tlv: Only write a tag if it was forced or the type is optional

2 files changed, 27 insertions, 5 deletions

diff --git a/core/TLV.st b/core/TLV.st
index e7785f9..381ec5b 100644
--- a/core/TLV.st
+++ b/core/TLV.st
@@ -132,7 +132,7 @@ Object subclass: TLVDescription [
 
     hasLength [
         <category: 'access'>
-        ^ type = self class tagLengthValue
+        ^ type = self class tagLengthValue or: [type = self class lengthValue]
     ]
 
     isLen16 [
@@ -150,6 +150,16 @@ Object subclass: TLVDescription [
         ^ force_tag
     ]
 
+    hasTag [
+        <category: 'access'>
+        ^type ~= self class lengthValue and: [type ~= self class valueOnly]
+    ]
+
+    needsTag [
+        <category: 'access'>
+        ^force_tag or: [self hasTag and: [self isOptional]].
+    ]
+
     presenceKind: aKind [
         <category: 'creation'>
         "Is this required, optional, variable?"
@@ -286,8 +296,7 @@ Object subclass: TLVParserBase [
 
             "Now write it"
             val isNil ifFalse: [
-                aMsg
-                    putByte: attr tag.
+                attr needsTag ifTrue: [aMsg putByte: attr tag].
                 val writeOn: aMsg with: attr.
             ].
         ]
diff --git a/core/TLVTests.st b/core/TLVTests.st
index 73c6b5a..c2675d6 100644
--- a/core/TLVTests.st
+++ b/core/TLVTests.st
@@ -42,8 +42,21 @@ TestCase subclass: TLVDescriptionTest [
         self assert: tlv tag = 16r23.
 
         tlv beLV.
-        self assert: tlv typeKind = #lv.
+        self
+            assert: tlv typeKind equals: #lv;
+            assert: tlv hasLength;
+            deny: tlv hasTag.
+
         tlv beTLV.
-        self assert: tlv typeKind = #tlv.
+        self
+            assert: tlv typeKind equals: #tlv;
+            assert: tlv hasLength;
+            assert: tlv hasTag.
+
+        tlv beTagOnly.
+        self
+            assert: tlv typeKind equals: #tagOnly;
+            assert: tlv hasTag;
+            deny: tlv hasLength.
     ]
 ]