#43 - ENH: Add gitter support to SimpleRetryHandler

Author: rbygrave

client/src/main/java/io/avaje/http/client/SimpleRetryHandler.java

@@ -4,6 +4,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.net.http.HttpResponse;
+import java.util.Random;
 
 /**
  * Simple retry with max attempts and linear backoff.
@@ -14,16 +15,31 @@ public class SimpleRetryHandler implements RetryHandler {
 
   private final int maxRetries;
   private final long backoffMillis;
+  private final int gitterMillis;
+  private final Random random;
 
   /**
    * Create with maximum number of retries and linear backoff time.
    *
    * @param maxRetries    The maximum number of retry attempts
    * @param backoffMillis The linear backoff between attempts in milliseconds
+   * @param gitterMillis  The maximum amount of gitter that gets added to backoffMillis
    */
-  public SimpleRetryHandler(int maxRetries, long backoffMillis) {
+  public SimpleRetryHandler(int maxRetries, int backoffMillis, int gitterMillis) {
     this.maxRetries = maxRetries;
     this.backoffMillis = backoffMillis;
+    this.gitterMillis = gitterMillis;
+    this.random = new Random();
+  }
+
+  /**
+   * Create with maximum number of retries and linear backoff time and no gitter.
+   *
+   * @param maxRetries    The maximum number of retry attempts
+   * @param backoffMillis The linear backoff between attempts in milliseconds
+   */
+  public SimpleRetryHandler(int maxRetries, int backoffMillis) {
+    this(maxRetries, backoffMillis, 0);
   }
 
   @Override
@@ -33,7 +49,8 @@ public boolean isRetry(int retryCount, HttpResponse<?> response) {
     }
     log.debug("retry count:{} status:{} uri:{}", retryCount, response.statusCode(), response.uri());
     try {
-      Thread.sleep(backoffMillis);
+      int gitter = gitterMillis < 1 ? 0 : random.nextInt(gitterMillis);
+      Thread.sleep(backoffMillis + gitter);
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
       return false;

client/src/test/java/io/avaje/http/client/RetryTest.java

@@ -1,28 +1,38 @@
 package io.avaje.http.client;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.jupiter.api.Test;
 
 import java.net.http.HttpResponse;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-public class RetryTest extends BaseWebTest {
+class RetryTest extends BaseWebTest {
 
-  final MyIntercept myIntercept = new MyIntercept();
-  final HttpClientContext clientContext = initClientWithRetry();
 
-  HttpClientContext initClientWithRetry() {
+  HttpClientContext initClientWithRetry(MyIntercept myIntercept, RetryHandler retryHandler) {
     return HttpClientContext.newBuilder()
       .baseUrl("http://localhost:8887")
       .bodyAdapter(new JacksonBodyAdapter())
-      .retryHandler(new SimpleRetryHandler(4, 1))
+      .retryHandler(retryHandler)
       .requestIntercept(myIntercept)
       .build();
   }
 
   @Test
   void retryTest() {
+    final MyIntercept myIntercept = new MyIntercept();
+    final HttpClientContext clientContext = initClientWithRetry(myIntercept, new SimpleRetryHandler(4, 1));
+    performGetRequestAndAssert(myIntercept, clientContext);
+  }
+
+  @Test
+  void retryWithGitterTest() {
+    final MyIntercept myIntercept = new MyIntercept();
+    final HttpClientContext clientContext = initClientWithRetry(myIntercept, new SimpleRetryHandler(4, 10, 20));
+    performGetRequestAndAssert(myIntercept, clientContext);
+  }
+
+  private void performGetRequestAndAssert(MyIntercept myIntercept, HttpClientContext clientContext) {
     HttpResponse<String> res = clientContext.request()
       .label("http_client_hello_retry")
       .path("hello/retry")