rsocket-replayprocessor-example

An example of storing and replaying messages when a new subscriber connects using Project Reactor and RSocket.

In this example, the count-service is generating a stream of numbers from 1 to 100 at a one second interval. When a count-client connects it requests a stream of the numbers. A ReplayProcessor handles catching the client up by replaying all previously generated numbers before it connected.

Building the Example

Run the following command to build the example:

./gradlew clean build

Running the Example

Follow the steps below to run the example:

1. Run the following command to start the count-service:

    ./gradlew :count-service:run
   

2. In a new terminal, run the following command to start the count-client:

    ./gradlew :count-client:run
   

   Notice how you receive a flurry of numbers when the subscriber connects starting at 1 up to the current count. Once you are all caught up with the current count you start receiving a new number every one second. This is the ReplayProcessor making sure that a subscriber does not miss a published message.

    > Task :count-client:run
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 1
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 2
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 3
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 4
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 5
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 6
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 7
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 8
   

3. In a new terminal, run the following command to start another count-client:

    ./gradlew :count-client:run
   

   Notice how this client instance is streamed all of the published numbers as well until it is caught up.

4. Now, let the count reach 100 where the request will then complete.

    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 99
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Received: 100
    [reactor-tcp-nio-1] INFO example.count.client.CountClient - Done
   

5. Once the request has completed start a new count-client by again running the following command:

    ./gradlew :count-client:run
   

   Notice that you did not have to wait for the numbers to arrive in one second intervals, you were just immediately streamed all one hundred messages. This is because the ReplayProcessor has stored the generated stream and simply replays it back to you.

Bugs and Feedback

For bugs, questions, and discussions please use the Github Issues.

License

MIT License

Copyright (c) 2020 Greg Whitaker

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.