Custom Topology Provider

If you are also running a Validator and Nym API for your network, you can specify that endpoint as such and interact with it as clients usually do (under the hood).
You can find this code here (opens in a new tab)
// Copyright 2023 - Nym Technologies SA <contact@nymtech.net>
// SPDX-License-Identifier: Apache-2.0
 
use nym_sdk::mixnet;
use nym_sdk::mixnet::MixnetMessageSender;
use nym_topology::provider_trait::{async_trait, TopologyProvider};
use nym_topology::{nym_topology_from_detailed, NymTopology};
use url::Url;
 
struct MyTopologyProvider {
    validator_client: nym_validator_client::client::NymApiClient,
}
 
impl MyTopologyProvider {
    fn new(nym_api_url: Url) -> MyTopologyProvider {
        MyTopologyProvider {
            validator_client: nym_validator_client::client::NymApiClient::new(nym_api_url),
        }
    }
 
    async fn get_topology(&self) -> NymTopology {
        let mixnodes = self
            .validator_client
            .get_cached_active_mixnodes()
            .await
            .unwrap();
 
        // in our topology provider only use mixnodes that have mix_id divisible by 3
        // and have more than 100k nym (i.e. 100'000'000'000 unym) in stake
        // why? because this is just an example to showcase arbitrary uses and capabilities of this trait
        let filtered_mixnodes = mixnodes
            .into_iter()
            .filter(|mix| {
                mix.mix_id() % 3 == 0 && mix.total_stake() > "100000000000".parse().unwrap()
            })
            .collect::<Vec<_>>();
 
        let gateways = self.validator_client.get_cached_gateways().await.unwrap();
 
        nym_topology_from_detailed(filtered_mixnodes, gateways)
    }
}
 
#[async_trait]
impl TopologyProvider for MyTopologyProvider {
    // this will be manually refreshed on a timer specified inside mixnet client config
    async fn get_new_topology(&mut self) -> Option<NymTopology> {
        Some(self.get_topology().await)
    }
}
 
#[tokio::main]
async fn main() {
    nym_bin_common::logging::setup_logging();
 
    let nym_api = "https://validator.nymtech.net/api/".parse().unwrap();
    let my_topology_provider = MyTopologyProvider::new(nym_api);
 
    // Passing no config makes the client fire up an ephemeral session and figure things out on its own
    let mut client = mixnet::MixnetClientBuilder::new_ephemeral()
        .custom_topology_provider(Box::new(my_topology_provider))
        .build()
        .unwrap()
        .connect_to_mixnet()
        .await
        .unwrap();
 
    let our_address = client.nym_address();
    println!("Our client nym address is: {our_address}");
 
    // Send a message through the mixnet to ourselves
    client
        .send_plain_message(*our_address, "hello there")
        .await
        .unwrap();
 
    println!("Waiting for message (ctrl-c to exit)");
    client
        .on_messages(|msg| println!("Received: {}", String::from_utf8_lossy(&msg.message)))
        .await;
}
Custom Network Topologies Manually Overwrite Topology