Cursors (or streams) produces an infinite loop

[ProgMaq]

Version

4.0.1-SNAPSHOT

Context

When using the cursors or stream an infinite loop is produced, stream.exceptionHandler or stream.endHandler will never be called. hasMore always indicates true.

Do you have a reproducer?

package org.example;

import io.vertx.core.Future;
import io.vertx.core.Vertx;
import io.vertx.core.json.JsonObject;
import io.vertx.jdbcclient.JDBCPool;

public class Example {

  public static void main(String[] args) {

    final Vertx vertx = Vertx.vertx();

    final JsonObject config = new JsonObject()
      .put("provider_class", "io.vertx.ext.jdbc.spi.impl.HikariCPDataSourceProvider")
      .put("jdbcUrl", "jdbc:sqlserver://****:1433;databaseName=****;")
      .put("driverClassName", "com.microsoft.sqlserver.jdbc.SQLServerDriver")
      .put("username", "****")
      .put("password", "****")
      .put("max_pool_size", 1)
      .put("initial_pool_size", 1)
      .put("min_pool_size", 1)
      .put("max_statements", 0)
      .put("max_statements_per_connection", 0)
      .put("max_idle_time", 0);

    final JDBCPool pool = JDBCPool.pool(vertx, config);

    pool.withTransaction(tx ->
      tx.prepare("SELECT 1")
        .map(pS -> pS.createStream(200))
        .flatMap(stream -> Future
          .future(promise -> {

            stream.exceptionHandler(err -> {
              System.out.println("Error: " + err.getMessage());
              promise.fail(err);
            });

            stream.endHandler(v -> {
              System.out.println("End of stream");
              promise.complete();
            });

            stream.handler(row -> {
              System.out.println(row.toJson().encode());
            });

          })
        )
    )
        .onFailure(Throwable::printStackTrace);

  }

}

Steps to reproduce

1. Add valid credentials
2. Create a basic POM with mssql driver and vertx-jdbc-client dependencies
3. Run

Extra

• MacOS 11.1
• AdoptOpenJDK (build 15.0.1+9)
• I have used stable versions of the MSSQL driver, and the latest one (9.1.1.jre15-preview) with the same results.
• I have used c3p0, Hikari and Agroal, also the same result.
• With Vert.x 4.0.0 it returns 'The statement must be executed before any results can be obtained'.
• I can avoid the infinite loop with one of these changes, but I understand that it could have repercussions:

ConnectionImpl.java: Line 126 -> change true to false

private <R> void handle(JDBCQueryAction<?, R> action, QueryResultHandler<R> handler, Promise<Boolean> promise) {
        Future<JDBCResponse<R>> fut = conn.schedule(action);
        fut.onComplete(ar -> {
            if (ar.succeeded()) {
                ar.result()
                  .handle(handler);

                promise.complete(false);
            } else {
                promise.fail(ar.cause());
            }
        });
    }

Or change CursorImpl.java: Line 66 -> ignore isSuspended value and always return false

    public synchronized boolean hasMore() {
        if (result == null) {
            throw new IllegalStateException("No current cursor read");
        }
        return false;
    }

[vietj]

we will fix this issue by loading everything in memory for 4.0.1 and reimplement it properly for a later version

[vietj]

@ProgMaq we will do a quick fix for 4.0.1 based on your suggestion and after we will implement a better solution (#208)

btw cool usage of withTransaction and Future.future in the test