[rabbitmq-discuss] How to handle full exchange history delivery

[Busoli, Simone]

Hi,

I am trying to achieve a scenario in which messages are published from some data source into a RabbitMQ exchange and clients should be able to receive the full history of messages flown through that exchange, regardless of the exact moment in time when they connect.

I've been thinking to solve it by setting up a proxy which subscribes to the exchange where messages are published using its own queue, keeps an internal storage of the messages and accepts requests from clients.
When a request from a client arrives it just replays the full message history to the client by publishing the messages to the client queue (supplied in the ReplyTo field), then binds the client queue to the messages exchange, so that the client from this moment onwards starts receiving the "live" messages, and is pretty much unaware of what's happened; it simply just receives the whole history.

Now I am under the impression that there's a fundamental flaw in this reasoning, since the proxy cannot know when the message history has completed and he can switch the client to the live stream, because while it is replaying historical messages to the client other live messages might be arriving on the proxy's queue, thus getting into an endless loop.

I'm probably missing something obvious, any advice about how others would approach this scenario is appreciated.

Simone

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