Remote: implement initial clone

As we have no commit source yet, Download() can only clone and store
the resulting pack somewhere. The directory is given as the argument
to the method.

There is no way to interact with the indexer yet.

Author: carlosmn

LibGit2Sharp/Pkt.cs

@@ -6,6 +6,11 @@ namespace LibGit2Sharp
 {
     public class Pkt
     {
+        static public char[] Line(string msg)
+        {
+            return string.Format("{0:x4}{1}\n", 4 + msg.Length + 1, msg).ToCharArray();
+        }
+
         static public Pkt Parse(BinaryReader reader)
         {
             var buf = reader.ReadBytes(4);

LibGit2Sharp/Remote.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using System.Linq;
 using System.Collections.Generic;
 using LibGit2Sharp.Core;
@@ -73,6 +74,43 @@ public void Connect()
             }
         }
 
+        public void Download(string path)
+        {
+            Ensure.ArgumentNotNullOrEmptyString(path, "path");
+            if (!Directory.Exists(path))
+                Directory.CreateDirectory(path);
+
+            /* First, let's see what we want. At this point we don't send any haves */
+            Stream stream = new MemoryStream();
+            var writer = new StreamWriter(stream);
+            foreach (PktRef p in Refs) {
+                if (!Refspec.Matches(p.Name))
+                    continue;
+
+                writer.Write(Pkt.Line("want " + p.Id.Sha));
+            }
+            /* Flush after the want lines */
+            writer.Write("0000");
+            /* We don't have anything locally, so just download the packfile */
+            writer.Write(Pkt.Line("done"));
+            writer.Flush();
+            stream.Seek(0, SeekOrigin.Begin);
+            transport.NegotiationStep(stream);
+
+            stream = transport.GetStream();
+            var parser = new PktParser(stream);
+            var pkt = parser.Next();
+            /*
+             * For now, simply check that it's one or the other. After this,
+             * the stream contains the pack data, so feed it to the indexer.
+             */
+            if (!(pkt is PktAck || pkt is PktNak))
+                throw new GitProtocolException("Expected ACK or NAK, got neither");
+
+            var indexer = new Indexer(path);
+            indexer.IndexStream(stream);
+        }
+
         private static readonly LambdaEqualityHelper<Remote> equalityHelper =
             new LambdaEqualityHelper<Remote>(new Func<Remote, object>[] { x => x.Name, x => x.Url });