Allow configuration of max transmission unit

src/config.rs

@@ -17,6 +17,7 @@ pub struct Config {
     pub(crate) endpoint_addr: SocketAddr,
     pub(crate) source_peer_ip: IpAddr,
     pub(crate) keepalive_seconds: Option<u16>,
+    pub(crate) max_transmission_unit: usize,
     pub(crate) log: String,
     pub(crate) warnings: Vec<String>,
 }
@@ -82,6 +83,13 @@ impl Config {
                     .long("keep-alive")
                     .env("ONETUN_KEEP_ALIVE")
                     .help("Configures a persistent keep-alive for the WireGuard tunnel, in seconds."),
+                Arg::with_name("max-transmission-unit")
+                    .required(false)
+                    .takes_value(true)
+                    .long("max-transmission-unit")
+                    .env("ONETUN_MTU")
+                    .default_value("1420")
+                    .help("Configures the max-transmission-unit (MTU) of the WireGuard tunnel."),
                 Arg::with_name("log")
                     .required(false)
                     .takes_value(true)
@@ -163,6 +171,8 @@ impl Config {
                 .with_context(|| "Invalid source peer IP")?,
             keepalive_seconds: parse_keep_alive(matches.value_of("keep-alive"))
                 .with_context(|| "Invalid keep-alive value")?,
+            max_transmission_unit: parse_mtu(matches.value_of("max-transmission-unit"))
+                .with_context(|| "Invalid max-transmission-unit value")?,
             log: matches.value_of("log").unwrap_or_default().into(),
             warnings,
         })
@@ -209,6 +219,12 @@ fn parse_keep_alive(s: Option<&str>) -> anyhow::Result<Option<u16>> {
     }
 }
 
+fn parse_mtu(s: Option<&str>) -> anyhow::Result<usize> {
+    s.with_context(|| "Missing MTU")?
+        .parse()
+        .with_context(|| "Invalid MTU")
+}
+
 #[cfg(unix)]
 fn is_file_insecurely_readable(path: &str) -> Option<(bool, bool)> {
     use std::fs::File;

src/virtual_device.rs

@@ -5,9 +5,6 @@ use smoltcp::phy::{Device, DeviceCapabilities, Medium};
 use smoltcp::time::Instant;
 use std::sync::Arc;
 
-/// The max transmission unit for WireGuard.
-const WG_MTU: usize = 1420;
-
 /// A virtual device that processes IP packets. IP packets received from the WireGuard endpoint
 /// are made available to this device using a channel receiver. IP packets sent from this device
 /// are asynchronously sent out to the WireGuard tunnel.
@@ -71,7 +68,7 @@ impl<'a> Device<'a> for VirtualIpDevice {
     fn capabilities(&self) -> DeviceCapabilities {
         let mut cap = DeviceCapabilities::default();
         cap.medium = Medium::Ip;
-        cap.max_transmission_unit = WG_MTU;
+        cap.max_transmission_unit = self.wg.max_transmission_unit;
         cap
     }
 }

src/wg.rs

@@ -30,6 +30,8 @@ pub struct WireGuardTunnel {
     virtual_port_ip_tx: dashmap::DashMap<VirtualPort, tokio::sync::mpsc::Sender<Vec<u8>>>,
     /// IP packet dispatcher for unroutable packets. `None` if not initialized.
     sink_ip_tx: RwLock<Option<tokio::sync::mpsc::Sender<Vec<u8>>>>,
+    /// The max transmission unit for WireGuard.
+    pub(crate) max_transmission_unit: usize,
 }
 
 impl WireGuardTunnel {
@@ -50,6 +52,7 @@ impl WireGuardTunnel {
             endpoint,
             virtual_port_ip_tx,
             sink_ip_tx: RwLock::new(None),
+            max_transmission_unit: config.max_transmission_unit,
         })
     }