[Reader] Should set either start message id or start message from roll back duration.

pulsar-broker/src/test/java/org/apache/pulsar/client/impl/ReaderTest.java

@@ -242,7 +242,7 @@ public void testReaderWithTimeLong() throws Exception {
 
         // (3) Create reader and set position 1 hour back so, it should only read messages which are 2 hours old which
         // published on step 2
-        Reader<byte[]> reader = pulsarClient.newReader().topic(topic).startMessageId(MessageId.earliest)
+        Reader<byte[]> reader = pulsarClient.newReader().topic(topic)
                 .startMessageFromRollbackDuration(2, TimeUnit.HOURS).create();
 
         List<MessageId> receivedMessageIds = Lists.newArrayList();

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ReaderBuilderImpl.java

@@ -82,9 +82,15 @@ public CompletableFuture<Reader<T>> createAsync() {
                     .failedFuture(new IllegalArgumentException("Topic name must be set on the reader builder"));
         }
 
-        if (conf.getStartMessageId() == null) {
+        if (conf.getStartMessageId() != null && conf.getStartMessageFromRollbackDurationInSec() > 0 ||
+                conf.getStartMessageId() == null && conf.getStartMessageFromRollbackDurationInSec() <= 0) {
             return FutureUtil
-                    .failedFuture(new IllegalArgumentException("Start message id must be set on the reader builder"));
+                    .failedFuture(new IllegalArgumentException(
+                            "Start message id or start message from roll back must be specified but they cannot be specified at the same time"));
+        }
+
+        if (conf.getStartMessageFromRollbackDurationInSec() > 0) {
+            conf.setStartMessageId(MessageId.earliest);
         }
 
         return client.createReaderAsync(conf, schema);

pulsar-client/src/test/java/org/apache/pulsar/client/impl/BuildersTest.java

@@ -26,8 +26,12 @@
 import java.lang.reflect.Field;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
 import org.apache.pulsar.client.api.MessageId;
 import org.apache.pulsar.client.api.PulsarClient;
+import org.apache.pulsar.client.api.PulsarClientException;
+import org.apache.pulsar.client.api.Reader;
 import org.apache.pulsar.client.impl.conf.ReaderConfigurationData;
 import org.testng.annotations.Test;
 
@@ -96,5 +100,26 @@ public void readerBuilderLoadConfTest() throws Exception {
         assertTrue(obj instanceof ReaderConfigurationData);
         assertEquals(((ReaderConfigurationData) obj).getTopicName(), topicName);
         assertEquals(((ReaderConfigurationData) obj).getStartMessageId(), messageId);
+        client.close();
+    }
+
+    @Test(expectedExceptions = {PulsarClientException.class}, expectedExceptionsMessageRegExp = ".* must be specified but they cannot be specified at the same time.*")
+    public void shouldNotSetTwoOptAtTheSameTime() throws Exception {
+        PulsarClient client = PulsarClient.builder().serviceUrl("pulsar://localhost:6650").build();
+        try (Reader reader = client.newReader().topic("abc").startMessageId(MessageId.earliest).startMessageFromRollbackDuration(10, TimeUnit.HOURS).create()) {
+            // no-op
+        } finally {
+            client.close();
+        }
+    }
+
+    @Test(expectedExceptions = {PulsarClientException.class}, expectedExceptionsMessageRegExp = ".* must be specified but they cannot be specified at the same time.*")
+    public void shouldSetOneStartOpt() throws Exception {
+        PulsarClient client = PulsarClient.builder().serviceUrl("pulsar://localhost:6650").build();
+        try (Reader reader = client.newReader().topic("abc").create()) {
+            // no-op
+        } finally {
+            client.close();
+        }
     }
 }