feat: First version of broker based WireGuard PSK interface

This allows us to run with minimal priviledges in the Rosenpass process itself

wireguard-broker/src/bin/priviledged.rs

@@ -0,0 +1,56 @@
+use std::io::{stdin, stdout, Read, Write};
+use std::result::Result;
+
+use rosenpass_wireguard_broker::api::msgs;
+use rosenpass_wireguard_broker::api::server::BrokerServer;
+use rosenpass_wireguard_broker::netlink as wg;
+
+#[derive(thiserror::Error, Debug)]
+pub enum BrokerAppError {
+    #[error(transparent)]
+    IoError(#[from] std::io::Error),
+    #[error(transparent)]
+    WgConnectError(#[from] wg::ConnectError),
+    #[error(transparent)]
+    WgSetPskError(#[from] wg::SetPskError),
+    #[error("Oversized message {}; something about the request is fatally wrong", .0)]
+    OversizedMessage(u64),
+}
+
+fn main() -> Result<(), BrokerAppError> {
+    let mut broker = BrokerServer::new(wg::NetlinkWireGuardBroker::new()?);
+
+    let mut stdin = stdin().lock();
+    let mut stdout = stdout().lock();
+    loop {
+        // Read the message length
+        let mut len = [0u8; 8];
+        stdin.read_exact(&mut len)?;
+
+        // Parse the message length
+        let len = u64::from_le_bytes(len);
+        if (len as usize) > msgs::REQUEST_MSG_BUFFER_SIZE {
+            return Err(BrokerAppError::OversizedMessage(len));
+        }
+
+        // Read the message itself
+        let mut req_buf = [0u8; msgs::REQUEST_MSG_BUFFER_SIZE];
+        let req_buf = &mut req_buf[..(len as usize)];
+        stdin.read_exact(req_buf)?;
+
+        // Process the message
+        let mut res_buf = [0u8; msgs::RESPONSE_MSG_BUFFER_SIZE];
+        let res = match broker.handle_message(req_buf, &mut res_buf) {
+            Ok(len) => &res_buf[..len],
+            Err(e) => {
+                eprintln!("Error processing message for wireguard PSK broker: {e:?}");
+                continue;
+            }
+        };
+
+        // Write the response
+        stdout.write_all(&(res.len() as u64).to_le_bytes())?;
+        stdout.write_all(&res)?;
+        stdout.flush()?;
+    }
+}