Exposing broker metadata

[shoothzj]

Motivation

Adapt PIP 90 in go client
allow go client retrieve brokermetadata

Modifications

• modify CommandConnect featureflags, turn SupportsBrokerEntryMetadata to true
• add index() brokerPublishTime methods on message interface
• add Skip method on bytebuffer

[wolfstudy]

Thanks @shoothzj work for this , just a little comments, please check

[wolfstudy]

It looks like we've checked above that the brokerMetadata object is nil by doing the following:

brokerMetadata, err := reader.ReadBrokerMetadata()
	if err != nil { // here
		// todo optimize use more appropriate error codes
		pc.discardCorruptedMessage(pbMsgID, pb.CommandAck_BatchDeSerializeError)
		return err
	}

Do we still need to double check here? Will someone concurrently modify the value of the brokerMetadata object?

[shoothzj]

brokermetadata can be null if broker not enable this feature

[wolfstudy]

Maybe instead of using pointers we can use the following definition:

		var messageIndex uint64
		var brokerPublishTime time.Time

[shoothzj]

@wolfstudy It can be null if broker not enable brokerMetadata feature

[wolfstudy]

Why is the error object returned as nil here? If we don't need this error field, maybe we can cancel it in function definition? Or we can use errors.new("xxx") to customize the error message

[shoothzj]

It's not an error, it means broker not enable brokermetadata feature

[wolfstudy]

LGTM +1