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feat: Increase default UDP send buffer size to 1MB #3495

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feat: Increase default UDP send buffer size to 1MB #3495

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27 changes: 13 additions & 14 deletions neqo-bin/src/udp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,20 +30,19 @@
let socket = std::net::UdpSocket::bind(addr)?;
let state = quinn_udp::UdpSocketState::new((&socket).into())?;

// FIXME: We need to experiment if increasing this actually improves performance.
// Also, on BSD and Apple targets, this seems to increase the `net.inet.udp.maxdgram`
// sysctl, which is not the same as the socket buffer.
// if send_buf_before < ONE_MB {
// state.set_send_buffer_size((&socket).into(), ONE_MB)?;
// let send_buf_after = state.send_buffer_size((&socket).into())?;
// qdebug!("Increasing socket send buffer size from {send_buf_before} to {ONE_MB}, now:
// {send_buf_after}"); } else {
// qdebug!("Default socket send buffer size is {send_buf_before}, not changing");
// }
qdebug!(
"Default socket send buffer size is {:?}",
state.send_buffer_size((&socket).into())
);
let send_buf_before = state.send_buffer_size((&socket).into())?;
if send_buf_before < ONE_MB {

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// Same as Firefox.
// The initial default equals `net.inet.udp.maxdgram` (9216 on macOS) but setting
// `SO_SNDBUF` does not modify that sysctl; it only changes the per-socket buffer.
state.set_send_buffer_size((&socket).into(), ONE_MB)?;
qdebug!(
"Increasing socket send buffer size from {send_buf_before} to {ONE_MB}, now: {:?}",
state.send_buffer_size((&socket).into())
);
Comment on lines +39 to +42

Copilot AI Mar 20, 2026

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state.send_buffer_size((&socket).into()) returns a Result, but here it's logged with {:?} without ?, so the message will print Ok(..)/Err(..) and any error is silently ignored. Consider capturing send_buf_after using ? (or handling/logging the error explicitly) and logging the actual size to keep the log message accurate and error handling consistent with the earlier send_buf_before query.

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} else {
qdebug!("Default socket send buffer size is {send_buf_before}, not changing");
}

let recv_buf_before = state.recv_buffer_size((&socket).into())?;
if recv_buf_before < ONE_MB {
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