# Tour of the Rust SDK

import { Callout } from 'nextra/components'

A quick walkthrough of the most important things you can do with `nym-sdk`. Each section shows working code and links to the module that covers it in depth.

<Callout type="warning">
The Mixnet is not like regular internet networking. There are no persistent connections, no guaranteed message ordering, and no TCP underneath. At its core, the Mixnet is a message-based anonymity network: you send individual payloads that are Sphinx-encrypted, mixed through multiple nodes, and independently reconstructed at the destination.

The raw [message API](./mixnet) therefore works differently from what most developers expect. The [Stream module](./stream) bridges this gap by providing `AsyncRead + AsyncWrite` byte streams on top of the Mixnet. If you are coming from socket-based networking, start with streams.
</Callout>

## Send a raw message payload

The message API gives you direct access to the Mixnet's native communication model: individually addressed payloads with no connections and no ordering guarantees. This is useful when you want full control, but it's not how most networking code works:

```rust
use nym_sdk::mixnet::{self, MixnetMessageSender};

#[tokio::main]
async fn main() {
    let mut client = mixnet::MixnetClient::connect_new().await.unwrap();
    let addr = *client.nym_address();
    println!("Connected: {addr}");

    // Send a message to ourselves
    client
        .send_plain_message(addr, "hello mixnet!")
        .await
        .unwrap();

    // Receive it (filter empty SURB management messages)
    if let Some(msgs) = client.wait_for_messages().await {
        for msg in msgs.iter().filter(|m| !m.message.is_empty()) {
            println!("Got: {}", String::from_utf8_lossy(&msg.message));
        }
    }

    // Always disconnect for clean shutdown
    client.disconnect().await;
}
```

The message is Sphinx-encrypted, mixed across 5 nodes, and reconstructed on arrival. The whole round trip takes a few seconds.

Next: [Mixnet module](./mixnet) | [Tutorial: Send Your First Private Message](./mixnet/tutorial)

## Reply anonymously with SURBs

Every received message carries a `sender_tag`, an opaque token that lets you reply **without knowing the sender's Nym address**. Replies travel back through pre-built Single Use Reply Blocks (SURBs):

```rust
// After receiving a message...
let tag = received_msg.sender_tag.expect("message includes sender tag");
client.send_reply(tag, "anonymous reply!").await.unwrap();
```

The replying side never learns where the reply is going, enabling anonymous communication without mutual identity disclosure.

## Open a bidirectional stream

If you're used to working with TCP sockets, this is where you'll feel at home. The [Stream module](./stream) provides persistent, bidirectional byte channels that implement tokio's `AsyncRead + AsyncWrite`, so any code that works with sockets works with `MixnetStream`:

```rust
use nym_sdk::mixnet;
use tokio::io::{AsyncReadExt, AsyncWriteExt};

#[tokio::main]
async fn main() {
    let mut sender = mixnet::MixnetClient::connect_new().await.unwrap();
    let mut receiver = mixnet::MixnetClient::connect_new().await.unwrap();
    let recv_addr = *receiver.nym_address();

    // Receiver creates a listener (activates stream mode)
    let mut listener = receiver.listener().unwrap();

    // Sender opens a stream to the receiver
    let mut out = sender.open_stream(recv_addr, None).await.unwrap();

    // Receiver accepts it
    let mut inc = listener.accept().await.unwrap();

    // Standard tokio I/O: write, flush, read
    out.write_all(b"hello stream").await.unwrap();
    out.flush().await.unwrap();

    let mut buf = vec![0u8; 1024];
    let n = inc.read(&mut buf).await.unwrap();
    println!("{}", String::from_utf8_lossy(&buf[..n]));

    drop(out);
    drop(inc);
    sender.disconnect().await;
    receiver.disconnect().await;
}
```

<Callout type="info">
Activating stream mode (by calling `listener()` or `open_stream()`) disables message-based methods like `send_plain_message()` and `wait_for_messages()`. A single client operates in one mode at a time.
</Callout>

Next: [Stream module](./stream) | [Tutorial: Build a Private Echo Server](./stream/tutorial)

## Use a client pool for bursty traffic

Creating a `MixnetClient` takes several seconds (gateway handshake, key generation, topology fetch). The [Client Pool](./client-pool) pre-creates clients in the background so they're ready when you need them:

```rust
use nym_sdk::client_pool::ClientPool;

#[tokio::main]
async fn main() {
    let pool = ClientPool::new(3); // maintain 3 clients in reserve
    let bg = pool.clone();
    tokio::spawn(async move { bg.start().await });

    // Wait for pool to fill, then grab a ready client
    tokio::time::sleep(std::time::Duration::from_secs(15)).await;

    if let Some(client) = pool.get_mixnet_client().await {
        println!("Got client: {}", client.nym_address());
        client.disconnect().await;
    }

    pool.disconnect_pool().await;
}
```

Clients are consumed, not returned; the pool creates replacements automatically.

Next: [Client Pool module](./client-pool) | [Tutorial: Handle Bursty Traffic](./client-pool/tutorial)

## Persist your identity

By default, `connect_new()` creates ephemeral keys that are discarded on disconnect. To keep the same Nym address across restarts, use the builder with on-disk storage:

```rust
use nym_sdk::mixnet::{MixnetClientBuilder, StoragePaths};
use std::path::PathBuf;

let storage = StoragePaths::new_from_dir(
    &PathBuf::from("/tmp/my-nym-client")
).unwrap();

let client = MixnetClientBuilder::new_with_default_storage(storage)
    .await
    .unwrap()
    .build()
    .unwrap()
    .connect_to_mixnet()
    .await
    .unwrap();

// This address is the same every time you run with the same path
println!("Persistent address: {}", client.nym_address());
```

## Where to go next

- [Installation](./importing): add `nym-sdk` to your project
- [Mixnet Tutorial](./mixnet/tutorial): send, receive, and reply with SURBs
- [Stream Tutorial](./stream/tutorial): build a private echo server
- [Client Pool Tutorial](./client-pool/tutorial): handle bursty traffic
- [API Reference on docs.rs](https://docs.rs/nym-sdk/latest/nym_sdk/): type details, method signatures, architecture docs