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-rw-r--r--cryptfs/intrablock.go39
1 files changed, 39 insertions, 0 deletions
diff --git a/cryptfs/intrablock.go b/cryptfs/intrablock.go
new file mode 100644
index 0000000..78fd140
--- /dev/null
+++ b/cryptfs/intrablock.go
@@ -0,0 +1,39 @@
+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]
+}