From aa829af43bddd54b2c7865385a3c8069379201bd Mon Sep 17 00:00:00 2001
From: Chris Eager <chris@signal.org>
Date: Mon, 31 Oct 2022 11:25:39 -0500
Subject: [PATCH] Handle expected case of empty flux in message deletion

---
 .../textsecuregcm/storage/MessagesDynamoDb.java     |  6 +++---
 .../textsecuregcm/storage/MessagesDynamoDbTest.java | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDb.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDb.java
index 6135b5043..294989118 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDb.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDb.java
@@ -175,9 +175,9 @@ public class MessagesDynamoDb extends AbstractDynamoDbStore {
           }
           return null;
         })
-        .last()
-        .toFuture()
-        .thenApply(Optional::ofNullable);
+        .map(Optional::ofNullable)
+        .last(Optional.empty()) // if the flux is empty, last() will throw without a default
+        .toFuture();
   }
 
   public CompletableFuture<Optional<MessageProtos.Envelope>> deleteMessage(final UUID destinationAccountUuid,
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDbTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDbTest.java
index eae1802ad..7d76b1069 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDbTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/storage/MessagesDynamoDbTest.java
@@ -11,6 +11,7 @@ import com.google.protobuf.ByteString;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 import java.util.Random;
 import java.util.UUID;
 import java.util.concurrent.ExecutorService;
@@ -240,15 +241,25 @@ class MessagesDynamoDbTest {
     assertThat(load(secondDestinationUuid, 1, MessagesDynamoDb.RESULT_SET_CHUNK_SIZE)).isNotNull()
         .hasSize(1).element(0).isEqualTo(MESSAGE2);
 
-    messagesDynamoDb.deleteMessageByDestinationAndGuid(secondDestinationUuid,
+    final Optional<MessageProtos.Envelope> deletedMessage = messagesDynamoDb.deleteMessageByDestinationAndGuid(
+        secondDestinationUuid,
         UUID.fromString(MESSAGE2.getServerGuid())).get(5, TimeUnit.SECONDS);
 
+    assertThat(deletedMessage).isPresent();
+
     assertThat(load(destinationUuid, 1, MessagesDynamoDb.RESULT_SET_CHUNK_SIZE)).isNotNull().hasSize(1)
         .element(0).isEqualTo(MESSAGE1);
     assertThat(load(destinationUuid, 2, MessagesDynamoDb.RESULT_SET_CHUNK_SIZE)).isNotNull().hasSize(1)
         .element(0).isEqualTo(MESSAGE3);
     assertThat(load(secondDestinationUuid, 1, MessagesDynamoDb.RESULT_SET_CHUNK_SIZE)).isNotNull()
         .isEmpty();
+
+    final Optional<MessageProtos.Envelope> alreadyDeletedMessage = messagesDynamoDb.deleteMessageByDestinationAndGuid(
+        secondDestinationUuid,
+        UUID.fromString(MESSAGE2.getServerGuid())).get(5, TimeUnit.SECONDS);
+
+    assertThat(alreadyDeletedMessage).isNotPresent();
+
   }
 
   @Test