added AsyncWrite and AsyncRead impls to WriteHalf and ReadHalf respectively

Cargo.toml

@@ -10,3 +10,5 @@ edition = "2018"
 tokio = {version = "0.2", features=["full"]}
 chacha20stream = {version = "1.0", features=["async"]}
 openssl = "0.10.33"
+stackalloc = "1.1.0"
+pin-project = "1.0.6"

src/ext.rs

@@ -1,4 +1,5 @@
 //! Extensions and macros
+use std::cell::RefCell;
 
 #[macro_export] macro_rules! basic_enum {
     ($(#[$meta:meta])* $vis:vis $name:ident $(; $tcomment:literal)?: $($var:ident $(=> $comment:literal)?),+ $(,)?) => {
@@ -124,3 +125,29 @@
 		  $crate::bool_type!($vis $name $(; $comment)? => Yes, No);
     }
 }
+
+/// Max size of bytes we'll allocate to the stack at runtime before using a heap allocated buffer.
+pub const STACK_SIZE_LIMIT: usize = 4096;
+
+/// Allocate `size` bytes. Allocates on the stack if size is lower than `STACK_SIZE_LIMIT`, otherwise allocates on the heap.
+pub fn alloca_limit<F, T>(size: usize, f: F) -> T
+where F: FnOnce(&mut [u8]) -> T
+{
+    if size > STACK_SIZE_LIMIT {
+	thread_local! {
+	    static BUFFER: RefCell<Vec<u8>> = RefCell::new(vec![0u8; STACK_SIZE_LIMIT*2]);
+	}
+	BUFFER.with(move |buf| {
+	    let mut buf = buf.borrow_mut();
+	    if buf.len() < size {
+		buf.resize(size, 0);
+	    }
+	    f(&mut buf[..size])
+	})
+    } else {
+	stackalloc::alloca_zeroed(size, f)
+	//
+	// TODO: Is this okay to do? I'm not sure it is.. We'll see
+	//stackalloc::alloca(size, move |buf| f(unsafe { stackalloc::helpers::slice_assume_init_mut(buf) }))
+    }
+}

src/lib.rs

@@ -1,6 +1,8 @@
 
 #![allow(dead_code)]
 
+#[macro_use] extern crate pin_project;
+
 // Extensions & macros
 #[macro_use] mod ext;
 #[allow(unused_imports)] use ext::*;

src/stream.rs

@@ -4,6 +4,12 @@ use tokio::io::{AsyncWrite, AsyncRead};
 use std::sync::Arc;
 use openssl::symm::Crypter;
 
+use std::{
+    pin::Pin,
+    task::{Poll, Context},
+    io,
+};
+
 use crypt::{
     RsaPublicKey,
     RsaPrivateKey,
@@ -30,6 +36,7 @@ where S: AsyncWrite
 }
 
 /// Readable half of `EncryptedStream`.
+#[pin_project]
 pub struct ReadHalf<S>
 where S: AsyncRead
 {
@@ -38,7 +45,7 @@ where S: AsyncRead
     /// chacha20_poly1305 decrypter for incoming reads from `S`
     //TODO: chacha20stream: implement a read version of AsyncSink so we don't need to keep this?
     cipher: Option<Crypter>,
-    backing_read: Box<S>,
+    #[pin] backing_read: Box<S>,
 }
 
 struct ReadWriteCombined<R, W>
@@ -62,6 +69,8 @@ where R: AsyncRead,
 }
 
 //TODO: How do we use this with a single AsyncStream instead of requiring 2? Will we need to make our own Arc wrapper?? Ugh,, for now let's ignore this I guess... Most read+write thingies have a Read/WriteHalf split mechanism.
+//
+// Note that this does actually work fine with things like tokio's `duplex()` (i think)
 impl<R: AsyncRead, W: AsyncWrite> EncryptedStream<R, W>
 {
     /// Has this stream done its RSA key exchange?
@@ -103,3 +112,44 @@ impl<R: AsyncRead, W: AsyncWrite> EncryptedStream<R, W>
 	todo!("Drop write's `meta`, consume read's `meta`. Move the streams into `ReadWriteCombined`")
     }
 }
+
+impl<S: AsyncWrite> AsyncWrite for WriteHalf<S>
+{
+    #[inline] fn poll_write(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8]) -> Poll<Result<usize, io::Error>> {
+	unsafe {self.map_unchecked_mut(|this| this.backing_write.as_mut())}.poll_write(cx, buf)
+    }
+    #[inline] fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+	unsafe {self.map_unchecked_mut(|this| this.backing_write.as_mut())}.poll_flush(cx)
+    }
+    #[inline] fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+	unsafe {self.map_unchecked_mut(|this| this.backing_write.as_mut())}.poll_shutdown(cx)
+    }
+}
+
+impl<S: AsyncRead> AsyncRead for ReadHalf<S>
+{
+    fn poll_read(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<io::Result<usize>> {
+	let this = self.project();
+	let cipher = this.cipher.as_mut();
+	let stream = unsafe {this.backing_read.map_unchecked_mut(|f| f.as_mut())};
+	
+	let res = stream.poll_read(cx,buf);
+	if let Some(cipher) = cipher {
+	    // Decrypt the buffer if the read succeeded
+	    res.map(move |res| res.and_then(move |sz| {
+		alloca_limit(sz, move |obuf| -> io::Result<usize> {
+		    // This `sz` and old `sz` should always be the same.
+		    let sz = cipher.update(&buf[..sz], &mut obuf[..])?;
+		    let _f = cipher.finalize(&mut obuf[..sz])?;
+		    debug_assert_eq!(_f, 0);
+
+		    // Copy decrypted buffer into output buffer
+		    buf.copy_from_slice(&obuf[..sz]);
+		    Ok(sz)
+		})
+	    }))
+	} else {
+	    res
+	}
+    }
+}