Merge pull request #66 from daern91/master

add initialJitter feature

Author: mdlavin

README.md

@@ -73,6 +73,7 @@ The following object shows the default options:
   factor: 0,
   timeout: 0,
   jitter: false,
+  initialJitter: false,
   handleError: null,
   handleTimeout: null,
   beforeAttempt: null,
@@ -155,6 +156,13 @@ to your target environment.
 
    (default: `false`)
 
+- **`initialJitter`**: `Boolean`
+
+  If `initialJitter` is `true` then a `jitter` will also be used in the
+  first call attempt.
+
+   (default: `false`)
+
 - **`minDelay`**: `Number`
 
   `minDelay` is used to set a lower bound of delay

src/index.ts

@@ -20,6 +20,7 @@ export interface AttemptOptions<T> {
   readonly maxAttempts: number;
   readonly timeout: number;
   readonly jitter: boolean;
+  readonly initialJitter: boolean;
   readonly handleError: HandleError<T> | null;
   readonly handleTimeout: HandleTimeout<T> | null;
   readonly beforeAttempt: BeforeAttempt<T> | null;
@@ -44,6 +45,7 @@ function applyDefaults<T> (options?: PartialAttemptOptions<T>): AttemptOptions<T
     maxAttempts: (options.maxAttempts === undefined) ? 3 : options.maxAttempts,
     timeout: (options.timeout === undefined) ? 0 : options.timeout,
     jitter: (options.jitter === true),
+    initialJitter: (options.initialJitter === true),
     handleError: (options.handleError === undefined) ? null : options.handleError,
     handleTimeout: (options.handleTimeout === undefined) ? null : options.handleTimeout,
     beforeAttempt: (options.beforeAttempt === undefined) ? null : options.beforeAttempt,
@@ -52,9 +54,7 @@ function applyDefaults<T> (options?: PartialAttemptOptions<T>): AttemptOptions<T
 }
 
 export async function sleep (delay: number) {
-  return new Promise((resolve, reject) => {
-    setTimeout(resolve, delay);
-  });
+  return new Promise((resolve) => setTimeout(resolve, delay));
 }
 
 export function defaultCalculateDelay<T> (context: AttemptContext, options: AttemptOptions<T>): number {
@@ -205,5 +205,11 @@ export async function retry<T> (
     await sleep(initialDelay);
   }
 
+  if (context.attemptNum < 1 && options.initialJitter) {
+    const delay = calculateDelay(context, options);
+    if (delay) {
+      await sleep(delay);
+    }
+  }
   return makeAttempt();
 }

test/index.test.ts

@@ -18,6 +18,7 @@ test('should be able to calculate delays', (t) => {
     maxAttempts: 0,
     timeout: 0,
     jitter: false,
+    initialJitter: false,
     handleError: null,
     handleTimeout: null,
     beforeAttempt: null,
@@ -87,6 +88,7 @@ test('should default to 3 attempts with 200 delay', async (t) => {
       maxAttempts: 3,
       timeout: 0,
       jitter: false,
+      initialJitter: false,
       handleError: null,
       handleTimeout: null,
       beforeAttempt: null,
@@ -334,6 +336,38 @@ test('should support jitter', async (t) => {
   });
 });
 
+test('should support jitter with initialJitter', async (t) => {
+  let expectedDelays = [
+    0,
+    100,
+    200,
+    400,
+    800
+  ];
+
+  let lastTime = Date.now();
+
+  return retry(async (context) => {
+    let newTime = Date.now();
+    let actualDelay = newTime - lastTime;
+    lastTime = newTime;
+
+    t.true(actualDelay <= (expectedDelays[context.attemptNum] + DELAY_TOLERANCE));
+
+    if (context.attemptsRemaining === 0) {
+      return 'success';
+    } else {
+      throw new Error('try again');
+    }
+  }, {
+    maxAttempts: expectedDelays.length,
+    delay: 100,
+    factor: 2,
+    jitter: true,
+    initialJitter: true
+  });
+});
+
 test('should support jitter with minDelay', async (t) => {
   let expectedDelays = [
     0,
@@ -371,6 +405,44 @@ test('should support jitter with minDelay', async (t) => {
   });
 });
 
+test('should support jitter with minDelay and initialJitter', async (t) => {
+  let expectedDelays = [
+    0,
+    100,
+    200,
+    400,
+    800
+  ];
+
+  let lastTime = Date.now();
+  const minDelay = 100;
+
+  return retry(async (context) => {
+    let newTime = Date.now();
+    let actualDelay = newTime - lastTime;
+    lastTime = newTime;
+
+    if (context.attemptNum > 0) {
+      t.true(actualDelay >= minDelay);
+    }
+
+    t.true(actualDelay <= (expectedDelays[context.attemptNum] + DELAY_TOLERANCE));
+
+    if (context.attemptsRemaining === 0) {
+      return 'success';
+    } else {
+      throw new Error('try again');
+    }
+  }, {
+    maxAttempts: expectedDelays.length,
+    delay: 100,
+    minDelay,
+    factor: 2,
+    jitter: true,
+    initialJitter: true
+  });
+});
+
 test('should detect invalid minDelay', async (t) => {
   const err = await t.throws(retry(async (context) => {
     throw new Error('should not get here');