write: Implement write for the attributes and the body

This will decode and re-create the message. It is the first
round-trip test.

codec/SMPPBodyBase.st

@@ -178,4 +178,22 @@ sub-classes will provide the specific bodies.'>
                 ifTrue: [^self error: 'Optional attributes not implemented!'].
         ]
     ]
+
+    writeOn: aMsg [
+        <category: 'serialize'>
+        "Custom write to avoid having to box String code"
+
+        "Write each element"
+        self class tlvDescription do: [:attr |
+            | val |
+            val := self instVarNamed: attr instVarName.
+
+            "Now write it"
+            val isNil ifFalse: [
+                attr needsTag
+                    ifTrue: [aMsg putByte: attr tag].
+                attr parseClass write: val on: aMsg with: attr.
+            ].
+        ]
+    ]
 ]

codec/attributes/SMPPInteger.st

@@ -33,4 +33,10 @@ Object subclass: SMPPInteger [
         "This is not implemented yet"
         ^self error: 'The base class does not support other value sizes'.
     ]
+
+    SMPPInteger class >> write: aValue on: aMsg with: anAttribute [
+        anAttribute valueSize = 1
+            ifTrue: [^aMsg putByte: aValue].
+        ^self error: 'This value size is not supported yet.'
+    ]
 ]

codec/attributes/SMPPOctetString.st

@@ -38,4 +38,11 @@ Object subclass: SMPPOctetString [
         "anAttribute... verify the max size"
         ^str contents
     ]
+
+    SMPPOctetString class >> write: aValue on: aMsg with: anAttr [
+        "Todo.. verify the size constraints..."
+        aMsg
+            putByteArray: aValue asByteArray;
+            putByte: 0
+    ]
 ]

test/SMPPMessageTest.st

@@ -45,6 +45,13 @@ TestCase subclass: SMPPMessageTest [
         self assert: msg body addressRange equals: ''.
     ]
 
+    testRoundTrip [
+        | msg res |
+        msg := SMPPMessage readFrom: self examplePdu readStream.
+        res := msg toMessage asByteArray.
+        self assert: res equals: self examplePdu
+    ]
+
     testWriteMessage [
         | data |
         data := (SMPPMessage new