--- a/mod_prometheus/mod_prometheus.lua	Wed Apr 28 08:21:54 2021 +0200
+++ b/mod_prometheus/mod_prometheus.lua	Wed Apr 28 08:22:47 2021 +0200
@@ -14,13 +14,15 @@
 local socket = require "socket";
 local statsman = require "core.statsmanager";
 local get_stats = statsman.get_stats;
+local get_metric_registry = statsman.get_metric_registry;
+local collect = statsman.collect;
 
 local function escape(text)
 	return text:gsub("\\", "\\\\"):gsub("\"", "\\\""):gsub("\n", "\\n");
 end
 
 local function escape_name(name)
-	return name:gsub("[^A-Za-z0-9_]", "_"):gsub("^[^A-Za-z_]", "_%1");
+	return name:gsub("/", "__"):gsub("[^A-Za-z0-9_]", "_"):gsub("^[^A-Za-z_]", "_%1");
 end
 
 local function get_timestamp()
@@ -33,6 +35,15 @@
 	return "# HELP "..escape_name(metric).." "..docstring.."\n";
 end
 
+local function repr_unit(metric, unit)
+	if not unit then
+		unit = ""
+	else
+		unit = unit:gsub("\\", "\\\\"):gsub("\n", "\\n");
+	end
+	return "# UNIT "..escape_name(metric).." "..unit.."\n";
+end
+
 -- local allowed_types = { counter = true, gauge = true, histogram = true, summary = true, untyped = true };
 -- local allowed_types = { "counter", "gauge", "histogram", "summary", "untyped" };
 local function repr_type(metric, type_)
@@ -46,10 +57,18 @@
 	return key.."=\""..escape(value).."\"";
 end
 
-local function repr_labels(labels)
+local function repr_labels(labelkeys, labelvalues, extra_labels)
 	local values = {}
-	for key, value in pairs(labels) do
-		t_insert(values, repr_label(escape_name(key), escape(value)));
+	if labelkeys then
+		for i, key in ipairs(labelkeys) do
+			local value = labelvalues[i]
+			t_insert(values, repr_label(escape_name(key), escape(value)));
+		end
+	end
+	if extra_labels then
+		for key, value in pairs(extra_labels) do
+			t_insert(values, repr_label(escape_name(key), escape(value)));
+		end
 	end
 	if #values == 0 then
 		return "";
@@ -57,90 +76,128 @@
 	return "{"..t_concat(values, ",").."}";
 end
 
-local function repr_sample(metric, labels, value, timestamp)
-	return escape_name(metric)..repr_labels(labels).." "..value.." "..timestamp.."\n";
-end
-
-local allowed_extras = { min = true, max = true, average = true };
-local function insert_extras(data, key, name, timestamp, extra)
-	if not extra then
-		return false;
-	end
-	local has_extra = false;
-	for extra_name in pairs(allowed_extras) do
-		if extra[extra_name] then
-			local field = {
-				value = extra[extra_name],
-				labels = {
-					["type"] = name,
-					field = extra_name,
-				},
-				typ = "gauge";
-				timestamp = timestamp,
-			};
-			t_insert(data[key], field);
-			has_extra = true;
-		end
-	end
-	return has_extra;
+local function repr_sample(metric, labelkeys, labelvalues, extra_labels, value)
+	return escape_name(metric)..repr_labels(labelkeys, labelvalues, extra_labels).." "..string.format("%.17g", value).."\n";
 end
 
-local function parse_stats()
-	local timestamp = tostring(get_timestamp());
-	local data = {};
-	local stats, changed_only, extras = get_stats();
-	for stat, value in pairs(stats) do
-		-- module:log("debug", "changed_stats[%q] = %s", stat, tostring(value));
-		local extra = extras[stat];
-		local host, sect, name, typ = stat:match("^/([^/]+)/([^/]+)/(.+):(%a+)$");
-		if host == nil then
-			sect, name, typ = stat:match("^([^.]+)%.(.+):(%a+)$");
-		elseif host == "*" then
-			host = nil;
-		end
-		if sect:find("^mod_measure_.") then
-			sect = sect:sub(13);
-		elseif sect:find("^mod_statistics_.") then
-			sect = sect:sub(16);
+local get_metrics;
+if statsman.get_metric_registry then
+	module:log("debug", "detected OpenMetrics statsmanager")
+	-- Prosody 0.12+ with OpenMetrics
+	function get_metrics(event)
+		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 key = escape_name("prosody_"..sect);
-		local field = {
-			value = value,
-			labels = { ["type"] = name},
-			-- TODO: Use the other types where it makes sense.
-			typ = (typ == "rate" and "counter" or "gauge"),
-			timestamp = timestamp,
-		};
-		if host then
-			field.labels.host = host;
+		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
+		local answer = {};
+		for metric_family_name, metric_family in pairs(registry:get_metric_families()) do
+			t_insert(answer, repr_help(metric_family_name, metric_family.description))
+			t_insert(answer, repr_unit(metric_family_name, metric_family.unit))
+			t_insert(answer, repr_type(metric_family_name, metric_family.type_))
+			for labelset, metric in metric_family:iter_metrics() do
+				for suffix, extra_labels, value in metric:iter_samples() do
+					t_insert(answer, repr_sample(metric_family_name..suffix, metric_family.label_keys, labelset, extra_labels, value))
+				end
+			end
 		end
-		if data[key] == nil then
-			data[key] = {};
-		end
-		if not insert_extras(data, key, name, timestamp, extra) then
-			t_insert(data[key], field);
-		end
+		t_insert(answer, "# EOF\n")
+		return t_concat(answer, "");
 	end
-	return data;
-end
+else
+	module:log("debug", "detected pre-OpenMetrics statsmanager")
+	-- Pre-OpenMetrics
 
-local function get_metrics(event)
-	local response = event.response;
-	response.headers.content_type = "text/plain; version=0.0.4";
-	if statsman.collect then
-		statsman.collect()
+	local allowed_extras = { min = true, max = true, average = true };
+	local function insert_extras(data, key, name, timestamp, extra)
+		if not extra then
+			return false;
+		end
+		local has_extra = false;
+		for extra_name in pairs(allowed_extras) do
+			if extra[extra_name] then
+				local field = {
+					value = extra[extra_name],
+					labels = {
+						["type"] = name,
+						field = extra_name,
+					},
+					typ = "gauge";
+					timestamp = timestamp,
+				};
+				t_insert(data[key], field);
+				has_extra = true;
+			end
+		end
+		return has_extra;
 	end
 
-	local answer = {};
-	for key, fields in pairs(parse_stats()) do
-		t_insert(answer, repr_help(key, "TODO: add a description here."));
-		t_insert(answer, repr_type(key, fields[1].typ));
-		for _, field in pairs(fields) do
-			t_insert(answer, repr_sample(key, field.labels, field.value, field.timestamp));
+	local function parse_stats()
+		local timestamp = tostring(get_timestamp());
+		local data = {};
+		local stats, changed_only, extras = get_stats();
+		for stat, value in pairs(stats) do
+			-- module:log("debug", "changed_stats[%q] = %s", stat, tostring(value));
+			local extra = extras[stat];
+			local host, sect, name, typ = stat:match("^/([^/]+)/([^/]+)/(.+):(%a+)$");
+			if host == nil then
+				sect, name, typ = stat:match("^([^.]+)%.(.+):(%a+)$");
+			elseif host == "*" then
+				host = nil;
+			end
+			if sect:find("^mod_measure_.") then
+				sect = sect:sub(13);
+			elseif sect:find("^mod_statistics_.") then
+				sect = sect:sub(16);
+			end
+
+			local key = escape_name("prosody_"..sect);
+			local field = {
+				value = value,
+				labels = { ["type"] = name},
+				-- TODO: Use the other types where it makes sense.
+				typ = (typ == "rate" and "counter" or "gauge"),
+				timestamp = timestamp,
+			};
+			if host then
+				field.labels.host = host;
+			end
+			if data[key] == nil then
+				data[key] = {};
+			end
+			if not insert_extras(data, key, name, timestamp, extra) then
+				t_insert(data[key], field);
+			end
 		end
+		return data;
 	end
-	return t_concat(answer, "");
+
+	function get_metrics(event)
+		local response = event.response;
+		response.headers.content_type = "text/plain; version=0.0.4";
+		if statsman.collect then
+			statsman.collect()
+		end
+
+		local answer = {};
+		for key, fields in pairs(parse_stats()) do
+			t_insert(answer, repr_help(key, ""));
+			t_insert(answer, repr_type(key, fields[1].typ));
+			for _, field in pairs(fields) do
+				t_insert(answer, repr_sample(key, nil, nil, field.labels, field.value, field.timestamp));
+			end
+		end
+		return t_concat(answer, "");
+	end
 end
 
 function module.add_host(module)