mod_http_openmetrics: Imported from prosody-modules mod_prometheus @df2246b15075

This version has several changes from the earlier mod_prometheus:

- Conversion of metrics into the text-based OpenMetrics format is moved to
  util.openmetrics
- Support for IP-based access control
- Compatibility with earlier Prosody versions removed

plugins/mod_http_openmetrics.lua

@@ -0,0 +1,62 @@
+-- Export statistics in OpenMetrics format
+--
+-- Copyright (C) 2014 Daurnimator
+-- Copyright (C) 2018 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
+-- Copyright (C) 2021 Jonas Schäfer <jonas@zombofant.net>
+--
+-- This module is MIT/X11 licensed.
+
+module:set_global();
+
+local statsman = require "core.statsmanager";
+local ip = require "util.ip";
+
+local get_metric_registry = statsman.get_metric_registry;
+local collect = statsman.collect;
+
+local get_metrics;
+
+local permitted_ips = module:get_option_set("openmetrics_allow_ips", { "::1", "127.0.0.1" });
+local permitted_cidr = module:get_option_string("openmetrics_allow_cidr");
+
+local function is_permitted(request)
+	local ip_raw = request.ip;
+	if permitted_ips:contains(ip_raw) or
+	   (permitted_cidr and ip.match(ip.new_ip(ip_raw), ip.parse_cidr(permitted_cidr))) then
+		return true;
+	end
+	return false;
+end
+
+function get_metrics(event)
+	if not is_permitted(event.request) then
+		return 403; -- Forbidden
+	end
+
+	local response = event.response;
+	response.headers.content_type = "application/openmetrics-text; version=0.0.4";
+
+	if collect then
+		-- Ensure to get up-to-date samples when running in manual mode
+		collect()
+	end
+
+	local registry = get_metric_registry()
+	if registry == nil then
+		response.headers.content_type = "text/plain; charset=utf-8"
+		response.status_code = 404
+		return "No statistics provider configured\n"
+	end
+
+	return registry:render();
+end
+
+function module.add_host(module)
+	module:depends "http";
+	module:provides("http", {
+		default_path = "metrics";
+		route = {
+			GET = get_metrics;
+		};
+	});
+end