Before you begin, ensure you have the following installed:
Step 1: Create a Rust Workspace
First, create a new directory for the project and navigate into it:
Copy
mkdir hello-world-ml
cd hello-world-ml
Next, create the packages inside the workspace:
Copy
cargo new subscriber --vcs none
cargo new publisher --vcs none
Finally, manually create a Cargo.toml file in the root directory for the workspace with the following content:
Copy
[workspace]
members = ["subscriber", "publisher"]
[workspace.dependencies]
nostr-sdk = "0.38.0"
nostr = "0.38.0"
tokio = { version = "1.38.0", features = ["full"] }
This ensures that both subscriber and publisher share the same dependency versions and avoids issues from creating the workspace Cargo.toml before the packages.
Step 2: Write the Subscriber Code
Edit subscriber/Cargo.toml to use workspace dependencies:
use nostr::{key::Keys, Kind};
use nostr_sdk::{Client, EventBuilder, Options, Tag};
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
// Initialize the Nostr client
let keys: Keys = Keys::generate(); // Generate a keypair for the publisher
let client_opts = Options::default();
let client = Client::builder()
.signer(keys.clone())
.opts(client_opts)
.build();
client.add_relay("wss://dev-relay.xephy.dev").await?;
client.connect().await;
// Create and send a "Hello World" event
let event = EventBuilder::new(Kind::Custom(1573), "Hello World").tags([
Tag::parse(["s".to_string(), "hello_session".to_string()]).unwrap(),
Tag::parse(["p".to_string(), "receiver_pubkey".to_string()]).unwrap(),
]);
client.send_event_builder(event).await?;
println!("Published 'Hello World' event to wss://dev-relay.xephy.dev");
Ok(())
}
Step 4: Compile and Run:
Run the Subscriber:
Copy
cargo run -p subscriber
This starts the subscriber, which will wait for events.
Run the Publisher (in a new terminal):
Copy
cargo run -p publisher
Expected Output:
Subscriber terminal:
Copy
Subscribed events on wss://dev-relay.xephy.dev
Publisher terminal:
Copy
Published 'Hello World' event to wss://dev-relay.xephy.dev
Subscriber terminal:
Copy
Received: Hello World
🎉At this point, the basic publish and subscribe functionality is complete, and the command line has output the results we expected!
Next, we will enhance this by integrating with the Solana blockchain and the Messaging Layer.Specifically, when publishing a greeting like "Hello World," the publisher will request a Solana airdrop.
Replace the contents of subscriber/src/main.rs with this code to subscribe to events and request a Solana airdrop:
Copy
use nostr::{key::Keys, types::{SingleLetterTag, Timestamp}, Kind};
use nostr_sdk::{Client, Filter, RelayPoolNotification};
use serde::Deserialize;
use solana_client::rpc_client::RpcClient;
use solana_sdk::pubkey::Pubkey;
use std::str::FromStr;
#[derive(Deserialize)]
struct Message {
greeting: String,
solana_pubkey: String,
}
const MENTION_TAG: SingleLetterTag = SingleLetterTag::lowercase(nostr::Alphabet::P);
const SESSION_TAG: SingleLetterTag = SingleLetterTag::lowercase(nostr::Alphabet::S);
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
// Initialize the Nostr client
let keys: Keys = Keys::generate();
let client_opts = nostr_sdk::Options::default();
let client = Client::builder()
.signer(keys.clone())
.opts(client_opts)
.build();
client.add_relay("wss://dev-relay.xephy.dev").await?;
client.connect().await;
// Define a filter for "Hello World" events
let filter = Filter::new()
.kind(Kind::Custom(1573))
.since(Timestamp::now())
.custom_tag(SESSION_TAG, ["hello_session"])
.custom_tag(MENTION_TAG, ["receiver_pubkey"]);
// Subscribe to the filter
client.subscribe(vec![filter], None).await?;
println!("Subscribed events on wss://dev-relay.xephy.dev");
// Initialize Solana testnet client
let solana_client = RpcClient::new("https://api.devnet.solana.com".to_string());
// Handle notifications asynchronously
client
.handle_notifications(|notification| async {
match notification {
RelayPoolNotification::Event { event, .. } => {
println!("Received {}", event.content);
// Parse the JSON content
if let Ok(message) = serde_json::from_str::<Message>(&event.content) {
// Request airdrop to the solana_pubkey
if let Ok(pubkey) = Pubkey::from_str(&message.solana_pubkey) {
match solana_client.request_airdrop(&pubkey, 1_000_000_000) {
Ok(signature) => {
println!(
"Airdrop requested for {}. Signature: {}",
pubkey, signature
);
if let Ok(confirmed) =
solana_client.confirm_transaction(&signature)
{
if confirmed {
println!("Airdrop confirmed for {}", pubkey);
}
}
}
Err(e) => println!("Airdrop failed: {:?}", e),
}
} else {
println!("Invalid Solana pubkey: {}", message.solana_pubkey);
}
} else {
println!("Failed to parse message content");
}
}
_ => {} // Ignore other notification types
}
Ok(false) // Keep listening (false means don't stop)
})
.await?;
Ok(())
}
Step 8: Compile and Run
Run the Subscriber (in one terminal):
Copy
cargo run -p subscriber
Run the Publisher (in a new terminal):
Copy
cargo run -p publisher
Expected Output:
Subscriber terminal:
Copy
Subscribed events on wss://dev-relay.xephy.dev
Publisher terminal:
Copy
Published 'Hello World' event to wss://dev-relay.xephy.dev
Airdrop request for [ ... ]
Subscriber terminal:
Copy
Received: {"greeting":"Hello World","solana_pubkey":"..."}
Airdrop requested for ... Signature: ...
Airdrop confirmed for ...
Next Steps
This example demonstrates a basic integration between Messaging Layer and Solana. You could extend this further by:
Deploying a Solana smart contract (program) to handle more complex interactions
Using Nostr events to trigger contract calls
Implementing payment verification or other blockchain-based logic
Adding error handling and retry mechanisms for airdrop requests
This simple integration opens the door to building decentralized applications that combine messaging capabilities with Solana's high-performance blockchain.
