Added api for session id of topic readers

topic/src/main/java/tech/ydb/topic/read/SyncReader.java

@@ -22,10 +22,18 @@ public interface SyncReader {
     void initAndWait();
 
     /**
-     * Receive a {@link Message}. Blocks until a Message is received.
+     * Return identifier of read session.
+     * @return current read session identifier or null if session has not started yet
+     */
+    @Nullable
+    String getSessionId();
+
+    /**
+     * Receive a {@link Message}.Blocks until a Message is received.
      *
      * @param settings  settings for receiving a Message
      * @return returns a {@link Message}, or null if the specified timeout time elapses before a message is available
+     * @throws java.lang.InterruptedException if current thread was interrupted
      */
     Message receive(ReceiveSettings settings) throws InterruptedException;
 
@@ -35,6 +43,7 @@ public interface SyncReader {
      * @param timeout  timeout to wait a Message with
      * @param unit  TimeUnit for timeout
      * @return returns a {@link Message}, or null if the specified waiting time elapses before a message is available
+     * @throws java.lang.InterruptedException if current thread was interrupted
      */
     @Nullable
     default Message receive(long timeout, TimeUnit unit) throws InterruptedException {
@@ -47,6 +56,7 @@ default Message receive(long timeout, TimeUnit unit) throws InterruptedException
      * Receive a {@link Message}. Blocks until a Message is received.
      *
      * @return {@link Message}
+     * @throws java.lang.InterruptedException if current thread was interrupted
      */
     default Message receive() throws InterruptedException {
         return receive(ReceiveSettings.newBuilder().build());

topic/src/main/java/tech/ydb/topic/read/events/ReadEventHandler.java

@@ -1,5 +1,7 @@
 package tech.ydb.topic.read.events;
 
+import tech.ydb.topic.read.impl.events.SessionStartedEvent;
+
 /**
  * @author Nikolay Perfilov
  */
@@ -22,4 +24,6 @@ default void onStopPartitionSession(StopPartitionSessionEvent event) {
     default void onPartitionSessionClosed(PartitionSessionClosedEvent event) { }
 
     default void onReaderClosed(ReaderClosedEvent event) { }
+
+    default void onSessionStarted(SessionStartedEvent event) { }
 }

topic/src/main/java/tech/ydb/topic/read/impl/AsyncReaderImpl.java

@@ -27,6 +27,7 @@
 import tech.ydb.topic.read.events.StopPartitionSessionEvent;
 import tech.ydb.topic.read.impl.events.CommitOffsetAcknowledgementEventImpl;
 import tech.ydb.topic.read.impl.events.PartitionSessionClosedEventImpl;
+import tech.ydb.topic.read.impl.events.SessionStartedEvent;
 import tech.ydb.topic.read.impl.events.StartPartitionSessionEventImpl;
 import tech.ydb.topic.read.impl.events.StopPartitionSessionEventImpl;
 import tech.ydb.topic.settings.ReadEventHandlersSettings;
@@ -76,6 +77,18 @@ public CompletableFuture<Status> updateOffsetsInTransaction(YdbTransaction trans
         return sendUpdateOffsetsInTransaction(transaction, offsets, settings);
     }
 
+    @Override
+    protected void handleSessionStarted(String sessionId) {
+        handlerExecutor.execute(() -> {
+            try {
+                eventHandler.onSessionStarted(new SessionStartedEvent(sessionId));
+            } catch (Throwable th) {
+                logUserThrowableAndStopWorking(th, "onSessionStarted");
+                throw th;
+            }
+        });
+    }
+
     @Override
     protected CompletableFuture<Void> handleDataReceivedEvent(DataReceivedEvent event) {
         return CompletableFuture.runAsync(() -> {

topic/src/main/java/tech/ydb/topic/read/impl/ReaderImpl.java

@@ -109,6 +109,7 @@ protected CompletableFuture<Void> initImpl() {
     }
 
     protected abstract CompletableFuture<Void> handleDataReceivedEvent(DataReceivedEvent event);
+    protected abstract void handleSessionStarted(String sessionId);
     protected abstract void handleCommitResponse(long committedOffset, PartitionSession partitionSession);
     protected abstract void handleStartPartitionSessionRequest(
             YdbTopic.StreamReadMessage.StartPartitionSessionRequest request,
@@ -385,6 +386,7 @@ private void onInitResponse(YdbTopic.StreamReadMessage.InitResponse response) {
             sizeBytesToRequest.set(settings.getMaxMemoryUsageBytes());
             logger.info("[{}] Session {} initialized. Requesting {} bytes...", streamId, sessionId,
                     settings.getMaxMemoryUsageBytes());
+            handleSessionStarted(sessionId);
             sendReadRequest();
         }
 

topic/src/main/java/tech/ydb/topic/read/impl/SyncReaderImpl.java

@@ -39,6 +39,7 @@ public class SyncReaderImpl extends ReaderImpl implements SyncReader {
     private final ReentrantLock queueLock = new ReentrantLock();
     private final Condition queueIsNotEmptyCondition = queueLock.newCondition();
     private int currentMessageIndex = 0;
+    private volatile String sessionId = null;
 
     public SyncReaderImpl(TopicRpc topicRpc, ReaderSettings settings) {
         super(topicRpc, settings);
@@ -54,6 +55,11 @@ private MessageBatchWrapper(List<Message> messages, CompletableFuture<Void> futu
         }
     }
 
+    @Override
+    public String getSessionId() {
+        return sessionId;
+    }
+
     @Override
     public void init() {
         initImpl();
@@ -160,6 +166,11 @@ protected CompletableFuture<Void> handleDataReceivedEvent(DataReceivedEvent even
         return resultFuture;
     }
 
+    @Override
+    protected void handleSessionStarted(String sessionId) {
+        this.sessionId = sessionId;
+    }
+
     @Override
     protected void handleCommitResponse(long committedOffset, PartitionSession partitionSession) {
         if (logger.isDebugEnabled()) {

topic/src/main/java/tech/ydb/topic/read/impl/events/SessionStartedEvent.java

@@ -0,0 +1,17 @@
+package tech.ydb.topic.read.impl.events;
+
+/**
+ *
+ * @author Aleksandr Gorshenin
+ */
+public class SessionStartedEvent {
+    private final String sessionId;
+
+    public SessionStartedEvent(String sessionId) {
+        this.sessionId = sessionId;
+    }
+
+    public String getSessionId() {
+        return this.sessionId;
+    }
+}