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Pre-allocate the full Vec prior to serializing as a Vec<u8>

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We end up generating a substantial amount of allocations just
doubling `Vec`s when serializing to them, and our
`serialized_length` method is generally rather effecient, so we
just rely on it and allocate correctly up front.
This commit is contained in:
Matt Corallo 2023-11-04 21:01:18 +00:00
parent e09afafc43
commit e4c6b70e8e
1 changed files with 8 additions and 1 deletions
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9
lightning/src/util/ser.rs
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@ -199,8 +199,14 @@ pub trait Writeable {
/// Writes `self` out to a `Vec<u8>`.
fn encode(&self) -> Vec<u8> {
let mut msg = VecWriter(Vec::new());
let len = self.serialized_length();
let mut msg = VecWriter(Vec::with_capacity(len));
self.write(&mut msg).unwrap();
// Note that objects with interior mutability may change size between when we called
// serialized_length and when we called write. That's okay, but shouldn't happen during
// testing as most of our tests are not threaded.
#[cfg(test)]
debug_assert_eq!(len, msg.0.len());
msg.0
}
@ -211,6 +217,7 @@ pub trait Writeable {
0u16.write(&mut msg).unwrap();
self.write(&mut msg).unwrap();
let len = msg.0.len();
debug_assert_eq!(len - 2, self.serialized_length());
msg.0[..2].copy_from_slice(&(len as u16 - 2).to_be_bytes());
msg.0
}