlock - crop a potentially larger plaintext block down to the relevant part
func (ib *IntraBlock) CropBlock(d []byte) []byte {
lenHave := len(d)
lenWant := int(ib.Skip + ib.Length)
if lenHave < lenWant {
return d[ib.Skip:lenHave]
}
return d[ib.Skip:lenWant]
}
// JointCiphertextRange is the ciphertext range corresponding to the sum of all
// "blocks" (complete blocks)
func (ib *IntraBlock) JointCiphertextRange(blocks []IntraBlock) (offset uint64, length uint64) {
firstBlock := blocks[0]
lastBlock := blocks[len(blocks)-1]
offset = ib.fs.BlockNoToCipherOff(firstBlock.BlockNo)
offsetLast := ib.fs.BlockNoToCipherOff(lastBlock.BlockNo)
length = offsetLast + ib.fs.cipherBS - offset
return offset, length
}
// JointPlaintextRange is the plaintext range corresponding to the sum of all
// "blocks" (complete blocks)
func JointPlaintextRange(blocks []IntraBlock) (offset uint64, length uint64) {
firstBlock := blocks[0]
lastBlock := blocks[len(blocks)-1]
offset = firstBlock.BlockPlainOff()
length = lastBlock.BlockPlainOff() + lastBlock.fs.PlainBS() - offset
return offset, length
}
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