Musubi/Packages/MusubiKit/Sources/Remote/Link.swift

import Foundation
import Network
import OSLog

/// One framed message connection (either side). Callbacks arrive on the main actor.
final class Link: @unchecked Sendable {
    let connection: NWConnection
    private let queue: DispatchQueue
    private var framer = MessageFramer() // queue only
    private let log = Logger(subsystem: "studio.zielke.musubi", category: "remote")

    var onMessage: (@MainActor (RemoteMessage) -> Void)?
    var onState: (@MainActor (NWConnection.State) -> Void)?

    init(connection: NWConnection, queue: DispatchQueue) {
        self.connection = connection
        self.queue = queue
    }

    func start() {
        connection.stateUpdateHandler = { [weak self] state in
            guard let self else { return }
            let handler = onState
            Task { @MainActor in handler?(state) }
        }
        connection.start(queue: queue)
        receive()
    }

    func cancel() {
        connection.cancel()
    }

    func send(_ message: RemoteMessage) {
        do {
            let data = try MessageFramer.encode(message)
            connection.send(content: data, completion: .contentProcessed { [log] error in
                if let error { log.error("Send failed: \(error.localizedDescription, privacy: .public)") }
            })
        } catch {
            log.error("Encode failed: \(error.localizedDescription, privacy: .public)")
        }
    }

    private func receive() {
        connection.receive(minimumIncompleteLength: 1, maximumLength: 65_536) { [weak self] data, _, isComplete, error in
            guard let self else { return }
            if let data, !data.isEmpty {
                do {
                    let messages = try framer.append(data)
                    let handler = onMessage
                    if !messages.isEmpty {
                        Task { @MainActor in messages.forEach { handler?($0) } }
                    }
                } catch {
                    log.error("Framing error, closing: \(String(describing: error), privacy: .public)")
                    connection.cancel()
                    return
                }
            }
            if isComplete || error != nil {
                connection.cancel()
                return
            }
            receive()
        }
    }
}

extension NWParameters {
    /// TCP bound to one interface, with Bonjour peer-to-peer off (technical network only).
    static func musubi(interface: NWInterface?) -> NWParameters {
        let parameters = NWParameters.tcp
        parameters.includePeerToPeer = false
        if let interface { parameters.requiredInterface = interface }
        if let tcp = parameters.defaultProtocolStack.transportProtocol as? NWProtocolTCP.Options {
            tcp.enableKeepalive = true
            tcp.keepaliveIdle = 2
            tcp.keepaliveInterval = 1
            tcp.keepaliveCount = 3
            tcp.noDelay = true
        }
        return parameters
    }
}