ParaCat: A multipath UDP forwarder for high reliability/throughput

In crowded Internet, all connections are not reliable. To minimize jitter and packet loss, we can send it through different routes simultaneously then get redundancy.

Structure

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flowchart LR
    C[UDP Client]
    PC[Paracat Client]
    D{Data}
    PS[Paracat Server]
    S(UDP Server)

    C -->|"handleForward()"| PC
    C <-->|MultiPort<->SinglePort| PC
    PC -->|"handleReverse()"| C

    PC -->|"
    SendUDPLoop()
    SendTCPLoop()
    Scatterer
    "| D
    PC <-->|MultiPort<->| D
    D -->|"
    handleUDPRelayRecv()
    ReceiveTCPLoop()
    Gather
    "| PC

    D -->|"
    handleUDPListener()
    ReceiveTCPLoop()
    Gather
    "| PS
    D <-->|<->SinglePort| PS
    PS -->|"
    SendUDPLoop()
    SendTCPLoop()
    Scatterer
    "| D

    PS -->|"handleForward()"| S
    PS <-->|MultiPort<->SinglePort| S
    S -->|"handleReverse()"| PS

    subgraph TCP/UDP Tunnel
        D
    end

TODO

• Round-robin mode
• Remove unused UDP connections
• Re-connect after EOF
• GRO & GSO
• Single direction for connection
• CRC check
• New udp socket for each connection
• UDP MTU discovery with DF
• Routing strategy
• API interface
• Heartbeat keepalive
• Optimize delay
• Congestion control algorithm
• Fake TCP with eBPF
• Test coverage
• Multi-user support