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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) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
-- luacheck: ignore 213/level

local pairs = pairs;
local ipairs = ipairs;
local require = require;

local _ENV = nil;
-- luacheck: std none

local level_sinks = {};

local make_logger;

local function init(name)
	local log_debug = make_logger(name, "debug");
	local log_info = make_logger(name, "info");
	local log_warn = make_logger(name, "warn");
	local log_error = make_logger(name, "error");

	return function (level, message, ...)
			if level == "debug" then
				return log_debug(message, ...);
			elseif level == "info" then
				return log_info(message, ...);
			elseif level == "warn" then
				return log_warn(message, ...);
			elseif level == "error" then
				return log_error(message, ...);
			end
		end
end

function make_logger(source_name, level)
	local level_handlers = level_sinks[level];
	if not level_handlers then
		level_handlers = {};
		level_sinks[level] = level_handlers;
	end

	local logger = function (message, ...)
		for i = 1,#level_handlers do
			level_handlers[i](source_name, level, message, ...);
		end
	end

	return logger;
end

local function reset()
	for level, handler_list in pairs(level_sinks) do
		-- Clear all handlers for this level
		for i = 1, #handler_list do
			handler_list[i] = nil;
		end
	end
end

local function add_level_sink(level, sink_function)
	if not level_sinks[level] then
		level_sinks[level] = { sink_function };
	else
		level_sinks[level][#level_sinks[level] + 1 ] = sink_function;
	end
end

local function add_simple_sink(simple_sink_function, levels)
	local format = require "util.format".format;
	local function sink_function(name, level, msg, ...)
		return simple_sink_function(name, level, format(msg, ...));
	end
	for _, level in ipairs(levels or {"debug", "info", "warn", "error"}) do
		add_level_sink(level, sink_function);
	end
end

return {
	init = init;
	make_logger = make_logger;
	reset = reset;
	add_level_sink = add_level_sink;
	add_simple_sink = add_simple_sink;
	new = make_logger;
};