[Bug] Producer fails to send message size equals to maxMessageSize in topic policy setting.

[Jason918]

Describe the bug
See the following unit test code to reproduce this issue.

The root cause of this is that in topic policy setting, it limits the size of message header and payload.
See

pulsar/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java

Line 413 in 6b8ebbd

if (isExceedMaximumMessageSize(headersAndPayload.readableBytes())) {

To Reproduce
Steps to reproduce the behavior:
Add this unit test code in org.apache.pulsar.broker.admin.TopicPoliciesTest

    @Test
    public void testTopicMaxMessageSizeThreshHold() throws Exception {
        @Cleanup
        Producer<byte[]> p = pulsarClient.newProducer().topic(testTopic).create();
        admin.topicPolicies().setMaxMessageSize(testTopic,1000);
        Awaitility.await().until(() -> pulsar.getTopicPoliciesService().getTopicPolicies(TopicName.get(testTopic)) != null);
        p.send(new byte[1000]);
    }

Got the following error:

org.apache.pulsar.client.api.PulsarClientException$NotAllowedException: The size of the message which is produced by producer test-0-2 to the topic persistent://my-tenant/my-namespace/test-set-backlog-quota-partition-0 is not allowed

Expected behavior
Message should produce success.

Screenshots
NA

Desktop (please complete the following information):

• OS: macOS

Additional context
NA

[Jason918]

I think we can add new field "payload size" in CommandSend API.
And make topic policy only checks the payload size.
What do you think? @codelipenghui @315157973 @eolivelli

[Jason918]

This will be fixed by PIP-132 in #13591
Close this issue.