70 lines
2.5 KiB
Swift
70 lines
2.5 KiB
Swift
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import Foundation
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import Network
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/// Measures round-trip time to an endpoint with an unprivileged TCP connect
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/// (time from start to `.ready` ≈ one handshake RTT). Results are cached.
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///
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/// We probe a port we've already seen traffic on, so we're not knocking on
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/// closed doors — and the connection carries no data, just the handshake.
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public actor LatencyProber {
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private var cache: [String: Double] = [:]
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public init() {}
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public func cached(_ host: String) -> Double? { cache[host] }
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/// Measure (or refresh) RTT in milliseconds. Returns nil if unreachable.
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public func measure(host: String, port: UInt16) async -> Double? {
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let rtt = await Self.tcpHandshakeRTT(host: host, port: port)
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if let rtt { cache[host] = rtt }
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return rtt
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}
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private static func tcpHandshakeRTT(host: String, port: UInt16) async -> Double? {
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guard let nwPort = NWEndpoint.Port(rawValue: port) else { return nil }
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return await withCheckedContinuation { (cont: CheckedContinuation<Double?, Never>) in
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let conn = NWConnection(host: NWEndpoint.Host(host), port: nwPort, using: .tcp)
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let queue = DispatchQueue(label: "latency.probe")
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let start = DispatchTime.now()
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let state = ProbeState(conn: conn, cont: cont)
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conn.stateUpdateHandler = { st in
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switch st {
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case .ready:
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let ns = DispatchTime.now().uptimeNanoseconds - start.uptimeNanoseconds
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state.finish(Double(ns) / 1_000_000)
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case .failed, .cancelled:
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state.finish(nil)
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default:
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break
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}
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}
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conn.start(queue: queue)
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queue.asyncAfter(deadline: .now() + 2) { state.finish(nil) } // timeout
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}
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}
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/// Resumes the continuation exactly once, whichever callback fires first.
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private final class ProbeState: @unchecked Sendable {
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private let lock = NSLock()
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private var done = false
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private let conn: NWConnection
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private let cont: CheckedContinuation<Double?, Never>
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init(conn: NWConnection, cont: CheckedContinuation<Double?, Never>) {
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self.conn = conn
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self.cont = cont
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}
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func finish(_ value: Double?) {
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lock.lock()
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if done { lock.unlock(); return }
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done = true
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lock.unlock()
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conn.cancel()
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cont.resume(returning: value)
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}
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}
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}
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