Adding validation in ExponentialBackoffPolicy to prevent overflows

Signed-off-by: Max Lambrecht <maxlambrecht@gmail.com>

java-spiffe-core/src/main/java/io/spiffe/workloadapi/retry/ExponentialBackoffPolicy.java

@@ -62,11 +62,11 @@ public class ExponentialBackoffPolicy {
      * @return a {@link Duration} representing the next delay
      */
     public Duration nextDelay(final Duration currentDelay) {
-        val next = backoffFunction.apply(currentDelay);
+        // current delay didn't exceed maxDelay already
-        if (next.compareTo(maxDelay) > 0) {
+        if (currentDelay.compareTo(maxDelay) < 0) {
-            return maxDelay;
+            return calculateNextDelay(currentDelay);
         }
-        return next;
+        return maxDelay;
     }
 
     /**
@@ -79,4 +79,12 @@ public class ExponentialBackoffPolicy {
     public boolean reachedMaxRetries(final int retriesCount) {
         return maxRetries != UNLIMITED_RETRIES && retriesCount >= maxRetries;
     }
+
+    private Duration calculateNextDelay(final Duration currentDelay) {
+        val next = backoffFunction.apply(currentDelay);
+        if (next.compareTo(maxDelay) > 0) {
+            return maxDelay;
+        }
+        return next;
+    }
 }

java-spiffe-core/src/test/java/io/spiffe/workloadapi/retry/ExponentialBackoffPolicyTest.java

@@ -27,6 +27,17 @@ class ExponentialBackoffPolicyTest {
         assertEquals(Duration.ofSeconds(60), exponentialBackoffPolicy.nextDelay(Duration.ofSeconds(50)));
     }
 
+    @Test
+    void testNextDelayDefaultPolicy_currentDelayExceedsMaxDelay_returnsMaxDelay() {
+        ExponentialBackoffPolicy exponentialBackoffPolicy = ExponentialBackoffPolicy
+                .builder()
+                .initialDelay(Duration.ofSeconds(1))
+                .maxDelay(Duration.ofSeconds(60))
+                .build();
+
+        assertEquals(Duration.ofSeconds(60), exponentialBackoffPolicy.nextDelay(Duration.ofSeconds(70)));
+    }
+
     @Test
     void testNextDelayCustomPolicy() {
         ExponentialBackoffPolicy exponentialBackoffPolicy = ExponentialBackoffPolicy