feat: Initial echo server

Sources/NioEcho/main.swift

@@ -0,0 +1,72 @@
+// 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!")