[P2P] Support multiple simultaneous routers

[bryanchriswhite]

Objective

Enable the P2P module to handle incoming messages from multiple router implementations simultaneously.

Origin Document

Currently, the message handling interaction between the P2P and the router looks like this:

flowchart LR
    subgraph p2p[P2P Module]
        subgraph rt[RainTree Router]
            nd[Nonce Deduper]
            rth[[`RainTreeMessage` Handler]]
        end

        p2ph[[`PocketEnvelope` message Handler]]
    end

rth --> nd
rth --> p2ph

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classDiagram
    class RainTreeMessage {
        <<protobuf>>
        +Level uint32
        +Data []byte
        +Nonce uint64
    }
    
    class PocketEnvelope {
        <<protobuf>>
        +Content *anypb.Any   
    }

    RainTreeMessage --* PocketEnvelope : serialized as `Data`
    
      
    class P2PModule {
        -handleNetworkData([]byte) error
        -handleStream(stream libp2pNetwork.Stream)
        -readStream(stream libp2pNetwork.Stream)
    }

    class RainTreeRouter {
        +HandleNetworkData func([]byte) ([]byte, error)
    }

    RainTreeRouter --> P2PModule
    P2PModule --> RainTreeRouter
    RainTreeRouter --o RainTreeMessage
    RainTreeRouter --* NonceDeduper
    P2PModule --o PocketEnvelope

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Goals

• Support handling message from multiple routers simultaneously
• Support message deduplication across all messages (i.e. not just raintree)
• Improve separation of concerns between P2P module and router(s)

Deliverable

flowchart LR
    subgraph p2p[P2P Module]
        subgraph rt[RainTree Router]
            rth[[`RainTreeMessage` Handler]]
        end

        nd[Nonce Deduper]
    
        p2ph[[`PocketEnvelope` message Handler]]
    end

p2ph --> nd
rth --> p2ph

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classDiagram
    class RainTreeMessage {
        <<protobuf>>
        +Level uint32
        +Data []byte
    }
    
    class PocketEnvelope {
        <<protobuf>>
        +Content *anypb.Any
        +Nonce uint64
    }

    RainTreeMessage --* PocketEnvelope : serialized as `Data`
    
    class P2PModule {
        -handleAppData([]byte) error
    }

    class RainTreeRouter {
        -appDataHandler RouterHandler
        -handleRainTreeMsg([]byte) ([]byte, error)
        -handleStream(stream libp2pNetwork.Stream)
        -readStream(stream libp2pNetwork.Stream)
    }

    RainTreeRouter --> P2PModule : `appDataHandler` == `handleAppData`
    RainTreeRouter --o RainTreeMessage

    P2PModule --* NonceDeduper
    P2PModule --o PocketEnvelope

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• Move NonceDeduper to the P2P module
• Refactor message handling logic to flow in one direction (from the router towards the application)
• Move Nonce proto field from RainTreeMessage to PocketEnvelope

Non-goals / Non-deliverables

• Integrating additional routers (e.g. BackgroundRouter)

General issue deliverables

• Update the appropriate CHANGELOG(s)
• Update any relevant local/global README(s)
• Update relevant source code tree explanations
• Add or update any relevant or supporting mermaid diagrams

Testing Methodology

• All tests: make test_all
• LocalNet: verify a LocalNet is still functioning correctly by following the instructions at docs/development/README.md
• k8s LocalNet: verify a k8s LocalNet is still functioning correctly by following the instructions here

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Creator: @bryanchriswhite