feat: add support for exemplars

index.d.ts

@@ -62,7 +62,7 @@ export class Registry {
 	getSingleMetricAsString(name: string): Promise<string>;
 
 	/**
-	 * Gets the Content-Type of the metrics for use in the response headers.
+	 * Gets or Sets the Content-Type of the metrics for use in the response headers.
 	 */
 	contentType: string;
 

lib/counter.js

@@ -6,23 +6,25 @@
 const util = require('util');
 const type = 'counter';
 const { hashObject, isObject, getLabels, removeLabels } = require('./util');
-const { validateLabel } = require('./validation');
+const { validateLabel, validateExemplar } = require('./validation');
 const { Metric } = require('./metric');
 
 class Counter extends Metric {
 	/**
 	 * Increment counter
 	 * @param {object} labels - What label you want to be incremented
 	 * @param {Number} value - Value to increment, if omitted increment with 1
+	 * @param {object} exemplars - What exemplars you want to pass to this metric
+	 * @param {Number} exemplarValue - Value to be set as the exemplar value
 	 * @returns {void}
 	 */
-	inc(labels, value) {
+	inc(labels, value, exemplars, exemplarValue) {
 		if (!isObject(labels)) {
-			return inc.call(this, null)(labels, value);
+			return inc.call(this, null, exemplars)(labels, value, exemplars);
 		}
 
-		const hash = hashObject(labels);
-		return inc.call(this, labels, hash)(value);
+		const hash = hashObject(labels, exemplars);
+		return inc.call(this, labels, exemplars, hash, exemplarValue)(value);
 	}
 
 	/**
@@ -50,9 +52,19 @@ class Counter extends Metric {
 	labels() {
 		const labels = getLabels(this.labelNames, arguments) || {};
 		validateLabel(this.labelNames, labels);
-		const hash = hashObject(labels);
+		const hash = hashObject(labels, {});
 		return {
-			inc: inc.call(this, labels, hash),
+			inc: inc.call(this, labels, null, hash),
+		};
+	}
+
+	exemplars() {
+		const exemplars = getLabels(this.exemplarNames, arguments) || {};
+		const exemplarValue = this.exemplarValue || 1;
+		validateExemplar(this.exemplarNames, exemplars, exemplarValue);
+		const hash = hashObject({}, exemplars);
+		return {
+			inc: inc.call(this, null, exemplars, hash, exemplarValue),
 		};
 	}
 
@@ -71,30 +83,46 @@ const reset = function () {
 	}
 };
 
-const inc = function (labels, hash) {
+const inc = function (labels, exemplars, hash, exemplarValue) {
 	return value => {
 		if (value && !Number.isFinite(value)) {
 			throw new TypeError(`Value is not a valid number: ${util.format(value)}`);
 		}
+		if (exemplarValue && !Number.isFinite(exemplarValue)) {
+			throw new TypeError(
+				`Exemplar value is not a valid number: ${util.format(exemplarValue)}`,
+			);
+		}
 		if (value < 0) {
 			throw new Error('It is not possible to decrease a counter');
 		}
 
 		labels = labels || {};
+		exemplars = exemplars || {};
 		validateLabel(this.labelNames, labels);
+		validateExemplar(this.exemplarNames, exemplars, exemplarValue);
 
 		const incValue = value === null || value === undefined ? 1 : value;
 
-		this.hashMap = setValue(this.hashMap, incValue, labels, hash);
+		this.hashMap = setValue(
+			this.hashMap,
+			incValue,
+			exemplarValue,
+			labels,
+			exemplars,
+			hash,
+		);
 	};
 };
 
-function setValue(hashMap, value, labels, hash) {
+function setValue(hashMap, value, exemplarValue, labels, exemplars, hash) {
 	hash = hash || '';
 	if (hashMap[hash]) {
 		hashMap[hash].value += value;
 	} else {
-		hashMap[hash] = { value, labels: labels || {} };
+		hashMap[hash] = exemplarValue
+			? { value, labels: labels || {}, exemplars, exemplarValue }
+			: { value, labels: labels || {} };
 	}
 	return hashMap;
 }

lib/metric.js

@@ -2,7 +2,11 @@
 
 const { globalRegistry } = require('./registry');
 const { isObject } = require('./util');
-const { validateMetricName, validateLabelName } = require('./validation');
+const {
+	validateMetricName,
+	validateLabelName,
+	validateExemplarName,
+} = require('./validation');
 
 /**
  * @abstract
@@ -18,6 +22,7 @@ class Metric {
 				labelNames: [],
 				registers: [globalRegistry],
 				aggregator: 'sum',
+				exemplarNames: [],
 			},
 			defaults,
 			config,
@@ -38,6 +43,9 @@ class Metric {
 		if (!validateLabelName(this.labelNames)) {
 			throw new Error('Invalid label name');
 		}
+		if (!validateExemplarName(this.exemplarNames)) {
+			throw new Error('Invalid exemplar name');
+		}
 		if (this.collect && typeof this.collect !== 'function') {
 			throw new Error('Optional "collect" parameter must be a function');
 		}

lib/registry.js

@@ -16,6 +16,7 @@ class Registry {
 		this._metrics = {};
 		this._collectors = [];
 		this._defaultLabels = {};
+		this._contentType = 'text/plain; version=0.0.4; charset=utf-8';
 	}
 
 	getMetricsAsArray() {
@@ -63,13 +64,79 @@ class Registry {
 		return `${help}\n${type}\n${values}`.trim();
 	}
 
-	async metrics() {
-		const promises = [];
+	async getMetricAsPrometheusOpenMetricsString(metric) {
+		const item = await metric.get();
+		const name = escapeString(item.name);
+		const help = `# HELP ${name} ${escapeString(item.help)}`;
+		const type = `# TYPE ${name} ${item.type}`;
+		const eof = '# EOF';
+		const defaultLabelNames = Object.keys(this._defaultLabels);
 
-		for (const metric of this.getMetricsAsArray()) {
-			promises.push(this.getMetricAsPrometheusString(metric));
+		let values = '';
+		for (const val of item.values || []) {
+			val.labels = val.labels || {};
+			val.exemplars = val.exemplars || {};
+
+			if (defaultLabelNames.length > 0) {
+				// Make a copy before mutating
+				val.labels = Object.assign({}, val.labels);
+
+				for (const labelName of defaultLabelNames) {
+					val.labels[labelName] =
+						val.labels[labelName] || this._defaultLabels[labelName];
+				}
+			}
+
+			let metricName = val.metricName || item.name;
+
+			const labelKeys = Object.keys(val.labels);
+			const labelSize = labelKeys.length;
+			if (labelSize > 0) {
+				let labels = '';
+				let i = 0;
+				for (; i < labelSize - 1; i++) {
+					labels += `${labelKeys[i]}="${escapeLabelValue(
+						val.labels[labelKeys[i]],
+					)}",`;
+				}
+				labels += `${labelKeys[i]}="${escapeLabelValue(
+					val.labels[labelKeys[i]],
+				)}"`;
+				metricName += `{${labels}}`;
+			}
+
+			const exemplarKeys = Object.keys(val.exemplars);
+			const exemplarSize = exemplarKeys.length;
+			let exemplars = '';
+			if (exemplarSize > 0) {
+				let i = 0;
+				for (; i < exemplarSize - 1; i++) {
+					exemplars += `${exemplarKeys[i]}="${escapeLabelValue(
+						val.exemplars[exemplarKeys[i]],
+					)}",`;
+				}
+				exemplars += `${exemplarKeys[i]}="${escapeLabelValue(
+					val.exemplars[exemplarKeys[i]],
+				)}"`;
+				metricName += ` ${getValueAsString(val.value)} # {${exemplars}}`;
+			}
+			values += `${metricName} ${getValueAsString(val.exemplarValue)}\n`;
 		}
 
+		return `${help}\n${type}\n${values}${eof}`.trim();
+	}
+
+	async metrics() {
+		const promises = [];
+		if (this.contentType === 'application/openmetrics-text') {
+			for (const metric of this.getMetricsAsArray()) {
+				promises.push(this.getMetricAsPrometheusOpenMetricsString(metric));
+			}
+		} else {
+			for (const metric of this.getMetricsAsArray()) {
+				promises.push(this.getMetricAsPrometheusString(metric));
+			}
+		}
 		const resolves = await Promise.all(promises);
 
 		return `${resolves.join('\n\n')}\n`;
@@ -88,6 +155,7 @@ class Registry {
 	clear() {
 		this._metrics = {};
 		this._defaultLabels = {};
+		this._contentType = 'text/plain; version=0.0.4; charset=utf-8';
 	}
 
 	async getMetricsAsJSON() {
@@ -144,7 +212,11 @@ class Registry {
 	}
 
 	get contentType() {
-		return 'text/plain; version=0.0.4; charset=utf-8';
+		return this._contentType;
+	}
+
+	set contentType(type) {
+		this._contentType = type;
 	}
 
 	static merge(registers) {

lib/util.js

@@ -14,13 +14,13 @@ exports.getValueAsString = function getValueString(value) {
 	}
 };
 
-exports.removeLabels = function removeLabels(hashMap, labels) {
-	const hash = hashObject(labels);
+exports.removeLabels = function removeLabels(hashMap, labels, exemplars) {
+	const hash = hashObject(labels, exemplars);
 	delete hashMap[hash];
 };
 
-exports.setValue = function setValue(hashMap, value, labels) {
-	const hash = hashObject(labels);
+exports.setValue = function setValue(hashMap, value, labels, exemplars) {
+	const hash = hashObject(labels, exemplars);
 	hashMap[hash] = {
 		value: typeof value === 'number' ? value : 0,
 		labels: labels || {},
@@ -45,11 +45,12 @@ exports.getLabels = function (labelNames, args) {
 	}, {});
 };
 
-function hashObject(labels) {
+function hashObject(labels, exemplars) {
 	// We don't actually need a hash here. We just need a string that
 	// is unique for each possible labels object and consistent across
 	// calls with equivalent labels objects.
-	let keys = Object.keys(labels);
+	const aggregatedMetada = { ...labels, ...exemplars };
+	let keys = Object.keys(aggregatedMetada);
 	if (keys.length === 0) {
 		return '';
 	}
@@ -62,9 +63,9 @@ function hashObject(labels) {
 	let i = 0;
 	const size = keys.length;
 	for (; i < size - 1; i++) {
-		hash += `${keys[i]}:${labels[keys[i]]},`;
+		hash += `${keys[i]}:${aggregatedMetada[keys[i]]},`;
 	}
-	hash += `${keys[i]}:${labels[keys[i]]}`;
+	hash += `${keys[i]}:${aggregatedMetada[keys[i]]}`;
 	return hash;
 }
 exports.hashObject = hashObject;

lib/validation.js

@@ -5,6 +5,7 @@ const util = require('util');
 // These are from https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels
 const metricRegexp = /^[a-zA-Z_:][a-zA-Z0-9_:]*$/;
 const labelRegexp = /^[a-zA-Z_][a-zA-Z0-9_]*$/;
+const exemplarRegexp = /^[a-zA-Z_][a-zA-Z0-9_]*$/;
 
 exports.validateMetricName = function (name) {
 	return metricRegexp.test(name);
@@ -20,6 +21,16 @@ exports.validateLabelName = function (names) {
 	return valid;
 };
 
+exports.validateExemplarName = function (names) {
+	let valid = true;
+	(names || []).forEach(name => {
+		if (!exemplarRegexp.test(name)) {
+			valid = false;
+		}
+	});
+	return valid;
+};
+
 exports.validateLabel = function validateLabel(savedLabels, labels) {
 	Object.keys(labels).forEach(label => {
 		if (savedLabels.indexOf(label) === -1) {
@@ -31,3 +42,30 @@ exports.validateLabel = function validateLabel(savedLabels, labels) {
 		}
 	});
 };
+
+exports.validateExemplar = function validateLabel(
+	savedExemplars,
+	exemplars,
+	exemplarValue,
+) {
+	Object.keys(exemplars).forEach(exemplar => {
+		if (savedExemplars.indexOf(exemplar) === -1) {
+			throw new Error(
+				`Added label "${exemplar}" is not included in initial exemplarSet: ${util.inspect(
+					savedExemplars,
+				)}`,
+			);
+		}
+	});
+
+	// TODO both the value and the label set cannot be more than 128 chars
+	// exemplar length cannot be more than 128 UTF-8 characters
+	const exemplarLabelString = Object.entries(exemplars)
+		.join('')
+		.replace(/,/g, '');
+	if ((exemplarLabelString + exemplarValue).length > 128) {
+		throw new Error(
+			`Exemplar label set cannot exceed 128 UTF-8 characters: current label set has ${exemplars.length} characters`,
+		);
+	}
+};

test/__snapshots__/counterTest.js.snap

@@ -2,6 +2,10 @@
 
 exports[`counter remove should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
+exports[`counter with params as object exemplars should throw error if exemplar lengths does not match 1`] = `"Invalid number of arguments"`;
+
+exports[`counter with params as object exemplars should throw error when exemplar and exemplar value combined is longer than 128 chars 1`] = `"Exemplar label set cannot exceed 128 UTF-8 characters: current label set has undefined characters"`;
+
 exports[`counter with params as object labels should throw error if label lengths does not match 1`] = `"Invalid number of arguments"`;
 
 exports[`counter with params as object should not be possible to decrease a counter 1`] = `"It is not possible to decrease a counter"`;