Replace sleep in tests with waiter channel handler

NWParameters is a class, so we don't need it to be inout when passing it to the configurator closure

.github/workflows/main.yml

@@ -14,6 +14,7 @@ jobs:
             linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
             linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
             linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
+            linux_6_1_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
             linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
             linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
 

.github/workflows/pull_request.yml

@@ -17,6 +17,7 @@ jobs:
             linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
             linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
             linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
+            linux_6_1_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
             linux_nightly_next_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
             linux_nightly_main_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
 

Package.swift

@@ -27,7 +27,7 @@ let strictConcurrencySettings: [SwiftSetting] = {
     if strictConcurrencyDevelopment {
         // -warnings-as-errors here is a workaround so that IDE-based development can
         // get tripped up on -require-explicit-sendable.
-        initialSettings.append(.unsafeFlags(["-require-explicit-sendable", "-warnings-as-errors"]))
+        initialSettings.append(.unsafeFlags(["-Xfrontend", "-require-explicit-sendable", "-warnings-as-errors"]))
     }
 
     return initialSettings

Sources/NIOTransportServices/Datagram/NIOTSDatagramBootstrap.swift

@@ -47,6 +47,7 @@ public final class NIOTSDatagramBootstrap {
     private var qos: DispatchQoS?
     private var udpOptions: NWProtocolUDP.Options = .init()
     private var tlsOptions: NWProtocolTLS.Options?
+    private var nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
 
     /// Create a `NIOTSDatagramConnectionBootstrap` on the `EventLoopGroup` `group`.
     ///
@@ -133,6 +134,14 @@ public final class NIOTSDatagramBootstrap {
         return self
     }
 
+    /// Customise the `NWParameters` to be used when creating the connection.
+    public func configureNWParameters(
+        _ configurator: @Sendable @escaping (NWParameters) -> Void
+    ) -> Self {
+        self.nwParametersConfigurator = configurator
+        return self
+    }
+
     /// Specify the `host` and `port` to connect to for the UDP `Channel` that will be established.
     ///
     /// - parameters:
@@ -188,7 +197,8 @@ public final class NIOTSDatagramBootstrap {
             eventLoop: self.group.next() as! NIOTSEventLoop,
             qos: self.qos,
             udpOptions: self.udpOptions,
-            tlsOptions: self.tlsOptions
+            tlsOptions: self.tlsOptions,
+            nwParametersConfigurator: self.nwParametersConfigurator
         )
         let initializer = self.channelInitializer ?? { @Sendable _ in conn.eventLoop.makeSucceededFuture(()) }
 

Sources/NIOTransportServices/Datagram/NIOTSDatagramChannel.swift

@@ -140,8 +140,12 @@ internal final class NIOTSDatagramChannel: StateManagedNWConnectionChannel {
     internal var allowLocalEndpointReuse = false
     internal var multipathServiceType: NWParameters.MultipathServiceType = .disabled
 
+    internal let nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
+
     var parameters: NWParameters {
-        NWParameters(dtls: self.tlsOptions, udp: self.udpOptions)
+        let parameters = NWParameters(dtls: self.tlsOptions, udp: self.udpOptions)
+        self.nwParametersConfigurator?(parameters)
+        return parameters
     }
 
     var _inboundStreamOpen: Bool {
@@ -182,7 +186,8 @@ internal final class NIOTSDatagramChannel: StateManagedNWConnectionChannel {
         minimumIncompleteReceiveLength: Int = 1,
         maximumReceiveLength: Int = 8192,
         udpOptions: NWProtocolUDP.Options,
-        tlsOptions: NWProtocolTLS.Options?
+        tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.tsEventLoop = eventLoop
         self.closePromise = eventLoop.makePromise()
@@ -192,6 +197,7 @@ internal final class NIOTSDatagramChannel: StateManagedNWConnectionChannel {
         self.connectionQueue = eventLoop.channelQueue(label: "nio.nioTransportServices.connectionchannel", qos: qos)
         self.udpOptions = udpOptions
         self.tlsOptions = tlsOptions
+        self.nwParametersConfigurator = nwParametersConfigurator
 
         // Must come last, as it requires self to be completely initialized.
         self._pipeline = ChannelPipeline(channel: self)
@@ -206,7 +212,8 @@ internal final class NIOTSDatagramChannel: StateManagedNWConnectionChannel {
         minimumIncompleteReceiveLength: Int = 1,
         maximumReceiveLength: Int = 8192,
         udpOptions: NWProtocolUDP.Options,
-        tlsOptions: NWProtocolTLS.Options?
+        tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             eventLoop: eventLoop,
@@ -215,7 +222,8 @@ internal final class NIOTSDatagramChannel: StateManagedNWConnectionChannel {
             minimumIncompleteReceiveLength: minimumIncompleteReceiveLength,
             maximumReceiveLength: maximumReceiveLength,
             udpOptions: udpOptions,
-            tlsOptions: tlsOptions
+            tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator
         )
         self.connection = connection
     }

Sources/NIOTransportServices/Datagram/NIOTSDatagramListener.swift

@@ -66,6 +66,7 @@ public final class NIOTSDatagramListenerBootstrap {
     private var udpOptions: NWProtocolUDP.Options = .init()
     private var tlsOptions: NWProtocolTLS.Options?
     private var bindTimeout: TimeAmount?
+    private var nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
 
     /// Create a ``NIOTSListenerBootstrap`` for the `EventLoopGroup` `group`.
     ///
@@ -236,6 +237,14 @@ public final class NIOTSDatagramListenerBootstrap {
         return self
     }
 
+    /// Customise the `NWParameters` to be used when creating the connection.
+    public func configureNWParameters(
+        _ configurator: @Sendable @escaping (NWParameters) -> Void
+    ) -> Self {
+        self.nwParametersConfigurator = configurator
+        return self
+    }
+
     /// Bind the `NIOTSListenerChannel` to `host` and `port`.
     ///
     /// - parameters:
@@ -327,10 +336,12 @@ public final class NIOTSDatagramListenerBootstrap {
                 qos: self.serverQoS,
                 udpOptions: self.udpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childUDPOptions: self.udpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         } else {
             serverChannel = NIOTSDatagramListenerChannel(
@@ -338,10 +349,12 @@ public final class NIOTSDatagramListenerBootstrap {
                 qos: self.serverQoS,
                 udpOptions: self.udpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childUDPOptions: self.udpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         }
 

Sources/NIOTransportServices/Datagram/NIOTSDatagramListenerChannel.swift

@@ -81,19 +81,23 @@ internal final class NIOTSDatagramListenerChannel: StateManagedListenerChannel<N
         qos: DispatchQoS? = nil,
         udpOptions: NWProtocolUDP.Options,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childUDPOptions: NWProtocolUDP.Options,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             eventLoop: eventLoop,
             protocolOptions: .udp(udpOptions),
             tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator,
             childLoopGroup: childLoopGroup,
             childChannelQoS: childChannelQoS,
             childProtocolOptions: .udp(childUDPOptions),
-            childTLSOptions: childTLSOptions
+            childTLSOptions: childTLSOptions,
+            childNWParametersConfigurator: childNWParametersConfigurator
         )
     }
 
@@ -104,20 +108,24 @@ internal final class NIOTSDatagramListenerChannel: StateManagedListenerChannel<N
         qos: DispatchQoS? = nil,
         udpOptions: NWProtocolUDP.Options,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childUDPOptions: NWProtocolUDP.Options,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             wrapping: listener,
             eventLoop: eventLoop,
             protocolOptions: .udp(udpOptions),
             tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator,
             childLoopGroup: childLoopGroup,
             childChannelQoS: childChannelQoS,
             childProtocolOptions: .udp(childUDPOptions),
-            childTLSOptions: childTLSOptions
+            childTLSOptions: childTLSOptions,
+            childNWParametersConfigurator: childNWParametersConfigurator
         )
     }
 
@@ -132,7 +140,8 @@ internal final class NIOTSDatagramListenerChannel: StateManagedListenerChannel<N
             on: self.childLoopGroup.next() as! NIOTSEventLoop,
             parent: self,
             udpOptions: self.childUDPOptions,
-            tlsOptions: self.childTLSOptions
+            tlsOptions: self.childTLSOptions,
+            nwParametersConfigurator: self.childNWParametersConfigurator
         )
 
         self.pipeline.fireChannelRead(newChannel)

Sources/NIOTransportServices/NIOTSConnectionBootstrap.swift

@@ -62,6 +62,7 @@ public final class NIOTSConnectionBootstrap {
     private var tcpOptions: NWProtocolTCP.Options = .init()
     private var tlsOptions: NWProtocolTLS.Options?
     private var protocolHandlers: (@Sendable () -> [ChannelHandler])? = nil
+    private var nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
 
     /// Create a `NIOTSConnectionBootstrap` on the `EventLoopGroup` `group`.
     ///
@@ -165,6 +166,14 @@ public final class NIOTSConnectionBootstrap {
         self.channelOption(NIOTSChannelOptions.multipathServiceType, value: type)
     }
 
+    /// Customise the `NWParameters` to be used when creating the connection.
+    public func configureNWParameters(
+        _ configurator: @Sendable @escaping (NWParameters) -> Void
+    ) -> Self {
+        self.nwParametersConfigurator = configurator
+        return self
+    }
+
     /// Specify the `host` and `port` to connect to for the TCP `Channel` that will be established.
     ///
     /// - parameters:
@@ -243,14 +252,16 @@ public final class NIOTSConnectionBootstrap {
                 wrapping: newConnection,
                 on: self.group.next() as! NIOTSEventLoop,
                 tcpOptions: self.tcpOptions,
-                tlsOptions: self.tlsOptions
+                tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator
             )
         } else {
             conn = NIOTSConnectionChannel(
                 eventLoop: self.group.next() as! NIOTSEventLoop,
                 qos: self.qos,
                 tcpOptions: self.tcpOptions,
-                tlsOptions: self.tlsOptions
+                tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator
             )
         }
         let initializer = self.channelInitializer
@@ -437,14 +448,16 @@ extension NIOTSConnectionBootstrap {
                 wrapping: newConnection,
                 on: self.group.next() as! NIOTSEventLoop,
                 tcpOptions: self.tcpOptions,
-                tlsOptions: self.tlsOptions
+                tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator
             )
         } else {
             connectionChannel = NIOTSConnectionChannel(
                 eventLoop: self.group.next() as! NIOTSEventLoop,
                 qos: self.qos,
                 tcpOptions: self.tcpOptions,
-                tlsOptions: self.tlsOptions
+                tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator
             )
         }
         let initializer = self.channelInitializer

Sources/NIOTransportServices/NIOTSConnectionChannel.swift

@@ -164,8 +164,12 @@ internal final class NIOTSConnectionChannel: StateManagedNWConnectionChannel {
     /// An `EventLoopPromise` that will be succeeded or failed when a connection attempt succeeds or fails.
     internal var connectPromise: EventLoopPromise<Void>?
 
+    internal let nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
+
     internal var parameters: NWParameters {
-        NWParameters(tls: self.tlsOptions, tcp: self.tcpOptions)
+        let parameters = NWParameters(tls: self.tlsOptions, tcp: self.tcpOptions)
+        self.nwParametersConfigurator?(parameters)
+        return parameters
     }
 
     /// The TCP options for this connection.
@@ -242,7 +246,8 @@ internal final class NIOTSConnectionChannel: StateManagedNWConnectionChannel {
         minimumIncompleteReceiveLength: Int = 1,
         maximumReceiveLength: Int = 8192,
         tcpOptions: NWProtocolTCP.Options,
-        tlsOptions: NWProtocolTLS.Options?
+        tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.tsEventLoop = eventLoop
         self.closePromise = eventLoop.makePromise()
@@ -252,6 +257,7 @@ internal final class NIOTSConnectionChannel: StateManagedNWConnectionChannel {
         self.connectionQueue = eventLoop.channelQueue(label: "nio.nioTransportServices.connectionchannel", qos: qos)
         self.tcpOptions = tcpOptions
         self.tlsOptions = tlsOptions
+        self.nwParametersConfigurator = nwParametersConfigurator
 
         // Must come last, as it requires self to be completely initialized.
         self._pipeline = ChannelPipeline(channel: self)
@@ -266,7 +272,8 @@ internal final class NIOTSConnectionChannel: StateManagedNWConnectionChannel {
         minimumIncompleteReceiveLength: Int = 1,
         maximumReceiveLength: Int = 8192,
         tcpOptions: NWProtocolTCP.Options,
-        tlsOptions: NWProtocolTLS.Options?
+        tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             eventLoop: eventLoop,
@@ -275,7 +282,8 @@ internal final class NIOTSConnectionChannel: StateManagedNWConnectionChannel {
             minimumIncompleteReceiveLength: minimumIncompleteReceiveLength,
             maximumReceiveLength: maximumReceiveLength,
             tcpOptions: tcpOptions,
-            tlsOptions: tlsOptions
+            tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator
         )
         self.connection = connection
     }

Sources/NIOTransportServices/NIOTSErrors.swift

@@ -21,7 +21,7 @@ import NIOCore
 public protocol NIOTSError: Error, Equatable {}
 
 @available(OSX 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *)
-public enum NIOTSErrors {
+public enum NIOTSErrors: Sendable {
     /// ``InvalidChannelStateTransition`` is thrown when a channel has been asked to do something
     /// that is incompatible with its current channel state: e.g. attempting to register an
     /// already registered channel.

Sources/NIOTransportServices/NIOTSListenerBootstrap.swift

@@ -66,6 +66,7 @@ public final class NIOTSListenerBootstrap {
     private var tcpOptions: NWProtocolTCP.Options = .init()
     private var tlsOptions: NWProtocolTLS.Options?
     private var bindTimeout: TimeAmount?
+    private var nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
 
     /// Create a ``NIOTSListenerBootstrap`` for the `EventLoopGroup` `group`.
     ///
@@ -239,6 +240,14 @@ public final class NIOTSListenerBootstrap {
         return self
     }
 
+    /// Customise the `NWParameters` to be used when creating the connection.
+    public func configureNWParameters(
+        _ configurator: @Sendable @escaping (NWParameters) -> Void
+    ) -> Self {
+        self.nwParametersConfigurator = configurator
+        return self
+    }
+
     /// Specifies a type of Multipath service to use for this listener, instead of the default
     /// service type for the event loop.
     ///
@@ -337,10 +346,12 @@ public final class NIOTSListenerBootstrap {
                 qos: self.serverQoS,
                 tcpOptions: self.tcpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childTCPOptions: self.tcpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         } else {
             serverChannel = NIOTSListenerChannel(
@@ -348,10 +359,12 @@ public final class NIOTSListenerBootstrap {
                 qos: self.serverQoS,
                 tcpOptions: self.tcpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childTCPOptions: self.tcpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         }
 
@@ -558,10 +571,12 @@ extension NIOTSListenerBootstrap {
                 qos: self.serverQoS,
                 tcpOptions: self.tcpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childTCPOptions: self.tcpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         } else {
             serverChannel = NIOTSListenerChannel(
@@ -569,10 +584,12 @@ extension NIOTSListenerBootstrap {
                 qos: self.serverQoS,
                 tcpOptions: self.tcpOptions,
                 tlsOptions: self.tlsOptions,
+                nwParametersConfigurator: self.nwParametersConfigurator,
                 childLoopGroup: self.childGroup,
                 childChannelQoS: self.childQoS,
                 childTCPOptions: self.tcpOptions,
-                childTLSOptions: self.tlsOptions
+                childTLSOptions: self.tlsOptions,
+                childNWParametersConfigurator: self.nwParametersConfigurator
             )
         }
 

Sources/NIOTransportServices/NIOTSListenerChannel.swift

@@ -81,19 +81,23 @@ internal final class NIOTSListenerChannel: StateManagedListenerChannel<NIOTSConn
         qos: DispatchQoS? = nil,
         tcpOptions: NWProtocolTCP.Options,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childTCPOptions: NWProtocolTCP.Options,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             eventLoop: eventLoop,
             protocolOptions: .tcp(tcpOptions),
             tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator,
             childLoopGroup: childLoopGroup,
             childChannelQoS: childChannelQoS,
             childProtocolOptions: .tcp(childTCPOptions),
-            childTLSOptions: childTLSOptions
+            childTLSOptions: childTLSOptions,
+            childNWParametersConfigurator: childNWParametersConfigurator
         )
     }
 
@@ -104,10 +108,12 @@ internal final class NIOTSListenerChannel: StateManagedListenerChannel<NIOTSConn
         qos: DispatchQoS? = nil,
         tcpOptions: NWProtocolTCP.Options,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childTCPOptions: NWProtocolTCP.Options,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             wrapping: listener,
@@ -115,10 +121,12 @@ internal final class NIOTSListenerChannel: StateManagedListenerChannel<NIOTSConn
             qos: qos,
             protocolOptions: .tcp(tcpOptions),
             tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator,
             childLoopGroup: childLoopGroup,
             childChannelQoS: childChannelQoS,
             childProtocolOptions: .tcp(childTCPOptions),
-            childTLSOptions: childTLSOptions
+            childTLSOptions: childTLSOptions,
+            childNWParametersConfigurator: childNWParametersConfigurator
         )
     }
 
@@ -134,7 +142,8 @@ internal final class NIOTSListenerChannel: StateManagedListenerChannel<NIOTSConn
             parent: self,
             qos: self.childChannelQoS,
             tcpOptions: self.childTCPOptions,
-            tlsOptions: self.childTLSOptions
+            tlsOptions: self.childTLSOptions,
+            nwParametersConfigurator: self.childNWParametersConfigurator
         )
 
         self.pipeline.fireChannelRead(newChannel)

Sources/NIOTransportServices/StateManagedListenerChannel.swift

@@ -67,6 +67,9 @@ internal class StateManagedListenerChannel<ChildChannel: StateManagedChannel>: S
     /// The TLS options for this listener.
     internal let tlsOptions: NWProtocolTLS.Options?
 
+    /// A customization point for this listener's `NWParameters`.
+    internal let nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?
+
     /// The `DispatchQueue` that socket events for this connection will be dispatched onto.
     internal let connectionQueue: DispatchQueue
 
@@ -113,6 +116,9 @@ internal class StateManagedListenerChannel<ChildChannel: StateManagedChannel>: S
     /// The TLS options to use for child channels.
     internal let childTLSOptions: NWProtocolTLS.Options?
 
+    /// A customization point for each child's `NWParameters`.
+    internal let childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
+
     /// The cache of the local and remote socket addresses. Must be accessed using _addressCacheLock.
     internal var addressCache = AddressCache(local: nil, remote: nil)
 
@@ -130,20 +136,24 @@ internal class StateManagedListenerChannel<ChildChannel: StateManagedChannel>: S
         qos: DispatchQoS? = nil,
         protocolOptions: ProtocolOptions,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childProtocolOptions: ProtocolOptions,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.tsEventLoop = eventLoop
         self.closePromise = eventLoop.makePromise()
         self.connectionQueue = eventLoop.channelQueue(label: "nio.transportservices.listenerchannel", qos: qos)
         self.protocolOptions = protocolOptions
         self.tlsOptions = tlsOptions
+        self.nwParametersConfigurator = nwParametersConfigurator
         self.childLoopGroup = childLoopGroup
         self.childChannelQoS = childChannelQoS
         self.childProtocolOptions = childProtocolOptions
         self.childTLSOptions = childTLSOptions
+        self.childNWParametersConfigurator = childNWParametersConfigurator
 
         // Must come last, as it requires self to be completely initialized.
         self._pipeline = ChannelPipeline(channel: self)
@@ -155,20 +165,24 @@ internal class StateManagedListenerChannel<ChildChannel: StateManagedChannel>: S
         qos: DispatchQoS? = nil,
         protocolOptions: ProtocolOptions,
         tlsOptions: NWProtocolTLS.Options?,
+        nwParametersConfigurator: (@Sendable (NWParameters) -> Void)?,
         childLoopGroup: EventLoopGroup,
         childChannelQoS: DispatchQoS?,
         childProtocolOptions: ProtocolOptions,
-        childTLSOptions: NWProtocolTLS.Options?
+        childTLSOptions: NWProtocolTLS.Options?,
+        childNWParametersConfigurator: (@Sendable (NWParameters) -> Void)?
     ) {
         self.init(
             eventLoop: eventLoop,
             qos: qos,
             protocolOptions: protocolOptions,
             tlsOptions: tlsOptions,
+            nwParametersConfigurator: nwParametersConfigurator,
             childLoopGroup: childLoopGroup,
             childChannelQoS: childChannelQoS,
             childProtocolOptions: childProtocolOptions,
-            childTLSOptions: childTLSOptions
+            childTLSOptions: childTLSOptions,
+            childNWParametersConfigurator: childNWParametersConfigurator
         )
         self.nwListener = listener
     }
@@ -398,6 +412,8 @@ extension StateManagedListenerChannel {
 
         parameters.multipathServiceType = self.multipathServiceType
 
+        self.nwParametersConfigurator?(parameters)
+
         let listener: NWListener
         do {
             listener = try NWListener(using: parameters)

Sources/NIOTransportServices/StateManagedNWConnectionChannel.swift

@@ -83,6 +83,8 @@ internal protocol StateManagedNWConnectionChannel: StateManagedChannel where Act
 
     var multipathServiceType: NWParameters.MultipathServiceType { get }
 
+    var nwParametersConfigurator: (@Sendable (NWParameters) -> Void)? { get }
+
     func setChannelSpecificOption0<Option: ChannelOption>(option: Option, value: Option.Value) throws
 
     func getChannelSpecificOption0<Option: ChannelOption>(option: Option) throws -> Option.Value
@@ -242,6 +244,7 @@ extension StateManagedNWConnectionChannel {
         connection.betterPathUpdateHandler = self.betterPathHandler
         connection.viabilityUpdateHandler = self.viabilityUpdateHandler
         connection.pathUpdateHandler = self.pathChangedHandler(newPath:)
+        self.nwParametersConfigurator?(connection.parameters)
         connection.start(queue: self.connectionQueue)
     }
 

Tests/NIOTransportServicesTests/NIOTSBootstrapTests.swift

@@ -18,7 +18,7 @@ import XCTest
 import Network
 import NIOCore
 import NIOEmbedded
-import NIOTransportServices
+@testable import NIOTransportServices
 import NIOConcurrencyHelpers
 import Foundation
 
@@ -371,6 +371,60 @@ final class NIOTSBootstrapTests: XCTestCase {
         XCTAssertEqual(try listenerChannel.getOption(NIOTSChannelOptions.multipathServiceType).wait(), .handover)
         XCTAssertEqual(try connectionChannel.getOption(NIOTSChannelOptions.multipathServiceType).wait(), .handover)
     }
+
+    func testNWParametersConfigurator() async throws {
+        final class WaitForConnectionHandler: ChannelInboundHandler, Sendable {
+            typealias InboundIn = Never
+
+            let connectionPromise: EventLoopPromise<Void>
+
+            init(connectionPromise: EventLoopPromise<Void>) {
+                self.connectionPromise = connectionPromise
+            }
+
+            func channelActive(context: ChannelHandlerContext) {
+                self.connectionPromise.succeed()
+            }
+        }
+
+        let group = NIOTSEventLoopGroup(loopCount: 1)
+
+        let configuratorListenerCounter = NIOLockedValueBox(0)
+        let configuratorConnectionCounter = NIOLockedValueBox(0)
+        let waitForConnectionHandler = WaitForConnectionHandler(
+            connectionPromise: group.next().makePromise()
+        )
+
+        let listenerChannel = try await NIOTSListenerBootstrap(group: group)
+            .childChannelInitializer { connectionChannel in
+                connectionChannel.eventLoop.makeCompletedFuture {
+                    try connectionChannel.pipeline.syncOperations.addHandler(waitForConnectionHandler)
+                }
+            }
+            .configureNWParameters { _ in
+                configuratorListenerCounter.withLockedValue { $0 += 1 }
+            }
+            .bind(host: "localhost", port: 0)
+            .get()
+
+        let connectionChannel: Channel = try await NIOTSConnectionBootstrap(group: group)
+            .configureNWParameters { _ in
+                configuratorConnectionCounter.withLockedValue { $0 += 1 }
+            }
+            .connect(to: listenerChannel.localAddress!)
+            .get()
+
+        // Wait for the server to activate the connection channel to the client.
+        try await waitForConnectionHandler.connectionPromise.futureResult.get()
+
+        try await listenerChannel.close().get()
+        try await connectionChannel.close().get()
+
+        XCTAssertEqual(2, configuratorListenerCounter.withLockedValue { $0 })
+        XCTAssertEqual(1, configuratorConnectionCounter.withLockedValue { $0 })
+
+        try await group.shutdownGracefully()
+    }
 }
 
 extension Channel {

Tests/NIOTransportServicesTests/NIOTSChannelMetadataTests.swift

@@ -37,13 +37,14 @@ final class NIOTSChannelMetadataTests: XCTestCase {
         }.wait()
 
     }
-    func testThowsIfCalledOnANonInitializedChannel() {
+    func testThrowsIfCalledOnANonInitializedChannel() {
         let eventLoopGroup = NIOTSEventLoopGroup()
         defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
         let channel = NIOTSConnectionChannel(
             eventLoop: eventLoopGroup.next() as! NIOTSEventLoop,
             tcpOptions: .init(),
-            tlsOptions: .init()
+            tlsOptions: .init(),
+            nwParametersConfigurator: nil
         )
         XCTAssertThrowsError(try channel.getMetadata(definition: NWProtocolTLS.definition).wait()) { error in
             XCTAssertTrue(error is NIOTSConnectionNotInitialized, "unexpected error \(error)")

Tests/NIOTransportServicesTests/NIOTSDatagramConnectionChannelTests.swift

@@ -18,6 +18,7 @@ import Network
 import NIOCore
 import NIOTransportServices
 import Foundation
+import NIOConcurrencyHelpers
 
 extension Channel {
     func wait<T: Sendable>(for type: T.Type, count: Int) throws -> [T] {
@@ -232,6 +233,65 @@ final class NIOTSDatagramConnectionChannelTests: XCTestCase {
         XCTAssertNoThrow(try connection.close().wait())
     }
 
+    func testNWParametersConfigurator() async throws {
+        final class WaitForConnectionHandler: ChannelInboundHandler, Sendable {
+            typealias InboundIn = Never
+
+            let connectionPromise: EventLoopPromise<Void>
+
+            init(connectionPromise: EventLoopPromise<Void>) {
+                self.connectionPromise = connectionPromise
+            }
+
+            func channelActive(context: ChannelHandlerContext) {
+                self.connectionPromise.succeed()
+            }
+        }
+
+        let group = NIOTSEventLoopGroup(loopCount: 1)
+
+        let configuratorListenerCounter = NIOLockedValueBox(0)
+        let configuratorConnectionCounter = NIOLockedValueBox(0)
+        let waitForConnectionHandler = WaitForConnectionHandler(
+            connectionPromise: group.next().makePromise()
+        )
+
+        let listenerChannel = try await NIOTSDatagramListenerBootstrap(group: group)
+            .childChannelInitializer { connectionChannel in
+                connectionChannel.eventLoop.makeCompletedFuture {
+                    try connectionChannel.pipeline.syncOperations.addHandler(waitForConnectionHandler)
+                }
+            }
+            .configureNWParameters { _ in
+                configuratorListenerCounter.withLockedValue { $0 += 1 }
+            }
+            .bind(host: "localhost", port: 0)
+            .get()
+
+        let connectionChannel: Channel = try await NIOTSDatagramBootstrap(group: group)
+            .configureNWParameters { _ in
+                configuratorConnectionCounter.withLockedValue { $0 += 1 }
+            }
+            .connect(to: listenerChannel.localAddress!)
+            .get()
+
+        // Need to write something so the server can activate the connection channel: this is UDP,
+        // so there is no handshaking that happens and thus the server cannot know that the
+        // connection has been established and the channel can be activated.
+        try await connectionChannel.writeAndFlush(ByteBuffer(bytes: [42]))
+
+        // Wait for the server to activate the connection channel to the client.
+        try await waitForConnectionHandler.connectionPromise.futureResult.get()
+
+        try await listenerChannel.close().get()
+        try await connectionChannel.close().get()
+
+        XCTAssertEqual(2, configuratorListenerCounter.withLockedValue { $0 })
+        XCTAssertEqual(1, configuratorConnectionCounter.withLockedValue { $0 })
+
+        try await group.shutdownGracefully()
+    }
+
     func testCanExtractTheConnection() throws {
         guard #available(macOS 14.0, iOS 17.0, watchOS 10.0, tvOS 17.0, *) else {
             throw XCTSkip("Option not available")