ethers-rs/book/subscriptions/subscriptions.md

Ethers-rs: Subscriptions

Here we will discuss how to use ethers-rs to subscribe and listen to blocks, events, and logs. Subscriptions provide a way to receive real-time updates on various activities on the Ethereum blockchain, allowing you to monitor the network and react to changes as they happen.

Overview

ethers-rs offers a convenient way to work with subscriptions, enabling you to listen to new blocks, transaction receipts, and logs. The main components you will work with are:

1. Provider: The main struct used to interact with the Ethereum network.
2. SubscriptionStream: A stream of updates you can subscribe to for real-time notifications.

Getting Started

Before working with subscriptions, make sure you have ethers-rs added to your project's dependencies in Cargo.toml:

[dependencies]
ethers = { version = "2.0.0", features = ["full"] }

Next, import the necessary components from the ethers-rs library:

use ethers::{prelude::\*,types::H256,};

Subscribing to Events

As we discussed in the previous section on events, you can subscribe to specific events emitted by smart contracts using the EventWatcher struct. To create a SubscriptionStream, call the subscribe method on your EventWatcher:

let mut stream = watcher.subscribe().await?;

Now, you can listen to events as they are emitted by the smart contract:

while let Some(event) = stream.next().await {
    match event {
        Ok(log) => {
            println!("New event: {:?}", log);
        }
        Err(e) => {
            eprintln!("Error: {:?}", e);
        }
    }
}

By using the subscription features provided by ethers-rs, you can efficiently monitor and react to various activities on the Ethereum network. Subscriptions are a powerful tool for building responsive and dynamic applications that can interact with smart contracts and stay up-to-date with the latest network events.

Unsubscribing from Subscriptions

In some cases, you may want to stop listening to a subscription. To do this, simply drop the SubscriptionStream:

drop(stream);

This will stop the stream from receiving any further updates.