From 6385598cab67bce2a45725864c5eae949c17da6a Mon Sep 17 00:00:00 2001
From: Chad Transtrum <chad.transtrum@earlywarning.com>
Date: Mon, 22 Apr 2024 12:12:51 -0700
Subject: [PATCH] Retry on 429, and handle Retry-After header

---
 spec/index.spec.ts | 57 ++++++++++++++++++++++++++++++++++++++++++++++
 src/index.ts       | 27 ++++++++++++++++++----
 2 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/spec/index.spec.ts b/spec/index.spec.ts
index 89f9369..983880e 100644
--- a/spec/index.spec.ts
+++ b/spec/index.spec.ts
@@ -6,6 +6,7 @@ import axiosRetry, {
   isSafeRequestError,
   isIdempotentRequestError,
   exponentialDelay,
+  retryAfter,
   isRetryableError,
   namespace
 } from '../src/index';
@@ -859,6 +860,62 @@ describe('exponentialDelay', () => {
   });
 });
 
+describe('retryAfter', () => {
+  it('should understand a numeric Retry-After header', () => {
+    const errorResponse = new AxiosError('Error response');
+    errorResponse.response = { status: 429 } as AxiosError['response'];
+    // @ts-ignore
+    errorResponse.response.headers = { 'retry-after': '10' };
+    const time = retryAfter(errorResponse);
+
+    expect(time).toBe(10000);
+  });
+
+  it('should ignore a negative numeric Retry-After header', () => {
+    const errorResponse = new AxiosError('Error response');
+    errorResponse.response = { status: 429 } as AxiosError['response'];
+    // @ts-ignore
+    errorResponse.response.headers = { 'retry-after': '-10' };
+    const time = retryAfter(errorResponse);
+
+    expect(time).toBe(0);
+  });
+
+  it('should understand a date Retry-After header', () => {
+    const errorResponse = new AxiosError('Error response');
+    errorResponse.response = { status: 429 } as AxiosError['response'];
+    const date = new Date();
+    date.setSeconds(date.getSeconds() + 10);
+    // @ts-ignore
+    errorResponse.response.headers = { 'retry-after': date.toUTCString() };
+    const time = retryAfter(errorResponse);
+
+    expect(time >= 9000 && time <= 10000).toBe(true);
+  });
+
+  it('should ignore a past Retry-After header', () => {
+    const errorResponse = new AxiosError('Error response');
+    errorResponse.response = { status: 429 } as AxiosError['response'];
+    const date = new Date();
+    date.setSeconds(date.getSeconds() - 10);
+    // @ts-ignore
+    errorResponse.response.headers = { 'retry-after': date.toUTCString() };
+    const time = retryAfter(errorResponse);
+
+    expect(time).toBe(0);
+  });
+
+  it('should ignore an invalid Retry-After header', () => {
+    const errorResponse = new AxiosError('Error response');
+    errorResponse.response = { status: 429 } as AxiosError['response'];
+    // @ts-ignore
+    errorResponse.response.headers = { 'retry-after': 'a couple minutes' };
+    const time = retryAfter(errorResponse);
+
+    expect(time).toBe(0);
+  });
+});
+
 describe('isRetryableError(error)', () => {
   it('should be false for aborted requests', () => {
     const errorResponse = new AxiosError('Error response');
diff --git a/src/index.ts b/src/index.ts
index 898ed07..dc70b88 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -102,7 +102,9 @@ const IDEMPOTENT_HTTP_METHODS = SAFE_HTTP_METHODS.concat(['put', 'delete']);
 export function isRetryableError(error: AxiosError): boolean {
   return (
     error.code !== 'ECONNABORTED' &&
-    (!error.response || (error.response.status >= 500 && error.response.status <= 599))
+    (!error.response ||
+      error.response.status === 429 ||
+      (error.response.status >= 500 && error.response.status <= 599))
   );
 }
 
@@ -127,16 +129,31 @@ export function isNetworkOrIdempotentRequestError(error: AxiosError): boolean {
   return isNetworkError(error) || isIdempotentRequestError(error);
 }
 
-function noDelay() {
-  return 0;
+export function retryAfter(error: AxiosError | undefined = undefined): number {
+  const retryAfterHeader = error?.response?.headers['retry-after'];
+  if (!retryAfterHeader) {
+    return 0;
+  }
+  // if the retry after header is a number, convert it to milliseconds
+  let retryAfterMs = (Number(retryAfterHeader) || 0) * 1000;
+  // If the retry after header is a date, get the number of milliseconds until that date
+  if (retryAfterMs === 0) {
+    retryAfterMs = (new Date(retryAfterHeader).valueOf() || 0) - Date.now();
+  }
+  return Math.max(0, retryAfterMs);
+}
+
+function noDelay(_retryNumber = 0, error: AxiosError | undefined = undefined) {
+  return Math.max(0, retryAfter(error));
 }
 
 export function exponentialDelay(
   retryNumber = 0,
-  _error: AxiosError | undefined = undefined,
+  error: AxiosError | undefined = undefined,
   delayFactor = 100
 ): number {
-  const delay = 2 ** retryNumber * delayFactor;
+  const calculatedDelay = 2 ** retryNumber * delayFactor;
+  const delay = Math.max(calculatedDelay, retryAfter(error));
   const randomSum = delay * 0.2 * Math.random(); // 0-20% of the delay
   return delay + randomSum;
 }