From e83007704670b5f567ca338c156441f6c569ecb5 Mon Sep 17 00:00:00 2001
From: Szymon Marczak <36894700+szmarczak@users.noreply.github.com>
Date: Tue, 27 Apr 2021 01:28:23 +0200
Subject: [PATCH] Add `noise` retry option

Fixes #1690
---
 source/core/calculate-retry-delay.ts |  2 +-
 source/core/options.ts               |  9 ++++-
 test/arguments.ts                    | 50 ++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/source/core/calculate-retry-delay.ts b/source/core/calculate-retry-delay.ts
index 1ace16d40..3f13b81fe 100644
--- a/source/core/calculate-retry-delay.ts
+++ b/source/core/calculate-retry-delay.ts
@@ -39,7 +39,7 @@ const calculateRetryDelay: Returns<RetryFunction, number> = ({
 		}
 	}
 
-	const noise = Math.random() * 100;
+	const noise = Math.random() * retryOptions.noise;
 	return Math.min(((2 ** (attemptCount - 1)) * 1000), retryOptions.backoffLimit) + noise;
 };
 
diff --git a/source/core/options.ts b/source/core/options.ts
index 3abdc3ee4..7374d02c9 100644
--- a/source/core/options.ts
+++ b/source/core/options.ts
@@ -295,6 +295,7 @@ export interface RetryOptions {
 	errorCodes: string[];
 	calculateDelay: RetryFunction;
 	backoffLimit: number;
+	noise: number;
 	maxRetryAfter?: number;
 }
 
@@ -618,7 +619,8 @@ const defaultInternals: Options['_internals'] = {
 		],
 		maxRetryAfter: undefined,
 		calculateDelay: ({computedValue}) => computedValue,
-		backoffLimit: Number.POSITIVE_INFINITY
+		backoffLimit: Number.POSITIVE_INFINITY,
+		noise: 100
 	},
 	localAddress: undefined,
 	method: 'GET',
@@ -1785,6 +1787,11 @@ export default class Options {
 		assert.any([is.array, is.undefined], value.methods);
 		assert.any([is.array, is.undefined], value.statusCodes);
 		assert.any([is.array, is.undefined], value.errorCodes);
+		assert.any([is.number, is.undefined], value.noise);
+
+		if (value.noise && Math.abs(value.noise) > 100) {
+			throw new Error(`The maximum acceptable retry noise is +/- 100ms, got ${value.noise}`);
+		}
 
 		for (const key in value) {
 			if (!(key in this._internals.retry)) {
diff --git a/test/arguments.ts b/test/arguments.ts
index d59c835b8..ac0910bc3 100644
--- a/test/arguments.ts
+++ b/test/arguments.ts
@@ -557,3 +557,53 @@ test('prefixUrl is properly replaced when extending', withServer, async (t, serv
 
 	t.is(await child.get('').text(), '/other/path/');
 });
+
+test('throws on too large noise', t => {
+	t.throws(() => {
+		new Options({
+			retry: {
+				noise: 101
+			}
+		});
+	}, {
+		message: 'The maximum acceptable retry noise is +/- 100ms, got 101'
+	});
+
+	t.throws(() => {
+		new Options({
+			retry: {
+				noise: -101
+			}
+		});
+	}, {
+		message: 'The maximum acceptable retry noise is +/- 100ms, got -101'
+	});
+
+	t.throws(() => {
+		new Options({
+			retry: {
+				noise: Number.POSITIVE_INFINITY
+			}
+		});
+	}, {
+		message: 'The maximum acceptable retry noise is +/- 100ms, got Infinity'
+	});
+
+	t.throws(() => {
+		new Options({
+			retry: {
+				noise: Number.NEGATIVE_INFINITY
+			}
+		});
+	}, {
+		message: 'The maximum acceptable retry noise is +/- 100ms, got -Infinity'
+	});
+
+	t.notThrows(() => {
+		new Options({
+			retry: {
+				noise: 0
+			}
+		});
+	});
+});