Fix NPE when an error is returned after timeout

Fix NPE happening when the server responds too late with an error, and
the request is already failed with timeout and request metadata is
removed

src/main/java/io/tarantool/driver/core/TarantoolRequestMetadata.java

@@ -32,9 +32,6 @@ public Long getRequestId() {
 
     @Override
     public String toString() {
-        Optional<TarantoolRequestSignature> requestSignature = request.getSignature();
-        return !requestSignature.isPresent() ?
-            String.format("request id: %d", getRequestId()) :
-            String.format("request signature: %s", requestSignature.get());
+        return request.toString();
     }
 }

src/main/java/io/tarantool/driver/handlers/TarantoolRequestHandler.java

@@ -5,15 +5,20 @@
 import io.netty.channel.ChannelOutboundHandlerAdapter;
 import io.netty.channel.ChannelPromise;
 import io.tarantool.driver.core.RequestFutureManager;
+import io.tarantool.driver.core.TarantoolRequestMetadata;
 import io.tarantool.driver.exceptions.TarantoolClientException;
 import io.tarantool.driver.protocol.TarantoolRequest;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * Performs registration of requests and pushes them forward. Should stay first in the channel pipeline
  *
  * @author Alexey Kuzin
  */
 public class TarantoolRequestHandler extends ChannelOutboundHandlerAdapter {
+    private final Logger log = LoggerFactory.getLogger(TarantoolRequestHandler.class);
     private final RequestFutureManager futureManager;
 
     public TarantoolRequestHandler(RequestFutureManager futureManager) {
@@ -25,8 +30,15 @@ public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise)
         TarantoolRequest request = (TarantoolRequest) msg;
         ctx.write(request).addListener((ChannelFutureListener) channelFuture -> {
             if (!channelFuture.isSuccess()) {
-                futureManager.getRequest(request.getHeader().getSync()).getFuture()
-                    .completeExceptionally(new TarantoolClientException(channelFuture.cause()));
+                TarantoolRequestMetadata requestMeta = futureManager.getRequest(request.getHeader().getSync());
+                // The request metadata may has been deleted already after timeout
+                if (requestMeta != null) {
+                    requestMeta.getFuture()
+                        .completeExceptionally(new TarantoolClientException(channelFuture.cause()));
+                } else {
+                    log.info(
+                        "Received an error for {} but it is already timed out: {}", request, channelFuture.cause());
+                }
             }
         });
     }

src/main/java/io/tarantool/driver/protocol/TarantoolRequest.java

@@ -85,6 +85,13 @@ public void toMessagePack(MessagePacker packer, MessagePackObjectMapper mapper)
         }
     }
 
+    @Override
+    public String toString() {
+        return !signature.isPresent() ?
+            String.format("request id: %d", header.getSync()) :
+            String.format("request signature: %s", signature.get());
+    }
+
     /**
      * Base class for request builder implementations
      */