--- a/plugins/mod_pubsub/mod_pubsub.lua	Sun Aug 05 11:44:49 2018 +0200
+++ b/plugins/mod_pubsub/mod_pubsub.lua	Mon Aug 06 08:21:55 2018 +0100
@@ -150,6 +150,10 @@
 	end
 end
 
+function get_service()
+	return service;
+end
+
 function set_service(new_service)
 	service = new_service;
 	module.environment.service = service;
@@ -196,6 +200,7 @@
 				publish = true;
 				retract = true;
 				get_nodes = true;
+				get_configuration = true;
 
 				subscribe = true;
 				unsubscribe = true;
@@ -220,6 +225,7 @@
 				delete = true;
 				get_nodes = true;
 				configure = true;
+				get_configuration = true;
 
 				subscribe = true;
 				unsubscribe = true;

--- a/plugins/mod_pubsub/pubsub.lib.lua	Sun Aug 05 11:44:49 2018 +0200
+++ b/plugins/mod_pubsub/pubsub.lib.lua	Mon Aug 06 08:21:55 2018 +0100
@@ -642,18 +642,12 @@
 		return true;
 	end
 
-	if not service:may(node, stanza.attr.from, "configure") then
-		origin.send(pubsub_error_reply(stanza, "forbidden"));
+	local ok, node_config = service:get_node_config(node, stanza.attr.from);
+	if not ok then
+		origin.send(pubsub_error_reply(stanza, node_config));
 		return true;
 	end
 
-	local node_obj = service.nodes[node];
-	if not node_obj then
-		origin.send(pubsub_error_reply(stanza, "item-not-found"));
-		return true;
-	end
-
-	local node_config = node_obj.config;
 	local pubsub_form_data = config_to_xep0060(node_config);
 	local reply = st.reply(stanza)
 		:tag("pubsub", { xmlns = xmlns_pubsub_owner })
@@ -678,7 +672,12 @@
 		origin.send(st.error_reply(stanza, "modify", "bad-request", "Missing dataform"));
 		return true;
 	end
-	local form_data, err = node_config_form:data(config_form);
+	local ok, old_config = service:get_node_config(node, stanza.attr.from);
+	if not ok then
+		origin.send(pubsub_error_reply(stanza, old_config));
+		return true;
+	end
+	local form_data, err = node_config_form:data(config_form, old_config);
 	if not form_data then
 		origin.send(st.error_reply(stanza, "modify", "bad-request", err));
 		return true;

--- a/spec/util_dataforms_spec.lua	Sun Aug 05 11:44:49 2018 +0200
+++ b/spec/util_dataforms_spec.lua	Mon Aug 06 08:21:55 2018 +0100
@@ -347,5 +347,44 @@
 			assert.truthy(f:find("field/option"));
 		end);
 	end);
+
+	describe("using current values in place of missing fields", function ()
+		it("gets back the previous values when given an empty form", function ()
+			local current = {
+				["list-multi-field"] = {
+					"list-multi-option-value#2";
+				};
+				["list-single-field"] = "list-single-value#2";
+				["hidden-field"] = "hidden-value";
+				["boolean-field"] = false;
+				["text-multi-field"] = "words\ngo\nhere";
+				["jid-single-field"] = "alice@example.com";
+				["text-private-field"] = "hunter2";
+				["text-single-field"] = "text-single-value";
+				["jid-multi-field"] = {
+					"bob@example.net";
+				};
+			};
+			local expect = {
+				-- FORM_TYPE = "xmpp:prosody.im/spec/util.dataforms#1"; -- does this need to be included?
+				["list-multi-field"] = {
+					"list-multi-option-value#2";
+				};
+				["list-single-field"] = "list-single-value#2";
+				["hidden-field"] = "hidden-value";
+				["boolean-field"] = false;
+				["text-multi-field"] = "words\ngo\nhere";
+				["jid-single-field"] = "alice@example.com";
+				["text-private-field"] = "hunter2";
+				["text-single-field"] = "text-single-value";
+				["jid-multi-field"] = {
+					"bob@example.net";
+				};
+			};
+			local data, err = some_form:data(st.stanza("x", {xmlns="jabber:x:data"}), current);
+			assert.is.table(data, err);
+			assert.same(expect, data, "got back the same data");
+		end);
+	end);
 end);
 

--- a/util/dataforms.lua	Sun Aug 05 11:44:49 2018 +0200
+++ b/util/dataforms.lua	Mon Aug 06 08:21:55 2018 +0100
@@ -142,7 +142,7 @@
 
 local field_readers = {};
 
-function form_t.data(layout, stanza)
+function form_t.data(layout, stanza, current)
 	local data = {};
 	local errors = {};
 	local present = {};
@@ -157,7 +157,9 @@
 		end
 
 		if not tag then
-			if field.required then
+			if current and current[field.name] ~= nil then
+				data[field.name] = current[field.name];
+			elseif field.required then
 				errors[field.name] = "Required value missing";
 			end
 		elseif field.name then

--- a/util/pubsub.lua	Sun Aug 05 11:44:49 2018 +0200
+++ b/util/pubsub.lua	Mon Aug 06 08:21:55 2018 +0100
@@ -565,6 +565,8 @@
 		return false, "item-not-found";
 	end
 
+	setmetatable(new_config, {__index=self.node_defaults})
+
 	if self.config.check_node_config then
 		local ok = self.config.check_node_config(node, actor, new_config);
 		if not ok then
@@ -573,7 +575,7 @@
 	end
 
 	local old_config = node_obj.config;
-	node_obj.config = setmetatable(new_config, {__index=self.node_defaults});
+	node_obj.config = new_config;
 
 	if self.config.nodestore then
 		local ok, err = save_node_to_store(self, node_obj);