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Remove unsafe from proto::h2 #2831

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Remove unsafe from proto::h2 #2831

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2 changes: 1 addition & 1 deletion src/proto/h2/client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -341,7 +341,7 @@ where
let (pending, on_upgrade) = crate::upgrade::pending();
let io = H2Upgraded {
ping,
send_stream: unsafe { UpgradedSendStream::new(send_stream) },
send_stream: UpgradedSendStream::new(send_stream),
recv_stream,
buf: Bytes::new(),
};
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50 changes: 9 additions & 41 deletions src/proto/h2/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@ use http::HeaderMap;
use pin_project_lite::pin_project;
use std::error::Error as StdError;
use std::io::{self, Cursor, IoSlice};
use std::mem;
use std::task::Context;
use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
use tracing::{debug, trace, warn};
Expand Down Expand Up @@ -409,63 +408,32 @@ fn h2_to_io_error(e: h2::Error) -> io::Error {
}
}

struct UpgradedSendStream<B>(SendStream<SendBuf<Neutered<B>>>);
struct UpgradedSendStream<B: Buf>(SendStream<SendBuf<B>>);

impl<B> UpgradedSendStream<B>
where
B: Buf,
{
unsafe fn new(inner: SendStream<SendBuf<B>>) -> Self {
assert_eq!(mem::size_of::<B>(), mem::size_of::<Neutered<B>>());
Self(mem::transmute(inner))
fn new(inner: SendStream<SendBuf<B>>) -> Self {
Self(inner)
}

fn reserve_capacity(&mut self, cnt: usize) {
unsafe { self.as_inner_unchecked().reserve_capacity(cnt) }
self.0.reserve_capacity(cnt)
}

fn poll_capacity(&mut self, cx: &mut Context<'_>) -> Poll<Option<Result<usize, h2::Error>>> {
unsafe { self.as_inner_unchecked().poll_capacity(cx) }
self.0.poll_capacity(cx)
}

fn poll_reset(&mut self, cx: &mut Context<'_>) -> Poll<Result<h2::Reason, h2::Error>> {
unsafe { self.as_inner_unchecked().poll_reset(cx) }
self.0.poll_reset(cx)
}

fn write(&mut self, buf: &[u8], end_of_stream: bool) -> Result<(), io::Error> {
let send_buf = SendBuf::Cursor(Cursor::new(buf.into()));
unsafe {
self.as_inner_unchecked()
.send_data(send_buf, end_of_stream)
.map_err(h2_to_io_error)
}
}

unsafe fn as_inner_unchecked(&mut self) -> &mut SendStream<SendBuf<B>> {
&mut *(&mut self.0 as *mut _ as *mut _)
}
}

#[repr(transparent)]
struct Neutered<B> {
_inner: B,
impossible: Impossible,
}
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FWIW, there have even been proposals that would make Neutered<B> have size 0, since it cannot ever be inhabited anyway. So this is definitely an incorrect pattern.

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@djkoloski djkoloski May 10, 2022 •
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That is checked in UpgradedSendStream's new, so I think that should be okay. It's not ideal but it shouldn't produce any UB.

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@RalfJung RalfJung May 11, 2022 •
edited
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Ah, you are guarding against the layout optimization there, okay.

Creating an instance of Neutered<T> is still most definitely UB though. In fact if there is any uncontroversial UB in Rust, unreachable_unchecked would be first on that list, and creating an instance of an uninhabited type is second. The reference is also clear about this and never was there any controversy in the UCG that this code should be UB.

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There is never a Neutered<T> being created anywhere, that's the thing.

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Ah, I see, that makes sense then that Miri didn't complain about hyper. :)


enum Impossible {}

unsafe impl<B> Send for Neutered<B> {}

impl<B> Buf for Neutered<B> {
fn remaining(&self) -> usize {
match self.impossible {}
}

fn chunk(&self) -> &[u8] {
match self.impossible {}
}

fn advance(&mut self, _cnt: usize) {
match self.impossible {}
self.0
.send_data(send_buf, end_of_stream)
.map_err(h2_to_io_error)
}
}
6 changes: 3 additions & 3 deletions src/proto/h2/server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -433,7 +433,7 @@ impl<F, B, E> H2Stream<F, B>
where
F: Future<Output = Result<Response<B>, E>>,
B: HttpBody,
B::Data: 'static,
B::Data: Send + 'static,
B::Error: Into<Box<dyn StdError + Send + Sync>>,
E: Into<Box<dyn StdError + Send + Sync>>,
{
Expand Down Expand Up @@ -489,7 +489,7 @@ where
H2Upgraded {
ping: connect_parts.ping,
recv_stream: connect_parts.recv_stream,
send_stream: unsafe { UpgradedSendStream::new(send_stream) },
send_stream: UpgradedSendStream::new(send_stream),
buf: Bytes::new(),
},
Bytes::new(),
Expand Down Expand Up @@ -527,7 +527,7 @@ impl<F, B, E> Future for H2Stream<F, B>
where
F: Future<Output = Result<Response<B>, E>>,
B: HttpBody,
B::Data: 'static,
B::Data: Send + 'static,
B::Error: Into<Box<dyn StdError + Send + Sync>>,
E: Into<Box<dyn StdError + Send + Sync>>,
{
Expand Down