Enforce stronger typing on registries

README.md

@@ -402,7 +402,7 @@ enabled. They get a single object with the format
 `{labels, value, exemplarLabels}`.
 
 When using exemplars, the registry used for metrics should be set to OpenMetrics
-type (including the global or default registry).
+type (including the global or default registry if no registries are specified).
 
 ### Registy type
 

example/exemplars.js

@@ -62,13 +62,28 @@ async function makeHistograms() {
 }
 
 async function main() {
-	// should only use exemplars with OpenMetrics registry types
+	// exemplars will be shown only by OpenMetrics registry types
 	register.setContentType(Registry.OPENMETRICS_CONTENT_TYPE);
 
 	makeCounters();
 	makeHistograms();
 
 	console.log(await register.metrics());
+	console.log('---');
+
+	// if you dont want to set the default registry to OpenMetrics type then you need to create a new registry and assign it to the metric
+
+	register.setContentType(Registry.PROMETHEUS_CONTENT_TYPE);
+	const omReg = new Registry(Registry.OPENMETRICS_CONTENT_TYPE);
+	const c = new Counter({
+		name: 'counter_with_exemplar',
+		help: 'Example of a counter',
+		labelNames: ['code'],
+		registers: [omReg],
+		enableExemplars: true,
+	});
+	c.inc();
+	console.log(await omReg.metrics());
 }
 
 main();

index.d.ts

@@ -1,14 +1,31 @@
 // Type definitions for prom-client
 // Definitions by: Simon Nyberg http://twitter.com/siimon_nyberg
 
+export type Charset = 'utf-8';
+
+export type PrometheusMIME = 'text/plain';
+export type PrometheusMetricsVersion = '0.0.4';
+
+export type OpenMetricsMIME = 'application/openmetrics-text';
+export type OpenMetricsVersion = '1.0.0';
+
+export type PrometheusContentType =
+	`${OpenMetricsMIME}; version=${OpenMetricsVersion}; charset=${Charset}`;
+export type OpenMetricsContentType =
+	`${PrometheusMIME}; version=${PrometheusMetricsVersion}; charset=${Charset}`;
+
+export type RegistryContentType =
+	| PrometheusContentType
+	| OpenMetricsContentType;
+
 /**
  * Container for all registered metrics
  * @property {string} PROMETHEUS_CONTENT_TYPE - Content-Type of Prometheus
  * registry type
  * @property {string} OPENMETRICS_CONTENT_TYPE - Content-Type of OpenMetrics
  * registry type.
  */
-export class Registry {
+export class Registry<RegistryContentType = PrometheusContentType> {
 	/**
 	 * Get string representation for all metrics
 	 */
@@ -68,14 +85,14 @@ export class Registry {
 	/**
 	 * Gets the Content-Type of the metrics for use in the response headers.
 	 */
-	contentType: string;
+	contentType: RegistryContentType;
 
 	/**
 	 * Set the content type of a registry. Used to change between Prometheus and
 	 * OpenMetrics versions.
 	 * @param contentType The type of the registry
 	 */
-	setContentType(contentType: string): void;
+	setContentType(contentType: RegistryContentType): void;
 
 	/**
 	 * Merge registers
@@ -94,17 +111,17 @@ export const register: Registry;
  * HTTP Content-Type for metrics response headers, defaults to Prometheus text
  * format.
  */
-export const contentType: string;
+export const contentType: RegistryContentType;
 
 /**
  * HTTP Prometheus Content-Type for metrics response headers.
  */
-export const prometheusContentType: string;
+export const prometheusContentType: PrometheusContentType;
 
 /**
  * HTTP OpenMetrics Content-Type for metrics response headers.
  */
-export const openMetricsContentType: string;
+export const openMetricsContentType: OpenMetricsContentType;
 
 export class AggregatorRegistry extends Registry {
 	/**

index.js

@@ -8,8 +8,10 @@
 exports.register = require('./lib/registry').globalRegistry;
 exports.Registry = require('./lib/registry');
 exports.contentType = require('./lib/registry').globalRegistry.contentType;
-exports.prometheusContentType = require('./lib/registry').PROMETHEUS_CONTENT_TYPE;
-exports.openMetricsContentType = require('./lib/registry').OPENMETRICS_CONTENT_TYPE;
+exports.prometheusContentType =
+	require('./lib/registry').PROMETHEUS_CONTENT_TYPE;
+exports.openMetricsContentType =
+	require('./lib/registry').OPENMETRICS_CONTENT_TYPE;
 exports.validateMetricName = require('./lib/validation').validateMetricName;
 
 exports.Counter = require('./lib/counter');
@@ -19,7 +21,8 @@ exports.Summary = require('./lib/summary');
 exports.Pushgateway = require('./lib/pushgateway');
 
 exports.linearBuckets = require('./lib/bucketGenerators').linearBuckets;
-exports.exponentialBuckets = require('./lib/bucketGenerators').exponentialBuckets;
+exports.exponentialBuckets =
+	require('./lib/bucketGenerators').exponentialBuckets;
 
 exports.collectDefaultMetrics = require('./lib/defaultMetrics');
 

lib/cluster.js

@@ -106,9 +106,7 @@ class AggregatorRegistry extends Registry {
 		const aggregatedRegistry = new Registry();
 		const metricsByName = new Grouper();
 
-		if (registryType === Registry.OPENMETRICS_CONTENT_TYPE) {
-			aggregatedRegistry.setContentType(registryType);
-		}
+		aggregatedRegistry.setContentType(registryType);
 
 		// Gather by name
 		metricsArr.forEach(metrics => {

lib/counter.js

@@ -30,18 +30,6 @@ class Counter extends Metric {
 		}
 	}
 
-	enableExemplars(enable = false) {
-		if (enable) {
-			this.enableExemplars = true;
-		}
-		if (this.enableExemplars) {
-			this.inc = this.incWithExemplar;
-		} else {
-			this.inc = this.incWithoutExemplar;
-		}
-		this.reset();
-	}
-
 	/**
 	 * Increment counter
 	 * @param {object} labels - What label you want to be incremented

lib/histogram.js

@@ -63,18 +63,6 @@ class Histogram extends Metric {
 		}
 	}
 
-	enableExemplars(enable = false) {
-		if (enable) {
-			this.enableExemplars = true;
-		}
-		if (this.enableExemplars) {
-			this.observe = this.observeWithExemplar;
-		} else {
-			this.observe = this.observeWithoutExemplar;
-		}
-		this.reset();
-	}
-
 	/**
 	 * Observe a value in histogram
 	 * @param {object} labels - Object with labels where key is the label key and value is label value. Can only be one level deep

lib/metric.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const { globalRegistry } = require('./registry');
+const Registry = require('./registry');
 const { isObject } = require('./util');
 const { validateMetricName, validateLabelName } = require('./validation');
 
@@ -16,7 +16,7 @@ class Metric {
 			this,
 			{
 				labelNames: [],
-				registers: [globalRegistry],
+				registers: [Registry.globalRegistry],
 				aggregator: 'sum',
 				enableExemplars: false,
 			},
@@ -25,7 +25,7 @@ class Metric {
 		);
 		if (!this.registers) {
 			// in case config.registers is `undefined`
-			this.registers = [globalRegistry];
+			this.registers = [Registry.globalRegistry];
 		}
 		if (!this.help) {
 			throw new Error('Missing mandatory help parameter');
@@ -46,6 +46,14 @@ class Metric {
 		this.reset();
 
 		for (const register of this.registers) {
+			if (
+				this.enableExemplars &&
+				register.contentType === Registry.PROMETHEUS_CONTENT_TYPE
+			) {
+				throw new TypeError(
+					'Exemplars are supported only on OpenMetrics registries',
+				);
+			}
 			register.registerMetric(this);
 		}
 	}

lib/metrics/gc.js

@@ -32,8 +32,7 @@ module.exports = (registry, config = {}) => {
 		: DEFAULT_GC_DURATION_BUCKETS;
 	const gcHistogram = new Histogram({
 		name: namePrefix + NODEJS_GC_DURATION_SECONDS,
-		help:
-			'Garbage collection duration by kind, one of major, minor, incremental or weakcb.',
+		help: 'Garbage collection duration by kind, one of major, minor, incremental or weakcb.',
 		labelNames: ['kind', ...labelNames],
 		enableExemplars: false,
 		buckets,

lib/metrics/processHandles.js

@@ -20,8 +20,7 @@ module.exports = (registry, config = {}) => {
 
 	new Gauge({
 		name: namePrefix + NODEJS_ACTIVE_HANDLES,
-		help:
-			'Number of active libuv handles grouped by handle type. Every handle type is C++ class name.',
+		help: 'Number of active libuv handles grouped by handle type. Every handle type is C++ class name.',
 		labelNames: ['type', ...labelNames],
 		registers,
 		collect() {

lib/metrics/processRequests.js

@@ -18,8 +18,7 @@ module.exports = (registry, config = {}) => {
 
 	new Gauge({
 		name: namePrefix + NODEJS_ACTIVE_REQUESTS,
-		help:
-			'Number of active libuv requests grouped by request type. Every request type is C++ class name.',
+		help: 'Number of active libuv requests grouped by request type. Every request type is C++ class name.',
 		labelNames: ['type', ...labelNames],
 		registers: registry ? [registry] : undefined,
 		collect() {

lib/metrics/processResources.js

@@ -17,8 +17,7 @@ module.exports = (registry, config = {}) => {
 
 	new Gauge({
 		name: namePrefix + NODEJS_ACTIVE_RESOURCES,
-		help:
-			'Number of active resources that are currently keeping the event loop alive, grouped by async resource type.',
+		help: 'Number of active resources that are currently keeping the event loop alive, grouped by async resource type.',
 		labelNames: ['type', ...labelNames],
 		registers: registry ? [registry] : undefined,
 		collect() {

lib/registry.js

@@ -1,4 +1,5 @@
 'use strict';
+
 const { getValueAsString } = require('./util');
 
 function escapeString(str) {
@@ -30,6 +31,12 @@ class Registry {
 		this._metrics = {};
 		this._collectors = [];
 		this._defaultLabels = {};
+		if (
+			regContentType !== Registry.PROMETHEUS_CONTENT_TYPE &&
+			regContentType !== Registry.OPENMETRICS_CONTENT_TYPE
+		) {
+			throw new TypeError('Content type unsupported');
+		}
 		this._contentType = regContentType;
 	}
 
@@ -74,7 +81,10 @@ class Registry {
 				metricName += `{${labels}}`;
 			}
 			values += `${metricName} ${getValueAsString(val.value)}`;
-			if (val.exemplar) {
+			if (
+				val.exemplar &&
+				this.contentType === Registry.OPENMETRICS_CONTENT_TYPE
+			) {
 				const exemplarKeys = Object.keys(val.exemplar.labelSet);
 				const exemplarSize = exemplarKeys.length;
 				if (exemplarSize > 0) {
@@ -209,21 +219,23 @@ class Registry {
 	}
 
 	setContentType(metricsContentType) {
-		if (metricsContentType === Registry.OPENMETRICS_CONTENT_TYPE) {
-			this._contentType = Registry.OPENMETRICS_CONTENT_TYPE;
+		if (
+			metricsContentType === Registry.OPENMETRICS_CONTENT_TYPE ||
+			metricsContentType === Registry.PROMETHEUS_CONTENT_TYPE
+		) {
+			this._contentType = metricsContentType;
 		} else {
-			this._contentType = Registry.PROMETHEUS_CONTENT_TYPE;
+			throw new Error('Content type unsupported');
 		}
 	}
 
-	/* Merge behaviour between registries of different types is undefined. The
-	 * user should only provide an array or registries of the same type. */
 	static merge(registers) {
-		let regType = Registry.PROMETHEUS_CONTENT_TYPE;
+		const regType = registers[0].contentType;
 		for (const reg of registers) {
-			if (reg.type && reg.type !== regType) {
-				regType = reg.type;
-				break;
+			if (reg.contentType !== regType) {
+				throw new Error(
+					'Registers can only be merged if they have the same content type',
+				);
 			}
 		}
 		const mergedRegistry = new Registry(regType);

package.json

@@ -41,7 +41,7 @@
 		"jest": "^26.0.1",
 		"lint-staged": "^10.0.4",
 		"nock": "^13.0.5",
-		"prettier": "2.0.5",
+		"prettier": "2.6.2",
 		"typescript": "^4.0.2"
 	},
 	"dependencies": {

test/__snapshots__/counterTest.js.snap

@@ -1,17 +1,17 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`counter with $tag registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
+exports[`counter with OpenMetrics registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`counter with $tag registry remove should throw error if label lengths does not match 2`] = `"Invalid number of arguments"`;
+exports[`counter with OpenMetrics registry with params as object labels should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`counter with $tag registry with params as object labels should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
+exports[`counter with OpenMetrics registry with params as object should not be possible to decrease a counter 1`] = `"It is not possible to decrease a counter"`;
 
-exports[`counter with $tag registry with params as object labels should throw error if label lengths does not match 2`] = `"Invalid number of arguments"`;
+exports[`counter with OpenMetrics registry with params as object should throw an error when the value is not a number 1`] = `"Value is not a valid number: 3ms"`;
 
-exports[`counter with $tag registry with params as object should not be possible to decrease a counter 1`] = `"It is not possible to decrease a counter"`;
+exports[`counter with Prometheus registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`counter with $tag registry with params as object should not be possible to decrease a counter 2`] = `"It is not possible to decrease a counter"`;
+exports[`counter with Prometheus registry with params as object labels should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`counter with $tag registry with params as object should throw an error when the value is not a number 1`] = `"Value is not a valid number: 3ms"`;
+exports[`counter with Prometheus registry with params as object should not be possible to decrease a counter 1`] = `"It is not possible to decrease a counter"`;
 
-exports[`counter with $tag registry with params as object should throw an error when the value is not a number 2`] = `"Value is not a valid number: 3ms"`;
+exports[`counter with Prometheus registry with params as object should throw an error when the value is not a number 1`] = `"Value is not a valid number: 3ms"`;

test/__snapshots__/gaugeTest.js.snap

@@ -1,5 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`gauge with $tag registry global registry with parameters as object should not allow non numbers 1`] = `"Value is not a valid number: asd"`;
+exports[`gauge with OpenMetrics registry global registry with parameters as object should not allow non numbers 1`] = `"Value is not a valid number: asd"`;
 
-exports[`gauge with $tag registry global registry with parameters as object should not allow non numbers 2`] = `"Value is not a valid number: asd"`;
+exports[`gauge with Prometheus registry global registry with parameters as object should not allow non numbers 1`] = `"Value is not a valid number: asd"`;

test/__snapshots__/histogramTest.js.snap

@@ -1,17 +1,17 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`histogram with $tag registry with object as params with global registry labels should not allow different number of labels 1`] = `"Invalid number of arguments"`;
+exports[`histogram with OpenMetrics registry with object as params with global registry labels should not allow different number of labels 1`] = `"Invalid number of arguments"`;
 
-exports[`histogram with $tag registry with object as params with global registry labels should not allow different number of labels 2`] = `"Invalid number of arguments"`;
+exports[`histogram with OpenMetrics registry with object as params with global registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`histogram with $tag registry with object as params with global registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
+exports[`histogram with OpenMetrics registry with object as params with global registry should not allow le as a custom label 1`] = `"le is a reserved label keyword"`;
 
-exports[`histogram with $tag registry with object as params with global registry remove should throw error if label lengths does not match 2`] = `"Invalid number of arguments"`;
+exports[`histogram with OpenMetrics registry with object as params with global registry should not allow non numbers 1`] = `"Value is not a valid number: asd"`;
 
-exports[`histogram with $tag registry with object as params with global registry should not allow le as a custom label 1`] = `"le is a reserved label keyword"`;
+exports[`histogram with Prometheus registry with object as params with global registry labels should not allow different number of labels 1`] = `"Invalid number of arguments"`;
 
-exports[`histogram with $tag registry with object as params with global registry should not allow le as a custom label 2`] = `"le is a reserved label keyword"`;
+exports[`histogram with Prometheus registry with object as params with global registry remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
-exports[`histogram with $tag registry with object as params with global registry should not allow non numbers 1`] = `"Value is not a valid number: asd"`;
+exports[`histogram with Prometheus registry with object as params with global registry should not allow le as a custom label 1`] = `"le is a reserved label keyword"`;
 
-exports[`histogram with $tag registry with object as params with global registry should not allow non numbers 2`] = `"Value is not a valid number: asd"`;
+exports[`histogram with Prometheus registry with object as params with global registry should not allow non numbers 1`] = `"Value is not a valid number: asd"`;