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Diffstat (limited to 'internal/contentenc/intrablock.go')
-rw-r--r--internal/contentenc/intrablock.go51
1 files changed, 51 insertions, 0 deletions
diff --git a/internal/contentenc/intrablock.go b/internal/contentenc/intrablock.go
new file mode 100644
index 0000000..330b980
--- /dev/null
+++ b/internal/contentenc/intrablock.go
@@ -0,0 +1,51 @@
+package contentenc
+
+// intraBlock identifies a part of a file block
+type intraBlock struct {
+ BlockNo uint64 // Block number in file
+ Skip uint64 // Offset into block plaintext
+ Length uint64 // Length of data from this block
+ 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
+}
+
+// CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
+// (complete block)
+func (ib *intraBlock) CiphertextRange() (offset uint64, length uint64) {
+ 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.fs.BlockNoToPlainOff(ib.BlockNo), 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.Skip + ib.Length)
+ if lenHave < lenWant {
+ return d[ib.Skip:lenHave]
+ }
+ 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
+}