diff --git a/modules/Makefile.am b/modules/Makefile.am
index 9484bfb99..8c4357633 100644
--- a/modules/Makefile.am
+++ b/modules/Makefile.am
@@ -245,6 +245,7 @@ federation_federation_query_la_SOURCES = federation/query.cc
 federation_federation_invite_la_SOURCES = federation/invite.cc
 federation_federation_make_join_la_SOURCES = federation/make_join.cc
 federation_federation_send_join_la_SOURCES = federation/send_join.cc
+federation_federation_state_ids_la_SOURCES = federation/state_ids.cc
 
 federation_module_LTLIBRARIES = \
 	federation/federation_send.la \
@@ -257,6 +258,7 @@ federation_module_LTLIBRARIES = \
 	federation/federation_invite.la \
 	federation/federation_make_join.la \
 	federation/federation_send_join.la \
+	federation/federation_state_ids.la \
 	###
 
 ###############################################################################
diff --git a/modules/federation/state_ids.cc b/modules/federation/state_ids.cc
new file mode 100644
index 000000000..dce63f167
--- /dev/null
+++ b/modules/federation/state_ids.cc
@@ -0,0 +1,90 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+using namespace ircd;
+
+mapi::header
+IRCD_MODULE
+{
+	"federation state_ids"
+};
+
+resource
+state_ids_resource
+{
+	"/_matrix/federation/v1/state_ids/",
+	{
+		"federation state_ids",
+		resource::DIRECTORY,
+	}
+};
+
+resource::response
+get__state_ids(client &client,
+               const resource::request &request)
+{
+	m::room::id::buf room_id
+	{
+		url::decode(request.parv[0], room_id)
+	};
+
+	m::event::id::buf event_id;
+	if(request.query["event_id"])
+		url::decode(request.query.at("event_id"), event_id);
+
+	 //TODO: direct to socket
+	const unique_buffer<mutable_buffer> buf{1_MiB}; //TODO: XXX
+	json::stack out{buf};
+	{
+		json::stack::object top{out};
+		json::stack::member pdus_m
+		{
+			top, "pdu_ids"
+		};
+
+		json::stack::array pdus
+		{
+			pdus_m
+		};
+
+		const m::room::state state
+		{
+			m::room
+			{
+				room_id, event_id
+			}
+		};
+
+		state.for_each([&pdus]
+		(const m::event &event)
+		{
+			const auto event_id
+			{
+				at<"event_id"_>(event)
+			};
+
+			pdus.append(event_id);
+		});
+	}
+
+	return resource::response
+	{
+		client, json::object{out.completed()}
+	};
+}
+
+resource::method
+method_get
+{
+	state_ids_resource, "GET", get__state_ids,
+	{
+		method_get.VERIFY_ORIGIN
+	}
+};