feat: Initial echo server

.editorconfig

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+root = true
+
+[*.swift]
+indent_style = space
+indent_size = 2
+tab_width = 2
+trim_trailing_whitespace = true

.gitignore

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+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

.swiftformat

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+--self init-only
+--indent 2
+--ifdef indent
+--trimwhitespace always
+--wraparguments before-first
+--wrapparameters before-first
+--wrapcollections preserve
+--wrapconditions after-first
+--typeblanklines preserve
+--commas inline
+--stripunusedargs closure-only

.swiftlint.yml

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+disabled_rules:
+  - closing_brace
+  - fuction_body_length
+
+included:
+  - Sources
+  - Tests
+
+ignore_multiline_statement_conditions: true

.swiftpm/xcode/xcshareddata/xcschemes/swift-nio-echo.xcscheme

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+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1610"
+   version = "1.7">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES"
+      buildArchitectures = "Automatic">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "nio-echo"
+               BuildableName = "nio-echo"
+               BlueprintName = "nio-echo"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      shouldAutocreateTestPlan = "YES">
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "nio-echo"
+            BuildableName = "nio-echo"
+            BlueprintName = "nio-echo"
+            ReferencedContainer = "container:">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "nio-echo"
+            BuildableName = "nio-echo"
+            BlueprintName = "nio-echo"
+            ReferencedContainer = "container:">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

Package.resolved

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+{
+  "originHash" : "20f1c21ae87f9bea31b5f7dfef662b3911d92dc048f13b9fb09d350230df3c34",
+  "pins" : [
+    {
+      "identity" : "swift-atomics",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-atomics.git",
+      "state" : {
+        "revision" : "cd142fd2f64be2100422d658e7411e39489da985",
+        "version" : "1.2.0"
+      }
+    },
+    {
+      "identity" : "swift-collections",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-collections.git",
+      "state" : {
+        "revision" : "671108c96644956dddcd89dd59c203dcdb36cec7",
+        "version" : "1.1.4"
+      }
+    },
+    {
+      "identity" : "swift-nio",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-nio.git",
+      "state" : {
+        "revision" : "914081701062b11e3bb9e21accc379822621995e",
+        "version" : "2.76.1"
+      }
+    },
+    {
+      "identity" : "swift-system",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-system.git",
+      "state" : {
+        "revision" : "c8a44d836fe7913603e246acab7c528c2e780168",
+        "version" : "1.4.0"
+      }
+    }
+  ],
+  "version" : 3
+}

Package.swift

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+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+  name: "swift-nio-echo",
+  platforms: [
+    .macOS(.v15)
+  ],
+  products: [
+    .executable(name: "nio-echo", targets: ["NIOEcho"])
+  ],
+  dependencies: [
+    .package(url: "https://github.com/apple/swift-nio.git", from: "2.76.1")
+  ],
+  targets: [
+    .executableTarget(
+      name: "NIOEcho",
+      dependencies: [
+        .product(name: "NIO", package: "swift-nio")
+      ]
+    )
+  ]
+)

Sources/NioEcho/main.swift

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+// The Swift Programming Language
+// https://docs.swift.org/swift-book
+import NIOCore
+import NIOPosix
+
+private final class EchoHandler: ChannelInboundHandler {
+  typealias InboundIn = ByteBuffer
+  typealias OutboundOut = BackPressureHandler
+
+  func channelRead(context: ChannelHandlerContext, data: NIOAny) {
+    context.write(data, promise: nil)
+  }
+
+  func channelReadComplete(context: ChannelHandlerContext) {
+    context.flush()
+  }
+
+  func errorCaught(context: ChannelHandlerContext, error: any Error) {
+    print("error: \(error)")
+    context.close(promise: nil)
+  }
+}
+
+let group = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount)
+let bootstrap = ServerBootstrap(group: group)
+  .serverChannelOption(.backlog, value: 256)
+  .serverChannelOption(.socketOption(.so_reuseaddr), value: 1)
+  // set the handlers that are applied.
+  .childChannelInitializer { channel in
+    channel.eventLoop.makeCompletedFuture {
+      try channel.pipeline.syncOperations.addHandler(BackPressureHandler())
+      try channel.pipeline.syncOperations.addHandler(EchoHandler())
+    }
+  }
+  .childChannelOption(.socketOption(.so_reuseaddr), value: 1)
+  .childChannelOption(.maxMessagesPerRead, value: 16)
+  .childChannelOption(.recvAllocator, value: AdaptiveRecvByteBufferAllocator())
+
+defer { try? group.syncShutdownGracefully() }
+
+// First argument is the program path
+let arguments = CommandLine.arguments
+let arg1 = arguments.dropFirst().first
+let arg2 = arguments.dropFirst(2).first
+
+let defaultHost = "::1"
+let defaultPort = 9999
+
+struct BindTo {
+  let host: String
+  let port: Int
+}
+
+let bindTarget: BindTo
+switch (arg1, arg1.flatMap(Int.init), arg2.flatMap(Int.init)) {
+case let (_, .some(port), _):
+  bindTarget = .init(host: defaultHost, port: port)
+case let (.some(host), _, .some(port)):
+  bindTarget = .init(host: host, port: port)
+case let (.some(host), .none, .none):
+  bindTarget = .init(host: host, port: defaultPort)
+default:
+  bindTarget = .init(host: defaultHost, port: defaultPort)
+}
+
+let channel = try bootstrap.bind(host: bindTarget.host, port: bindTarget.port).wait()
+
+print("Server started and listening on: \(channel.localAddress!)")
+
+try channel.closeFuture.wait()
+
+print("Server closed!")