fix(udp): pre-allocate receive buffer (#1707)

Instead of allocating a new receive buffer on each call to
`neqo_common::udp::Socket::recv`, preallocate a long-lived buffer in
`Socket::bind` and reuse this buffer on each read.

neqo-client/src/main.rs

@@ -763,7 +763,7 @@ fn to_headers(values: &[impl AsRef<str>]) -> Vec<Header> {
 
 struct ClientRunner<'a> {
     local_addr: SocketAddr,
-    socket: &'a udp::Socket,
+    socket: &'a mut udp::Socket,
     client: Http3Client,
     handler: Handler<'a>,
     timeout: Option<Pin<Box<Sleep>>>,
@@ -773,7 +773,7 @@ struct ClientRunner<'a> {
 impl<'a> ClientRunner<'a> {
     fn new(
         args: &'a mut Args,
-        socket: &'a udp::Socket,
+        socket: &'a mut udp::Socket,
         local_addr: SocketAddr,
         remote_addr: SocketAddr,
         hostname: &str,
@@ -998,7 +998,7 @@ async fn main() -> Res<()> {
             SocketAddr::V6(..) => SocketAddr::new(IpAddr::V6(Ipv6Addr::from([0; 16])), 0),
         };
 
-        let socket = udp::Socket::bind(local_addr)?;
+        let mut socket = udp::Socket::bind(local_addr)?;
         let real_local = socket.local_addr().unwrap();
         println!(
             "{} Client connecting: {:?} -> {:?}",
@@ -1022,7 +1022,7 @@ async fn main() -> Res<()> {
             token = if args.use_old_http {
                 old::ClientRunner::new(
                     &args,
-                    &socket,
+                    &mut socket,
                     real_local,
                     remote_addr,
                     &hostname,
@@ -1034,7 +1034,7 @@ async fn main() -> Res<()> {
             } else {
                 ClientRunner::new(
                     &mut args,
-                    &socket,
+                    &mut socket,
                     real_local,
                     remote_addr,
                     &hostname,
@@ -1249,7 +1249,7 @@ mod old {
 
     pub struct ClientRunner<'a> {
         local_addr: SocketAddr,
-        socket: &'a udp::Socket,
+        socket: &'a mut udp::Socket,
         client: Connection,
         handler: HandlerOld<'a>,
         timeout: Option<Pin<Box<Sleep>>>,
@@ -1259,7 +1259,7 @@ mod old {
     impl<'a> ClientRunner<'a> {
         pub fn new(
             args: &'a Args,
-            socket: &'a udp::Socket,
+            socket: &'a mut udp::Socket,
             local_addr: SocketAddr,
             remote_addr: SocketAddr,
             origin: &str,

neqo-common/src/udp.rs

@@ -21,6 +21,7 @@ use crate::{Datagram, IpTos};
 pub struct Socket {
     socket: tokio::net::UdpSocket,
     state: UdpSocketState,
+    recv_buf: Vec<u8>,
 }
 
 impl Socket {
@@ -31,6 +32,7 @@ impl Socket {
         Ok(Self {
             state: quinn_udp::UdpSocketState::new((&socket).into())?,
             socket: tokio::net::UdpSocket::from_std(socket)?,
+            recv_buf: vec![0; u16::MAX as usize],
         })
     }
 
@@ -70,15 +72,13 @@ impl Socket {
     }
 
     /// Receive a UDP datagram on the specified socket.
-    pub fn recv(&self, local_address: &SocketAddr) -> Result<Option<Datagram>, io::Error> {
-        let mut buf = [0; u16::MAX as usize];
-
+    pub fn recv(&mut self, local_address: &SocketAddr) -> Result<Option<Datagram>, io::Error> {
         let mut meta = RecvMeta::default();
 
         match self.socket.try_io(Interest::READABLE, || {
             self.state.recv(
                 (&self.socket).into(),
-                &mut [IoSliceMut::new(&mut buf)],
+                &mut [IoSliceMut::new(&mut self.recv_buf)],
                 slice::from_mut(&mut meta),
             )
         }) {
@@ -101,16 +101,19 @@ impl Socket {
             return Ok(None);
         }
 
-        if meta.len == buf.len() {
-            eprintln!("Might have received more than {} bytes", buf.len());
+        if meta.len == self.recv_buf.len() {
+            eprintln!(
+                "Might have received more than {} bytes",
+                self.recv_buf.len()
+            );
         }
 
         Ok(Some(Datagram::new(
             meta.addr,
             *local_address,
             meta.ecn.map(|n| IpTos::from(n as u8)).unwrap_or_default(),
             None, // TODO: get the real TTL https://github.com/quinn-rs/quinn/issues/1749
-            &buf[..meta.len],
+            &self.recv_buf[..meta.len],
         )))
     }
 }
@@ -124,7 +127,7 @@ mod tests {
     async fn datagram_tos() -> Result<(), io::Error> {
         let sender = Socket::bind("127.0.0.1:0")?;
         let receiver_addr: SocketAddr = "127.0.0.1:0".parse().unwrap();
-        let receiver = Socket::bind(receiver_addr)?;
+        let mut receiver = Socket::bind(receiver_addr)?;
 
         let datagram = Datagram::new(
             sender.local_addr()?,