Project: Message-driver 0.5.0

Publisher: Message Driver

Middleware Basics

@bunny
@in_memory

Middlewares can be used to transform messages that are about to be published
or that are about to be consumed. This allows for handling of things like
serializing and deserializing the message body in a way that is transparent to
your application code.

Middlewares are applied in a stack to destinations, much like Rack middleware.
As a message that is about to be consumed, it starts by coming in the top of
the middleware stack and works it's way down before it is returned by
pop_message or passed to a consumer.

For messages that are being published, they start at the bottom of the stack
and work their way up until they are finally passed to the underlying driver
and sent to the message broker.

Background

Given

I am connected to the broker

And

I have a destination :middleware_queue with no messages on it

And

I have a middleware class

class ExampleMiddleware < MessageDriver::Middleware::Base
  def on_publish(body, headers, properties)
    [body+':about_to_publish', headers, properties]
  end

  def on_consume(body, headers, properties)
    ['about_to_be_consumed:'+body, headers, properties]
  end
end

Scenarios

The middleware stack of a destination is initially empty
Adding a piece of middleware to a destination
Middleware is applied to messages as they are published
Middleware is applied to messages as they are consumed

The middleware stack of a destination is initially empty

When

I execute the following code

destination = MessageDriver::Client.find_destination(:middleware_queue)
expect(destination.middleware).to be_empty

Then

I expect to have no errors

Adding a piece of middleware to a destination

When

I execute the following code

destination = MessageDriver::Client.find_destination(:middleware_queue)
destination.middleware.append ExampleMiddleware

Then

I expect the following check to pass

destination = MessageDriver::Client.find_destination(:middleware_queue)
expect(destination.middleware).to include(an_instance_of(ExampleMiddleware))

Middleware is applied to messages as they are published

When

I append middleware "ExampleMiddleware" to :middleware_queue

And

I send the following messages to :middleware_queue

body

Test Message 1

Test Message 2

Then

I expect to find the following 2 messages on :middleware_queue

raw_body

Test Message 1:about_to_publish

Test Message 2:about_to_publish

Middleware is applied to messages as they are consumed

Given

I have a destination :dest_queue with no messages on it

When

I send the following messages to :middleware_queue

body

Test Message 1

Test Message 2

And

I append middleware "ExampleMiddleware" to :middleware_queue

And

I create a subscription

MessageDriver::Client.subscribe_with(:middleware_queue) do |message|
  MessageDriver::Client.publish(:dest_queue, message.body)
end

And

I let the subscription process

Then

I expect to find no messages on :middleware_queue

And

I expect to find the following 2 messages on :dest_queue

raw_body

about_to_be_consumed:Test Message 1

about_to_be_consumed:Test Message 2

Last published about 7 years ago by soupmatt.

Middleware Basics

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