Allow setting Gauge values to NaN.

CHANGELOG.md

@@ -11,6 +11,8 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+* Allow setting Gauge values to NaN, +Inf, and -Inf
+
 ### Added
 
 ## [11.1.1] - 2018-06-29

lib/gauge.js

@@ -215,7 +215,7 @@ function inc(labels) {
 
 function set(labels) {
 	return (value, timestamp) => {
-		if (!Number.isFinite(value)) {
+		if (typeof value !== 'number') {
 			throw new TypeError(`Value is not a valid number: ${util.format(value)}`);
 		}
 		if (timestamp && !isDate(timestamp) && !Number.isFinite(timestamp)) {

lib/registry.js

@@ -1,4 +1,5 @@
 'use strict';
+const getValueAsString = require('./util').getValueAsString;
 
 function escapeString(str) {
 	return str.replace(/\n/g, '\\n').replace(/\\(?!n)/g, '\\\\');
@@ -44,7 +45,7 @@ class Registry {
 				metricName += `{${labels.join(',')}}`;
 			}
 
-			const line = [metricName, val.value];
+			const line = [metricName, getValueAsString(val.value)];
 			if (opts.timestamps) {
 				line.push(val.timestamp);
 			}

lib/util.js

@@ -9,10 +9,24 @@ exports.getPropertiesFromObj = function(hashMap) {
 	return obj;
 };
 
+exports.getValueAsString = function getValueString(value) {
+	if (Number.isNaN(value)) {
+		return 'Nan';
+	} else if (!Number.isFinite(value)) {
+		if (value < 0) {
+			return '-Inf';
+		} else {
+			return '+Inf';
+		}
+	} else {
+		return `${value}`;
+	}
+};
+
 exports.setValue = function setValue(hashMap, value, labels, timestamp) {
 	const hash = hashObject(labels);
 	hashMap[hash] = {
-		value: Number.isFinite(value) ? value : 0,
+		value: typeof value === 'number' ? value : 0,
 		labels: labels || {},
 		timestamp: isDate(timestamp)
 			? timestamp.valueOf()

test/gaugeTest.js

@@ -64,6 +64,21 @@ describe('gauge', () => {
 				expect(fn).toThrowErrorMatchingSnapshot();
 			});
 
+			it('should allow NaN as a value', () => {
+				instance.set(NaN);
+				expectValue(NaN);
+			});
+
+			it('should allow +Inf as a value', () => {
+				instance.set(Infinity);
+				expectValue(Infinity);
+			});
+
+			it('should allow -Inf as a value', () => {
+				instance.set(-Infinity);
+				expectValue(-Infinity);
+			});
+
 			describe('with labels', () => {
 				beforeEach(() => {
 					instance = new Gauge('name', 'help', ['code']);

test/registerTest.js

@@ -44,6 +44,66 @@ describe('register', () => {
 		);
 	});
 
+	it('should handle and output a metric with a NaN value', () => {
+		register.registerMetric({
+			get() {
+				return {
+					name: 'test_metric',
+					type: 'gauge',
+					help: 'A test metric',
+					values: [
+						{
+							value: NaN
+						}
+					]
+				};
+			}
+		});
+		const lines = register.metrics().split('\n');
+		expect(lines).toHaveLength(4);
+		expect(lines[2]).toEqual('test_metric Nan');
+	});
+
+	it('should handle and output a metric with an +Infinity value', () => {
+		register.registerMetric({
+			get() {
+				return {
+					name: 'test_metric',
+					type: 'gauge',
+					help: 'A test metric',
+					values: [
+						{
+							value: Infinity
+						}
+					]
+				};
+			}
+		});
+		const lines = register.metrics().split('\n');
+		expect(lines).toHaveLength(4);
+		expect(lines[2]).toEqual('test_metric +Inf');
+	});
+
+	it('should handle and output a metric with an -Infinity value', () => {
+		register.registerMetric({
+			get() {
+				return {
+					name: 'test_metric',
+					type: 'gauge',
+					help: 'A test metric',
+					values: [
+						{
+							value: -Infinity
+						}
+					]
+				};
+			}
+		});
+		const lines = register.metrics().split('\n');
+		expect(lines).toHaveLength(4);
+		expect(lines[2]).toEqual('test_metric -Inf');
+	});
+
 	it('should handle a metric without labels', () => {
 		register.registerMetric({
 			get() {