transport: introduce parse_transport_option() method

Add the `parse_transport_option()` method to parse the `push.pushOption`
configuration. This method will also be used in the next commit to
handle the new `remote.<name>.serverOption` configuration for setting
server options in Git protocol v2.

Signed-off-by: Xing Xin <xingxin.xx@bytedance.com>
Reviewed-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/push.c

@@ -519,14 +519,7 @@ static int git_push_config(const char *k, const char *v,
 			RECURSE_SUBMODULES_ON_DEMAND : RECURSE_SUBMODULES_OFF;
 		recurse_submodules = val;
 	} else if (!strcmp(k, "push.pushoption")) {
-		if (!v)
+		return parse_transport_option(k, v, &push_options_config);
-			return config_error_nonbool(k);
-		else
-			if (!*v)
-				string_list_clear(&push_options_config, 0);
-			else
-				string_list_append(&push_options_config, v);
-		return 0;
 	} else if (!strcmp(k, "color.push")) {
 		push_use_color = git_config_colorbool(k, v);
 		return 0;

transport.c

@@ -1108,6 +1108,18 @@ int is_transport_allowed(const char *type, int from_user)
 	BUG("invalid protocol_allow_config type");
 }
 
+int parse_transport_option(const char *var, const char *value,
+			   struct string_list *transport_options)
+{
+	if (!value)
+		return config_error_nonbool(var);
+	if (!*value)
+		string_list_clear(transport_options, 0);
+	else
+		string_list_append(transport_options, value);
+	return 0;
+}
+
 void transport_check_allowed(const char *type)
 {
 	if (!is_transport_allowed(type, -1))

transport.h

@@ -342,4 +342,8 @@ void transport_print_push_status(const char *dest, struct ref *refs,
 /* common method used by transport-helper.c and send-pack.c */
 void reject_atomic_push(struct ref *refs, int mirror_mode);
 
+/* common method to parse push-option or server-option from config */
+int parse_transport_option(const char *var, const char *value,
+			   struct string_list *transport_options);
+
 #endif