'there is no reactor running, must be called from the context of a Tokio 1.x runtime'

[nikkolasg]

Hi all,

Very new user to rust-libp2p (and libp2p in general) here, so please bear with me if I'm forgetting something obvious. I've basically took the rendezvous examples, for the rendezvous point and the register+discover node.
I'm using tokio, and running all this inside a #[tokio::test] rendezvous() -> Result<()> { ... } test method.
Running the discover loop seem to work fine but when I run the "discovering" nodes (inside my test) I get the following:

thread 'libp2p-swarm-task-0' panicked at 'there is no reactor running, must be called from the context of a Tokio 1.x runtime', /.../.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/context.rs:29:26

2 notes:

1. I see only one event coming from the swarm where it actually listens, i.e. Handled event NewListenAddr { listener_id: ListenerId(1), address: "/ip4/127.0.0.1/tcp/5004" } and then I see this this error msg.
2. My code is indeed running inside a tokio runtime, since the test runs, I'm using async everywhere and my loop { tokio::select { .... } } is still running as I see the tick appearing (to ask for more peers from rendezvous server). Problem is I have zero events coming from the swarm (except the NewListenAddr shown before), which makes sense since apparently it panic'd.
3. Relevant lines of cargo:

libp2p = { version = "^0.43" , default-features = false, features = ["rendezvous","yamux","mplex","noise","websocket","tcp-tokio","dns-tokio","ping","identify"] }
tokio = { version = "1.17", features = ["full"] }

Any idea what could be causing this ?

Thank you 🙏

[nikkolasg]

Ok, I found the related issue #2230 and then found how to setup properly the tokio executor here

For reference, solved it with

let mut swarm = SwarmBuilder::new(
            tokio_development_transport(self.kp.clone()).unwrap(),
            MyBehaviour { ... }, ... )
        .executor(Box::new(|fut| {
            tokio::spawn(fut);
        }))
        .build();

[michael-herwig]

I want to add, as with version 0.50 of libp2p, the SwarmBuilder::new is deprecated and encourages usage of constructors explicitly stating the executor (SwarmBuilder::with_executor/SwarmBuilder::wihtout_executor). For this particular example, there is a method for tokio, namely SwarmBuilder::with_tokio_executor. Just in case someone runs into the sample problem as me upgrading libp2p.

[mxinden]

@nikkolasg thanks for referencing the solution. Mind proposing a patch improving the docs, preventing future users to run down the same rabbit hole?