Provide a method to write a tree to an archive

Add Repository.write_archive() to write a given tree to an archive. As
there are many customisation options, we only provide a method to write
to an archive which is created by the user.

docs/repository.rst

@@ -69,3 +69,4 @@ Below there are some general attributes and methods:
 .. automethod:: pygit2.Repository.write
 .. automethod:: pygit2.Repository.reset
 .. automethod:: pygit2.Repository.state_cleanup
+.. automethod:: pygit2.Repository.write_archive

pygit2/repository.py

@@ -35,6 +35,7 @@ from string import hexdigits
 from _pygit2 import Repository as _Repository
 from _pygit2 import Oid, GIT_OID_HEXSZ, GIT_OID_MINPREFIXLEN
 from _pygit2 import GIT_CHECKOUT_SAFE_CREATE, GIT_DIFF_NORMAL
+from _pygit2 import GIT_FILEMODE_LINK
 from _pygit2 import Reference, Tree, Commit, Blob
 
 from .config import Config
@@ -43,7 +44,7 @@ from .ffi import ffi, C
 from .index import Index
 from .remote import Remote
 from .blame import Blame
-from .utils import to_bytes, to_str
+from .utils import to_bytes, to_str, is_string
 
 
 class Repository(_Repository):
@@ -488,3 +489,73 @@ class Repository(_Repository):
         check_error(err, True)
 
         return Index.from_c(self, cindex)
+
+    #
+    # Utility for writing a tree into an archive
+    #
+    def write_archive(self, treeish, archive, timestamp=None):
+        """Write treeish into an archive
+
+        If no timestamp is provided and 'treeish' is a commit, its committer
+        timestamp will be used. Otherwise the current time will be used.
+
+        Arguments:
+
+        treeish
+            The treeish to write.
+        archive
+            An archive from the 'tarfile' module
+        timestamp
+            Timestamp to use for the files in the archive.
+
+        Example::
+
+            >>> import tarfile, pygit2
+            >>>> with tarfile.open('foo.tar', 'w') as archive:
+            >>>>     repo = pygit2.Repsitory('.')
+            >>>>     repo.write_archive(archive, repo.head.target)
+        """
+
+        import tarfile, sys
+        from time import time
+        if sys.version_info[0] < 3:
+            from cStringIO import StringIO
+        else:
+            from io import BytesIO as StringIO
+
+        # Try to get a tree form whatever we got
+        if isinstance(treeish, Tree):
+            tree = treeish
+
+        if isinstance(treeish, Oid) or is_string(treeish):
+            treeish = self[treeish]
+
+        # if we don't have a timestamp, try to get it from a commit
+        if not timestamp:
+            try:
+                commit = treeish.peel(Commit)
+                timestamp = commit.committer.time
+            except:
+                pass
+
+        # as a last resort, use the current timestamp
+        if not timestamp:
+            timestamp = int(time())
+
+        tree = treeish.peel(Tree)
+
+        index = Index()
+        index.read_tree(tree)
+
+        for entry in index:
+            content = self[entry.id].read_raw()
+            info = tarfile.TarInfo(entry.path)
+            info.size = len(content)
+            info.mtime = timestamp
+            info.uname = info.gname = 'root' # just because git does this
+            if entry.mode == GIT_FILEMODE_LINK:
+                info.type = archive.SYMTYPE
+                info.linkname = content
+                info.mode = 0o777 # symlinks get placeholder
+
+            archive.addfile(info, StringIO(content))

test/test_archive.py

@@ -0,0 +1,74 @@
+# -*- coding: UTF-8 -*-
+#
+# Copyright 2010-2014 The pygit2 contributors
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License, version 2,
+# as published by the Free Software Foundation.
+#
+# In addition to the permissions in the GNU General Public License,
+# the authors give you unlimited permission to link the compiled
+# version of this file into combinations with other programs,
+# and to distribute those combinations without any restriction
+# coming from the use of this file.  (The General Public License
+# restrictions do apply in other respects; for example, they cover
+# modification of the file, and distribution when not linked into
+# a combined executable.)
+#
+# This file is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; see the file COPYING.  If not, write to
+# the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+# Boston, MA 02110-1301, USA.
+
+"""Tests for Blame objects."""
+
+from __future__ import absolute_import
+from __future__ import unicode_literals
+import unittest
+import pygit2
+from pygit2 import Index, Oid, Tree, Object
+import tarfile
+import os
+from . import utils
+from time import time
+
+TREE_HASH = 'fd937514cb799514d4b81bb24c5fcfeb6472b245'
+COMMIT_HASH = '2be5719152d4f82c7302b1c0932d8e5f0a4a0e98'
+
+class ArchiveTest(utils.RepoTestCase):
+
+    def check_writing(self, treeish, timestamp=None):
+        archive = tarfile.open('foo.tar', mode='w')
+        self.repo.write_archive(treeish, archive)
+
+        index = Index()
+        if isinstance(treeish, Object):
+            index.read_tree(treeish.peel(Tree))
+        else:
+            index.read_tree(self.repo[treeish].peel(Tree))
+    
+        self.assertEqual(len(index), len(archive.getmembers()))
+
+        if timestamp:
+            fileinfo = archive.getmembers()[0]
+            self.assertEqual(timestamp, fileinfo.mtime)
+
+        archive.close()
+        self.assertTrue(os.path.isfile('foo.tar'))
+        os.remove('foo.tar')
+    
+    def test_write_tree(self):
+        self.check_writing(TREE_HASH)
+        self.check_writing(Oid(hex=TREE_HASH))
+        self.check_writing(self.repo[TREE_HASH])
+
+    def test_write_commit(self):
+        commit_timestamp = self.repo[COMMIT_HASH].committer.time
+        self.check_writing(COMMIT_HASH, commit_timestamp)
+        self.check_writing(Oid(hex=COMMIT_HASH), commit_timestamp)
+        self.check_writing(self.repo[COMMIT_HASH], commit_timestamp)