Move oscore parse code to Oscore.kt, add constants

Author: zalenskivolt

koap-core/src/commonMain/kotlin/Message.kt

@@ -626,49 +626,10 @@ sealed class Message {
                 return "Oscore($args)"
             }
 
-            fun optionValue(): ByteArray {
-                val partialIvLength = partialIv.size
-                if (partialIvLength > 5) {
-                    throw IllegalArgumentException("Partial IV length of $partialIvLength is outside allowable range of 0..5")
-                }
-                val kidContextLength = if (kidContext != null) kidContext.size else 0
-                val kidFlag = if (kid != null) 0x08 else 0
-                val kidContextFlag = if (kidContext != null) 0x10 else 0
-                val flagBits = partialIvLength or kidFlag or kidContextFlag
-                if (flagBits == 0) {
-                    // If the OSCORE flag bits are all zero (0x00), the option value SHALL be empty
-                    return byteArrayOf()
-                }
-                var value = byteArrayOf(flagBits.toByte()) + partialIv
-                if (kidContext != null) {
-                    value += byteArrayOf(kidContextLength.toByte()) + kidContext
-                }
-                if (kid != null) {
-                    value += kid
-                }
-                return value
-            }
+            fun optionValue(): ByteArray = oscoreOptionValue(this)
 
             companion object {
-                fun fromOptionValue(value: ByteArray): Oscore {
-                    if (value.size == 0) {
-                        return Oscore(byteArrayOf(), null, null)
-                    }
-                    val flagBits = value[0].toInt()
-                    val partialIvLength = flagBits and 0x07
-                    val kidFlag = (flagBits and 0x08) != 0
-                    val kidContextFlag = (flagBits and 0x10) != 0
-                    val partialIv = value.sliceArray(1 until 1 + partialIvLength)
-                    val kidContextLength = if (kidContextFlag) value[1 + partialIvLength].toInt() else 0
-                    val kidContext = if (kidContextFlag) {
-                        value.sliceArray(2 + partialIvLength until 2 + partialIvLength + kidContextLength)
-                    } else {
-                        null
-                    }
-                    val kidOffset = (if (kidContextFlag) 2 else 1) + partialIvLength + kidContextLength
-                    val kid = if (kidFlag) value.sliceArray(kidOffset until value.size) else null
-                    return Oscore(partialIv, kidContext, kid)
-                }
+                fun fromOptionValue(value: ByteArray): Oscore = oscoreFromOptionValue(value)
             }
         }
 

koap-core/src/commonMain/kotlin/Oscore.kt

@@ -0,0 +1,60 @@
+package com.juul.koap
+
+import com.juul.koap.Message.Option.Oscore
+
+private val PARTIAL_IV_LENGTH_RANGE = 0..5
+private const val PARTIAL_IV_LENGTH_MASK = 0x07
+private const val KID_FLAG = 0x08
+private const val KID_CONTEXT_FLAG = 0x10
+
+/**
+ * Creates a binary OSCORE option value from an Oscore option object.
+ *
+ * - [RFC 8613](https://tools.ietf.org/html/rfc8613#section-2) 2. The OSCORE Option
+ * - [RFC 8613](https://tools.ietf.org/html/rfc8613#section-6.1) 6.1. Encoding of the OSCORE Option Value
+ */
+internal fun oscoreOptionValue(oscore: Oscore): ByteArray {
+    val partialIvLength = oscore.partialIv.size
+    require(partialIvLength in PARTIAL_IV_LENGTH_RANGE) {
+        "Partial IV length of $partialIvLength is outside allowable range of $PARTIAL_IV_LENGTH_RANGE"
+    }
+    val kidContextLength = if (oscore.kidContext != null) oscore.kidContext.size else 0
+    val kidFlagBit = if (oscore.kid != null) KID_FLAG else 0
+    val kidContextFlagBit = if (oscore.kidContext != null) KID_CONTEXT_FLAG else 0
+    val flagBits = partialIvLength or kidFlagBit or kidContextFlagBit
+    if (flagBits == 0) {
+        // If the OSCORE flag bits are all zero (0x00), the option value SHALL be empty
+        return byteArrayOf()
+    }
+    var value = byteArrayOf(flagBits.toByte()) + oscore.partialIv
+    if (oscore.kidContext != null) {
+        value += kotlin.byteArrayOf(kidContextLength.toByte()) + oscore.kidContext
+    }
+    if (oscore.kid != null) {
+        value += oscore.kid
+    }
+    return value
+}
+
+/**
+ * Parses an Oscore option object from a binary OSCORE option value.
+ */
+internal fun oscoreFromOptionValue(value: ByteArray): Oscore {
+    if (value.size == 0) {
+        return Oscore(byteArrayOf(), null, null)
+    }
+    val flagBits = value[0].toInt()
+    val partialIvLength = flagBits and PARTIAL_IV_LENGTH_MASK
+    val kidFlag = (flagBits and KID_FLAG) != 0
+    val kidContextFlag = (flagBits and KID_CONTEXT_FLAG) != 0
+    val partialIv = value.sliceArray(1 until 1 + partialIvLength)
+    val kidContextLength = if (kidContextFlag) value[1 + partialIvLength].toInt() else 0
+    val kidContext = if (kidContextFlag) {
+        value.sliceArray(2 + partialIvLength until 2 + partialIvLength + kidContextLength)
+    } else {
+        null
+    }
+    val kidOffset = (if (kidContextFlag) 2 else 1) + partialIvLength + kidContextLength
+    val kid = if (kidFlag) value.sliceArray(kidOffset until value.size) else null
+    return Oscore(partialIv, kidContext, kid)
+}