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Calculate Trampoline onion packet sizes dynamically. #3333

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Jan 28, 2025
Merged

Calculate Trampoline onion packet sizes dynamically. #3333

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24 changes: 21 additions & 3 deletions lightning/src/ln/onion_utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -427,12 +427,30 @@ pub(super) fn construct_onion_packet(
#[allow(unused)]
pub(super) fn construct_trampoline_onion_packet(
payloads: Vec<msgs::OutboundTrampolinePayload>, onion_keys: Vec<OnionKeys>,
prng_seed: [u8; 32], associated_data: &PaymentHash, length: u16,
prng_seed: [u8; 32], associated_data: &PaymentHash, length: Option<u16>,
) -> Result<msgs::TrampolineOnionPacket, ()> {
let mut packet_data = vec![0u8; length as usize];
let minimum_packet_length = payloads.iter().map(|p| p.serialized_length() + 32).sum();

debug_assert!(
minimum_packet_length < ONION_DATA_LEN,
"Trampoline onion packet must be smaller than outer onion"
);
if minimum_packet_length >= ONION_DATA_LEN {
return Err(());
}

let packet_length = length.map(|l| usize::from(l)).unwrap_or(minimum_packet_length);
debug_assert!(
packet_length >= minimum_packet_length,
"Packet length cannot be smaller than the payloads require."
);
if packet_length < minimum_packet_length {
return Err(());
}

let mut packet_data = vec![0u8; packet_length];
let mut chacha = ChaCha20::new(&prng_seed, &[0; 8]);
chacha.process(&vec![0u8; length as usize], &mut packet_data);
chacha.process_in_place(&mut packet_data);

construct_onion_packet_with_init_noise::<_, _>(
payloads,
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