[BUG] Incorrect batch size estimation

[VeselovAndrey]

Library name and version

Azure.Messaging.ServiceBus 7.18.1

Describe the bug

There is some error when estimating batch size.
Some batches (with size that almost hit size limit) were created but failed to send.

Expected behavior

Send created baches.

Actual behavior

Got the ServiceBusException: The message is larger than is currently allowed (262144 bytes).

Reproduction Steps

1. Create batch(es)

ServiceBusSender sender = _serviceBusClient.CreateSender(queueName);
ServiceBusMessageBatch batch = await sender.CreateMessageBatchAsync(ct);

2. Add messages to almost hit the limit (usign TryAddMessage to hit limit)

ServiceBusMessage sbMessage = GetNextMessage();
while (batch.TryAddMessage(sbMessage)) { sbMessage = GetNextMessage(); }

In my case batch.SizeInBytes was 261889 (MaxSizeInBytes == 262144)

3. Try to send batch

await sender.SendMessagesAsync(batch, ct);

Got an exception:

Azure.Messaging.ServiceBus.ServiceBusException: The message (id:redacted, size:263525 bytes) is larger than is currently allowed (262144 bytes). (MessageSizeExceeded). For troubleshooting information, see
https://aka.ms/azsdk/net/servicebus/exceptions/troubleshoot.

The message size became 263525 (was 261889)

Workaround: set MaxSizeInBytes when creating batch to 262144 - (2 * 1024) (default max size - 2KB)

Environment

Windows 11
.NET 8.0.402 / Console App
Visual Studio 17.11.4

[github-actions]

Thank you for your feedback. Tagging and routing to the team member best able to assist.

[jsquire]

@m-redding : Would you please take a look and coordinate with the Service Bus team? I'm not sure from context if the batch overhead calculation is off or the service is sending the wrong size limit on a link when opened.