chore: Nextdelay must be greater than 0

Signed-off-by: Javier Aliaga <javier@diagrid.io>

Author: javier-aliaga

durabletask-client/src/main/java/io/dapr/durabletask/RetryPolicy.java

@@ -14,8 +14,9 @@
 package io.dapr.durabletask;
 
 import javax.annotation.Nullable;
+
 import java.time.Duration;
-import java.util.Objects;
+import java.util.Random;
 
 /**
  * A declarative retry policy that can be configured for activity or sub-orchestration calls.
@@ -206,4 +207,22 @@ public RetryPolicy setJitterFactor(double jitterFactor) {
   public double getJitterFactor() {
     return this.jitterFactor;
   }
+
+  /**
+   * Applies jitter to a delay value, reducing it by a deterministic random fraction
+   * in [0, jitterFactor). The result is guaranteed to be at least 1ms.
+   *
+   * @param delayInMillis the base delay in milliseconds (must be positive)
+   * @param jitterFactor  the jitter factor in [0.0, 1.0]
+   * @param seed          deterministic seed for the random number generator
+   * @return the jittered delay in milliseconds, always >= 1
+   */
+  static long applyJitter(long delayInMillis, double jitterFactor, long seed) {
+    if (jitterFactor > 0.0) {
+      double reduction = new Random(seed).nextDouble() * jitterFactor;
+      delayInMillis = (long) (delayInMillis * (1.0 - reduction));
+      return Math.max(delayInMillis, 1);
+    }
+    return delayInMillis;
+  }
 }

durabletask-client/src/main/java/io/dapr/durabletask/TaskOrchestrationExecutor.java

@@ -38,7 +38,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
-import java.util.Random;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.CancellationException;
@@ -1520,12 +1519,9 @@ private Duration getNextDelay() {
           // Apply jitter: reduce delay by a random fraction in [0, jitterFactor).
           // Seed is deterministic so that replay computes the same finalFireAt, preventing
           // the createTimerChain callback from creating spurious extra sub-timers.
-          double jitterFactor = this.policy.getJitterFactor();
-          if (jitterFactor > 0.0) {
-            long seed = this.firstAttempt.toEpochMilli() + this.attemptNumber;
-            double reduction = new Random(seed).nextDouble() * jitterFactor;
-            nextDelayInMillis = (long) (nextDelayInMillis * (1.0 - reduction));
-          }
+          long seed = this.firstAttempt.toEpochMilli() + this.attemptNumber;
+          nextDelayInMillis = RetryPolicy.applyJitter(
+              nextDelayInMillis, this.policy.getJitterFactor(), seed);
 
           return Duration.ofMillis(nextDelayInMillis);
         }

durabletask-client/src/test/java/io/dapr/durabletask/RetryPolicyTest.java

@@ -16,7 +16,6 @@
 import org.junit.jupiter.api.Test;
 
 import java.time.Duration;
-import java.util.Random;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -82,18 +81,26 @@ void jitterFactorPositiveInfinityThrows() {
 
 
   /**
-
    * With jitterFactor=0 the delay must be unchanged.
    */
   @Test
   void zeroJitterLeavesDelayUnchanged() {
     long baseDelayMillis = 3000L;
-    double jitterFactor = 0.0;
-
-    long seed = 42L;
-    double reduction = new Random(seed).nextDouble() * jitterFactor;
-    long reduced = (long) (baseDelayMillis * (1.0 - reduction));
+    assertEquals(baseDelayMillis, RetryPolicy.applyJitter(baseDelayMillis, 0.0, 42L));
+  }
 
-    assertEquals(baseDelayMillis, reduced);
+  /**
+   * With jitterFactor=1.0 the delay must never drop below 1ms,
+   * even when nextDouble() approaches 1.0.
+   */
+  @Test
+  void jitterWithMaxFactorNeverProducesZeroDelay() {
+    long baseDelayMillis = 1L; // smallest meaningful delay
+
+    for (int seed = 0; seed < 1000; seed++) {
+      long result = RetryPolicy.applyJitter(baseDelayMillis, 1.0, seed);
+      assertTrue(result >= 1,
+          "Delay must be at least 1ms, but was " + result + " for seed " + seed);
+    }
   }
 }