Add archive as tar functionality

Implemented as an extension method of `ObjectDatabase`.
Lots of logic taken from [archive-tar.c](https://github.com/git/git/blob/master/archive-tar.c).

1 files changed, 88 insertions, 0 deletions

diff --git a/LibGit2Sharp/TarArchiver.cs b/LibGit2Sharp/TarArchiver.cs
new file mode 100644
index 00000000..f6fe7520
--- /dev/null
+++ b/LibGit2Sharp/TarArchiver.cs
@@ -0,0 +1,88 @@
+using System;
+using System.IO;
+using System.Text;
+using LibGit2Sharp.Core;
+
+namespace LibGit2Sharp
+{
+    /// <summary>
+    /// Logic for tar archiving (not the actual tar format, but the overal logic related to tar+git) is taken
+    /// from https://github.com/git/git/blob/master/archive-tar.c.
+    /// </summary>
+    internal class TarArchiver : ArchiverBase, IDisposable
+    {
+        private readonly TarWriter writer;
+
+        public TarArchiver(FileStream output)
+        {
+            writer = new TarWriter(output);
+        }
+
+        #region Overrides of ArchiverBase
+
+        public override void BeforeArchiving(Tree tree, ObjectId oid, DateTimeOffset modificationTime)
+        {
+            if (oid == null)
+            {
+                return;
+            }
+
+            // Store the sha in the pax_global_header
+            using (var stream = new MemoryStream(Encoding.ASCII.GetBytes(string.Format("52 comment={0}\n", oid.Sha))))
+            {
+                writer.Write("pax_global_header", stream, modificationTime, "666".OctalToInt32(), 
+                    "0", "0", 'g', "root", "root", "0", "0", oid.Sha, false);
+            }
+        }
+
+        protected override void AddTreeEntry(string path, TreeEntry entry, DateTimeOffset modificationTime)
+        {
+            switch (entry.Mode)
+            {
+                case Mode.GitLink:
+                case Mode.Directory:
+                    writer.Write(path + "/", null, modificationTime, "775".OctalToInt32(), 
+                        "0", "0", '5', "root", "root", "0", "0", entry.TargetId.Sha, false);
+                    break;
+                case Mode.ExecutableFile:
+                case Mode.NonExecutableFile:
+                case Mode.NonExecutableGroupWritableFile:
+                    var blob = ((Blob) entry.Target);
+
+                    WriteStream(path, entry, modificationTime,
+                        () => blob.IsBinary ? blob.GetContentStream() : blob.GetContentStream(new FilteringOptions(path)));
+                    break;
+                case Mode.SymbolicLink:
+                    using (Stream contentStream = ((Blob)entry.Target).GetContentStream(new FilteringOptions(path)))
+                    {
+                        writer.Write(path, contentStream, modificationTime, "777".OctalToInt32(), 
+                            "0", "0", '2', "root", "root", "0", "0", entry.TargetId.Sha, true);
+                    }
+                    break;
+                default:
+                    throw new InvalidOperationException(string.Format("Unsupported file mode: {0} (sha1: {1}).", entry.Mode, entry.TargetId.Sha));
+            }
+        }
+
+        private void WriteStream(string path, TreeEntry entry, DateTimeOffset modificationTime, Func<Stream> streamer)
+        {
+            using (Stream contentStream = streamer())
+            {
+                writer.Write(path, contentStream, modificationTime,
+                    (entry.Mode == Mode.ExecutableFile) ? "775".OctalToInt32() : "664".OctalToInt32(),
+                    "0", "0", '0', "root", "root", "0", "0", entry.TargetId.Sha, false);
+            }
+        }
+
+        #endregion
+
+        #region Implementation of IDisposable
+
+        public void Dispose()
+        {
+            writer.Dispose();
+        }
+
+        #endregion
+    }
+}