Add X-LaunchDarkly-Payload-ID header on event post. (#169)

src/main/java/com/launchdarkly/client/DefaultEventProcessor.java

@@ -15,6 +15,7 @@
 import java.util.Date;
 import java.util.List;
 import java.util.Random;
+import java.util.UUID;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Executors;
@@ -42,6 +43,7 @@ final class DefaultEventProcessor implements EventProcessor {
   private static final Logger logger = LoggerFactory.getLogger(DefaultEventProcessor.class);
   private static final String EVENT_SCHEMA_HEADER = "X-LaunchDarkly-Event-Schema";
   private static final String EVENT_SCHEMA_VERSION = "3";
+  private static final String EVENT_PAYLOAD_ID_HEADER = "X-LaunchDarkly-Payload-ID";
 
   private final BlockingQueue<EventProcessorMessage> inbox;
   private final ScheduledExecutorService scheduler;
@@ -542,7 +544,8 @@ void stop() {
 
     private void postEvents(String json, int outputEventCount) {
       String uriStr = config.eventsURI.toString() + "/bulk";
-
+      String eventPayloadId = UUID.randomUUID().toString();
+
       logger.debug("Posting {} event(s) to {} with payload: {}",
           outputEventCount, uriStr, json);
 
@@ -558,6 +561,7 @@ private void postEvents(String json, int outputEventCount) {
             .post(RequestBody.create(MediaType.parse("application/json; charset=utf-8"), json))
             .addHeader("Content-Type", "application/json")
             .addHeader(EVENT_SCHEMA_HEADER, EVENT_SCHEMA_VERSION)
+            .addHeader(EVENT_PAYLOAD_ID_HEADER, eventPayloadId)
             .build();
 
         long startTime = System.currentTimeMillis();

src/test/java/com/launchdarkly/client/DefaultEventProcessorTest.java

@@ -11,6 +11,7 @@
 
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
 import static com.launchdarkly.client.TestHttpUtil.httpsServerWithSelfSignedCert;
@@ -22,6 +23,7 @@
 import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
 import static org.junit.Assert.assertEquals;
@@ -485,6 +487,50 @@ public void eventSchemaIsSent() throws Exception {
     }
   }
 
+  @Test
+  public void eventPayloadIdIsSent() throws Exception {
+    Event e = EventFactory.DEFAULT.newIdentifyEvent(user);
+
+    try (MockWebServer server = makeStartedServer(eventsSuccessResponse())) {
+      try (DefaultEventProcessor ep = new DefaultEventProcessor(SDK_KEY, baseConfig(server).build())) {
+        ep.sendEvent(e);
+      }
+
+      RecordedRequest req = server.takeRequest();
+      String payloadHeaderValue = req.getHeader("X-LaunchDarkly-Payload-ID");
+      assertThat(payloadHeaderValue, notNullValue(String.class));
+      assertThat(UUID.fromString(payloadHeaderValue), notNullValue(UUID.class));
+    }
+  }
+
+  @Test
+  public void eventPayloadIdReusedOnRetry() throws Exception {
+    MockResponse errorResponse = new MockResponse().setResponseCode(429);
+    Event e = EventFactory.DEFAULT.newIdentifyEvent(user);
+
+    try (MockWebServer server = makeStartedServer(errorResponse, eventsSuccessResponse(), eventsSuccessResponse())) {
+      try (DefaultEventProcessor ep = new DefaultEventProcessor(SDK_KEY, baseConfig(server).build())) {
+        ep.sendEvent(e);
+        ep.flush();
+        // Necessary to ensure the retry occurs before the second request for test assertion ordering
+        ep.waitUntilInactive();
+        ep.sendEvent(e);
+      }
+
+      // Failed response request
+      RecordedRequest req = server.takeRequest(0, TimeUnit.SECONDS);
+      String payloadId = req.getHeader("X-LaunchDarkly-Payload-ID");
+      // Retry request has same payload ID as failed request
+      req = server.takeRequest(0, TimeUnit.SECONDS);
+      String retryId = req.getHeader("X-LaunchDarkly-Payload-ID");
+      assertThat(retryId, equalTo(payloadId));
+      // Second request has different payload ID from first request
+      req = server.takeRequest(0, TimeUnit.SECONDS);
+      payloadId = req.getHeader("X-LaunchDarkly-Payload-ID");
+      assertThat(retryId, not(equalTo(payloadId)));
+    }
+  }
+
   @Test
   public void http400ErrorIsRecoverable() throws Exception {
     testRecoverableHttpError(400);