diff --git a/Documentation/config.txt b/Documentation/config.txt
index a1e36d7e42..76173dbc5d 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1461,6 +1461,10 @@ remote.<name>.tagopt::
 	Setting this value to \--no-tags disables automatic tag following when
 	fetching from remote <name>
 
+remote.<name>.vcs::
+	Setting this to a value <vcs> will cause git to interact with
+	the remote with the git-remote-<vcs> helper.
+
 remotes.<group>::
 	The list of remotes which are fetched by "git remote update
 	<group>".  See linkgit:git-remote[1].
diff --git a/Documentation/git-remote-helpers.txt b/Documentation/git-remote-helpers.txt
index 8beb42dbb9..5cfdc0cfc5 100644
--- a/Documentation/git-remote-helpers.txt
+++ b/Documentation/git-remote-helpers.txt
@@ -79,6 +79,17 @@ style string if it contains an LF.
 +
 Supported if the helper has the "push" capability.
 
+'import' <name>::
+	Produces a fast-import stream which imports the current value
+	of the named ref. It may additionally import other refs as
+	needed to construct the history efficiently. The script writes
+	to a helper-specific private namespace. The value of the named
+	ref should be written to a location in this namespace derived
+	by applying the refspecs from the "refspec" capability to the
+	name of the ref.
++
+Supported if the helper has the "import" capability.
+
 If a fatal error occurs, the program writes the error message to
 stderr and exits. The caller should expect that a suitable error
 message has been printed if the child closes the connection without
@@ -99,6 +110,19 @@ CAPABILITIES
 'push'::
 	This helper supports the 'push' command.
 
+'import'::
+	This helper supports the 'import' command.
+
+'refspec' 'spec'::
+	When using the import command, expect the source ref to have
+	been written to the destination ref. The earliest applicable
+	refspec takes precedence. For example
+	"refs/heads/*:refs/svn/origin/branches/*" means that, after an
+	"import refs/heads/name", the script has written to
+	refs/svn/origin/branches/name. If this capability is used at
+	all, it must cover all refs reported by the list command; if
+	it is not used, it is effectively "*:*"
+
 REF LIST ATTRIBUTES
 -------------------
 
@@ -107,6 +131,10 @@ REF LIST ATTRIBUTES
 	commands.  A helper might chose to acquire the ref list by
 	opening a different type of connection to the destination.
 
+'unchanged'::
+	This ref is unchanged since the last import or fetch, although
+	the helper cannot necessarily determine what value that produced.
+
 OPTIONS
 -------
 'option verbosity' <N>::
diff --git a/Makefile b/Makefile
index 4a1e5bcc4d..fd4919c0ad 100644
--- a/Makefile
+++ b/Makefile
@@ -168,6 +168,8 @@ all::
 #
 # Define NO_PERL if you do not want Perl scripts or libraries at all.
 #
+# Define NO_PYTHON if you do not want Python scripts or libraries at all.
+#
 # Define NO_TCLTK if you do not want Tcl/Tk GUI.
 #
 # The TCL_PATH variable governs the location of the Tcl interpreter
@@ -341,6 +343,7 @@ LIB_H =
 LIB_OBJS =
 PROGRAMS =
 SCRIPT_PERL =
+SCRIPT_PYTHON =
 SCRIPT_SH =
 TEST_PROGRAMS =
 
@@ -379,6 +382,7 @@ SCRIPT_PERL += git-svn.perl
 
 SCRIPTS = $(patsubst %.sh,%,$(SCRIPT_SH)) \
 	  $(patsubst %.perl,%,$(SCRIPT_PERL)) \
+	  $(patsubst %.py,%,$(SCRIPT_PYTHON)) \
 	  git-instaweb
 
 # Empty...
@@ -434,8 +438,12 @@ endif
 ifndef PERL_PATH
 	PERL_PATH = /usr/bin/perl
 endif
+ifndef PYTHON_PATH
+	PYTHON_PATH = /usr/bin/python
+endif
 
 export PERL_PATH
+export PYTHON_PATH
 
 LIB_FILE=libgit.a
 XDIFF_LIB=xdiff/lib.a
@@ -1346,6 +1354,10 @@ ifeq ($(PERL_PATH),)
 NO_PERL=NoThanks
 endif
 
+ifeq ($(PYTHON_PATH),)
+NO_PYTHON=NoThanks
+endif
+
 QUIET_SUBDIR0  = +$(MAKE) -C # space to separate -C and subdir
 QUIET_SUBDIR1  =
 
@@ -1393,6 +1405,7 @@ prefix_SQ = $(subst ','\'',$(prefix))
 
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 PERL_PATH_SQ = $(subst ','\'',$(PERL_PATH))
+PYTHON_PATH_SQ = $(subst ','\'',$(PYTHON_PATH))
 TCLTK_PATH_SQ = $(subst ','\'',$(TCLTK_PATH))
 
 LIBS = $(GITLIBS) $(EXTLIBS)
@@ -1439,6 +1452,9 @@ ifndef NO_TCLTK
 endif
 ifndef NO_PERL
 	$(QUIET_SUBDIR0)perl $(QUIET_SUBDIR1) PERL_PATH='$(PERL_PATH_SQ)' prefix='$(prefix_SQ)' all
+endif
+ifndef NO_PYTHON
+	$(QUIET_SUBDIR0)git_remote_helpers $(QUIET_SUBDIR1) PYTHON_PATH='$(PYTHON_PATH_SQ)' prefix='$(prefix_SQ)' all
 endif
 	$(QUIET_SUBDIR0)templates $(QUIET_SUBDIR1)
 
@@ -1566,11 +1582,41 @@ $(patsubst %.perl,%,$(SCRIPT_PERL)) git-instaweb: % : unimplemented.sh
 	mv $@+ $@
 endif # NO_PERL
 
+
 ifdef JSMIN
 gitweb/gitweb.min.js: gitweb/gitweb.js
 	$(QUIET_GEN)$(JSMIN) <$< >$@
 endif # JSMIN
 
+ifndef NO_PYTHON
+$(patsubst %.py,%,$(SCRIPT_PYTHON)): GIT-CFLAGS
+$(patsubst %.py,%,$(SCRIPT_PYTHON)): % : %.py
+	$(QUIET_GEN)$(RM) $@ $@+ && \
+	INSTLIBDIR=`MAKEFLAGS= $(MAKE) -C git_remote_helpers -s \
+		--no-print-directory prefix='$(prefix_SQ)' DESTDIR='$(DESTDIR_SQ)' \
+		instlibdir` && \
+	sed -e '1{' \
+	    -e '	s|#!.*python|#!$(PYTHON_PATH_SQ)|' \
+	    -e '}' \
+	    -e 's|^import sys.*|&; \\\
+	           import os; \\\
+	           sys.path[0] = os.environ.has_key("GITPYTHONLIB") and \\\
+	                         os.environ["GITPYTHONLIB"] or \\\
+	                         "@@INSTLIBDIR@@"|' \
+	    -e 's|@@INSTLIBDIR@@|'"$$INSTLIBDIR"'|g' \
+	    $@.py >$@+ && \
+	chmod +x $@+ && \
+	mv $@+ $@
+else # NO_PYTHON
+$(patsubst %.py,%,$(SCRIPT_PYTHON)): % : unimplemented.sh
+	$(QUIET_GEN)$(RM) $@ $@+ && \
+	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
+	    -e 's|@@REASON@@|NO_PYTHON=$(NO_PYTHON)|g' \
+	    unimplemented.sh >$@+ && \
+	chmod +x $@+ && \
+	mv $@+ $@
+endif # NO_PYTHON
+
 configure: configure.ac
 	$(QUIET_GEN)$(RM) $@ $<+ && \
 	sed -e 's/@@GIT_VERSION@@/$(GIT_VERSION)/g' \
@@ -1697,6 +1743,7 @@ GIT-BUILD-OPTIONS: .FORCE-GIT-BUILD-OPTIONS
 	@echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@
 	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@
+	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@
 
 ### Detect Tck/Tk interpreter path changes
 ifndef NO_TCLTK
@@ -1796,6 +1843,9 @@ install: all
 ifndef NO_PERL
 	$(MAKE) -C perl prefix='$(prefix_SQ)' DESTDIR='$(DESTDIR_SQ)' install
 endif
+ifndef NO_PYTHON
+	$(MAKE) -C git_remote_helpers prefix='$(prefix_SQ)' DESTDIR='$(DESTDIR_SQ)' install
+endif
 ifndef NO_TCLTK
 	$(MAKE) -C gitk-git install
 	$(MAKE) -C git-gui gitexecdir='$(gitexec_instdir_SQ)' install
@@ -1912,6 +1962,9 @@ clean:
 ifndef NO_PERL
 	$(RM) gitweb/gitweb.cgi
 	$(MAKE) -C perl clean
+endif
+ifndef NO_PYTHON
+	$(MAKE) -C git_remote_helpers clean
 endif
 	$(MAKE) -C templates/ clean
 	$(MAKE) -C t/ clean
diff --git a/builtin-clone.c b/builtin-clone.c
index caf3025031..5df8b0f72c 100644
--- a/builtin-clone.c
+++ b/builtin-clone.c
@@ -362,9 +362,10 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	const char *repo_name, *repo, *work_tree, *git_dir;
 	char *path, *dir;
 	int dest_exists;
-	const struct ref *refs, *remote_head, *mapped_refs;
+	const struct ref *refs, *remote_head;
 	const struct ref *remote_head_points_at;
 	const struct ref *our_head_points_at;
+	struct ref *mapped_refs;
 	struct strbuf key = STRBUF_INIT, value = STRBUF_INIT;
 	struct strbuf branch_top = STRBUF_INIT, reflog_msg = STRBUF_INIT;
 	struct transport *transport = NULL;
diff --git a/builtin-fetch.c b/builtin-fetch.c
index 5b7db616dc..8654fa7a2d 100644
--- a/builtin-fetch.c
+++ b/builtin-fetch.c
@@ -322,7 +322,10 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	if (!fp)
 		return error("cannot open %s: %s\n", filename, strerror(errno));
 
-	url = transport_anonymize_url(raw_url);
+	if (raw_url)
+		url = transport_anonymize_url(raw_url);
+	else
+		url = xstrdup("foreign");
 	for (rm = ref_map; rm; rm = rm->next) {
 		struct ref *ref = NULL;
 
@@ -819,7 +822,7 @@ static int fetch_one(struct remote *remote, int argc, const char **argv)
 	if (!remote)
 		die("Where do you want to fetch from today?");
 
-	transport = transport_get(remote, remote->url[0]);
+	transport = transport_get(remote, NULL);
 	if (verbosity >= 2)
 		transport->verbose = verbosity <= 3 ? verbosity : 3;
 	if (verbosity < 0)
diff --git a/builtin-ls-remote.c b/builtin-ls-remote.c
index b5bad0c184..70f5622d9d 100644
--- a/builtin-ls-remote.c
+++ b/builtin-ls-remote.c
@@ -89,7 +89,7 @@ int cmd_ls_remote(int argc, const char **argv, const char *prefix)
 	remote = remote_get(dest);
 	if (!remote->url_nr)
 		die("remote %s has no configured URL", dest);
-	transport = transport_get(remote, remote->url[0]);
+	transport = transport_get(remote, NULL);
 	if (uploadpack != NULL)
 		transport_set_option(transport, TRANS_OPT_UPLOADPACK, uploadpack);
 
diff --git a/builtin-push.c b/builtin-push.c
index 356d7c1fd3..dcfb53f188 100644
--- a/builtin-push.c
+++ b/builtin-push.c
@@ -87,6 +87,37 @@ static void setup_default_push_refspecs(void)
 	}
 }
 
+static int push_with_options(struct transport *transport, int flags)
+{
+	int err;
+	int nonfastforward;
+	if (receivepack)
+		transport_set_option(transport,
+				     TRANS_OPT_RECEIVEPACK, receivepack);
+	if (thin)
+		transport_set_option(transport, TRANS_OPT_THIN, "yes");
+
+	if (flags & TRANSPORT_PUSH_VERBOSE)
+		fprintf(stderr, "Pushing to %s\n", transport->url);
+	err = transport_push(transport, refspec_nr, refspec, flags,
+			     &nonfastforward);
+	if (err != 0)
+		error("failed to push some refs to '%s'", transport->url);
+
+	err |= transport_disconnect(transport);
+
+	if (!err)
+		return 0;
+
+	if (nonfastforward && advice_push_nonfastforward) {
+		printf("To prevent you from losing history, non-fast-forward updates were rejected\n"
+		       "Merge the remote changes before pushing again.  See the 'non-fast-forward'\n"
+		       "section of 'git push --help' for details.\n");
+	}
+
+	return 1;
+}
+
 static int do_push(const char *repo, int flags)
 {
 	int i, errs;
@@ -135,33 +166,19 @@ static int do_push(const char *repo, int flags)
 		url = remote->url;
 		url_nr = remote->url_nr;
 	}
-	for (i = 0; i < url_nr; i++) {
-		struct transport *transport =
-			transport_get(remote, url[i]);
-		int err;
-		int nonfastforward;
-		if (receivepack)
-			transport_set_option(transport,
-					     TRANS_OPT_RECEIVEPACK, receivepack);
-		if (thin)
-			transport_set_option(transport, TRANS_OPT_THIN, "yes");
-
-		if (flags & TRANSPORT_PUSH_VERBOSE)
-			fprintf(stderr, "Pushing to %s\n", url[i]);
-		err = transport_push(transport, refspec_nr, refspec, flags,
-				     &nonfastforward);
-		err |= transport_disconnect(transport);
-
-		if (!err)
-			continue;
-
-		error("failed to push some refs to '%s'", url[i]);
-		if (nonfastforward && advice_push_nonfastforward) {
-			printf("To prevent you from losing history, non-fast-forward updates were rejected\n"
-			       "Merge the remote changes before pushing again.  See the 'non-fast-forward'\n"
-			       "section of 'git push --help' for details.\n");
+	if (url_nr) {
+		for (i = 0; i < url_nr; i++) {
+			struct transport *transport =
+				transport_get(remote, url[i]);
+			if (push_with_options(transport, flags))
+				errs++;
 		}
-		errs++;
+	} else {
+		struct transport *transport =
+			transport_get(remote, NULL);
+
+		if (push_with_options(transport, flags))
+			errs++;
 	}
 	return !!errs;
 }
diff --git a/configure.ac b/configure.ac
index 4625b8672b..78345ebb60 100644
--- a/configure.ac
+++ b/configure.ac
@@ -276,6 +276,9 @@ GIT_ARG_SET_PATH(shell)
 # Define PERL_PATH to provide path to Perl.
 GIT_ARG_SET_PATH(perl)
 #
+# Define PYTHON_PATH to provide path to Python.
+GIT_ARG_SET_PATH(python)
+#
 # Define ZLIB_PATH to provide path to zlib.
 GIT_ARG_SET_PATH(zlib)
 #
diff --git a/git_remote_helpers/.gitignore b/git_remote_helpers/.gitignore
new file mode 100644
index 0000000000..2247d5f95a
--- /dev/null
+++ b/git_remote_helpers/.gitignore
@@ -0,0 +1,2 @@
+/build
+/dist
diff --git a/git_remote_helpers/Makefile b/git_remote_helpers/Makefile
new file mode 100644
index 0000000000..c62dfd0f4d
--- /dev/null
+++ b/git_remote_helpers/Makefile
@@ -0,0 +1,35 @@
+#
+# Makefile for the git_remote_helpers python support modules
+#
+pysetupfile:=setup.py
+
+# Shell quote (do not use $(call) to accommodate ancient setups);
+DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
+
+ifndef PYTHON_PATH
+	PYTHON_PATH = /usr/bin/python
+endif
+ifndef prefix
+	prefix = $(HOME)
+endif
+ifndef V
+	QUIET = @
+	QUIETSETUP = --quiet
+endif
+
+PYLIBDIR=$(shell $(PYTHON_PATH) -c \
+	 "import sys; \
+	 print 'lib/python%i.%i/site-packages' % sys.version_info[:2]")
+
+all: $(pysetupfile)
+	$(QUIET)$(PYTHON_PATH) $(pysetupfile) $(QUIETSETUP) build
+
+install: $(pysetupfile)
+	$(PYTHON_PATH) $(pysetupfile) install --prefix $(DESTDIR_SQ)$(prefix)
+
+instlibdir: $(pysetupfile)
+	@echo "$(DESTDIR_SQ)$(prefix)/$(PYLIBDIR)"
+
+clean:
+	$(QUIET)$(PYTHON_PATH) $(pysetupfile) $(QUIETSETUP) clean -a
+	$(RM) *.pyo *.pyc
diff --git a/git_remote_helpers/__init__.py b/git_remote_helpers/__init__.py
new file mode 100644
index 0000000000..00f69cbeda
--- /dev/null
+++ b/git_remote_helpers/__init__.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+
+"""Support library package for git remote helpers.
+
+Git remote helpers are helper commands that interfaces with a non-git
+repository to provide automatic import of non-git history into a Git
+repository.
+
+This package provides the support library needed by these helpers..
+The following modules are included:
+
+- git.git - Interaction with Git repositories
+
+- util - General utility functionality use by the other modules in
+         this package, and also used directly by the helpers.
+"""
diff --git a/git_remote_helpers/git/__init__.py b/git_remote_helpers/git/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/git_remote_helpers/git/git.py b/git_remote_helpers/git/git.py
new file mode 100644
index 0000000000..a383e6c08d
--- /dev/null
+++ b/git_remote_helpers/git/git.py
@@ -0,0 +1,678 @@
+#!/usr/bin/env python
+
+"""Functionality for interacting with Git repositories.
+
+This module provides classes for interfacing with a Git repository.
+"""
+
+import os
+import re
+import time
+from binascii import hexlify
+from cStringIO import StringIO
+import unittest
+
+from git_remote_helpers.util import debug, error, die, start_command, run_command
+
+
+def get_git_dir ():
+    """Return the path to the GIT_DIR for this repo."""
+    args = ("git", "rev-parse", "--git-dir")
+    exit_code, output, errors = run_command(args)
+    if exit_code:
+        die("Failed to retrieve git dir")
+    assert not errors
+    return output.strip()
+
+
+def parse_git_config ():
+    """Return a dict containing the parsed version of 'git config -l'."""
+    exit_code, output, errors = run_command(("git", "config", "-z", "-l"))
+    if exit_code:
+        die("Failed to retrieve git configuration")
+    assert not errors
+    return dict([e.split('\n', 1) for e in output.split("\0") if e])
+
+
+def git_config_bool (value):
+    """Convert the given git config string value to True or False.
+
+    Raise ValueError if the given string was not recognized as a
+    boolean value.
+
+    """
+    norm_value = str(value).strip().lower()
+    if norm_value in ("true", "1", "yes", "on", ""):
+        return True
+    if norm_value in ("false", "0", "no", "off", "none"):
+        return False
+    raise ValueError("Failed to parse '%s' into a boolean value" % (value))
+
+
+def valid_git_ref (ref_name):
+    """Return True iff the given ref name is a valid git ref name."""
+    # The following is a reimplementation of the git check-ref-format
+    # command.  The rules were derived from the git check-ref-format(1)
+    # manual page.  This code should be replaced by a call to
+    # check_ref_format() in the git library, when such is available.
+    if ref_name.endswith('/') or \
+       ref_name.startswith('.') or \
+       ref_name.count('/.') or \
+       ref_name.count('..') or \
+       ref_name.endswith('.lock'):
+        return False
+    for c in ref_name:
+        if ord(c) < 0x20 or ord(c) == 0x7f or c in " ~^:?*[":
+            return False
+    return True
+
+
+class GitObjectFetcher(object):
+
+    """Provide parsed access to 'git cat-file --batch'.
+
+    This provides a read-only interface to the Git object database.
+
+    """
+
+    def __init__ (self):
+        """Initiate a 'git cat-file --batch' session."""
+        self.queue = []  # List of object names to be submitted
+        self.in_transit = None  # Object name currently in transit
+
+        # 'git cat-file --batch' produces binary output which is likely
+        # to be corrupted by the default "rU"-mode pipe opened by
+        # start_command.  (Mode == "rU" does universal new-line
+        # conversion, which mangles carriage returns.) Therefore, we
+        # open an explicitly binary-safe pipe for transferring the
+        # output from 'git cat-file --batch'.
+        pipe_r_fd, pipe_w_fd = os.pipe()
+        pipe_r = os.fdopen(pipe_r_fd, "rb")
+        pipe_w = os.fdopen(pipe_w_fd, "wb")
+        self.proc = start_command(("git", "cat-file", "--batch"),
+                                  stdout = pipe_w)
+        self.f = pipe_r
+
+    def __del__ (self):
+        """Verify completed communication with 'git cat-file --batch'."""
+        assert not self.queue
+        assert self.in_transit is None
+        self.proc.stdin.close()
+        assert self.proc.wait() == 0  # Zero exit code
+        assert self.f.read() == ""  # No remaining output
+
+    def _submit_next_object (self):
+        """Submit queue items to the 'git cat-file --batch' process.
+
+        If there are items in the queue, and there is currently no item
+        currently in 'transit', then pop the first item off the queue,
+        and submit it.
+
+        """
+        if self.queue and self.in_transit is None:
+            self.in_transit = self.queue.pop(0)
+            print >> self.proc.stdin, self.in_transit[0]
+
+    def push (self, obj, callback):
+        """Push the given object name onto the queue.
+
+        The given callback function will at some point in the future
+        be called exactly once with the following arguments:
+        - self - this GitObjectFetcher instance
+        - obj  - the object name provided to push()
+        - sha1 - the SHA1 of the object, if 'None' obj is missing
+        - t    - the type of the object (tag/commit/tree/blob)
+        - size - the size of the object in bytes
+        - data - the object contents
+
+        """
+        self.queue.append((obj, callback))
+        self._submit_next_object()  # (Re)start queue processing
+
+    def process_next_entry (self):
+        """Read the next entry off the queue and invoke callback."""
+        obj, cb = self.in_transit
+        self.in_transit = None
+        header = self.f.readline()
+        if header == "%s missing\n" % (obj):
+            cb(self, obj, None, None, None, None)
+            return
+        sha1, t, size = header.split(" ")
+        assert len(sha1) == 40
+        assert t in ("tag", "commit", "tree", "blob")
+        assert size.endswith("\n")
+        size = int(size.strip())
+        data = self.f.read(size)
+        assert self.f.read(1) == "\n"
+        cb(self, obj, sha1, t, size, data)
+        self._submit_next_object()
+
+    def process (self):
+        """Process the current queue until empty."""
+        while self.in_transit is not None:
+            self.process_next_entry()
+
+    # High-level convenience methods:
+
+    def get_sha1 (self, objspec):
+        """Return the SHA1 of the object specified by 'objspec'.
+
+        Return None if 'objspec' does not specify an existing object.
+
+        """
+        class _ObjHandler(object):
+            """Helper class for getting the returned SHA1."""
+            def __init__ (self, parser):
+                self.parser = parser
+                self.sha1 = None
+
+            def __call__ (self, parser, obj, sha1, t, size, data):
+                # FIXME: Many unused arguments. Could this be cheaper?
+                assert parser == self.parser
+                self.sha1 = sha1
+
+        handler = _ObjHandler(self)
+        self.push(objspec, handler)
+        self.process()
+        return handler.sha1
+
+    def open_obj (self, objspec):
+        """Return a file object wrapping the contents of a named object.
+
+        The caller is responsible for calling .close() on the returned
+        file object.
+
+        Raise KeyError if 'objspec' does not exist in the repo.
+
+        """
+        class _ObjHandler(object):
+            """Helper class for parsing the returned git object."""
+            def __init__ (self, parser):
+                """Set up helper."""
+                self.parser = parser
+                self.contents = StringIO()
+                self.err = None
+
+            def __call__ (self, parser, obj, sha1, t, size, data):
+                """Git object callback (see GitObjectFetcher documentation)."""
+                assert parser == self.parser
+                if not sha1:  # Missing object
+                    self.err = "Missing object '%s'" % obj
+                else:
+                    assert size == len(data)
+                    self.contents.write(data)
+
+        handler = _ObjHandler(self)
+        self.push(objspec, handler)
+        self.process()
+        if handler.err:
+            raise KeyError(handler.err)
+        handler.contents.seek(0)
+        return handler.contents
+
+    def walk_tree (self, tree_objspec, callback, prefix = ""):
+        """Recursively walk the given Git tree object.
+
+        Recursively walk all subtrees of the given tree object, and
+        invoke the given callback passing three arguments:
+        (path, mode, data) with the path, permission bits, and contents
+        of all the blobs found in the entire tree structure.
+
+        """
+        class _ObjHandler(object):
+            """Helper class for walking a git tree structure."""
+            def __init__ (self, parser, cb, path, mode = None):
+                """Set up helper."""
+                self.parser = parser
+                self.cb = cb
+                self.path = path
+                self.mode = mode
+                self.err = None
+
+            def parse_tree (self, treedata):
+                """Parse tree object data, yield tree entries.
+
+                Each tree entry is a 3-tuple (mode, sha1, path)
+
+                self.path is prepended to all paths yielded
+                from this method.
+
+                """
+                while treedata:
+                    mode = int(treedata[:6], 10)
+                    # Turn 100xxx into xxx
+                    if mode > 100000:
+                        mode -= 100000
+                    assert treedata[6] == " "
+                    i = treedata.find("\0", 7)
+                    assert i > 0
+                    path = treedata[7:i]
+                    sha1 = hexlify(treedata[i + 1: i + 21])
+                    yield (mode, sha1, self.path + path)
+                    treedata = treedata[i + 21:]
+
+            def __call__ (self, parser, obj, sha1, t, size, data):
+                """Git object callback (see GitObjectFetcher documentation)."""
+                assert parser == self.parser
+                if not sha1:  # Missing object
+                    self.err = "Missing object '%s'" % (obj)
+                    return
+                assert size == len(data)
+                if t == "tree":
+                    if self.path:
+                        self.path += "/"
+                    # Recurse into all blobs and subtrees
+                    for m, s, p in self.parse_tree(data):
+                        parser.push(s,
+                                    self.__class__(self.parser, self.cb, p, m))
+                elif t == "blob":
+                    self.cb(self.path, self.mode, data)
+                else:
+                    raise ValueError("Unknown object type '%s'" % (t))
+
+        self.push(tree_objspec, _ObjHandler(self, callback, prefix))
+        self.process()
+
+
+class GitRefMap(object):
+
+    """Map Git ref names to the Git object names they currently point to.
+
+    Behaves like a dictionary of Git ref names -> Git object names.
+
+    """
+
+    def __init__ (self, obj_fetcher):
+        """Create a new Git ref -> object map."""
+        self.obj_fetcher = obj_fetcher
+        self._cache = {}  # dict: refname -> objname
+
+    def _load (self, ref):
+        """Retrieve the object currently bound to the given ref.
+
+        The name of the object pointed to by the given ref is stored
+        into this mapping, and also returned.
+
+        """
+        if ref not in self._cache:
+            self._cache[ref] = self.obj_fetcher.get_sha1(ref)
+        return self._cache[ref]
+
+    def __contains__ (self, refname):
+        """Return True if the given refname is present in this cache."""
+        return bool(self._load(refname))
+
+    def __getitem__ (self, refname):
+        """Return the git object name pointed to by the given refname."""
+        commit = self._load(refname)
+        if commit is None:
+            raise KeyError("Unknown ref '%s'" % (refname))
+        return commit
+
+    def get (self, refname, default = None):
+        """Return the git object name pointed to by the given refname."""
+        commit = self._load(refname)
+        if commit is None:
+            return default
+        return commit
+
+
+class GitFICommit(object):
+
+    """Encapsulate the data in a Git fast-import commit command."""
+
+    SHA1RE = re.compile(r'^[0-9a-f]{40}$')
+
+    @classmethod
+    def parse_mode (cls, mode):
+        """Verify the given git file mode, and return it as a string."""
+        assert mode in (644, 755, 100644, 100755, 120000)
+        return "%i" % (mode)
+
+    @classmethod
+    def parse_objname (cls, objname):
+        """Return the given object name (or mark number) as a string."""
+        if isinstance(objname, int):  # Object name is a mark number
+            assert objname > 0
+            return ":%i" % (objname)
+
+        # No existence check is done, only checks for valid format
+        assert cls.SHA1RE.match(objname)  # Object name is valid SHA1
+        return objname
+
+    @classmethod
+    def quote_path (cls, path):
+        """Return a quoted version of the given path."""
+        path = path.replace("\\", "\\\\")
+        path = path.replace("\n", "\\n")
+        path = path.replace('"', '\\"')
+        return '"%s"' % (path)
+
+    @classmethod
+    def parse_path (cls, path):
+        """Verify that the given path is valid, and quote it, if needed."""
+        assert not isinstance(path, int)  # Cannot be a mark number
+
+        # These checks verify the rules on the fast-import man page
+        assert not path.count("//")
+        assert not path.endswith("/")
+        assert not path.startswith("/")
+        assert not path.count("/./")
+        assert not path.count("/../")
+        assert not path.endswith("/.")
+        assert not path.endswith("/..")
+        assert not path.startswith("./")
+        assert not path.startswith("../")
+
+        if path.count('"') + path.count('\n') + path.count('\\'):
+            return cls.quote_path(path)
+        return path
+
+    def __init__ (self, name, email, timestamp, timezone, message):
+        """Create a new Git fast-import commit, with the given metadata."""
+        self.name = name
+        self.email = email
+        self.timestamp = timestamp
+        self.timezone = timezone
+        self.message = message
+        self.pathops = []  # List of path operations in this commit
+
+    def modify (self, mode, blobname, path):
+        """Add a file modification to this Git fast-import commit."""
+        self.pathops.append(("M",
+                             self.parse_mode(mode),
+                             self.parse_objname(blobname),
+                             self.parse_path(path)))
+
+    def delete (self, path):
+        """Add a file deletion to this Git fast-import commit."""
+        self.pathops.append(("D", self.parse_path(path)))
+
+    def copy (self, path, newpath):
+        """Add a file copy to this Git fast-import commit."""
+        self.pathops.append(("C",
+                             self.parse_path(path),
+                             self.parse_path(newpath)))
+
+    def rename (self, path, newpath):
+        """Add a file rename to this Git fast-import commit."""
+        self.pathops.append(("R",
+                             self.parse_path(path),
+                             self.parse_path(newpath)))
+
+    def note (self, blobname, commit):
+        """Add a note object to this Git fast-import commit."""
+        self.pathops.append(("N",
+                             self.parse_objname(blobname),
+                             self.parse_objname(commit)))
+
+    def deleteall (self):
+        """Delete all files in this Git fast-import commit."""
+        self.pathops.append("deleteall")
+
+
+class TestGitFICommit(unittest.TestCase):
+
+    """GitFICommit selftests."""
+
+    def test_basic (self):
+        """GitFICommit basic selftests."""
+
+        def expect_fail (method, data):
+            """Verify that the method(data) raises an AssertionError."""
+            try:
+                method(data)
+            except AssertionError:
+                return
+            raise AssertionError("Failed test for invalid data '%s(%s)'" %
+                                 (method.__name__, repr(data)))
+
+    def test_parse_mode (self):
+        """GitFICommit.parse_mode() selftests."""
+        self.assertEqual(GitFICommit.parse_mode(644), "644")
+        self.assertEqual(GitFICommit.parse_mode(755), "755")
+        self.assertEqual(GitFICommit.parse_mode(100644), "100644")
+        self.assertEqual(GitFICommit.parse_mode(100755), "100755")
+        self.assertEqual(GitFICommit.parse_mode(120000), "120000")
+        self.assertRaises(AssertionError, GitFICommit.parse_mode, 0)
+        self.assertRaises(AssertionError, GitFICommit.parse_mode, 123)
+        self.assertRaises(AssertionError, GitFICommit.parse_mode, 600)
+        self.assertRaises(AssertionError, GitFICommit.parse_mode, "644")
+        self.assertRaises(AssertionError, GitFICommit.parse_mode, "abc")
+
+    def test_parse_objname (self):
+        """GitFICommit.parse_objname() selftests."""
+        self.assertEqual(GitFICommit.parse_objname(1), ":1")
+        self.assertRaises(AssertionError, GitFICommit.parse_objname, 0)
+        self.assertRaises(AssertionError, GitFICommit.parse_objname, -1)
+        self.assertEqual(GitFICommit.parse_objname("0123456789" * 4),
+                         "0123456789" * 4)
+        self.assertEqual(GitFICommit.parse_objname("2468abcdef" * 4),
+                         "2468abcdef" * 4)
+        self.assertRaises(AssertionError, GitFICommit.parse_objname,
+                          "abcdefghij" * 4)
+
+    def test_parse_path (self):
+        """GitFICommit.parse_path() selftests."""
+        self.assertEqual(GitFICommit.parse_path("foo/bar"), "foo/bar")
+        self.assertEqual(GitFICommit.parse_path("path/with\n and \" in it"),
+                         '"path/with\\n and \\" in it"')
+        self.assertRaises(AssertionError, GitFICommit.parse_path, 1)
+        self.assertRaises(AssertionError, GitFICommit.parse_path, 0)
+        self.assertRaises(AssertionError, GitFICommit.parse_path, -1)
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo//bar")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo/bar/")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "/foo/bar")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo/./bar")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo/../bar")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo/bar/.")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "foo/bar/..")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "./foo/bar")
+        self.assertRaises(AssertionError, GitFICommit.parse_path, "../foo/bar")
+
+
+class GitFastImport(object):
+
+    """Encapsulate communication with git fast-import."""
+
+    def __init__ (self, f, obj_fetcher, last_mark = 0):
+        """Set up self to communicate with a fast-import process through f."""
+        self.f = f  # File object where fast-import stream is written
+        self.obj_fetcher = obj_fetcher  # GitObjectFetcher instance
+        self.next_mark = last_mark + 1  # Next mark number
+        self.refs = set()  # Keep track of the refnames we've seen
+
+    def comment (self, s):
+        """Write the given comment in the fast-import stream."""
+        assert "\n" not in s, "Malformed comment: '%s'" % (s)
+        self.f.write("# %s\n" % (s))
+
+    def commit (self, ref, commitdata):
+        """Make a commit on the given ref, with the given GitFICommit.
+
+        Return the mark number identifying this commit.
+
+        """
+        self.f.write("""\
+commit %(ref)s
+mark :%(mark)i
+committer %(name)s <%(email)s> %(timestamp)i %(timezone)s
+data %(msgLength)i
+%(msg)s
+""" % {
+    'ref': ref,
+    'mark': self.next_mark,
+    'name': commitdata.name,
+    'email': commitdata.email,
+    'timestamp': commitdata.timestamp,
+    'timezone': commitdata.timezone,
+    'msgLength': len(commitdata.message),
+    'msg': commitdata.message,
+})
+
+        if ref not in self.refs:
+            self.refs.add(ref)
+            parent = ref + "^0"
+            if self.obj_fetcher.get_sha1(parent):
+                self.f.write("from %s\n" % (parent))
+
+        for op in commitdata.pathops:
+            self.f.write(" ".join(op))
+            self.f.write("\n")
+        self.f.write("\n")
+        retval = self.next_mark
+        self.next_mark += 1
+        return retval
+
+    def blob (self, data):
+        """Import the given blob.
+
+        Return the mark number identifying this blob.
+
+        """
+        self.f.write("blob\nmark :%i\ndata %i\n%s\n" %
+                     (self.next_mark, len(data), data))
+        retval = self.next_mark
+        self.next_mark += 1
+        return retval
+
+    def reset (self, ref, objname):
+        """Reset the given ref to point at the given Git object."""
+        self.f.write("reset %s\nfrom %s\n\n" %
+                     (ref, GitFICommit.parse_objname(objname)))
+        if ref not in self.refs:
+            self.refs.add(ref)
+
+
+class GitNotes(object):
+
+    """Encapsulate access to Git notes.
+
+    Simulates a dictionary of object name (SHA1) -> Git note mappings.
+
+    """
+
+    def __init__ (self, notes_ref, obj_fetcher):
+        """Create a new Git notes interface, bound to the given notes ref."""
+        self.notes_ref = notes_ref
+        self.obj_fetcher = obj_fetcher  # Used to get objects from repo
+        self.imports = []  # list: (objname, note data blob name) tuples
+
+    def __del__ (self):
+        """Verify that self.commit_notes() was called before destruction."""
+        if self.imports:
+            error("Missing call to self.commit_notes().")
+            error("%i notes are not committed!", len(self.imports))
+
+    def _load (self, objname):
+        """Return the note data associated with the given git object.
+
+        The note data is returned in string form. If no note is found
+        for the given object, None is returned.
+
+        """
+        try:
+            f = self.obj_fetcher.open_obj("%s:%s" % (self.notes_ref, objname))
+            ret = f.read()
+            f.close()
+        except KeyError:
+            ret = None
+        return ret
+
+    def __getitem__ (self, objname):
+        """Return the note contents associated with the given object.
+
+        Raise KeyError if given object has no associated note.
+
+        """
+        blobdata = self._load(objname)
+        if blobdata is None:
+            raise KeyError("Object '%s' has no note" % (objname))
+        return blobdata
+
+    def get (self, objname, default = None):
+        """Return the note contents associated with the given object.
+
+        Return given default if given object has no associated note.
+
+        """
+        blobdata = self._load(objname)
+        if blobdata is None:
+            return default
+        return blobdata
+
+    def import_note (self, objname, data, gfi):
+        """Tell git fast-import to store data as a note for objname.
+
+        This method uses the given GitFastImport object to create a
+        blob containing the given note data.  Also an entry mapping the
+        given object name to the created blob is stored until
+        commit_notes() is called.
+
+        Note that this method only works if it is later followed by a
+        call to self.commit_notes() (which produces the note commit
+        that refers to the blob produced here).
+
+        """
+        if not data.endswith("\n"):
+            data += "\n"
+        gfi.comment("Importing note for object %s" % (objname))
+        mark = gfi.blob(data)
+        self.imports.append((objname, mark))
+
+    def commit_notes (self, gfi, author, message):
+        """Produce a git fast-import note commit for the imported notes.
+
+        This method uses the given GitFastImport object to create a
+        commit on the notes ref, introducing the notes previously
+        submitted to import_note().
+
+        """
+        if not self.imports:
+            return
+        commitdata = GitFICommit(author[0], author[1],
+                                 time.time(), "0000", message)
+        for objname, blobname in self.imports:
+            assert isinstance(objname, int) and objname > 0
+            assert isinstance(blobname, int) and blobname > 0
+            commitdata.note(blobname, objname)
+        gfi.commit(self.notes_ref, commitdata)
+        self.imports = []
+
+
+class GitCachedNotes(GitNotes):
+
+    """Encapsulate access to Git notes (cached version).
+
+    Only use this class if no caching is done at a higher level.
+
+    Simulates a dictionary of object name (SHA1) -> Git note mappings.
+
+    """
+
+    def __init__ (self, notes_ref, obj_fetcher):
+        """Set up a caching wrapper around GitNotes."""
+        GitNotes.__init__(self, notes_ref, obj_fetcher)
+        self._cache = {}  # Cache: object name -> note data
+
+    def __del__ (self):
+        """Verify that GitNotes' destructor is called."""
+        GitNotes.__del__(self)
+
+    def _load (self, objname):
+        """Extend GitNotes._load() with a local objname -> note cache."""
+        if objname not in self._cache:
+            self._cache[objname] = GitNotes._load(self, objname)
+        return self._cache[objname]
+
+    def import_note (self, objname, data, gfi):
+        """Extend GitNotes.import_note() with a local objname -> note cache."""
+        if not data.endswith("\n"):
+            data += "\n"
+        assert objname not in self._cache
+        self._cache[objname] = data
+        GitNotes.import_note(self, objname, data, gfi)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/git_remote_helpers/setup.py b/git_remote_helpers/setup.py
new file mode 100644
index 0000000000..4d434b65cb
--- /dev/null
+++ b/git_remote_helpers/setup.py
@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+
+"""Distutils build/install script for the git_remote_helpers package."""
+
+from distutils.core import setup
+
+setup(
+    name = 'git_remote_helpers',
+    version = '0.1.0',
+    description = 'Git remote helper program for non-git repositories',
+    license = 'GPLv2',
+    author = 'The Git Community',
+    author_email = 'git@vger.kernel.org',
+    url = 'http://www.git-scm.com/',
+    package_dir = {'git_remote_helpers': ''},
+    packages = ['git_remote_helpers', 'git_remote_helpers.git'],
+)
diff --git a/git_remote_helpers/util.py b/git_remote_helpers/util.py
new file mode 100644
index 0000000000..dce83e6066
--- /dev/null
+++ b/git_remote_helpers/util.py
@@ -0,0 +1,194 @@
+#!/usr/bin/env python
+
+"""Misc. useful functionality used by the rest of this package.
+
+This module provides common functionality used by the other modules in
+this package.
+
+"""
+
+import sys
+import os
+import subprocess
+
+
+# Whether or not to show debug messages
+DEBUG = False
+
+def notify(msg, *args):
+    """Print a message to stderr."""
+    print >> sys.stderr, msg % args
+
+def debug (msg, *args):
+    """Print a debug message to stderr when DEBUG is enabled."""
+    if DEBUG:
+        print >> sys.stderr, msg % args
+
+def error (msg, *args):
+    """Print an error message to stderr."""
+    print >> sys.stderr, "ERROR:", msg % args
+
+def warn(msg, *args):
+    """Print a warning message to stderr."""
+    print >> sys.stderr, "warning:", msg % args
+
+def die (msg, *args):
+    """Print as error message to stderr and exit the program."""
+    error(msg, *args)
+    sys.exit(1)
+
+
+class ProgressIndicator(object):
+
+    """Simple progress indicator.
+
+    Displayed as a spinning character by default, but can be customized
+    by passing custom messages that overrides the spinning character.
+
+    """
+
+    States = ("|", "/", "-", "\\")
+
+    def __init__ (self, prefix = "", f = sys.stdout):
+        """Create a new ProgressIndicator, bound to the given file object."""
+        self.n = 0  # Simple progress counter
+        self.f = f  # Progress is written to this file object
+        self.prev_len = 0  # Length of previous msg (to be overwritten)
+        self.prefix = prefix  # Prefix prepended to each progress message
+        self.prefix_lens = [] # Stack of prefix string lengths
+
+    def pushprefix (self, prefix):
+        """Append the given prefix onto the prefix stack."""
+        self.prefix_lens.append(len(self.prefix))
+        self.prefix += prefix
+
+    def popprefix (self):
+        """Remove the last prefix from the prefix stack."""
+        prev_len = self.prefix_lens.pop()
+        self.prefix = self.prefix[:prev_len]
+
+    def __call__ (self, msg = None, lf = False):
+        """Indicate progress, possibly with a custom message."""
+        if msg is None:
+            msg = self.States[self.n % len(self.States)]
+        msg = self.prefix + msg
+        print >> self.f, "\r%-*s" % (self.prev_len, msg),
+        self.prev_len = len(msg.expandtabs())
+        if lf:
+            print >> self.f
+            self.prev_len = 0
+        self.n += 1
+
+    def finish (self, msg = "done", noprefix = False):
+        """Finalize progress indication with the given message."""
+        if noprefix:
+            self.prefix = ""
+        self(msg, True)
+
+
+def start_command (args, cwd = None, shell = False, add_env = None,
+                   stdin = subprocess.PIPE, stdout = subprocess.PIPE,
+                   stderr = subprocess.PIPE):
+    """Start the given command, and return a subprocess object.
+
+    This provides a simpler interface to the subprocess module.
+
+    """
+    env = None
+    if add_env is not None:
+        env = os.environ.copy()
+        env.update(add_env)
+    return subprocess.Popen(args, bufsize = 1, stdin = stdin, stdout = stdout,
+                            stderr = stderr, cwd = cwd, shell = shell,
+                            env = env, universal_newlines = True)
+
+
+def run_command (args, cwd = None, shell = False, add_env = None,
+                 flag_error = True):
+    """Run the given command to completion, and return its results.
+
+    This provides a simpler interface to the subprocess module.
+
+    The results are formatted as a 3-tuple: (exit_code, output, errors)
+
+    If flag_error is enabled, Error messages will be produced if the
+    subprocess terminated with a non-zero exit code and/or stderr
+    output.
+
+    The other arguments are passed on to start_command().
+
+    """
+    process = start_command(args, cwd, shell, add_env)
+    (output, errors) = process.communicate()
+    exit_code = process.returncode
+    if flag_error and errors:
+        error("'%s' returned errors:\n---\n%s---", " ".join(args), errors)
+    if flag_error and exit_code:
+        error("'%s' returned exit code %i", " ".join(args), exit_code)
+    return (exit_code, output, errors)
+
+
+def file_reader_method (missing_ok = False):
+    """Decorator for simplifying reading of files.
+
+    If missing_ok is True, a failure to open a file for reading will
+    not raise the usual IOError, but instead the wrapped method will be
+    called with f == None.  The method must in this case properly
+    handle f == None.
+
+    """
+    def _wrap (method):
+        """Teach given method to handle both filenames and file objects.
+
+        The given method must take a file object as its second argument
+        (the first argument being 'self', of course).  This decorator
+        will take a filename given as the second argument and promote
+        it to a file object.
+
+        """
+        def _wrapped_method (self, filename, *args, **kwargs):
+            if isinstance(filename, file):
+                f = filename
+            else:
+                try:
+                    f = open(filename, 'r')
+                except IOError:
+                    if missing_ok:
+                        f = None
+                    else:
+                        raise
+            try:
+                return method(self, f, *args, **kwargs)
+            finally:
+                if not isinstance(filename, file) and f:
+                    f.close()
+        return _wrapped_method
+    return _wrap
+
+
+def file_writer_method (method):
+    """Decorator for simplifying writing of files.
+
+    Enables the given method to handle both filenames and file objects.
+
+    The given method must take a file object as its second argument
+    (the first argument being 'self', of course).  This decorator will
+    take a filename given as the second argument and promote it to a
+    file object.
+
+    """
+    def _new_method (self, filename, *args, **kwargs):
+        if isinstance(filename, file):
+            f = filename
+        else:
+            # Make sure the containing directory exists
+            parent_dir = os.path.dirname(filename)
+            if not os.path.isdir(parent_dir):
+                os.makedirs(parent_dir)
+            f = open(filename, 'w')
+        try:
+            return method(self, f, *args, **kwargs)
+        finally:
+            if not isinstance(filename, file):
+                f.close()
+    return _new_method
diff --git a/remote.c b/remote.c
index b979a9642b..e3afecdb10 100644
--- a/remote.c
+++ b/remote.c
@@ -53,6 +53,11 @@ static struct rewrites rewrites_push;
 #define BUF_SIZE (2048)
 static char buffer[BUF_SIZE];
 
+static int valid_remote(const struct remote *remote)
+{
+	return (!!remote->url) || (!!remote->foreign_vcs);
+}
+
 static const char *alias_url(const char *url, struct rewrites *r)
 {
 	int i, j;
@@ -441,6 +446,8 @@ static int handle_config(const char *key, const char *value, void *cb)
 	} else if (!strcmp(subkey, ".proxy")) {
 		return git_config_string((const char **)&remote->http_proxy,
 					 key, value);
+	} else if (!strcmp(subkey, ".vcs")) {
+		return git_config_string(&remote->foreign_vcs, key, value);
 	}
 	return 0;
 }
@@ -668,6 +675,16 @@ static struct refspec *parse_push_refspec(int nr_refspec, const char **refspec)
 	return parse_refspec_internal(nr_refspec, refspec, 0, 0);
 }
 
+void free_refspec(int nr_refspec, struct refspec *refspec)
+{
+	int i;
+	for (i = 0; i < nr_refspec; i++) {
+		free(refspec[i].src);
+		free(refspec[i].dst);
+	}
+	free(refspec);
+}
+
 static int valid_remote_nick(const char *name)
 {
 	if (!name[0] || is_dot_or_dotdot(name))
@@ -690,14 +707,14 @@ struct remote *remote_get(const char *name)
 
 	ret = make_remote(name, 0);
 	if (valid_remote_nick(name)) {
-		if (!ret->url)
+		if (!valid_remote(ret))
 			read_remotes_file(ret);
-		if (!ret->url)
+		if (!valid_remote(ret))
 			read_branches_file(ret);
 	}
-	if (name_given && !ret->url)
+	if (name_given && !valid_remote(ret))
 		add_url_alias(ret, name);
-	if (!ret->url)
+	if (!valid_remote(ret))
 		return NULL;
 	ret->fetch = parse_fetch_refspec(ret->fetch_refspec_nr, ret->fetch_refspec);
 	ret->push = parse_push_refspec(ret->push_refspec_nr, ret->push_refspec);
@@ -810,6 +827,23 @@ static int match_name_with_pattern(const char *key, const char *name,
 	return ret;
 }
 
+char *apply_refspecs(struct refspec *refspecs, int nr_refspec,
+		     const char *name)
+{
+	int i;
+	char *ret = NULL;
+	for (i = 0; i < nr_refspec; i++) {
+		struct refspec *refspec = refspecs + i;
+		if (refspec->pattern) {
+			if (match_name_with_pattern(refspec->src, name,
+						    refspec->dst, &ret))
+				return ret;
+		} else if (!strcmp(refspec->src, name))
+			return strdup(refspec->dst);
+	}
+	return NULL;
+}
+
 int remote_find_tracking(struct remote *remote, struct refspec *refspec)
 {
 	int find_src = refspec->src == NULL;
diff --git a/remote.h b/remote.h
index d0aba81ead..8b7ecf9197 100644
--- a/remote.h
+++ b/remote.h
@@ -11,6 +11,8 @@ struct remote {
 	const char *name;
 	int origin;
 
+	const char *foreign_vcs;
+
 	const char **url;
 	int url_nr;
 	int url_alloc;
@@ -89,6 +91,11 @@ void ref_remove_duplicates(struct ref *ref_map);
 int valid_fetch_refspec(const char *refspec);
 struct refspec *parse_fetch_refspec(int nr_refspec, const char **refspec);
 
+void free_refspec(int nr_refspec, struct refspec *refspec);
+
+char *apply_refspecs(struct refspec *refspecs, int nr_refspec,
+		     const char *name);
+
 int match_refs(struct ref *src, struct ref **dst,
 	       int nr_refspec, const char **refspec, int all);
 
diff --git a/t/test-lib.sh b/t/test-lib.sh
index ec3336aba5..2d523fe0f0 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -632,20 +632,29 @@ GIT_CONFIG_NOSYSTEM=1
 GIT_CONFIG_NOGLOBAL=1
 export PATH GIT_EXEC_PATH GIT_TEMPLATE_DIR GIT_CONFIG_NOSYSTEM GIT_CONFIG_NOGLOBAL
 
+. ../GIT-BUILD-OPTIONS
+
 GITPERLLIB=$(pwd)/../perl/blib/lib:$(pwd)/../perl/blib/arch/auto/Git
 export GITPERLLIB
 test -d ../templates/blt || {
 	error "You haven't built things yet, have you?"
 }
 
+if test -z "$GIT_TEST_INSTALLED" && test -z "$NO_PYTHON"
+then
+	GITPYTHONLIB="$(pwd)/../git_remote_helpers/build/lib"
+	export GITPYTHONLIB
+	test -d ../git_remote_helpers/build || {
+		error "You haven't built git_remote_helpers yet, have you?"
+	}
+fi
+
 if ! test -x ../test-chmtime; then
 	echo >&2 'You need to build test-chmtime:'
 	echo >&2 'Run "make test-chmtime" in the source (toplevel) directory'
 	exit 1
 fi
 
-. ../GIT-BUILD-OPTIONS
-
 # Test repository
 test="trash directory.$(basename "$0" .sh)"
 test -n "$root" && test="$root/$test"
@@ -729,6 +738,7 @@ case $(uname -s) in
 esac
 
 test -z "$NO_PERL" && test_set_prereq PERL
+test -z "$NO_PYTHON" && test_set_prereq PYTHON
 
 # test whether the filesystem supports symbolic links
 ln -s x y 2>/dev/null && test -h y 2>/dev/null && test_set_prereq SYMLINKS
diff --git a/transport-helper.c b/transport-helper.c
index 5078c7100f..11f3d7ec52 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -6,6 +6,7 @@
 #include "diff.h"
 #include "revision.h"
 #include "quote.h"
+#include "remote.h"
 
 struct helper_data
 {
@@ -13,8 +14,12 @@ struct helper_data
 	struct child_process *helper;
 	FILE *out;
 	unsigned fetch : 1,
+		import : 1,
 		option : 1,
 		push : 1;
+	/* These go from remote name (as in "list") to private name */
+	struct refspec *refspecs;
+	int refspec_nr;
 };
 
 static struct child_process *get_helper(struct transport *transport)
@@ -22,6 +27,9 @@ static struct child_process *get_helper(struct transport *transport)
 	struct helper_data *data = transport->data;
 	struct strbuf buf = STRBUF_INIT;
 	struct child_process *helper;
+	const char **refspecs = NULL;
+	int refspec_nr = 0;
+	int refspec_alloc = 0;
 
 	if (data->helper)
 		return data->helper;
@@ -55,7 +63,25 @@ static struct child_process *get_helper(struct transport *transport)
 			data->option = 1;
 		if (!strcmp(buf.buf, "push"))
 			data->push = 1;
+		if (!strcmp(buf.buf, "import"))
+			data->import = 1;
+		if (!data->refspecs && !prefixcmp(buf.buf, "refspec ")) {
+			ALLOC_GROW(refspecs,
+				   refspec_nr + 1,
+				   refspec_alloc);
+			refspecs[refspec_nr++] = strdup(buf.buf + strlen("refspec "));
+		}
 	}
+	if (refspecs) {
+		int i;
+		data->refspec_nr = refspec_nr;
+		data->refspecs = parse_fetch_refspec(refspec_nr, refspecs);
+		for (i = 0; i < refspec_nr; i++) {
+			free((char *)refspecs[i]);
+		}
+		free(refspecs);
+	}
+	strbuf_release(&buf);
 	return data->helper;
 }
 
@@ -72,7 +98,6 @@ static int disconnect_helper(struct transport *transport)
 		free(data->helper);
 		data->helper = NULL;
 	}
-	free(data);
 	return 0;
 }
 
@@ -154,8 +179,18 @@ static void standard_options(struct transport *t)
 	set_helper_option(t, "verbosity", buf);
 }
 
+static int release_helper(struct transport *transport)
+{
+	struct helper_data *data = transport->data;
+	free_refspec(data->refspec_nr, data->refspecs);
+	data->refspecs = NULL;
+	disconnect_helper(transport);
+	free(transport->data);
+	return 0;
+}
+
 static int fetch_with_fetch(struct transport *transport,
-			    int nr_heads, const struct ref **to_fetch)
+			    int nr_heads, struct ref **to_fetch)
 {
 	struct helper_data *data = transport->data;
 	int i;
@@ -197,8 +232,64 @@ static int fetch_with_fetch(struct transport *transport,
 	return 0;
 }
 
+static int get_importer(struct transport *transport, struct child_process *fastimport)
+{
+	struct child_process *helper = get_helper(transport);
+	memset(fastimport, 0, sizeof(*fastimport));
+	fastimport->in = helper->out;
+	fastimport->argv = xcalloc(5, sizeof(*fastimport->argv));
+	fastimport->argv[0] = "fast-import";
+	fastimport->argv[1] = "--quiet";
+
+	fastimport->git_cmd = 1;
+	return start_command(fastimport);
+}
+
+static int fetch_with_import(struct transport *transport,
+			     int nr_heads, struct ref **to_fetch)
+{
+	struct child_process fastimport;
+	struct child_process *helper = get_helper(transport);
+	struct helper_data *data = transport->data;
+	int i;
+	struct ref *posn;
+	struct strbuf buf = STRBUF_INIT;
+
+	if (get_importer(transport, &fastimport))
+		die("Couldn't run fast-import");
+
+	for (i = 0; i < nr_heads; i++) {
+		posn = to_fetch[i];
+		if (posn->status & REF_STATUS_UPTODATE)
+			continue;
+
+		strbuf_addf(&buf, "import %s\n", posn->name);
+		write_in_full(helper->in, buf.buf, buf.len);
+		strbuf_reset(&buf);
+	}
+	disconnect_helper(transport);
+	finish_command(&fastimport);
+	free(fastimport.argv);
+	fastimport.argv = NULL;
+
+	for (i = 0; i < nr_heads; i++) {
+		char *private;
+		posn = to_fetch[i];
+		if (posn->status & REF_STATUS_UPTODATE)
+			continue;
+		if (data->refspecs)
+			private = apply_refspecs(data->refspecs, data->refspec_nr, posn->name);
+		else
+			private = strdup(posn->name);
+		read_ref(private, posn->old_sha1);
+		free(private);
+	}
+	strbuf_release(&buf);
+	return 0;
+}
+
 static int fetch(struct transport *transport,
-		 int nr_heads, const struct ref **to_fetch)
+		 int nr_heads, struct ref **to_fetch)
 {
 	struct helper_data *data = transport->data;
 	int i, count;
@@ -214,6 +305,9 @@ static int fetch(struct transport *transport,
 	if (data->fetch)
 		return fetch_with_fetch(transport, nr_heads, to_fetch);
 
+	if (data->import)
+		return fetch_with_import(transport, nr_heads, to_fetch);
+
 	return -1;
 }
 
@@ -343,6 +437,22 @@ static int push_refs(struct transport *transport,
 	return 0;
 }
 
+static int has_attribute(const char *attrs, const char *attr) {
+	int len;
+	if (!attrs)
+		return 0;
+
+	len = strlen(attr);
+	for (;;) {
+		const char *space = strchrnul(attrs, ' ');
+		if (len == space - attrs && !strncmp(attrs, attr, len))
+			return 1;
+		if (!*space)
+			return 0;
+		attrs = space + 1;
+	}
+}
+
 static struct ref *get_refs_list(struct transport *transport, int for_push)
 {
 	struct helper_data *data = transport->data;
@@ -379,6 +489,12 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 			(*tail)->symref = xstrdup(buf.buf + 1);
 		else if (buf.buf[0] != '?')
 			get_sha1_hex(buf.buf, (*tail)->old_sha1);
+		if (eon) {
+			if (has_attribute(eon + 1, "unchanged")) {
+				(*tail)->status |= REF_STATUS_UPTODATE;
+				read_ref((*tail)->name, (*tail)->old_sha1);
+			}
+		}
 		tail = &((*tail)->next);
 	}
 	strbuf_release(&buf);
@@ -399,6 +515,6 @@ int transport_helper_init(struct transport *transport, const char *name)
 	transport->get_refs_list = get_refs_list;
 	transport->fetch = fetch;
 	transport->push_refs = push_refs;
-	transport->disconnect = disconnect_helper;
+	transport->disconnect = release_helper;
 	return 0;
 }
diff --git a/transport.c b/transport.c
index 7362ec09b2..3eea836a33 100644
--- a/transport.c
+++ b/transport.c
@@ -204,7 +204,7 @@ static struct ref *get_refs_via_rsync(struct transport *transport, int for_push)
 }
 
 static int fetch_objs_via_rsync(struct transport *transport,
-				int nr_objs, const struct ref **to_fetch)
+				int nr_objs, struct ref **to_fetch)
 {
 	struct strbuf buf = STRBUF_INIT;
 	struct child_process rsync;
@@ -379,7 +379,7 @@ static struct ref *get_refs_from_bundle(struct transport *transport, int for_pus
 }
 
 static int fetch_refs_from_bundle(struct transport *transport,
-			       int nr_heads, const struct ref **to_fetch)
+			       int nr_heads, struct ref **to_fetch)
 {
 	struct bundle_transport_data *data = transport->data;
 	return unbundle(&data->header, data->fd);
@@ -457,7 +457,7 @@ static struct ref *get_refs_via_connect(struct transport *transport, int for_pus
 }
 
 static int fetch_refs_via_pack(struct transport *transport,
-			       int nr_heads, const struct ref **to_fetch)
+			       int nr_heads, struct ref **to_fetch)
 {
 	struct git_transport_data *data = transport->data;
 	char **heads = xmalloc(nr_heads * sizeof(*heads));
@@ -788,8 +788,26 @@ struct transport *transport_get(struct remote *remote, const char *url)
 		die("No remote provided to transport_get()");
 
 	ret->remote = remote;
+
+	if (!url && remote && remote->url)
+		url = remote->url[0];
 	ret->url = url;
 
+	/* maybe it is a foreign URL? */
+	if (url) {
+		const char *p = url;
+
+		while (isalnum(*p))
+			p++;
+		if (!prefixcmp(p, "::"))
+			remote->foreign_vcs = xstrndup(url, p - url);
+	}
+
+	if (remote && remote->foreign_vcs) {
+		transport_helper_init(ret, remote->foreign_vcs);
+		return ret;
+	}
+
 	if (!prefixcmp(url, "rsync:")) {
 		ret->get_refs_list = get_refs_via_rsync;
 		ret->fetch = fetch_objs_via_rsync;
@@ -896,16 +914,17 @@ const struct ref *transport_get_remote_refs(struct transport *transport)
 	return transport->remote_refs;
 }
 
-int transport_fetch_refs(struct transport *transport, const struct ref *refs)
+int transport_fetch_refs(struct transport *transport, struct ref *refs)
 {
 	int rc;
 	int nr_heads = 0, nr_alloc = 0, nr_refs = 0;
-	const struct ref **heads = NULL;
-	const struct ref *rm;
+	struct ref **heads = NULL;
+	struct ref *rm;
 
 	for (rm = refs; rm; rm = rm->next) {
 		nr_refs++;
 		if (rm->peer_ref &&
+		    !is_null_sha1(rm->old_sha1) &&
 		    !hashcmp(rm->peer_ref->old_sha1, rm->old_sha1))
 			continue;
 		ALLOC_GROW(heads, nr_heads + 1, nr_alloc);
diff --git a/transport.h b/transport.h
index e4e6177e26..9e74406fa2 100644
--- a/transport.h
+++ b/transport.h
@@ -18,11 +18,48 @@ struct transport {
 	int (*set_option)(struct transport *connection, const char *name,
 			  const char *value);
 
+	/**
+	 * Returns a list of the remote side's refs. In order to allow
+	 * the transport to try to share connections, for_push is a
+	 * hint as to whether the ultimate operation is a push or a fetch.
+	 *
+	 * If the transport is able to determine the remote hash for
+	 * the ref without a huge amount of effort, it should store it
+	 * in the ref's old_sha1 field; otherwise it should be all 0.
+	 **/
 	struct ref *(*get_refs_list)(struct transport *transport, int for_push);
-	int (*fetch)(struct transport *transport, int refs_nr, const struct ref **refs);
+
+	/**
+	 * Fetch the objects for the given refs. Note that this gets
+	 * an array, and should ignore the list structure.
+	 *
+	 * If the transport did not get hashes for refs in
+	 * get_refs_list(), it should set the old_sha1 fields in the
+	 * provided refs now.
+	 **/
+	int (*fetch)(struct transport *transport, int refs_nr, struct ref **refs);
+
+	/**
+	 * Push the objects and refs. Send the necessary objects, and
+	 * then, for any refs where peer_ref is set and
+	 * peer_ref->new_sha1 is different from old_sha1, tell the
+	 * remote side to update each ref in the list from old_sha1 to
+	 * peer_ref->new_sha1.
+	 *
+	 * Where possible, set the status for each ref appropriately.
+	 *
+	 * The transport must modify new_sha1 in the ref to the new
+	 * value if the remote accepted the change. Note that this
+	 * could be a different value from peer_ref->new_sha1 if the
+	 * process involved generating new commits.
+	 **/
 	int (*push_refs)(struct transport *transport, struct ref *refs, int flags);
 	int (*push)(struct transport *connection, int refspec_nr, const char **refspec, int flags);
 
+	/** get_refs_list(), fetch(), and push_refs() can keep
+	 * resources (such as a connection) reserved for futher
+	 * use. disconnect() releases these resources.
+	 **/
 	int (*disconnect)(struct transport *connection);
 	char *pack_lockfile;
 	signed verbose : 3;
@@ -74,7 +111,7 @@ int transport_push(struct transport *connection,
 
 const struct ref *transport_get_remote_refs(struct transport *transport);
 
-int transport_fetch_refs(struct transport *transport, const struct ref *refs);
+int transport_fetch_refs(struct transport *transport, struct ref *refs);
 void transport_unlock_pack(struct transport *transport);
 int transport_disconnect(struct transport *transport);
 char *transport_anonymize_url(const char *url);