Fix and beautify OCTET STRING class hierarchy

datatypes/src/commonMain/kotlin/at/asitplus/crypto/datatypes/asn1/Asn1Elements.kt

@@ -204,22 +204,32 @@ class Asn1Sequence(children: List<Asn1Element>) : Asn1Structure(DERTags.DER_SEQU
  * ASN.1 OCTET STRING 0x04 ([BERTags.OCTET_STRING]) containing an [Asn1Element]
  * @param children the elements to put into this sequence
  */
-class Asn1EncapsulatingOctetString(children: List<Asn1Element>) : Asn1Structure(BERTags.OCTET_STRING, children) {
+class Asn1EncapsulatingOctetString(children: List<Asn1Element>) : Asn1Structure(BERTags.OCTET_STRING, children),
+    Asn1OctetString<Asn1EncapsulatingOctetString> {
+    override val content: ByteArray by lazy {
+        children.fold(byteArrayOf()) { acc, asn1Element -> acc + asn1Element.derEncoded }
+    }
+
+    override fun unwrap() = this
+
     override fun toString() = "OCTET STRING Encapsulating" + super.toString()
 
 
     override fun prettyPrint(indent: Int) =
         (" " * indent) + "OCTET STRING Encapsulating" + super.prettyPrint(indent + 2)
-
-
-    public override val content: ByteArray get() = super.content
 }
 
 /**
  * ASN.1 OCTET STRING 0x04 ([BERTags.OCTET_STRING]) containing data, which does not decode to an [Asn1Element]
  * @param content the data to hold
  */
-class Asn1PrimitiveOctetString(content: ByteArray) : Asn1Primitive(BERTags.OCTET_STRING, content) {
+class Asn1PrimitiveOctetString(content: ByteArray) : Asn1Primitive(BERTags.OCTET_STRING, content),
+    Asn1OctetString<Asn1PrimitiveOctetString> {
+
+    override val content: ByteArray get() = super.content
+
+    override fun unwrap() = this
+
     override fun toString() = "OCTET STRING " + super.toString()
 
     override fun prettyPrint(indent: Int) = (" " * indent) + "OCTET STRING Primitive" + tlv.toString().substring(3)
@@ -247,12 +257,40 @@ open class Asn1Primitive(tag: UByte, content: ByteArray) : Asn1Element(TLV(tag,
     override fun prettyPrint(indent: Int) = (" " * indent) + "Primitive" + super.prettyPrint(indent)
 
     /**
-     * Data contained in this ASN.1 primitive in its encoded form. Requires decoding to interpret it
+     * Raw data contained in this ASN.1 primitive in its encoded form. Requires decoding to interpret it
      */
     public override val content: ByteArray
         get() = super.content
 }
 
+
+/**
+ * Interface describing an ASN.1 OCTET STRING.
+ * This is really more of a crutch, since an octet string is either an
+ *
+ *  * [Asn1Primitive] if it contains bytes, that cannot be interpreted as an ASN.1 Structure
+ *  * [Asn1Structure] if it contains one or more valid [Asn1Element]s
+ *
+ *  This interface is implemented by [Asn1PrimitiveOctetString] for the former case and by [Asn1EncapsulatingOctetString] to cover the latter case
+ *  Hence, [T] will either be [Asn1Primitive]/[Asn1PrimitiveOctetString] or [Asn1Structure]/[Asn1EncapsulatingOctetString]
+ */
+interface Asn1OctetString<T : Asn1Element> {
+
+    /**
+     * Raw data contained in this ASN.1 primitive in its encoded form. Requires decoding to interpret it.
+     *
+     * It makes sense to have this for both kinds of octet strings, since many intermediate processing steps don't care about semantics.
+     */
+    val content: ByteArray
+
+    /**
+     * Returns the actual type of this object inside the [Asn1Element] class hierarchy
+     * [T] will either be [Asn1Primitive]/[Asn1PrimitiveOctetString] or [Asn1Structure]/[Asn1EncapsulatingOctetString]
+     */
+    fun unwrap(): T
+}
+
+
 data class TLV(val tag: UByte, val content: ByteArray) {
 
     val encodedLength by lazy { length.encodeLength() }