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refactor(lib): resolve FIXME messages #3348

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merged 1 commit into from
Oct 20, 2023
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refactor(lib): resolve FIXME messages #3348

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2 changes: 0 additions & 2 deletions src/common/io/rewind.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,8 +107,6 @@ where

#[cfg(test)]
mod tests {
// FIXME: re-implement tests with `async/await`, this import should
// trigger a warning to remind us
use super::super::compat;
use super::Rewind;
use bytes::Bytes;
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37 changes: 10 additions & 27 deletions src/proto/h1/role.rs
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Expand Up @@ -135,18 +135,13 @@ impl Http1Transaction for Server {
let len;
let headers_len;

// Unsafe: both headers_indices and headers are using uninitialized memory,
// Both headers_indices and headers are using uninitialized memory,
// but we *never* read any of it until after httparse has assigned
// values into it. By not zeroing out the stack memory, this saves
// a good ~5% on pipeline benchmarks.
let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
// SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
MaybeUninit::uninit().assume_init()
};
let mut headers_indices = [MaybeUninit::<HeaderIndices>::uninit(); MAX_HEADERS];
{
/* SAFETY: it is safe to go from MaybeUninit array to array of MaybeUninit */
let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] =
unsafe { MaybeUninit::uninit().assume_init() };
let mut headers = [MaybeUninit::<httparse::Header<'_>>::uninit(); MAX_HEADERS];
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Does this result in the same generated code? Or at least same performance? I mean, logically it makes sense. But it doesn't initialize an array to then declare the stuff inside is uninitialized, right?

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The generated code in debug-mode is slightly different, but in release mode it's identical. Here is a link to the assembly: https://godbolt.org/z/6rvbz8qWd

trace!(bytes = buf.len(), "Request.parse");
let mut req = httparse::Request::new(&mut []);
let bytes = buf.as_ref();
Expand Down Expand Up @@ -230,7 +225,7 @@ impl Http1Transaction for Server {

for header in &headers_indices[..headers_len] {
// SAFETY: array is valid up to `headers_len`
let header = unsafe { &*header.as_ptr() };
let header = unsafe { header.assume_init_ref() };
let name = header_name!(&slice[header.name.0..header.name.1]);
let value = header_value!(slice.slice(header.value.0..header.value.1));

Expand Down Expand Up @@ -936,15 +931,9 @@ impl Http1Transaction for Client {

// Loop to skip information status code headers (100 Continue, etc).
loop {
// Unsafe: see comment in Server Http1Transaction, above.
let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
// SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
MaybeUninit::uninit().assume_init()
};
let mut headers_indices = [MaybeUninit::<HeaderIndices>::uninit(); MAX_HEADERS];
let (len, status, reason, version, headers_len) = {
// SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] =
unsafe { MaybeUninit::uninit().assume_init() };
let mut headers = [MaybeUninit::<httparse::Header<'_>>::uninit(); MAX_HEADERS];
trace!(bytes = buf.len(), "Response.parse");
let mut res = httparse::Response::new(&mut []);
let bytes = buf.as_ref();
Expand Down Expand Up @@ -994,7 +983,7 @@ impl Http1Transaction for Client {
{
for header in &mut headers_indices[..headers_len] {
// SAFETY: array is valid up to `headers_len`
let header = unsafe { &mut *header.as_mut_ptr() };
let header = unsafe { header.assume_init_mut() };
Client::obs_fold_line(&mut slice, header);
}
}
Expand All @@ -1021,7 +1010,7 @@ impl Http1Transaction for Client {
headers.reserve(headers_len);
for header in &headers_indices[..headers_len] {
// SAFETY: array is valid up to `headers_len`
let header = unsafe { &*header.as_ptr() };
let header = unsafe { header.assume_init_ref() };
let name = header_name!(&slice[header.name.0..header.name.1]);
let value = header_value!(slice.slice(header.value.0..header.value.1));

Expand Down Expand Up @@ -1455,16 +1444,10 @@ fn record_header_indices(
let value_start = header.value.as_ptr() as usize - bytes_ptr;
let value_end = value_start + header.value.len();

// FIXME(maybe_uninit_extra)
// FIXME(addr_of)
// Currently we don't have `ptr::addr_of_mut` in stable rust or
// MaybeUninit::write, so this is some way of assigning into a MaybeUninit
// safely
let new_header_indices = HeaderIndices {
indices.write(HeaderIndices {
name: (name_start, name_end),
value: (value_start, value_end),
};
*indices = MaybeUninit::new(new_header_indices);
});
}

Ok(())
Expand Down