writeDataUnsupported in ChannelInboundHandler (Swift-NIO)

Question

I am trying to make a simple echo UDP server that sends back all incoming datagrams prefixed with a UTF8 string.

In my attempts to reach this goal, I succeeded in sending back the incoming data, but when I try to prefix this data with the string: "You sent: ", I get an error writeDataUnsupported

This is my code:

I made a ChannelInboundHandler called Echo all it does is: For each incoming datagram, it sends the string "You sent: " and then the data of the incoming datagram.

final class Echo: ChannelInboundHandler {
    typealias   InboundIn = ByteBuffer
    typealias OutboundOut = ByteBuffer

    var wroteResponse = false
    static let response = "You sent: ".data(using: .utf8)!

    func channelRead(ctx: ChannelHandlerContext, data: NIOAny) {
        if !wroteResponse {
            var buffer = ctx.channel.allocator.buffer(capacity: Echo.response.count)
            buffer.write(bytes: Echo.response)
            ctx.write(self.wrapOutboundOut(buffer), promise: nil)
            wroteResponse = true
        }
        ctx.write(data, promise: nil)
    }

    func channelReadComplete(ctx: ChannelHandlerContext) {
        ctx.flush()
        wroteResponse = false
    }
}

Then I made a single threaded event loop group and assigned a datagram bootsrap to it. Then I bound the bootstrap to port 4065.

let  = MultiThreadedEventLoopGroup(numThreads: 1)
let bootstrap = DatagramBootstrap(group: )
    .channelOption(ChannelOptions.socket(SocketOptionLevel(SOL_SOCKET), SO_REUSEADDR), value: 1)
    .channelInitializer { $0.pipeline.add(handler: Echo()) }
defer {
    try! .syncShutdownGracefully()
}


try bootstrap
    .bind(host: "127.0.0.1", port: 4065)
    .wait()
    .closeFuture
    .wait()

Why do I always get this writeDataUnsupported while trying to send the string: "You sent: "?

score 2 · Accepted Answer · answered Mar 20 '18 at 19:48

2

For DatagramChannel you need to wrap your ByteBuffer into an AddressEnvelope. Which also means your ChannelInboundHandler should operate on AddressedEnvelope<ByteBuffer>.

answered Mar 20 '18 at 19:48

Norman Maurer

23,104
2
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31

Thanks Norman, is this documented somewhere? (the fact that DatagramChannel works with `AddressedEnvelope`'s) – Damiaan Dufaux Mar 20 '18 at 20:28
2

I think no... I will add some documentation and an example to SwiftNIO – Norman Maurer Mar 21 '18 at 07:26

score 2 · Answer 2 · answered Mar 21 '18 at 07:24

To make the ChannelInboundHandler operate on AddressedEnvelope<ByteBuffer>, as Norman Maurer suggests, you can rewrite Echo so it looks more like:

final class Echo: ChannelInboundHandler {
    typealias  InboundIn  = AddressedEnvelope<ByteBuffer>
    typealias OutboundOut = AddressedEnvelope<ByteBuffer>

    static let response = "You sent: ".data(using: .utf8)!

    func channelRead(ctx: ChannelHandlerContext, data: NIOAny) {
        var incomingEnvelope = unwrapInboundIn(data)
        var buffer = ctx.channel.allocator.buffer(capacity: Echo.response.count + incomingEnvelope.data.readableBytes)
        buffer.write(bytes: Echo.response)
        buffer.write(buffer: &incomingEnvelope.data)

        let envelope = AddressedEnvelope(remoteAddress: incomingEnvelope.remoteAddress, data: buffer)
        ctx.write(wrapOutboundOut(envelope), promise: nil)
    }

    func channelReadComplete(ctx: ChannelHandlerContext) {
        ctx.flush()
    }
}

writeDataUnsupported in ChannelInboundHandler (Swift-NIO)

2 Answers2