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feat: add mtu option for dynamic calculation of mss #70

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Orvaxis wants to merge 4 commits into from
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feat: add mtu option for dynamic calculation of mss #70

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78ffed7
feat: add mtu option for dynamic calculation of mss
Orvaxis Oct 9, 2025
146bee5
refactor: remove redundant IpMtu option, use TCB MTU value instead.
Orvaxis Oct 9, 2025
651101d
fix: calculate mss only during handshake
Orvaxis Oct 9, 2025
a29c1f1
chore: clean code
Orvaxis Oct 9, 2025
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24 changes: 18 additions & 6 deletions src/stream/tcp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ use crate::{
},
stream::tcb::{PacketType, Tcb, TcpState},
};
use etherparse::{IpNumber, Ipv4Header, Ipv6FlowLabel, TcpHeader, TcpOptionElement};
use etherparse::{IpNumber, Ipv4Header, Ipv6FlowLabel, TcpHeader};
use std::{
future::Future,
io::ErrorKind::{BrokenPipe, ConnectionRefused, InvalidInput, UnexpectedEof},
Expand All @@ -28,6 +28,7 @@ const CLOSE_WAIT_TIMEOUT: Duration = Duration::from_secs(5);
const LAST_ACK_MAX_RETRIES: usize = 3;
const LAST_ACK_TIMEOUT: Duration = Duration::from_millis(500);
const TIMEOUT: Duration = Duration::from_secs(60);
const TCP_HEADER_LEN: u16 = 20;

#[non_exhaustive]
#[derive(Debug, Clone)]
Expand Down Expand Up @@ -451,7 +452,16 @@ async fn tcp_main_logic_loop(
&up_packet_sender,
network_tuple,
&tcb,
config.options.as_ref(),
config.options.as_ref().map(|o| {
(
o,
if network_tuple.src.is_ipv4() && network_tuple.dst.is_ipv4() {
tcb.get_mtu() - 20 - TCP_HEADER_LEN
} else {
tcb.get_mtu() - 40 - TCP_HEADER_LEN
},
)
}),
ACK | SYN,
None,
None,
Expand Down Expand Up @@ -861,7 +871,7 @@ pub(crate) fn write_packet_to_device(
up_packet_sender: &PacketSender,
tuple: NetworkTuple,
tcb: &Tcb,
options: Option<&Vec<TcpOptions>>,
options: Option<(&Vec<TcpOptions>, u16)>,
flags: u8,
seq: Option<SeqNum>,
payload: Option<Vec<u8>>,
Expand Down Expand Up @@ -899,7 +909,7 @@ pub(crate) fn create_raw_packet(
ack: u32,
win: u16,
mut payload: Vec<u8>,
options: Option<&Vec<TcpOptions>>,
options: Option<(&Vec<TcpOptions>, u16)>,
) -> std::io::Result<NetworkPacket> {
let mut tcp_header = etherparse::TcpHeader::new(src_addr.port(), dst_addr.port(), seq, win);
tcp_header.acknowledgment_number = ack;
Expand All @@ -909,17 +919,19 @@ pub(crate) fn create_raw_packet(
tcp_header.fin = flags & FIN != 0;
tcp_header.psh = flags & PSH != 0;

if let Some(opts) = options {
if let Some((opts, mut mss)) = options {
let mut tcp_options = Vec::new();
for opt in opts {
match opt {
TcpOptions::MaximumSegmentSize(mss) => tcp_options.push(TcpOptionElement::MaximumSegmentSize(*mss)),
TcpOptions::MaximumSegmentSize(fixed_mss) => mss = *fixed_mss,
}
}
tcp_options.push(etherparse::TcpOptionElement::MaximumSegmentSize(mss));
tcp_header
.set_options(&tcp_options)
.map_err(|e| std::io::Error::new(InvalidInput, e))?;
}

let ip_header = match (src_addr.ip(), dst_addr.ip()) {
(std::net::IpAddr::V4(src), std::net::IpAddr::V4(dst)) => {
let mut ip_h =
Expand Down