feat: add linearDelay for retryDelay option

README.md

@@ -29,6 +29,9 @@ axios.get('http://example.com/test') // The first request fails and the second r
 // Exponential back-off retry delay between requests
 axiosRetry(axios, { retryDelay: axiosRetry.exponentialDelay });
 
+// Liner retry delay between requests
+axiosRetry(axios, { retryDelay: axiosRetry.linearDelay() });
+
 // Custom retry delay
 axiosRetry(axios, { retryDelay: (retryCount) => {
   return retryCount * 1000;
@@ -64,7 +67,7 @@ client
 | retries | `Number` | `3` | The number of times to retry before failing. 1 = One retry after first failure |
 | retryCondition | `Function` | `isNetworkOrIdempotentRequestError` | A callback to further control if a request should be retried.  By default, it retries if it is a network error or a 5xx error on an idempotent request (GET, HEAD, OPTIONS, PUT or DELETE). |
 | shouldResetTimeout | `Boolean` | false | Defines if the timeout should be reset between retries |
-| retryDelay | `Function` | `function noDelay() { return 0; }` | A callback to further control the delay in milliseconds between retried requests. By default there is no delay between retries. Another option is exponentialDelay ([Exponential Backoff](https://developers.google.com/analytics/devguides/reporting/core/v3/errors#backoff)). The function is passed `retryCount` and `error`. |
+| retryDelay | `Function` | `function noDelay() { return 0; }` | A callback to further control the delay in milliseconds between retried requests. By default there is no delay between retries. Another option is exponentialDelay ([Exponential Backoff](https://developers.google.com/analytics/devguides/reporting/core/v3/errors#backoff)) or `linearDelay`. The function is passed `retryCount` and `error`. |
 | onRetry | `Function` | `function onRetry(retryCount, error, requestConfig) { return; }` | A callback to notify when a retry is about to occur. Useful for tracing and you can any async process for example refresh a token on 401. By default nothing will occur. The function is passed `retryCount`, `error`, and `requestConfig`. |
 | onMaxRetryTimesExceeded | `Function` | `function onMaxRetryTimesExceeded(error, retryCount) { return; }` | After all the retries are failed, this callback will be called with the last error before throwing the error. |
 | validateResponse | `Function \| null` | `null` | A callback to define whether a response should be resolved or rejected. If null is passed, it will fallback to the axios default (only 2xx status codes are resolved). |

spec/index.spec.ts

@@ -8,7 +8,8 @@ import axiosRetry, {
   exponentialDelay,
   retryAfter,
   isRetryableError,
-  namespace
+  namespace,
+  linearDelay
 } from '../src/index';
 
 const NETWORK_ERROR = new AxiosError('Some connection error');
@@ -614,6 +615,53 @@ describe('axiosRetry(axios, { retries, retryDelay })', () => {
       }, done.fail);
     });
   });
+
+  describe('when linearDelay is supplied', () => {
+    it('should take more than 600 milliseconds with default delay and 4 retries', (done) => {
+      const client = axios.create();
+      setupResponses(client, [
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').reply(200, 'It worked!')
+      ]);
+      const timeStart = new Date().getTime();
+      axiosRetry(client, {
+        retries: 4,
+        retryCondition: () => true,
+        retryDelay: linearDelay()
+      });
+      client.get('http://example.com/test').then(() => {
+        // 100 + 200 + 300 = 600
+        expect(new Date().getTime() - timeStart).toBeGreaterThanOrEqual(600);
+        expect(new Date().getTime() - timeStart).toBeLessThan(700);
+
+        done();
+      }, done.fail);
+    });
+
+    it('should take more than 300 milliseconds with 50ms delay and 4 retries', (done) => {
+      const client = axios.create();
+      setupResponses(client, [
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').replyWithError(NETWORK_ERROR),
+        () => nock('http://example.com').get('/test').reply(200, 'It worked!')
+      ]);
+      const timeStart = new Date().getTime();
+      axiosRetry(client, {
+        retries: 4,
+        retryCondition: () => true,
+        retryDelay: linearDelay(50)
+      });
+      client.get('http://example.com/test').then(() => {
+        // 50 + 100 + 150 = 300
+        expect(new Date().getTime() - timeStart).toBeGreaterThanOrEqual(300);
+        expect(new Date().getTime() - timeStart).toBeLessThan(400);
+        done();
+      }, done.fail);
+    });
+  });
 });
 
 describe('axiosRetry(axios, { retries, onRetry })', () => {
@@ -1054,6 +1102,33 @@ describe('exponentialDelay', () => {
   });
 });
 
+describe('linearDelay', () => {
+  it('should return liner retry delay', () => {
+    const linearDelayFunc = linearDelay();
+
+    function assertTime(retryNumber) {
+      const time = linearDelayFunc(retryNumber, undefined);
+
+      expect(time).toBe(100 * retryNumber);
+    }
+
+    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].forEach(assertTime);
+  });
+
+  it('should change delay time when specifying delay factor', () => {
+    const delayFactor = 300;
+    const linearDelayFunc = linearDelay(delayFactor);
+
+    function assertTime(retryNumber) {
+      const time = linearDelayFunc(retryNumber, undefined);
+
+      expect(time).toBe(delayFactor * retryNumber);
+    }
+
+    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].forEach(assertTime);
+  });
+});
+
 describe('retryAfter', () => {
   it('should understand a numeric Retry-After header', () => {
     const errorResponse = new AxiosError('Error response');

src/index.ts

@@ -81,6 +81,7 @@ export interface AxiosRetry {
   isIdempotentRequestError(error: AxiosError): boolean;
   isNetworkOrIdempotentRequestError(error: AxiosError): boolean;
   exponentialDelay(retryNumber?: number, error?: AxiosError, delayFactor?: number): number;
+  linearDelay(delayFactor?: number): (retryNumber: number, error: AxiosError | undefined) => number;
 }
 
 declare module 'axios' {
@@ -169,6 +170,20 @@ export function exponentialDelay(
   return delay + randomSum;
 }
 
+/**
+ * Linear delay
+ * @param {number | undefined} delayFactor - delay factor in milliseconds (default: 100)
+ * @returns {function} (retryNumber: number, error: AxiosError | undefined) => number
+ */
+export function linearDelay(
+  delayFactor: number | undefined = 100
+): (retryNumber: number, error: AxiosError | undefined) => number {
+  return (retryNumber = 0, error = undefined) => {
+    const delay = retryNumber * delayFactor;
+    return Math.max(delay, retryAfter(error));
+  };
+}
+
 export const DEFAULT_OPTIONS: Required<IAxiosRetryConfig> = {
   retries: 3,
   retryCondition: isNetworkOrIdempotentRequestError,
@@ -322,5 +337,6 @@ axiosRetry.isSafeRequestError = isSafeRequestError;
 axiosRetry.isIdempotentRequestError = isIdempotentRequestError;
 axiosRetry.isNetworkOrIdempotentRequestError = isNetworkOrIdempotentRequestError;
 axiosRetry.exponentialDelay = exponentialDelay;
+axiosRetry.linearDelay = linearDelay;
 axiosRetry.isRetryableError = isRetryableError;
 export default axiosRetry;