transport-helper: call do_take_over() in connect_helper

After successfully connecting to the smart transport by calling
process_connect_service() in connect_helper(), run do_take_over() to
replace the old vtable with a new one which has methods ready for the
smart transport connection. This fixes the exit code of git-archive
in test case "archive remote http repository" of t5003.

The connect_helper() function is used as the connect method of the
vtable in "transport-helper.c", and it is called by transport_connect()
in "transport.c" to setup a connection. The only place that we call
transport_connect() so far is in "builtin/archive.c". Without running
do_take_over(), it may fail to call transport_disconnect() in
run_remote_archiver() of "builtin/archive.c". This is because for a
stateless connection and a service like "git-upload-archive", the
remote helper may receive a SIGPIPE signal and exit early. Call
do_take_over() to have a graceful disconnect method, so that we still
call transport_disconnect() even if the remote helper exits early.

Helped-by: Linus Arver <linusa@google.com>
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jiangxin

t/t5003-archive-zip.sh

@@ -268,7 +268,7 @@ test_expect_success 'remote archive does not work with protocol v1' '
 '
 
 test_expect_success 'archive remote http repository' '
-	test_must_fail git archive --remote="$HTTPD_URL/auth/smart/bare.git" \
+	git archive --remote="$HTTPD_URL/auth/smart/bare.git" \
 		--output=remote-http.zip HEAD &&
 	test_cmp_bin d.zip remote-http.zip
 '

transport-helper.c

@@ -669,6 +669,8 @@ static int connect_helper(struct transport *transport, const char *name,
 
 	fd[0] = data->helper->out;
 	fd[1] = data->helper->in;
+
+	do_take_over(transport);
 	return 0;
 }