The seed node

Let's create an instance of dchat inside our main function and pass the p2p network into it. Then we'll add dchat::start() to our async loop in the main function.

#[async_std::main]
async fn main() -> Result<()> {
    let settings: Result<Settings> = match std::env::args().nth(1) {
        Some(id) => match id.as_str() {
            "a" => alice(),
            "b" => bob(),
            _ => Err(MissingSpecifier.into()),
        },
        None => Err(MissingSpecifier.into()),
    };

    let p2p = net::P2p::new(settings?.into()).await;

    let dchat = Dchat::new(p2p);

    let nthreads = num_cpus::get();
    let (signal, shutdown) = async_channel::unbounded::<()>();

    let ex = Arc::new(Executor::new());
    let ex2 = ex.clone();

    let (_, result) = Parallel::new()
        .each(0..nthreads, |_| {
            smol::future::block_on(ex.run(shutdown.recv()))
        })
        .finish(|| {
            smol::future::block_on(async move {
                dchat.start(ex2).await?;
                drop(signal);
                Ok(())
            })
        });

    result
}

Now try to run the program, don't forget to add a specifier a or b to define the type of node.

It should output the following error:

Error: NetworkOperationFailed

That's because there is no seed node online for our nodes to connect to. A seed node is used when connecting to the network: it is a special kind of inbound node that gets connected to, sends over a list of addresses and disconnects again. This behavior is defined in the ProtocolSeed.

Everytime we run p2p.start() we attempt to connect to a seed using a SeedSyncSession. If the SeedSyncSession fails, p2p.start() will fail, so without a seed node, our inbound and outbound nodes cannot establish a connection to the network. Let's remedy that.

We have two options here. First, we could implement our own seed node. Alternatively, DarkFi maintains a master seed node called lilith that can act as the seed for many different protocols at the same time. For the purpose of this tutorial let's use lilith.

What lilith does in the background is very simple. Just like any p2p daemon, a seed node defines its networks settings into a type called Settings and creates a new instance of the p2p network. It then runs p2p::start() and p2p::run(). The difference is in the settings: a seed node just specifies an inbound address which other nodes will connect to.

Crucially, this inbound address must match the seed address we specified earlier in Alice and Bob's settings.