FE: Handle previousCursor in first page (kafbat#550)

Author: hadisfr

api/src/main/java/io/kafbat/ui/service/MessagesService.java

@@ -46,6 +46,7 @@
 import org.apache.kafka.clients.producer.RecordMetadata;
 import org.apache.kafka.common.TopicPartition;
 import org.apache.kafka.common.serialization.ByteArraySerializer;
+import org.jetbrains.annotations.NotNull;
 import org.springframework.stereotype.Service;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -216,42 +217,29 @@ public Flux<TopicMessageEventDTO> loadMessages(KafkaCluster cluster,
                                                  @Nullable Integer limit,
                                                  @Nullable String keySerde,
                                                  @Nullable String valueSerde) {
-    return loadMessages(
-        cluster,
-        topic,
+    Cursor cursor = new Cursor(
         deserializationService.deserializerFor(cluster, topic, keySerde, valueSerde),
         consumerPosition,
         getMsgFilter(containsStringFilter, filterId),
-        fixPageSize(limit),
-        null
+        fixPageSize(limit)
     );
+    String cursorId = cursorsStorage.register(cursor, null);
+    return loadMessages(cluster, topic, cursorId, cursor);
   }
 
   public Flux<TopicMessageEventDTO> loadMessages(KafkaCluster cluster, String topic, String cursorId) {
     Cursor cursor = cursorsStorage.getCursor(cursorId)
         .orElseThrow(() -> new ValidationException("Next page cursor not found. Maybe it was evicted from cache."));
-    return loadMessages(
-        cluster,
-        topic,
-        cursor.deserializer(),
-        cursor.consumerPosition(),
-        cursor.filter(),
-        cursor.limit(),
-        cursorId
-    );
+    return loadMessages(cluster, topic, cursorId, cursor);
   }
 
-  private Flux<TopicMessageEventDTO> loadMessages(KafkaCluster cluster,
-                                                  String topic,
-                                                  ConsumerRecordDeserializer deserializer,
-                                                  ConsumerPosition consumerPosition,
-                                                  Predicate<TopicMessageDTO> filter,
-                                                  int limit,
-                                                  String cursorId) {
+  private @NotNull Flux<TopicMessageEventDTO> loadMessages(KafkaCluster cluster, String topic,
+                                                           String cursorId, Cursor cursor) {
     return withExistingTopic(cluster, topic)
         .flux()
         .publishOn(Schedulers.boundedElastic())
-        .flatMap(td -> loadMessagesImpl(cluster, deserializer, consumerPosition, filter, limit, cursorId));
+        .flatMap(td -> loadMessagesImpl(cluster,
+            cursor.deserializer(), cursor.consumerPosition(), cursor.filter(), cursor.limit(), cursorId));
   }
 
   private Flux<TopicMessageEventDTO> loadMessagesImpl(KafkaCluster cluster,

api/src/main/java/io/kafbat/ui/service/PollingCursorsStorage.java

@@ -29,28 +29,25 @@ public Cursor.Tracking createNewCursor(ConsumerRecordDeserializer deserializer,
                                          ConsumerPosition originalPosition,
                                          Predicate<TopicMessageDTO> filter,
                                          int limit,
-                                         @Nullable String cursorId) {
-    return new Cursor.Tracking(deserializer, originalPosition, filter, limit, cursorId, this::register,
-        this::getPreviousCursorId);
+                                         String cursorId) {
+    return new Cursor.Tracking(deserializer, originalPosition, filter, limit, cursorId,
+        this::register, this::getPreviousCursorId);
   }
 
   public Optional<Cursor> getCursor(String id) {
     return Optional.ofNullable(cursorsCache.getIfPresent(id));
   }
 
-  public String register(Cursor nextCursor, @Nullable String currentCursorId) {
+  public String register(Cursor cursor, @Nullable String previousCursorId) {
     var id = RandomStringUtils.random(8, true, true);
-    cursorsCache.put(id, nextCursor);
-    if (currentCursorId != null) {
-      previousCursorsMap.put(id, currentCursorId);
+    cursorsCache.put(id, cursor);
+    if (previousCursorId != null) {
+      previousCursorsMap.put(id, previousCursorId);
     }
     return id;
   }
 
-  public Optional<String> getPreviousCursorId(@Nullable String cursorId) {
-    if (cursorId == null) {
-      return Optional.empty();
-    }
+  public Optional<String> getPreviousCursorId(String cursorId) {
     return Optional.ofNullable(previousCursorsMap.getIfPresent(cursorId));
   }