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Statistics: Rewrite statistics backends to use OpenMetrics The metric subsystem of Prosody has had some shortcomings from the perspective of the current state-of-the-art in metric observability. The OpenMetrics standard [0] is a formalization of the data model (and serialization format) of the well-known and widely-used Prometheus [1] software stack. The previous stats subsystem of Prosody did not map well to that format (see e.g. [2] and [3]); the key reason is that it was trying to do too much math on its own ([2]) while lacking first-class support for "families" of metrics ([3]) and structured metric metadata (despite the `extra` argument to metrics, there was no standard way of representing common things like "tags" or "labels"). Even though OpenMetrics has grown from the Prometheus world of monitoring, it maps well to other popular monitoring stacks such as: - InfluxDB (labels can be mapped to tags and fields as necessary) - Carbon/Graphite (labels can be attached to the metric name with dot-separation) - StatsD (see graphite when assuming that graphite is used as backend, which is the default) The util.statsd module has been ported to use the OpenMetrics model as a proof of concept. An implementation which exposes the util.statistics backend data as Prometheus metrics is ready for publishing in prosody-modules (most likely as mod_openmetrics_prometheus to avoid breaking existing 0.11 deployments). At the same time, the previous measure()-based API had one major advantage: It is really simple and easy to use without requiring lots of knowledge about OpenMetrics or similar concepts. For that reason as well as compatibility with existing code, it is preserved and may even be extended in the future. However, code relying on the `stats-updated` event as well as `get_stats` from `statsmanager` will break because the data model has changed completely; in case of `stats-updated`, the code will simply not run (as the event was renamed in order to avoid conflicts); the `get_stats` function has been removed completely (so it will cause a traceback when it is attempted to be used). Note that the measure_*_event methods have been removed from the module API. I was unable to find any uses or documentation and thus deemed they should not be ported. Re-implementation is possible when necessary. [0]: https://openmetrics.io/ [1]: https://prometheus.io/ [2]: #959 [3]: #960

-- Prosody IM
-- Copyright (C) 2008-2017 Matthew Wild
-- Copyright (C) 2008-2017 Waqas Hussain
-- Copyright (C) 2011-2017 Kim Alvefur
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
-- XEP-0313: Message Archive Management for Prosody
--
-- luacheck: ignore 122/prosody

local global_default_policy = module:get_option_string("default_archive_policy", true);
if global_default_policy ~= "roster" then
	global_default_policy = module:get_option_boolean("default_archive_policy", global_default_policy);
end
local smart_enable = module:get_option_boolean("mam_smart_enable", false);

do
	-- luacheck: ignore 211/prefs_format
	local prefs_format = {
		[false] = "roster",
		-- default ::= true | false | "roster"
		-- true = always, false = never, nil = global default
		["romeo@montague.net"] = true, -- always
		["montague@montague.net"] = false, -- newer
	};
end

local sessions = prosody.hosts[module.host].sessions;
local archive_store = module:get_option_string("archive_store", "archive");
local prefs = module:open_store(archive_store .. "_prefs");

local function get_prefs(user, explicit)
	local user_sessions = sessions[user];
	local user_prefs = user_sessions and user_sessions.archive_prefs
	if not user_prefs then
		-- prefs not cached
		user_prefs = prefs:get(user);
		if not user_prefs then
			-- prefs not set
			if smart_enable and explicit then
				-- a mam-capable client was involved in this action, set defaults
				user_prefs = { [false] = global_default_policy };
				prefs:set(user, user_prefs);
			end
		end
		if user_sessions then
			-- cache settings if they originate from user action
			user_sessions.archive_prefs = user_prefs;
		end
		if not user_prefs then
			if smart_enable then
				-- not yet enabled, either explicitly or "smart"
				user_prefs = { [false] = false };
			else
				-- no explicit settings, return defaults
				user_prefs = { [false] = global_default_policy };
			end
		end
	end
	return user_prefs;
end

local function set_prefs(user, user_prefs)
	local user_sessions = sessions[user];
	if user_sessions then
		user_sessions.archive_prefs = user_prefs;
	end
	return prefs:set(user, user_prefs);
end

return {
	get = get_prefs,
	set = set_prefs,
}