libgocryptfs/cryptfs/intrablock.go

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2015-09-05 20:30:20 +02:00
package cryptfs
// intraBlock identifies a part of a file block
type intraBlock struct {
BlockNo uint64 // Block number in file
Offset uint64 // Offset into block plaintext
Length uint64 // Length of data from this block
fs *CryptFS
}
// isPartial - is the block partial? This means we have to do read-modify-write.
func (ib *intraBlock) IsPartial() bool {
if ib.Offset > 0 || ib.Length < ib.fs.plainBS {
return true
}
return false
}
// CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
// (complete block)
func (ib *intraBlock) CiphertextRange() (offset uint64, length uint64) {
return ib.BlockNo * ib.fs.cipherBS, ib.fs.cipherBS
}
// PlaintextRange - get byte range in plaintext corresponding to BlockNo
// (complete block)
func (ib *intraBlock) PlaintextRange() (offset uint64, length uint64) {
return ib.BlockNo * ib.fs.plainBS, ib.fs.plainBS
}
// 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.Offset+ib.Length)
if lenHave < lenWant {
return d[ib.Offset:lenHave]
}
return d[ib.Offset:lenWant]
}