Refactor ciphertext <-> plaintext offset translation functions

Move all the intelligence into the new file address_translation.go.
That the calculations were spread out too much became apparent when adding
the file header. This should make the code much easier to modify in the
future.

1 files changed, 14 insertions, 2 deletions

diff --git a/cryptfs/intrablock.go b/cryptfs/intrablock.go
index c83976c..faff471 100644
--- a/cryptfs/intrablock.go
+++ b/cryptfs/intrablock.go
@@ -19,13 +19,13 @@ func (ib *intraBlock) IsPartial() bool {
 // CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
 // (complete block)
 func (ib *intraBlock) CiphertextRange() (offset uint64, length uint64) {
-	return HEADER_LEN + ib.BlockNo * ib.fs.cipherBS, ib.fs.cipherBS
+	return ib.fs.BlockNoToCipherOff(ib.BlockNo), 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
+	return ib.fs.BlockNoToPlainOff(ib.BlockNo), ib.fs.plainBS
 }
 
 // CropBlock - crop a potentially larger plaintext block down to the relevant part
@@ -37,3 +37,15 @@ func (ib *intraBlock) CropBlock(d []byte) []byte {
 	}
 	return d[ib.Skip:lenWant]
 }
+
+// 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
+}