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use std::io::{Read, Write};
use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
/// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
#[derive(Debug)]
pub struct SyncIoBridge<T> {
src: T,
rt: tokio::runtime::Handle,
}
impl<T: AsyncRead + Unpin> Read for SyncIoBridge<T> {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let src = &mut self.src;
self.rt.block_on(AsyncReadExt::read(src, buf))
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> std::io::Result<usize> {
let src = &mut self.src;
self.rt.block_on(src.read_to_end(buf))
}
fn read_to_string(&mut self, buf: &mut String) -> std::io::Result<usize> {
let src = &mut self.src;
self.rt.block_on(src.read_to_string(buf))
}
fn read_exact(&mut self, buf: &mut [u8]) -> std::io::Result<()> {
let src = &mut self.src;
// The AsyncRead trait returns the count, synchronous doesn't.
let _n = self.rt.block_on(src.read_exact(buf))?;
Ok(())
}
}
impl<T: AsyncWrite + Unpin> Write for SyncIoBridge<T> {
fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
let src = &mut self.src;
self.rt.block_on(src.write(buf))
}
fn flush(&mut self) -> std::io::Result<()> {
let src = &mut self.src;
self.rt.block_on(src.flush())
}
fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()> {
let src = &mut self.src;
self.rt.block_on(src.write_all(buf))
}
fn write_vectored(&mut self, bufs: &[std::io::IoSlice<'_>]) -> std::io::Result<usize> {
let src = &mut self.src;
self.rt.block_on(src.write_vectored(bufs))
}
}
// Because https://doc.rust-lang.org/std/io/trait.Write.html#method.is_write_vectored is at the time
// of this writing still unstable, we expose this as part of a standalone method.
impl<T: AsyncWrite> SyncIoBridge<T> {
/// Determines if the underlying [`tokio::io::AsyncWrite`] target supports efficient vectored writes.
///
/// See [`tokio::io::AsyncWrite::is_write_vectored`].
pub fn is_write_vectored(&self) -> bool {
self.src.is_write_vectored()
}
}
impl<T: Unpin> SyncIoBridge<T> {
/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
/// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
///
/// When this struct is created, it captures a handle to the current thread's runtime with [`tokio::runtime::Handle::current`].
/// It is hence OK to move this struct into a separate thread outside the runtime, as created
/// by e.g. [`tokio::task::spawn_blocking`].
///
/// Stated even more strongly: to make use of this bridge, you *must* move
/// it into a separate thread outside the runtime. The synchronous I/O will use the
/// underlying handle to block on the backing asynchronous source, via
/// [`tokio::runtime::Handle::block_on`]. As noted in the documentation for that
/// function, an attempt to `block_on` from an asynchronous execution context
/// will panic.
///
/// # Wrapping `!Unpin` types
///
/// Use e.g. `SyncIoBridge::new(Box::pin(src))`.
///
/// # Panic
///
/// This will panic if called outside the context of a Tokio runtime.
pub fn new(src: T) -> Self {
Self::new_with_handle(src, tokio::runtime::Handle::current())
}
/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
/// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
///
/// This is the same as [`SyncIoBridge::new`], but allows passing an arbitrary handle and hence may
/// be initially invoked outside of an asynchronous context.
pub fn new_with_handle(src: T, rt: tokio::runtime::Handle) -> Self {
Self { src, rt }
}
}
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