Example of using rust-web3 crate to listen to certain event as emitted from target contract.

wss_sub_rustweb3.rs

use hex_literal::hex;
use web3::{
    contract::{Contract, Options},
    futures::{future, StreamExt},
    types::{FilterBuilder, Address},
};
use std::str::FromStr;

#[tokio::main]
async fn main() -> web3::contract::Result<()> {
    let web3 = web3::Web3::new(web3::transports::WebSocket::new("<wss-provider-url>").await?);
    let filter = FilterBuilder::default()
        // this is BSC: TokenHub
        .address(vec![Address::from_str("0x0000000000000000000000000000000000001004").unwrap()])
        .topics(
            // this is 'Transfer (index_topic_1 address from, index_topic_2 address to, uint256 value)' event
            // use https://emn178.github.io/online-tools/keccak_256.html, and type in 'Transfer(address,address,uint256)'
            // it will return result hash as used in next line
            Some(vec![hex!("ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef").into()]),
            None,
            None,
            None,
        )
        .build();

    let sub = web3.eth_subscribe().subscribe_logs(filter).await?;

    sub.for_each(|log| {
        println!("{:?}", log);
        future::ready(())
    }).await;

    Ok(())
}

Note: current state of rust-web3 doesn't implement re-connect to disconnected websocket, nor pings just yet. Also see tomusdrw/rust-web3#151 for timeout issue in websocket (to not silently hang waiting while connection is disconnected), and tomusdrw/rust-web3#249 for the case of reconnection.