diff --git a/crates/hyperion/src/lib.rs b/crates/hyperion/src/lib.rs index 6cfd975d..bef510b8 100644 --- a/crates/hyperion/src/lib.rs +++ b/crates/hyperion/src/lib.rs @@ -383,26 +383,21 @@ impl HyperionCore { /// A scratch buffer for intermediate operations. This will return an empty [`Vec`] when calling [`Scratch::obtain`]. #[derive(Debug)] pub struct Scratch { - inner: Vec, + inner: Box<[u8], A>, } impl Default for Scratch { fn default() -> Self { - let inner = Vec::with_capacity(MAX_PACKET_SIZE); - Self { inner } + std::alloc::Global.into() } } /// Nice for getting a buffer that can be used for intermediate work -/// -/// # Safety -/// - every single time [`ScratchBuffer::obtain`] is called, the buffer will be cleared before returning -/// - the buffer has capacity of at least `MAX_PACKET_SIZE` -pub unsafe trait ScratchBuffer: sealed::Sealed + Debug { +pub trait ScratchBuffer: sealed::Sealed + Debug { /// The type of the allocator the [`Vec`] uses. type Allocator: Allocator; - /// Obtains a buffer that can be used for intermediate work. - fn obtain(&mut self) -> &mut Vec; + /// Obtains a buffer that can be used for intermediate work. The contents are unspecified. + fn obtain(&mut self) -> &mut [u8]; } mod sealed { @@ -411,20 +406,23 @@ mod sealed { impl sealed::Sealed for Scratch {} -unsafe impl ScratchBuffer for Scratch { +impl ScratchBuffer for Scratch { type Allocator = A; - fn obtain(&mut self) -> &mut Vec { - self.inner.clear(); + fn obtain(&mut self) -> &mut [u8] { &mut self.inner } } impl From for Scratch { fn from(allocator: A) -> Self { - Self { - inner: Vec::with_capacity_in(MAX_PACKET_SIZE, allocator), - } + // A zeroed slice is allocated to avoid reading from uninitialized memory, which is UB. + // Allocating zeroed memory is usually very cheap, so there are minimal performance + // penalties from this. + let inner = Box::new_zeroed_slice_in(MAX_PACKET_SIZE, allocator); + // SAFETY: The box was initialized to zero, and u8 can be represented by zero + let inner = unsafe { inner.assume_init() }; + Self { inner } } } diff --git a/crates/hyperion/src/net/encoder/mod.rs b/crates/hyperion/src/net/encoder/mod.rs index 2f1900e5..e30a195c 100644 --- a/crates/hyperion/src/net/encoder/mod.rs +++ b/crates/hyperion/src/net/encoder/mod.rs @@ -9,7 +9,6 @@ use std::{ fmt::Debug, io::{Cursor, Write}, - mem::MaybeUninit, }; use anyhow::ensure; @@ -129,37 +128,27 @@ impl PacketEncoder { if data_len > threshold { let scratch = scratch.obtain(); - debug_assert!(scratch.is_empty()); - let data_slice = &mut slice [usize::try_from(data_write_start)?..usize::try_from(end_data_position_exclusive)?]; - { - // todo: I think this kinda safe maybe??? ... lol. well I know at least scratch is always large enough - let written = { - let scratch = scratch.spare_capacity_mut(); - let scratch = unsafe { MaybeUninit::slice_assume_init_mut(scratch) }; - - let len = data_slice.len(); - let span = tracing::trace_span!("zlib_compress", bytes = len); - let _enter = span.enter(); - compressor.zlib_compress(data_slice, scratch)? - }; + let written = { + let len = data_slice.len(); + let span = tracing::trace_span!("zlib_compress", bytes = len); + let _enter = span.enter(); + compressor.zlib_compress(data_slice, scratch).unwrap() + }; - unsafe { - scratch.set_len(scratch.len() + written); - } - } + let compressed = &scratch[..written]; let data_len = VarInt(data_len as u32 as i32); - let packet_len = data_len.written_size() + scratch.len(); + let packet_len = data_len.written_size() + compressed.len(); let packet_len = VarInt(packet_len as u32 as i32); let mut write = Cursor::new(&mut slice[..]); packet_len.encode(&mut write)?; data_len.encode(&mut write)?; - write.write_all(scratch)?; + write.write_all(compressed)?; let len = write.position();