swift-nio/Sources/NIOUDPEchoServer/main.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftNIO open source project
//
// Copyright (c) 2017-2018 Apple Inc. and the SwiftNIO project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
import NIO

private final class EchoHandler: ChannelInboundHandler {
    public typealias InboundIn = ByteBuffer
    public typealias OutboundOut = ByteBuffer

    public func channelRead(context: ChannelHandlerContext, data: NIOAny) {
        // As we are not really interested getting notified on success or failure we just pass nil as promise to
        // reduce allocations.
        context.write(data, promise: nil)
    }

    public func channelReadComplete(context: ChannelHandlerContext) {
        // As we are not really interested getting notified on success or failure we just pass nil as promise to
        // reduce allocations.
        context.flush()
    }

    public func errorCaught(context: ChannelHandlerContext, error: Error) {
        print("error: ", error)

        // As we are not really interested getting notified on success or failure we just pass nil as promise to
        // reduce allocations.
        context.close(promise: nil)
    }
}

// We don't need more than one thread, as we're creating only one datagram channel.
let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
var bootstrap = DatagramBootstrap(group: group)
    // Specify backlog and enable SO_REUSEADDR
    .channelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEADDR), value: 1)

    // Set the handlers that are applied to the bound channel
    .channelInitializer { channel in
        // Ensure we don't read faster than we can write by adding the BackPressureHandler into the pipeline.
        channel.pipeline.addHandler(EchoHandler())
    }

defer {
    try! group.syncShutdownGracefully()
}

var arguments = CommandLine.arguments.dropFirst(0) // just to get an ArraySlice<String> from [String]
if arguments.dropFirst().first == .some("--enable-gathering-reads") {
    bootstrap = bootstrap.channelOption(ChannelOptions.datagramVectorReadMessageCount, value: 30)
    bootstrap = bootstrap.channelOption(ChannelOptions.recvAllocator, value: FixedSizeRecvByteBufferAllocator(capacity: 30 * 2048))
    arguments = arguments.dropFirst()
}
let arg1 = arguments.dropFirst().first
let arg2 = arguments.dropFirst().dropFirst().first

let defaultHost = "::1"
let defaultPort = 9999

enum BindTo {
    case ip(host: String, port: Int)
    case unixDomainSocket(path: String)
}

let bindTarget: BindTo
switch (arg1, arg1.flatMap(Int.init), arg2.flatMap(Int.init)) {
case (.some(let h), _ , .some(let p)):
    /* we got two arguments, let's interpret that as host and port */
    bindTarget = .ip(host: h, port: p)
case (.some(let portString), .none, _):
    /* couldn't parse as number, expecting unix domain socket path */
    bindTarget = .unixDomainSocket(path: portString)
case (_, .some(let p), _):
    /* only one argument --> port */
    bindTarget = .ip(host: defaultHost, port: p)
default:
    bindTarget = .ip(host: defaultHost, port: defaultPort)
}

let channel = try { () -> Channel in
    switch bindTarget {
    case .ip(let host, let port):
        return try bootstrap.bind(host: host, port: port).wait()
    case .unixDomainSocket(let path):
        return try bootstrap.bind(unixDomainSocketPath: path).wait()
    }
    }()

print("Server started and listening on \(channel.localAddress!)")

// This will never unblock as we don't close the channel
try channel.closeFuture.wait()

print("Server closed")