Use single shared method for return code checking.

This defers the return code logic to a named method `isLibsodiumSuccessCode`
to reduce the liklihood of error when checking codes.
This will also now throw an `IllegalStateException` in the event that an
unknown code is returned.

multiplatform-crypto-libsodium-bindings/src/commonMain/kotlin/com.ionspin.kotlin.crypto/GeneralLibsodiumException.kt

@@ -1,11 +1,19 @@
 package com.ionspin.kotlin.crypto
 
+import com.ionspin.kotlin.crypto.util.isLibsodiumSuccessCode
+
 class GeneralLibsodiumException : RuntimeException("Libsodium reported error! Returned value was -1") {
     companion object {
+        /**
+         * Throws a [GeneralLibsodiumException] if the return code is not
+         * successful.
+         *
+         * This will throw an [IllegalStateException] if the return code is invalid/unknown.
+         */
         fun Int.ensureLibsodiumSuccess() {
-            if (this == -1) {
+            if (!isLibsodiumSuccessCode()) {
                 throw GeneralLibsodiumException()
             }
         }
     }
-}
+}

multiplatform-crypto-libsodium-bindings/src/commonMain/kotlin/com.ionspin.kotlin.crypto/util/Util.kt

@@ -36,3 +36,16 @@ fun UByteArray.hexColumnsPrint(chunk: Int = 16) {
     val printout = this.map { it.toString(16).padStart(2, '0') }.chunked(chunk)
     printout.forEach { println(it.joinToString(separator = " ") { it.uppercase() }) }
 }
+
+/**
+ * Functions returning an int return 0 on success and -1 to indicate an error.
+ *
+ * This will throw an [IllegalStateException] if the return code is invalid/unknown.
+ */
+fun Int.isLibsodiumSuccessCode(): Boolean {
+    return when (this) {
+        0 -> true
+        -1 -> false
+        else -> throw IllegalStateException("Libsodium returned an unexpected return code $this")
+    }
+}