Alloy Book

Example: subscribe_blocks

Example

To run this example:

• Clone the examples repository: git clone git@github.com:alloy-rs/examples.git
• Run: cargo run --example subscribe_blocks

//! Example of subscribing to blocks and watching block headers by polling.

use alloy::{
    node_bindings::Anvil,
    providers::{Provider, ProviderBuilder, WsConnect},
};
use eyre::Result;
use futures_util::{stream, StreamExt};

#[tokio::main]
async fn main() -> Result<()> {
    // Spin up a local Anvil node.
    // Ensure `anvil` is available in $PATH.
    let anvil = Anvil::new().block_time(1).try_spawn()?;

    // Create a provider.
    let ws = WsConnect::new(anvil.ws_endpoint());
    let provider = ProviderBuilder::new().on_ws(ws).await?;

    // Subscribe to blocks.
    let subscription = provider.subscribe_blocks().await?;
    let mut stream = subscription.into_stream().take(2);

    while let Some(block) = stream.next().await {
        println!("Received block number: {}", block.header.number);
    }

    // Poll for block headers.
    let poller = provider.watch_blocks().await?;
    let mut stream = poller.into_stream().flat_map(stream::iter).take(2);

    while let Some(block_hash) = stream.next().await {
        println!("Polled for block header: {block_hash:?}");
    }

    Ok(())
}

Find the source code on Github here.