fix: decorrelatedJitter backoff returning NaN after many iterations

Closes #86

changelog.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 3.1.3
+
+- **fix:** decorrelatedJitter backoff returning NaN after many iterations ([#86](https://github.com/connor4312/cockatiel/issues/86))
+
 ## 3.1.2
 
 - **chore:** remove test files from dist package ([#84](https://github.com/connor4312/cockatiel/issues/84))

src/backoff/ExponentialBackoffGenerators.test.ts

@@ -35,4 +35,21 @@ describe('ExponentialBackoff Generators', () => {
       }
     });
   }
+
+  it('fixes issue #86', () => {
+    const options: IExponentialBackoffOptions<any> = {
+      generator: decorrelatedJitterGenerator,
+      maxDelay: 15 * 60_000,
+      exponent: 2,
+      initialDelay: 45_000,
+    };
+
+    let state: any;
+    for (let k = 1; k < 3000; k++) {
+      const [delay, nextState] = decorrelatedJitterGenerator(state, options);
+      expect(delay).to.not.be.NaN;
+      expect(delay).to.be.gte(0);
+      state = nextState;
+    }
+  });
 });

src/backoff/ExponentialBackoffGenerators.ts

@@ -56,7 +56,7 @@ export const decorrelatedJitterGenerator: GeneratorFn<[number, number]> = (state
   const [attempt, prev] = state || [0, 0];
   const t = attempt + Math.random();
   const next = Math.pow(options.exponent, t) * Math.tanh(Math.sqrt(pFactor * t));
-  const formulaIntrinsicValue = Math.max(0, next - prev);
+  const formulaIntrinsicValue = isFinite(next) ? Math.max(0, next - prev) : Infinity;
   return [
     Math.min(formulaIntrinsicValue * rpScalingFactor * options.initialDelay, options.maxDelay),
     [attempt + 1, next],