[monkeydoc] Introduce support for versioned tree and gracefully handl…

…e old trees.

mcs/tools/monkeydoc/MonkeyDoc/Tree.cs

@@ -18,6 +18,7 @@ namespace MonkeyDoc
 	 */
 	public class Tree
 	{
+		const long CurrentVersionNumber = 1;
 		public readonly HelpSource HelpSource;
 
 		FileStream InputStream;
@@ -31,6 +32,7 @@ public class Tree
 		/// </summary>
 		public Tree (HelpSource hs, string filename)
 		{
+			HelpSource = hs;
 			Encoding utf8 = new UTF8Encoding (false, true);
 
 			if (!File.Exists (filename)){
@@ -45,11 +47,15 @@ public Tree (HelpSource hs, string filename)
 				throw new Exception ("Invalid file format");
 
 			InputStream.Position = 4;
+			// Try to read version information
+			if (InputReader.ReadInt32 () == -(int)'v')
+				VersionNumber = InputReader.ReadInt64 ();
+			else
+				InputStream.Position -= 4;
+
 			var position = InputReader.ReadInt32 ();
 			rootNode = new Node (this, position);
 			InflateNode (rootNode);
-
-			HelpSource = hs;
 		}
 
 		/// <summary>
@@ -73,14 +79,16 @@ public void Save (string file)
 			Encoding utf8 = new UTF8Encoding (false, true);
 			using (FileStream output = File.OpenWrite (file)){
 				// Skip over the pointer to the first node.
-				output.Position = 8;
+				output.Position = 4 + 4 + 8 + 4;
 
 				using (BinaryWriter writer = new BinaryWriter (output, utf8)) {
 					// Recursively dump
 					rootNode.Serialize (output, writer);
 
 					output.Position = 0;
 					writer.Write (new byte [] { (byte) 'M', (byte) 'o', (byte) 'H', (byte) 'P' });
+					writer.Write (-(int)'v');
+					writer.Write (CurrentVersionNumber);
 					writer.Write (rootNode.Address);
 				}
 			}
@@ -92,6 +100,11 @@ public void Save (string file)
 			}
 		}
 
+		public long VersionNumber {
+			get;
+			private set;
+		}
+
 		static bool GoodSig (byte [] sig)
 		{
 			if (sig.Length != 4)