--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_devices/README.markdown	Thu Dec 06 16:57:01 2018 +0000
@@ -0,0 +1,46 @@
+---
+labels:
+- 'Stage-Alpha'
+summary: 'Device identification'
+...
+
+Description
+============
+
+This is an experimental module that aims to identify the different
+devices (technically clients) that a user uses with their account.
+
+It is expected that at some point this will be backed by a nicer protocol,
+but it currently uses a variety of hacky methods to track devices between
+sessions.
+
+Usage
+=====
+
+``` {.lua}
+modules_enabled = {
+    -- ...
+    "devices",
+    -- ...
+}
+```
+
+Configuration
+=============
+
+Option summary
+--------------
+
+  option                         type                    default
+  ------------------------------ ----------------------- -----------
+  max\_user\_devices             number                  `5`
+
+
+Compatibility
+=============
+
+  ------- -----------------------
+  trunk   Works
+  0.11    Works
+  0.10    Does not work
+  ------- -----------------------

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_devices/mod_devices.lua	Thu Dec 06 16:57:01 2018 +0000
@@ -0,0 +1,125 @@
+local it = require "util.iterators";
+local new_id = require "util.id".medium;
+
+local max_user_devices = module:get_option_number("max_user_devices", 5);
+
+local device_store = module:open_store("devices");
+local device_map_store = module:open_store("devices", "map");
+
+--- Helper functions
+
+local function _compare_device_timestamps(a, b)
+	return (a.last_activity_at or 0) < (b.last_activity_at or 0);
+end
+local function sorted_devices(devices)
+	return it.sorted_pairs(devices, _compare_device_timestamps);
+end
+
+local function new_device(username, alt_ids)
+	local current_time = os.time();
+	local device = {
+		id = "dv-"..new_id();
+		created_at = current_time;
+		last_activity = "created";
+		last_activity_at = current_time;
+		alt_ids = alt_ids or {};
+	};
+
+	local devices = device_store:get(username);
+	if not devices then
+		devices = {};
+	end
+	devices[device.id] = device;
+	local devices_ordered = {};
+	for id in sorted_devices(devices) do
+		table.insert(devices_ordered, id);
+	end
+	if #devices_ordered > max_user_devices then
+		-- Iterate through oldest devices that are above limit, backwards
+		for i = #devices_ordered, max_user_devices+1, -1 do
+			local id = table.remove(devices_ordered, i);
+			devices[id] = nil;
+			module:log("debug", "Removing old device for %s: %s", username, id);
+		end
+	end
+	device_store:set(username, devices);
+	return device;
+end
+
+local function get_device_with_alt_id(username, alt_id_type, alt_id)
+	local devices = device_store:get(username);
+	if not devices then
+		return nil;
+	end
+
+	for _, device in pairs(devices) do
+		if device.alt_ids[alt_id_type] == alt_id then
+			return device;
+		end
+	end
+end
+
+local function set_device_alt_id(username, device_id, alt_id_type, alt_id)
+	local devices = device_store:get(username);
+	if not devices or not devices[device_id] then
+		return nil, "no such device";
+	end
+	devices[device_id].alt_ids[alt_id_type] = alt_id;
+end
+
+local function record_device_state(username, device_id, activity, time)
+	local device = device_map_store:get(username, device_id);
+	device.last_activity = activity;
+	device.last_activity_at = time or os.time();
+	device_map_store:set(username, device_id, device);
+end
+
+local function find_device(username, info)
+	for _, alt_id_type in ipairs({ "resumption_token", "resource" }) do
+		local alt_id = info[alt_id_type];
+		if alt_id then
+			local device = get_device_with_alt_id(username, alt_id_type, alt_id);
+			if device then
+				return device, alt_id_type;
+			end
+		end
+	end
+end
+
+--- Information gathering
+
+module:hook("pre-resource-bind", function (event)
+	event.session.device_requested_resource = event.resource;
+end, 1000);
+
+
+local function store_resumption_token(session, stanza)
+	session.device_requested_resume = stanza.attr.previd;
+end
+module:hook_stanza("urn:xmpp:sm:2", "resume", store_resumption_token, 5);
+module:hook_stanza("urn:xmpp:sm:3", "resume", store_resumption_token, 5);
+
+--- Identify device after resource bind
+
+module:hook("resource-bind", function (event)
+	local info = {
+		resource = event.session.device_requested_resource;
+		resumption_token = event.session.device_requested_resume;
+	};
+	local device, source = find_device(event.session.username, info);
+	if device then
+		event.session.log("debug", "Associated with device %s (from %s)", device.id, source);
+		event.session.device_id = device.id;
+	else
+		device = new_device(event.session.username, info);
+		event.session.log("debug", "Creating new device %s for session", device.id);
+		event.session.device_id = device.id;
+	end
+	record_device_state(event.session.username, device.id, "login");
+end, 1000);
+
+module:hook("resource-unbind", function (event)
+	if event.session.device_id then
+		record_device_state(event.session.username, event.session.device_id, "logout");
+	end
+end);