#48 RetransmissionBackOff: add configurable random factory

open-coap · Apr 24, 2023 · 07d2c7a · 07d2c7a
1 parent ca83ef3
commit 07d2c7a
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Showing 2 changed files with 25 additions and 1 deletion.
diff --git a/coap-core/src/main/java/com/mbed/coap/transmission/RetransmissionBackOff.java b/coap-core/src/main/java/com/mbed/coap/transmission/RetransmissionBackOff.java
@@ -41,6 +41,12 @@ static RetransmissionBackOff ofFixed(Duration interval) {
     }
 
     static RetransmissionBackOff ofExponential(Duration first, int maxAttempts) {
+        return ofExponential(first, maxAttempts, CoapConstants.ACK_RANDOM_FACTOR);
+    }
+
+    static RetransmissionBackOff ofExponential(Duration first, int maxAttempts, float randomFactor) {
+        require(randomFactor >= 1);
+        require(maxAttempts >= 0);
         final Random rnd = new Random();
         long firstMs = first.toMillis();
 
@@ -50,7 +56,7 @@ static RetransmissionBackOff ofExponential(Duration first, int maxAttempts) {
                 return Duration.ZERO;
             }
 
-            float rndFactor = 1 + (CoapConstants.ACK_RANDOM_FACTOR - 1) * rnd.nextFloat();
+            float rndFactor = 1 + (randomFactor - 1) * rnd.nextFloat();
             return Duration.ofMillis((long) (firstMs * rndFactor * (1L << (attempt - 1))));
         };
     }

diff --git a/coap-core/src/test/java/com/mbed/coap/transmission/RetransmissionBackOffTest.java b/coap-core/src/test/java/com/mbed/coap/transmission/RetransmissionBackOffTest.java
@@ -111,4 +111,22 @@ public void singleTimeoutTest() {
         assertThrows(IllegalArgumentException.class, () -> singleTimeout.next(0));
         assertThrows(IllegalArgumentException.class, () -> singleTimeout.next(-1));
     }
+
+    @Test
+    public void retransmission_with_custom_random_factor() {
+        RetransmissionBackOff backOff = RetransmissionBackOff.ofExponential(ofSeconds(2), 2, 1.0f);
+
+        assertEquals(2000, backOff.next(1).toMillis());
+        assertEquals(4000, backOff.next(2).toMillis());
+    }
+
+    @Test
+    void should_fail_with_wrong_parameters() {
+        assertThrows(IllegalArgumentException.class, () -> RetransmissionBackOff.ofExponential(ofSeconds(2), 2, 0.99f));
+        assertThrows(IllegalArgumentException.class, () -> RetransmissionBackOff.ofExponential(ofSeconds(2), 2, 0f));
+        assertThrows(IllegalArgumentException.class, () -> RetransmissionBackOff.ofExponential(ofSeconds(2), 2, -1.321f));
+
+
+        assertThrows(IllegalArgumentException.class, () -> RetransmissionBackOff.ofExponential(ofSeconds(2), -1, 2f));
+    }
 }