pathiv: move block IV algorithm into this package

This was implemented in fusefrontend_reverse, but we need it
in fusefrontend as well. Move the algorithm into pathiv.BlockIV().

1 files changed, 28 insertions, 0 deletions

diff --git a/internal/pathiv/pathiv_test.go b/internal/pathiv/pathiv_test.go
new file mode 100644
index 0000000..0cecba1
--- /dev/null
+++ b/internal/pathiv/pathiv_test.go
@@ -0,0 +1,28 @@
+package pathiv
+
+import (
+	"bytes"
+	"encoding/hex"
+	"testing"
+)
+
+// TestBlockIV makes sure we don't change the block iv derivation algorithm "BlockIV()"
+// inadvertedly.
+func TestBlockIV(t *testing.T) {
+	b0 := make([]byte, 16)
+	b0x := BlockIV(b0, 0)
+	if !bytes.Equal(b0, b0x) {
+		t.Errorf("b0x should be equal to b0")
+	}
+	b27 := BlockIV(b0, 0x27)
+	expected, _ := hex.DecodeString("00000000000000000000000000000027")
+	if !bytes.Equal(b27, expected) {
+		t.Error()
+	}
+	bff := bytes.Repeat([]byte{0xff}, 16)
+	b28 := BlockIV(bff, 0x28)
+	expected, _ = hex.DecodeString("ffffffffffffffff0000000000000027")
+	if !bytes.Equal(b28, expected) {
+		t.Errorf("\nhave=%s\nwant=%s", hex.EncodeToString(b28), hex.EncodeToString(expected))
+	}
+}