added rust sdk surb example

sdk/rust/nym-sdk/examples/surb-reply.rs

@@ -0,0 +1,64 @@
+use nym_sdk::mixnet::{
+    AnonymousSenderTag, MixnetClient, MixnetClientBuilder, ReconstructedMessage, StoragePaths,
+};
+use std::path::PathBuf; 
+
+#[tokio::main]
+async fn main() {
+    nym_bin_common::logging::setup_logging();
+
+    // Specify some config options
+    let config_dir = PathBuf::from("/tmp/surb-example-client");
+    let storage_paths = StoragePaths::new_from_dir(&config_dir).unwrap();
+
+    // Create the client with a storage backend, and enable it by giving it some paths. If keys
+    // exists at these paths, they will be loaded, otherwise they will be generated.
+    let client = MixnetClientBuilder::new_with_default_storage(storage_paths)
+        .await
+        .unwrap()
+        .build()
+        .await
+        .unwrap();
+
+    // Now we connect to the mixnet, using keys now stored in the paths provided.
+    let mut client = client.connect_to_mixnet().await.unwrap();
+
+    // Be able to get our client address
+    let our_address = client.nym_address();
+    println!("\nOur client nym address is: {our_address}"); 
+
+    // Send a message through the mixnet to ourselves using our nym address
+    client.send_str(*our_address, "hello there").await;
+
+    // we're going to parse the sender_tag (AnonymousSenderTag) from the incoming message and use it to 'reply' to ourselves instead of our Nym address. 
+    // we know there will be a sender_tag since the sdk sends SURBs along with messages by default. 
+    println!("Waiting for message\n");
+
+    // get the actual message - discard the empty vec sent along with a potential SURB topup request
+    let mut message: Vec<ReconstructedMessage> = Vec::new();
+    while let Some(new_message) = client.wait_for_messages().await {
+        if new_message.is_empty() {
+            continue;
+        }
+        message = new_message;
+        break;
+    }
+
+    let mut parsed = String::new();
+    if let Some(r) = message.iter().next() {
+        parsed = String::from_utf8(r.message.clone()).unwrap();
+    }
+    // parse sender_tag: we will use this to reply to sender without needing their Nym address 
+    let return_recipient: AnonymousSenderTag = message[0].sender_tag.unwrap();
+    println!("\nReceived the following message: {} \nfrom sender with surb bucket {}", parsed, return_recipient); 
+
+    // reply to self with it: note we use `send_str_reply` instead of `send_str`
+    println!("Replying with using SURBs"); 
+    client.send_str_reply(return_recipient, "hi an0n!").await; 
+
+    println!("Waiting for message (once you see it, ctrl-c to exit)\n");
+    client
+        .on_messages(|msg| println!("\nReceived: {}", String::from_utf8_lossy(&msg.message)))
+        .await;
+
+}