transport-helper: skip ls-refs if unnecessary

Commit e70a3030e7 ("fetch: do not list refs if fetching only hashes",
2018-10-07) and its ancestors taught Git, as an optimization, to skip
the ls-refs step when it is not necessary during a protocol v2 fetch
(for example, when lazy fetching a missing object in a partial clone, or
when running "git fetch --no-tags <remote> <SHA-1>"). But that was only
done for natively supported protocols; in particular, HTTP was not
supported.

Teach Git to skip ls-refs when using remote helpers that support connect
or stateless-connect. To do this, fetch() is made an acceptable entry
point. Because fetch() can now be the first function in the vtable
called, "get_helper(transport);" has to be added to the beginning of
that function to set the transport up (if not yet set up) before
process_connect() is invoked.

When fetch() is called, the transport could be taken over (this happens
if "connect" or "stateless-connect" is successfully run without any
"fallback" response), or not. If the transport is taken over, execution
continues like execution for natively supported protocols
(fetch_refs_via_pack() is executed, which will fetch refs using ls-refs
if needed). If not, the remote helper interface will invoke
get_refs_list() if it hasn't been invoked yet, preserving existing
behavior.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5702-protocol-v2.sh

@@ -631,6 +631,19 @@ test_expect_success 'fetch with http:// using protocol v2' '
 	grep "git< version 2" log
 '
 
+test_expect_success 'fetch with http:// by hash without tag following with protocol v2 does not list refs' '
+	test_when_finished "rm -f log" &&
+
+	test_commit -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" two_a &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" rev-parse two_a >two_a_hash &&
+
+	GIT_TRACE_PACKET="$(pwd)/log" git -C http_child -c protocol.version=2 \
+		fetch --no-tags origin $(cat two_a_hash) &&
+
+	grep "fetch< version 2" log &&
+	! grep "fetch> command=ls-refs" log
+'
+
 test_expect_success 'fetch from namespaced repo respects namespaces' '
 	test_when_finished "rm -f log" &&
 

transport-helper.c

@@ -33,6 +33,16 @@ struct helper_data {
 		check_connectivity : 1,
 		no_disconnect_req : 1,
 		no_private_update : 1;
+
+	/*
+	 * As an optimization, the transport code may invoke fetch before
+	 * get_refs_list. If this happens, and if the transport helper doesn't
+	 * support connect or stateless_connect, we need to invoke
+	 * get_refs_list ourselves if we haven't already done so. Keep track of
+	 * whether we have invoked get_refs_list.
+	 */
+	unsigned get_refs_list_called : 1;
+
 	char *export_marks;
 	char *import_marks;
 	/* These go from remote name (as in "list") to private name */
@@ -652,17 +662,25 @@ static int connect_helper(struct transport *transport, const char *name,
 	return 0;
 }
 
+static struct ref *get_refs_list_using_list(struct transport *transport,
+					    int for_push);
+
 static int fetch(struct transport *transport,
 		 int nr_heads, struct ref **to_fetch)
 {
 	struct helper_data *data = transport->data;
 	int i, count;
 
+	get_helper(transport);
+
 	if (process_connect(transport, 0)) {
 		do_take_over(transport);
 		return transport->vtable->fetch(transport, nr_heads, to_fetch);
 	}
 
+	if (!data->get_refs_list_called)
+		get_refs_list_using_list(transport, 0);
+
 	count = 0;
 	for (i = 0; i < nr_heads; i++)
 		if (!(to_fetch[i]->status & REF_STATUS_UPTODATE))
@@ -1058,6 +1076,19 @@ static int has_attribute(const char *attrs, const char *attr)
 
 static struct ref *get_refs_list(struct transport *transport, int for_push,
 				 const struct argv_array *ref_prefixes)
+{
+	get_helper(transport);
+
+	if (process_connect(transport, for_push)) {
+		do_take_over(transport);
+		return transport->vtable->get_refs_list(transport, for_push, ref_prefixes);
+	}
+
+	return get_refs_list_using_list(transport, for_push);
+}
+
+static struct ref *get_refs_list_using_list(struct transport *transport,
+					    int for_push)
 {
 	struct helper_data *data = transport->data;
 	struct child_process *helper;
@@ -1066,13 +1097,9 @@ static struct ref *get_refs_list(struct transport *transport, int for_push,
 	struct ref *posn;
 	struct strbuf buf = STRBUF_INIT;
 
+	data->get_refs_list_called = 1;
 	helper = get_helper(transport);
 
-	if (process_connect(transport, for_push)) {
-		do_take_over(transport);
-		return transport->vtable->get_refs_list(transport, for_push, ref_prefixes);
-	}
-
 	if (data->push && for_push)
 		write_str_in_full(helper->in, "list for-push\n");
 	else
@@ -1119,7 +1146,7 @@ static struct ref *get_refs_list(struct transport *transport, int for_push,
 }
 
 static struct transport_vtable vtable = {
-	0,
+	1,
 	set_helper_option,
 	get_refs_list,
 	fetch,