Fix file comment serialization

SaneTsv/SaneTsv.cs

@@ -1174,13 +1174,23 @@ public class SaneTsv
 
   public static byte[] SerializeCommentedTsv<T>(IList<T> data, string fileComment) where T : CommentedTsvRecord
   {
-    return SerializeTsv<T>(data, FormatType.COMMENTED_TSV);
+    return SerializeTsv<T>(data, FormatType.COMMENTED_TSV, fileComment);
   }
 
-  protected static byte[] SerializeTsv<T>(IList<T> data, FormatType tsvFormat)
+  protected static byte[] SerializeTsv<T>(IList<T> data, FormatType tsvFormat, string fileComment = null)
   {
     var bytes = new List<byte>();
 
+    if (fileComment != null)
+    {
+      if (tsvFormat != FormatType.COMMENTED_TSV)
+      {
+        throw new Exception($"File comments are not valid for {tsvFormat}");
+      }
+
+      bytes.AddRange(Encoding.UTF8.GetBytes("#" + fileComment.Replace("\n", "\n#") + "\n"));
+    }
+
     var columnTypes = new List<Type>();
     var columnNames = new List<string>();
     var columnPropertyInfos = new List<PropertyInfo>();

SaneTsv/SaneTsvTest/Program.cs

@@ -759,6 +759,30 @@ internal class Program : SaneTsv
       }
     }
 
+    {
+      string testName = "File comment serde";
+
+      string testString1 = "#this is a file comment" +
+        "\n# and one more line since you're such a good customer" +
+        "\ncolumn1:type:boolean\tcolumn2:binary\tcolumnthree\\nyep:string" +
+        "\nTRUE\tvalue\\\\t\0woo\tvaluetrhee" +
+        "\nFALSE\tnother\tno\\ther";
+
+
+      CommentedTsv<BoolTestRecord2> parsed = SaneTsv.ParseCommentedTsv<BoolTestRecord2>(Encoding.UTF8.GetBytes(testString1));
+
+      string reserialized = Encoding.UTF8.GetString(SaneTsv.SerializeCommentedTsv<BoolTestRecord2>(parsed.Records, parsed.FileComment));
+
+      if (reserialized == testString1)
+      {
+        Console.WriteLine($"Passed {testName}");
+      }
+      else
+      {
+        Console.WriteLine($"Failed {testName}");
+      }
+    }
+
     Console.WriteLine("Done with tests");
   }
 }