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//! Uniform interface to send and receive UDP packets with advanced features useful for QUIC
//!
//! This crate exposes kernel UDP stack features available on most modern systems which are required
//! for an efficient and conformant QUIC implementation. As of this writing, these are not available
//! in std or major async runtimes, and their niche character and complexity are a barrier to adding
//! them. Hence, a dedicated crate.
//!
//! Exposed features include:
//!
//! - Segmentation offload for bulk send and receive operations, reducing CPU load.
//! - Reporting the exact destination address of received packets and specifying explicit source
//! addresses for sent packets, allowing responses to be sent from the address that the peer
//! expects when there are multiple possibilities. This is common when bound to a wildcard address
//! in IPv6 due to [RFC 8981] temporary addresses.
//! - [Explicit Congestion Notification], which is required by QUIC to prevent packet loss and reduce
//! latency on congested links when supported by the network path.
//! - Disabled IP-layer fragmentation, which allows the true physical MTU to be detected and reduces
//! risk of QUIC packet loss.
//!
//! Some features are unavailable in some environments. This can be due to an outdated operating
//! system or drivers. Some operating systems may not implement desired features at all, or may not
//! yet be supported by the crate. When support is unavailable, functionality will gracefully
//! degrade.
//!
#![warn(unreachable_pub)]
#![warn(clippy::use_self)]
#[cfg(unix)]
use std::os::unix::io::AsFd;
#[cfg(windows)]
use std::os::windows::io::AsSocket;
use std::{
net::{IpAddr, Ipv6Addr, SocketAddr},
sync::Mutex,
time::{Duration, Instant},
};
#[cfg(all(feature = "direct-log", not(feature = "tracing")))]
use log::warn;
#[cfg(feature = "tracing")]
use tracing::warn;
#[cfg(any(unix, windows))]
mod cmsg;
#[cfg(unix)]
#[path = "unix.rs"]
mod imp;
#[cfg(windows)]
#[path = "windows.rs"]
mod imp;
// No ECN support
#[cfg(not(any(unix, windows)))]
#[path = "fallback.rs"]
mod imp;
pub use imp::UdpSocketState;
/// Number of UDP packets to send/receive at a time
pub const BATCH_SIZE: usize = imp::BATCH_SIZE;
/// Metadata for a single buffer filled with bytes received from the network
///
/// This associated buffer can contain one or more datagrams, see [`stride`].
///
/// [`stride`]: RecvMeta::stride
#[derive(Debug, Copy, Clone)]
pub struct RecvMeta {
/// The source address of the datagram(s) contained in the buffer
pub addr: SocketAddr,
/// The number of bytes the associated buffer has
pub len: usize,
/// The size of a single datagram in the associated buffer
///
/// When GRO (Generic Receive Offload) is used this indicates the size of a single
/// datagram inside the buffer. If the buffer is larger, that is if [`len`] is greater
/// then this value, then the individual datagrams contained have their boundaries at
/// `stride` increments from the start. The last datagram could be smaller than
/// `stride`.
///
/// [`len`]: RecvMeta::len
pub stride: usize,
/// The Explicit Congestion Notification bits for the datagram(s) in the buffer
pub ecn: Option<EcnCodepoint>,
/// The destination IP address which was encoded in this datagram
///
/// Populated on platforms: Windows, Linux, Android, FreeBSD, OpenBSD, NetBSD, macOS,
/// and iOS.
pub dst_ip: Option<IpAddr>,
}
impl Default for RecvMeta {
/// Constructs a value with arbitrary fields, intended to be overwritten
fn default() -> Self {
Self {
addr: SocketAddr::new(Ipv6Addr::UNSPECIFIED.into(), 0),
len: 0,
stride: 0,
ecn: None,
dst_ip: None,
}
}
}
/// An outgoing packet
#[derive(Debug, Clone)]
pub struct Transmit<'a> {
/// The socket this datagram should be sent to
pub destination: SocketAddr,
/// Explicit congestion notification bits to set on the packet
pub ecn: Option<EcnCodepoint>,
/// Contents of the datagram
pub contents: &'a [u8],
/// The segment size if this transmission contains multiple datagrams.
/// This is `None` if the transmit only contains a single datagram
pub segment_size: Option<usize>,
/// Optional source IP address for the datagram
pub src_ip: Option<IpAddr>,
}
/// Log at most 1 IO error per minute
const IO_ERROR_LOG_INTERVAL: Duration = std::time::Duration::from_secs(60);
/// Logs a warning message when sendmsg fails
///
/// Logging will only be performed if at least [`IO_ERROR_LOG_INTERVAL`]
/// has elapsed since the last error was logged.
#[cfg(any(feature = "tracing", feature = "direct-log"))]
fn log_sendmsg_error(
last_send_error: &Mutex<Instant>,
err: impl core::fmt::Debug,
transmit: &Transmit,
) {
let now = Instant::now();
let last_send_error = &mut *last_send_error.lock().expect("poisend lock");
if now.saturating_duration_since(*last_send_error) > IO_ERROR_LOG_INTERVAL {
*last_send_error = now;
warn!(
"sendmsg error: {:?}, Transmit: {{ destination: {:?}, src_ip: {:?}, enc: {:?}, len: {:?}, segment_size: {:?} }}",
err, transmit.destination, transmit.src_ip, transmit.ecn, transmit.contents.len(), transmit.segment_size);
}
}
// No-op
#[cfg(not(any(feature = "tracing", feature = "direct-log")))]
fn log_sendmsg_error(_: &Mutex<Instant>, _: impl core::fmt::Debug, _: &Transmit) {}
/// A borrowed UDP socket
///
/// On Unix, constructible via `From<T: AsFd>`. On Windows, constructible via `From<T:
/// AsSocket>`.
// Wrapper around socket2 to avoid making it a public dependency and incurring stability risk
pub struct UdpSockRef<'a>(socket2::SockRef<'a>);
#[cfg(unix)]
impl<'s, S> From<&'s S> for UdpSockRef<'s>
where
S: AsFd,
{
fn from(socket: &'s S) -> Self {
Self(socket.into())
}
}
#[cfg(windows)]
impl<'s, S> From<&'s S> for UdpSockRef<'s>
where
S: AsSocket,
{
fn from(socket: &'s S) -> Self {
Self(socket.into())
}
}
/// Explicit congestion notification codepoint
#[repr(u8)]
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum EcnCodepoint {
#[doc(hidden)]
Ect0 = 0b10,
#[doc(hidden)]
Ect1 = 0b01,
#[doc(hidden)]
Ce = 0b11,
}
impl EcnCodepoint {
/// Create new object from the given bits
pub fn from_bits(x: u8) -> Option<Self> {
use self::EcnCodepoint::*;
Some(match x & 0b11 {
0b10 => Ect0,
0b01 => Ect1,
0b11 => Ce,
_ => {
return None;
}
})
}
}