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Diffstat (limited to 'internal/contentenc/offsets.go')
-rw-r--r--internal/contentenc/offsets.go97
1 files changed, 97 insertions, 0 deletions
diff --git a/internal/contentenc/offsets.go b/internal/contentenc/offsets.go
new file mode 100644
index 0000000..1b5952f
--- /dev/null
+++ b/internal/contentenc/offsets.go
@@ -0,0 +1,97 @@
+package contentenc
+
+import (
+ "github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+
+// Contentenc methods that translate offsets between ciphertext and plaintext
+
+// get the block number at plain-text offset
+func (be *ContentEnc) PlainOffToBlockNo(plainOffset uint64) uint64 {
+ return plainOffset / be.plainBS
+}
+
+// get the block number at ciphter-text offset
+func (be *ContentEnc) CipherOffToBlockNo(cipherOffset uint64) uint64 {
+ return (cipherOffset - HEADER_LEN) / be.cipherBS
+}
+
+// get ciphertext offset of block "blockNo"
+func (be *ContentEnc) BlockNoToCipherOff(blockNo uint64) uint64 {
+ return HEADER_LEN + blockNo*be.cipherBS
+}
+
+// get plaintext offset of block "blockNo"
+func (be *ContentEnc) BlockNoToPlainOff(blockNo uint64) uint64 {
+ return blockNo * be.plainBS
+}
+
+// PlainSize - calculate plaintext size from ciphertext size
+func (be *ContentEnc) CipherSizeToPlainSize(cipherSize uint64) uint64 {
+
+ // Zero sized files stay zero-sized
+ if cipherSize == 0 {
+ return 0
+ }
+
+ if cipherSize == HEADER_LEN {
+ toggledlog.Warn.Printf("cipherSize %d == header size: interrupted write?\n", cipherSize)
+ return 0
+ }
+
+ if cipherSize < HEADER_LEN {
+ toggledlog.Warn.Printf("cipherSize %d < header size: corrupt file\n", cipherSize)
+ return 0
+ }
+
+ // Block number at last byte
+ blockNo := be.CipherOffToBlockNo(cipherSize - 1)
+ blockCount := blockNo + 1
+
+ overhead := be.BlockOverhead()*blockCount + HEADER_LEN
+
+ return cipherSize - overhead
+}
+
+// CipherSize - calculate ciphertext size from plaintext size
+func (be *ContentEnc) PlainSizeToCipherSize(plainSize uint64) uint64 {
+
+ // Block number at last byte
+ blockNo := be.PlainOffToBlockNo(plainSize - 1)
+ blockCount := blockNo + 1
+
+ overhead := be.BlockOverhead()*blockCount + HEADER_LEN
+
+ return plainSize + overhead
+}
+
+// Split a plaintext byte range into (possibly partial) blocks
+func (be *ContentEnc) ExplodePlainRange(offset uint64, length uint64) []intraBlock {
+ var blocks []intraBlock
+ var nextBlock intraBlock
+ nextBlock.fs = be
+
+ for length > 0 {
+ nextBlock.BlockNo = be.PlainOffToBlockNo(offset)
+ nextBlock.Skip = offset - be.BlockNoToPlainOff(nextBlock.BlockNo)
+
+ // Minimum of remaining data and remaining space in the block
+ nextBlock.Length = MinUint64(length, be.plainBS-nextBlock.Skip)
+
+ blocks = append(blocks, nextBlock)
+ offset += nextBlock.Length
+ length -= nextBlock.Length
+ }
+ return blocks
+}
+
+func (be *ContentEnc) BlockOverhead() uint64 {
+ return be.cipherBS - be.plainBS
+}
+
+func MinUint64(x uint64, y uint64) uint64 {
+ if x < y {
+ return x
+ }
+ return y
+}