Schedule a Message

[ricardoromaobr]

What about the schedule a message, some hosts like rabbitmq has a native message schedule. I'm experimenting with SlimMassagebus. But some of my projects uses Massage Schedule that is implemented at MassTransit. Find for the feature in project and I not found that feature.

[zarusz]

Hello, let me look into that feature and get back to you.

If a broker supports that then we could add an abstraction to SMB to expose that. The question is what if a broker does not support it?

Additionally, the outbox could get a scheduled capability quite easily. When it selects messages to send in the loop, it could look at a scheduled field in the SQL.

Cc @EtherZa

[ricardoromaobr]

No way to it works!

I make the settings:

I use the code to initializer with a exchange with type of x-delayed-message for schedule to works.

The ExchangeType enum doesn't have that type.

 cfg.UseTopologyInitializer((channel, applyTopologyInitializer) =>
         {
             channel.ExchangeDeclare(
                 "my-schedule", "x-delayed-message", true, true, new Dictionary<string, object>()
                 {
                     ["x-delayed-type"] = "direct"

                 });
         });

But when I try to publish:

The exchange was created nice.

at the moment I not make the binds yet!

If is the case it works. I will need to make a convention on my project:

for each event I want to schedule I need to do:

create a message schedule. For example:

TimeExpired_delay bind to normal exchange TimeExpired that will be a bind for all consumers of that event.

MassTransit transparently do it. Wen I do a Schedule of some message he creates a schedule exchange and bind with the produce.

[zarusz]

@ricardoromaobr The error you're getting is due to a missing serialization plugin configuration - you need to select your serialization approach.

The following should not be necessary, as you should be able to do it within the x.Produce() (the enum type could be extended if that's missing):

 cfg.UseTopologyInitializer((channel, applyTopologyInitializer) =>
         {
             channel.ExchangeDeclare(
                 "my-schedule", "x-delayed-message", true, true, new Dictionary<string, object>()
                 {
                     ["x-delayed-type"] = "direct"
                 });
         });

Yes, MassTransit was abstracting away it all. But my point is that I will plan for a message scheduling feature that would also abstract this for Rabbit, Azure Service Bus, and Amazon SQS. Until then I think you could make it work with just this extra headers verbosity (not ideal but will work until feature is ready).

Let me know once you get past the Serializer issue.

Ideally if you could push a code sample (onto a git hub repo?) that I could try and run.

[ricardoromaobr]

Ok. Works!
Here are the settings and publish side by side:

But I have to link everything by hands.
May be I'm doing wrong.

I think that the AddServicesFromAssemblyContaining would create the queue and connect with appropriated exchange.

I will read more the documentation to see what I can do.

about the ExchangeType internal the library use direct conversion of the enumerated to string, that the name will be same of the enum type.

in the case of x-delayed-message need a special care at the conversion.

[zarusz]

Nice! I will try to solve the enum problem. Then you will be able to avoid the topology initializer.
As for the rest of the overhead (headers, attributes) you would have to wait for an proper scheduled message abstraction in SMB - I will raise an feature request issue soon.

[zarusz]

@ricardoromaobr I've made the change for the ExchangeType enum to become a string (PR #398)
There is a preview version released 3.2.0-rc102 that you can try.

Hopefully with that change, you won't have to use the mbb.UseTopologyInitializer() and instead simply declare the additional exchange attributes and the exchange type x-delayed-message (ExchangeType.XDelayedMessage) as part of the mbb.Produce(...).

Let me know if you run into any issues.

[zarusz]

Some links:
https://www.rabbitmq.com/blog/2015/04/16/scheduling-messages-with-rabbitmq

[EtherZa]

ASB supports scheduled messages too. The outbox publisher could prioritise unscheduled messages ahead of scheduled (provided the scheduled date is still in the future), but I would let the queue handle the scheuling asap.

[ricardoromaobr]

@zarusz Nice! I will be appreciating it. I will be watching to have it.
Thanks!