AMQP: Avoid allocating a new ByteString on each consumed message

[dimamo5]

Avoids copying a new array and a new allocation by using the fromArrayUnsafe method. It should be ok to build from this unsafe method as long as body is not exposed to the outside.

[pjfanning]

Thanks @dimamo5 but I am not sure that this is necessarily a good idea. How can we be sure that AMQP provider does not reuse byte arrays? We can only use fromArrayUnsafe if we are 100% sure that the byte array won't be reused. Even if 1 AMQP solution can be proved not to reuse arrays, can we be sure that all AMQP solutions don't?

[dimamo5]

The critical bit is the implementation of com.rabbitmq.client.Channel used in the DefaultConsumer. The default ChannelN and RecoveryAwareChannelN from rabbitmq client do not reuse byte arrays, since they eventually call https://github.com/rabbitmq/rabbitmq-java-client/blob/ca510a078092a3c64b1219feac527bc738b63313/src/main/java/com/rabbitmq/client/impl/CommandAssembler.java#L145 that performs a System.arraycopy.

Regarding the AMQP provider, I don't think this connector allows for customization of the channel directly from the provider so either one of the abovementioned channels will be used.

[pjfanning]

RabbitMQ is not the only AMQP implementation. We could make the ByteString behaviour configurable but I don't think we can hardcore this change.

[pjfanning]

Blocking merge while this change is debated.

[pjfanning]

@dimamo5 I added an avoidArrayCopy setting that defaults to false (existing behaviour). I pushed this change to your PR, if you don't mind. Could you have a look?

If this approach is ok, new tests will need to be added - that test with avoidArrayCopy=true.

[dimamo5]

@pjfanning sorry for the slow response. This is what I was looking for. Thank you.

[pjfanning]

@dimamo5 I've added code so that message writing can also avoid copying the array data for the ByteStrings - also based on settings.avoidArrayCopy

I'm pretty busy with other Pekko stuff. Would you have time to add some test cases that say duplicate existing test cases for read and write cases but where settings.avoidArrayCopy is set to true?