Unexpected behavior when seeking and receiving messages in the first batch of the topic

In the dotnet client, when forcing 100 messages to be put into the same batch, and then seek the middle one like 50, it will start receiving from the first message. If batch sending is not enabled or forced to send one by one, it works normally.

This problem seems to only appear in the first batch of the topic.

Example codes:

const string serviceUrl = "pulsar://localhost:6650";

var client = await new PulsarClientBuilder()
    .ServiceUrl(serviceUrl)
    .BuildAsync();

var topicName = "public/default/topic-" + Guid.NewGuid().ToString("N");
logger.WriteLine(topicName);

var producer = await client.NewProducer()
    .Topic(topicName)
    .EnableBatching(true)
    .BatchingMaxPublishDelay(TimeSpan.FromSeconds(3))
    .CreateAsync();

var consumer = await client.NewConsumer()
    .Topic(topicName)
    .SubscriptionName("test-subscription")
    .SubscribeAsync();

// Act
int num = 100;
List<MessageId> msgs = new List<MessageId>(num);
List<Task<MessageId>> tasks = new List<Task<MessageId>>();

// When uncomment this, it will send the first batch, and the problem will not appear in the following batches.
// await producer.SendAsync(Encoding.UTF8.GetBytes("first-batch-message"));

for (int i = 0; i < num; i++)
{
    tasks.Add(producer.SendAsync(
        Encoding.UTF8.GetBytes($"[{i}]")));
}

await Task.WhenAll(tasks); // Force 100 messages to be sent in the same batch.
foreach (var task in tasks)
{
    msgs.Add(await task);
}

await consumer.SeekAsync(msgs[50]);

for (int i = 0; i < 10; i++)
{
    var reMsg = await consumer.ReceiveAsync();
    String msg = Encoding.UTF8.GetString(reMsg.Data);
    logger.WriteLine(msg);
}

Running these codes will output:

public/default/topic-215bd2ac57be47729b233b77695e2eb7
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]

When uncommenting the line await producer.SendAsync(Encoding.UTF8.GetBytes("first-batch-message")); to send the first batch first. It will output the expected result. Expected output:

public/default/topic-215bd2ac57be47729b233b77695e2eb7
[51]
[52]
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[60]

[Lanayx]

@RobertIndie Nice to hear! Please don’t forget to star the project if you find it useful 😃

[Lanayx]

@RobertIndie Yes, I’m aware of that 😃 That’s why I wrote “If message is received by Client between 5 and 6 steps”, which is before that logic happens