connect: request remote refs using v2

Teach the client to be able to request a remote's refs using protocol
v2.  This is done by having a client issue a 'ls-refs' request to a v2
server.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5702-protocol-v2.sh

@@ -0,0 +1,57 @@
+#!/bin/sh
+
+test_description='test git wire-protocol version 2'
+
+TEST_NO_CREATE_REPO=1
+
+. ./test-lib.sh
+
+# Test protocol v2 with 'git://' transport
+#
+. "$TEST_DIRECTORY"/lib-git-daemon.sh
+start_git_daemon --export-all --enable=receive-pack
+daemon_parent=$GIT_DAEMON_DOCUMENT_ROOT_PATH/parent
+
+test_expect_success 'create repo to be served by git-daemon' '
+	git init "$daemon_parent" &&
+	test_commit -C "$daemon_parent" one
+'
+
+test_expect_success 'list refs with git:// using protocol v2' '
+	test_when_finished "rm -f log" &&
+
+	GIT_TRACE_PACKET="$(pwd)/log" git -c protocol.version=2 \
+		ls-remote --symref "$GIT_DAEMON_URL/parent" >actual &&
+
+	# Client requested to use protocol v2
+	grep "git> .*\\\0\\\0version=2\\\0$" log &&
+	# Server responded using protocol v2
+	grep "git< version 2" log &&
+
+	git ls-remote --symref "$GIT_DAEMON_URL/parent" >expect &&
+	test_cmp actual expect
+'
+
+stop_git_daemon
+
+# Test protocol v2 with 'file://' transport
+#
+test_expect_success 'create repo to be served by file:// transport' '
+	git init file_parent &&
+	test_commit -C file_parent one
+'
+
+test_expect_success 'list refs with file:// using protocol v2' '
+	test_when_finished "rm -f log" &&
+
+	GIT_TRACE_PACKET="$(pwd)/log" git -c protocol.version=2 \
+		ls-remote --symref "file://$(pwd)/file_parent" >actual &&
+
+	# Server responded using protocol v2
+	grep "git< version 2" log &&
+
+	git ls-remote --symref "file://$(pwd)/file_parent" >expect &&
+	test_cmp actual expect
+'
+
+test_done