Contrail reworked and finished

src/commonMain/kotlin/net/sergeych/crypto2/Contrail.kt

@@ -0,0 +1,30 @@
+package net.sergeych.crypto2
+
+import net.sergeych.bintools.CRC
+
+/**
+ * The crc8-protected binary data manipulation. It uses crc8-bluetooth polynomial (0xA7)
+ * flavor. Note that crc8 provides good protection only for relatively small data sets.
+ */
+object Contrail {
+
+    /**
+     *  Create a contrail by adding a crc byte to the end of [data]. The Result is always one byte longer.
+     */
+    fun create(data: UByteArray): UByteArray = data + CRC.crc8(data.toByteArray())
+
+    /**
+     * Check the contrail is valid.
+     */
+    fun isValid(data: UByteArray): Boolean = CRC.crc8(
+        data.copyOfRange(0, data.size - 1).toByteArray()
+    ) == data.last()
+
+
+    /**
+     * Check that the contrail is valid and extracts its data
+     * @return the data without crc or null if it is not valid
+     */
+    fun unpack(contrailData: UByteArray): UByteArray? =
+        if (isValid(contrailData)) contrailData.sliceArray(0..<contrailData.size - 1) else null
+}

src/commonMain/kotlin/net/sergeych/crypto2/contrail.kt

@@ -1,9 +0,0 @@
-package net.sergeych.crypto2
-
-import net.sergeych.bintools.CRC
-
-fun isValidContrail(data: UByteArray): Boolean = CRC.crc8(
-    data.copyOfRange(1, data.size).toByteArray()
-) == data[0]
-
-fun createContrail(data: UByteArray): UByteArray = ubyteArrayOf(CRC.crc8(data.toByteArray())) + data

src/commonTest/kotlin/ToolsTest.kt

@@ -1,19 +1,21 @@
 import kotlinx.coroutines.test.runTest
+import net.sergeych.crypto2.Contrail
 import net.sergeych.crypto2.NumericNonce
-import net.sergeych.crypto2.createContrail
 import net.sergeych.crypto2.initCrypto
-import net.sergeych.crypto2.isValidContrail
 import kotlin.test.*
 
 class ToolsTest {
     @Test
     fun testContrails() = runTest {
         initCrypto()
-        val c = createContrail(ubyteArrayOf(1u, 2u, 3u, 4u, 5u))
+        val data = ubyteArrayOf(1u, 2u, 3u, 4u, 5u)
-        assertEquals(134u, c[0])
+        val c = Contrail.create(data)
-        assertTrue { isValidContrail(c) }
+        assertTrue { Contrail.isValid(c) }
-        c[2] = 11u
+        c[2] = c[2] xor 11u
-        assertFalse { isValidContrail(c) }
+        assertFalse { Contrail.isValid(c) }
+        c[2] = c[2] xor 11u
+        assertTrue { Contrail.isValid(c) }
+        assertContentEquals(data,Contrail.unpack(c))
     }
 
     @Test