ber: Create a simple DER Stream and test re-encoding

BERTLVStream.st

@@ -283,3 +283,29 @@ of X.690 and provide very basic reading of a stream.'>
         ^ ret
     ]
 ]
+
+BERTLVStream subclass: DERTLVStream [
+    <comment: 'I am DER Stream. I can produce valid DER streams
+from a tupled input.'>
+
+    nextPut: aTuple [
+        aTuple first writeOn: base.
+        aTuple first isConstructed
+            ifTrue: [
+                | stream der |
+                stream := WriteStream on: (base species new: 1).
+                (self class on: stream) nextPutAll: aTuple second.
+
+                BERLength writeLength: stream contents size on: base.
+                base nextPutAll: stream contents.
+            ]
+            ifFalse: [
+                BERLength writeLength: aTuple second size on: base.
+                base nextPutAll: aTuple second.
+            ].
+    ]
+
+    nextPutAll: aTupleList [
+        aTupleList do: [:each | self nextPut: each].
+    ]
+]

BERTLVStreamTest.st

@@ -112,3 +112,25 @@ TestCase subclass: BERTLVStreamTest [
         self assert: value second size = 3.
     ]
 ]
+
+TestCase subclass: DERTLVStreamTest [
+    <comment: 'I test DER encoding to some degree'>
+
+    testDecodeEncodeAll [
+        | data decoded stream |
+        "I test that we can encode what we decode. At least to
+         some very very basic degree."
+
+        data := #(16rA1 16r13 16r02 16r01 16r04 16r02 16r01 16r3B
+                  16r30 16r0B 16r04 16r01 16r0F 16r04 16r06 16r2A
+                  16rD5 16r4C 16r16 16r1B 16r01) asByteArray.
+
+        decoded := (DERTLVStream on: data readStream) nextAllRecursive.
+
+        stream := WriteStream on: (ByteArray new: 20).
+        (DERTLVStream on: stream) nextPutAll: decoded.
+
+        self assert: data ~= decoded.
+        self assert: stream contents = data.
+    ]
+]

package.xml

@@ -10,6 +10,7 @@
         <sunit>Osmo.BERTagTest</sunit>
         <sunit>Osmo.BERTLVStreamTest</sunit>
         <sunit>Osmo.BERLengthTest</sunit>
+        <sunit>Osmo.DERTLVStreamTest</sunit>
         <filein>Tests.st</filein>
         <filein>BERTLVStreamTest.st</filein>
     </test>