Fix EndOfStreamException when a comment is the final token in a file (#…

…102)

Fixes #101

ValveKeyValue/ValveKeyValue.Test/Text/TrailingCommentTestCase.cs

@@ -0,0 +1,37 @@
+namespace ValveKeyValue.Test.Text
+{
+    class TrailingCommentTestCase
+    {
+        [Test]
+        public void CanReadTrailingEmptyComment()
+        {
+            var data = """
+            "vertexlitgeneric" { 	"$basetexture" "models/props_oil/doors/oil_door" 	"$surfaceprop" "metal"	"%keywords" "tf"	} 
+
+            /
+            """;
+            var kv = KVSerializer.Create(KVSerializationFormat.KeyValues1Text).Deserialize(data);
+
+            Assert.That(kv.Name, Is.EqualTo("vertexlitgeneric"));
+            Assert.That(((string)kv["$basetexture"]), Is.EqualTo("models/props_oil/doors/oil_door"));
+            Assert.That(((string)kv["$surfaceprop"]), Is.EqualTo("metal"));
+            Assert.That(((string)kv["%keywords"]), Is.EqualTo("tf"));
+        }
+
+        [Test]
+        public void CanReadTrailingCommentWithText()
+        {
+            var data = """
+            "vertexlitgeneric" { 	"$basetexture" "models/props_oil/doors/oil_door" 	"$surfaceprop" "metal"	"%keywords" "tf"	} 
+
+            // foo
+            """;
+            var kv = KVSerializer.Create(KVSerializationFormat.KeyValues1Text).Deserialize(data);
+
+            Assert.That(kv.Name, Is.EqualTo("vertexlitgeneric"));
+            Assert.That(((string)kv["$basetexture"]), Is.EqualTo("models/props_oil/doors/oil_door"));
+            Assert.That(((string)kv["$surfaceprop"]), Is.EqualTo("metal"));
+            Assert.That(((string)kv["%keywords"]), Is.EqualTo("tf"));
+        }
+    }
+}

ValveKeyValue/ValveKeyValue/Deserialization/KVTokenReader.cs

@@ -34,26 +34,29 @@ public void Dispose()
             }
         }
 
-        protected char Next()
+        protected char Next() => TryGetNext(out var next) ? next : throw new EndOfStreamException();
+
+        protected bool TryGetNext(out char next)
         {
-            int next;
+            int nextValue;
 
             if (peekedNext.HasValue)
             {
-                next = peekedNext.Value;
+                nextValue = peekedNext.Value;
                 peekedNext = null;
             }
             else
             {
-                next = textReader.Read();
+                nextValue = textReader.Read();
             }
 
-            if (next == -1)
+            if (nextValue == -1)
             {
-                throw new EndOfStreamException();
+                next = default;
+                return false;
             }
 
-            if (next is '\n')
+            if (nextValue is '\n')
             {
                 lineOffset++;
                 columnOffset = 0;
@@ -63,7 +66,8 @@ protected char Next()
                 columnOffset++;
             }
 
-            return (char)next;
+            next = (char)nextValue;
+            return true;
         }
 
         protected int Peek()

ValveKeyValue/ValveKeyValue/Deserialization/KeyValues1/KV1TokenReader.cs

@@ -70,18 +70,24 @@ KVToken ReadComment()
             ReadChar(CommentBegin);
 
             var sb = new StringBuilder();
-            var next = Next();
 
             // Some keyvalues implementations have a bug where only a single slash is needed for a comment
+            // If the file ends with a single slash then we have an empty comment, bail out
+            if (!TryGetNext(out var next))
+            {
+                return new KVToken(KVTokenType.Comment, string.Empty);
+            }
+
+            // If the next character is not a slash, then we have a comment that starts with a single slash
+            // Otherwise pretend the comment is a double-slash and ignore this new second slash.
             if (next != CommentBegin)
             {
                 sb.Append(next);
             }
 
-            while (true)
+            // Be more permissive here than in other places, as comments can be the last token in a file.
+            while (TryGetNext(out next))
             {
-                next = Next();
-
                 if (next == '\n')
                 {
                     break;