76 lines
2.4 KiB
Swift
76 lines
2.4 KiB
Swift
import Foundation
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import Network
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final class DNSLocalClient {
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private var connections: [NWConnection] = []
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// 准备多个公共 DNS
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private let dnsServers = ["114.114.114.114", "223.5.5.5", "8.8.8.8"]
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public let packetFlow: AsyncStream<Data>
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private let packetContinuation: AsyncStream<Data>.Continuation
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init() {
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let (stream, continuation) = AsyncStream.makeStream(of: Data.self, bufferingPolicy: .unbounded)
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self.packetFlow = stream
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self.packetContinuation = continuation
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}
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func start() {
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for server in dnsServers {
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let endpoint = NWEndpoint.hostPort(host: NWEndpoint.Host(server), port: 53)
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let parameters = NWParameters.udp
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parameters.prohibitedInterfaceTypes = [.other]
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let conn = NWConnection(to: endpoint, using: parameters)
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conn.stateUpdateHandler = { [weak self] state in
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switch state {
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case .ready:
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self?.receiveLoop(for: conn)
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case .failed(let error):
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self?.stop()
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case .cancelled:
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self?.packetContinuation.finish()
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default:
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()
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}
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}
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conn.start(queue: .global())
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connections.append(conn)
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}
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}
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/// 并发查询：对所有服务器广播
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func query(dnsPayload: Data) {
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for conn in connections where conn.state == .ready {
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conn.send(content: dnsPayload, completion: .contentProcessed({ _ in }))
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}
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}
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private func receiveLoop(for conn: NWConnection) {
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conn.receiveMessage { [weak self] content, _, _, error in
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if let data = content {
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// ！！！核心：由于 AsyncStream 是流式的
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// 谁先 yield，上层就先收到谁。
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// 只要上层收到了第一个有效响应并回填给系统，
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// 后面迟到的重复响应会被系统协议栈自动忽略（因为 Transaction ID 已失效）
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self?.packetContinuation.yield(data)
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}
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if error == nil && conn.state == .ready {
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self?.receiveLoop(for: conn)
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}
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}
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}
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func stop() {
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connections.forEach { conn in
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conn.cancel()
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}
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self.connections.removeAll()
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}
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}
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