GSM48: Parse the reject cause properly

GSM48.st

@@ -215,6 +215,39 @@ Object subclass: GSM48MIdentity [
     ]
 ]
 
+Object subclass: GSM48RejectCause [
+    | cause |
+
+    GSM48RejectCause class >> createDefault [
+        <category: 'creation'>
+        ^ self new
+            cause: 11;
+            yourself.
+    ]
+
+    GSM48RejectCause class >> length: aByteArray [
+        ^ 1
+    ]
+
+    GSM48RejectCause class >> parseFrom: aByteArray [
+        ^ self new
+            cause: (aByteArray at: 1);
+            yourself
+    ]
+
+    cause [
+        ^ cause
+    ]
+
+    cause: aCause [
+        cause := aCause.
+    ]
+
+    writeOnDirect: aMsg [
+        aMsg putByte: cause.
+    ]
+]
+
 
 IEMessage subclass: GSM48MSG [
     <category: 'osmo-message'>

Tests.st

@@ -163,6 +163,20 @@ TestCase subclass: GSM48Test [
         self assert: gsm imsi = imsi.
     ]
 
+    testRejectCause [
+        | rej msg target |
+        target := #(11) asByteArray.
+
+        msg := Osmo.MessageBuffer new.
+        rej := GSM48RejectCause createDefault.
+        rej writeOnDirect: msg.
+        self assert: msg asByteArray = target.
+
+        self assert: (GSM48RejectCause length: target) = 1.
+        rej := GSM48RejectCause parseFrom: target.
+        self assert: rej cause = 11.
+    ]
+
     testLU [
         | gsm msg res |