serve: advertise object-info feature

In order for a client to know what object-info components a server can
provide, advertise supported object-info features. This will allow a
client to decide whether to query the server for object-info or fetch
as a fallback.

Helped-by: Jonathan Tan <[email protected]>
Helped-by: Christian Couder <[email protected]>
Signed-off-by: Calvin Wan <[email protected]>
Signed-off-by: Eric Ju  <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: calvin-wan-google

serve.c

@@ -68,14 +68,16 @@ static void session_id_receive(struct repository *r UNUSED,
 	trace2_data_string("transfer", NULL, "client-sid", client_sid);
 }
 
-static int object_info_advertise(struct repository *r, struct strbuf *value UNUSED)
+static int object_info_advertise(struct repository *r, struct strbuf *value)
 {
 	if (advertise_object_info == -1 &&
 	    repo_config_get_bool(r, "transfer.advertiseobjectinfo",
 				 &advertise_object_info)) {
 		/* disabled by default */
 		advertise_object_info = 0;
 	}
+	if (value && advertise_object_info)
+		strbuf_addstr(value, "size");
 	return advertise_object_info;
 }