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//! Asynchronous I/O
//!
//! This crate contains the `AsyncRead` and `AsyncWrite` traits, the
//! asynchronous analogs to `std::io::{Read, Write}`. The primary difference is
//! that these traits integrate with the asynchronous task system.
#![no_std]
#![deny(missing_docs, missing_debug_implementations)]
#![doc(html_rnoot_url = "https://docs.rs/futures-io/0.2.2")]
macro_rules! if_std {
($($i:item)*) => ($(
#[cfg(feature = "std")]
$i
)*)
}
if_std! {
extern crate futures_core;
extern crate iovec;
extern crate std;
use futures_core::{Async, Poll, task};
use std::boxed::Box;
use std::io as StdIo;
use std::ptr;
use std::vec::Vec;
// Re-export IoVec for convenience
pub use iovec::IoVec;
// Re-export io::Error so that users don't have to deal
// with conflicts when `use`ing `futures::io` and `std::io`.
pub use StdIo::Error as Error;
pub use StdIo::ErrorKind as ErrorKind;
pub use StdIo::Result as Result;
/// A type used to conditionally initialize buffers passed to `AsyncRead`
/// methods, modeled after `std`.
#[derive(Debug)]
pub struct Initializer(bool);
impl Initializer {
/// Returns a new `Initializer` which will zero out buffers.
#[inline]
pub fn zeroing() -> Initializer {
Initializer(true)
}
/// Returns a new `Initializer` which will not zero out buffers.
///
/// # Safety
///
/// This method may only be called by `AsyncRead`ers which guarantee
/// that they will not read from the buffers passed to `AsyncRead`
/// methods, and that the return value of the method accurately reflects
/// the number of bytes that have been written to the head of the buffer.
#[inline]
pub unsafe fn nop() -> Initializer {
Initializer(false)
}
/// Indicates if a buffer should be initialized.
#[inline]
pub fn should_initialize(&self) -> bool {
self.0
}
/// Initializes a buffer if necessary.
#[inline]
pub fn initialize(&self, buf: &mut [u8]) {
if self.should_initialize() {
unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
}
}
}
/// Read bytes asynchronously.
///
/// This trait is analogous to the `std::io::Read` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_read`
/// method, unlike `Read::read`, will automatically queue the current task
/// for wakeup and return if data is not yet available, rather than blocking
/// the calling thread.
pub trait AsyncRead {
/// Determines if this `AsyncRead`er can work with buffers of
/// uninitialized memory.
///
/// The default implementation returns an initializer which will zero
/// buffers.
///
/// # Safety
///
/// This method is `unsafe` because and `AsyncRead`er could otherwise
/// return a non-zeroing `Initializer` from another `AsyncRead` type
/// without an `unsafe` block.
#[inline]
unsafe fn initializer(&self) -> Initializer {
Initializer::zeroing()
}
/// Attempt to read from the `AsyncRead` into `buf`.
///
/// On success, returns `Ok(Async::Ready(num_bytes_read))`.
///
/// If no data is available for reading, the method returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_read(&mut self, cx: &mut task::Context, buf: &mut [u8])
-> Poll<usize, Error>;
/// Attempt to read from the `AsyncRead` into `vec` using vectored
/// IO operations.
///
/// This method is similar to `poll_read`, but allows data to be read
/// into multiple buffers using a single operation.
///
/// On success, returns `Ok(Async::Ready(num_bytes_read))`.
///
/// If no data is available for reading, the method returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object becomes
/// readable or is closed.
/// By default, this method delegates to using `poll_read` on the first
/// buffer in `vec`. Objects which support vectored IO should override
/// this method.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_vectored_read(&mut self, cx: &mut task::Context, vec: &mut [&mut IoVec])
-> Poll<usize, Error>
{
if let Some(ref mut first_iovec) = vec.get_mut(0) {
self.poll_read(cx, first_iovec)
} else {
// `vec` is empty.
return Ok(Async::Ready(0));
}
}
}
/// Write bytes asynchronously.
///
/// This trait is analogous to the `std::io::Write` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_write`
/// method, unlike `Write::write`, will automatically queue the current task
/// for wakeup and return if data is not yet available, rather than blocking
/// the calling thread.
pub trait AsyncWrite {
/// Attempt to write bytes from `buf` into the object.
///
/// On success, returns `Ok(Async::Ready(num_bytes_written))`.
///
/// If the object is not ready for writing, the method returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_write(&mut self, cx: &mut task::Context, buf: &[u8])
-> Poll<usize, Error>;
/// Attempt to write bytes from `vec` into the object using vectored
/// IO operations.
///
/// This method is similar to `poll_write`, but allows data from multiple buffers to be written
/// using a single operation.
///
/// On success, returns `Ok(Async::Ready(num_bytes_written))`.
///
/// If the object is not ready for writing, the method returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// By default, this method delegates to using `poll_write` on the first
/// buffer in `vec`. Objects which support vectored IO should override
/// this method.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_vectored_write(&mut self, cx: &mut task::Context, vec: &[&IoVec])
-> Poll<usize, Error>
{
if let Some(ref first_iovec) = vec.get(0) {
self.poll_write(cx, &*first_iovec)
} else {
// `vec` is empty.
return Ok(Async::Ready(0));
}
}
/// Attempt to flush the object, ensuring that any buffered data reach
/// their destination.
///
/// On success, returns `Ok(Async::Ready(()))`.
///
/// If flushing cannot immediately complete, this method returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object can make
/// progress towards flushing.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_flush(&mut self, cx: &mut task::Context) -> Poll<(), Error>;
/// Attempt to close the object.
///
/// On success, returns `Ok(Async::Ready(()))`.
///
/// If closing cannot immediately complete, this function returns
/// `Ok(Async::Pending)` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object can make
/// progress towards closing.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Async::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Error>;
}
macro_rules! deref_async_read {
() => {
unsafe fn initializer(&self) -> Initializer {
(**self).initializer()
}
fn poll_read(&mut self, cx: &mut task::Context, buf: &mut [u8])
-> Poll<usize, Error>
{
(**self).poll_read(cx, buf)
}
fn poll_vectored_read(&mut self, cx: &mut task::Context, vec: &mut [&mut IoVec])
-> Poll<usize, Error>
{
(**self).poll_vectored_read(cx, vec)
}
}
}
impl<T: ?Sized + AsyncRead> AsyncRead for Box<T> {
deref_async_read!();
}
impl<'a, T: ?Sized + AsyncRead> AsyncRead for &'a mut T {
deref_async_read!();
}
/// `unsafe` because the `StdIo::Read` type must not access the buffer
/// before reading data into it.
macro_rules! unsafe_delegate_async_read_to_stdio {
() => {
unsafe fn initializer(&self) -> Initializer {
Initializer::nop()
}
fn poll_read(&mut self, _: &mut task::Context, buf: &mut [u8])
-> Poll<usize, Error>
{
Ok(Async::Ready(StdIo::Read::read(self, buf)?))
}
}
}
impl<'a> AsyncRead for &'a [u8] {
unsafe_delegate_async_read_to_stdio!();
}
impl AsyncRead for StdIo::Repeat {
unsafe_delegate_async_read_to_stdio!();
}
impl<T: AsRef<[u8]>> AsyncRead for StdIo::Cursor<T> {
unsafe_delegate_async_read_to_stdio!();
}
macro_rules! deref_async_write {
() => {
fn poll_write(&mut self, cx: &mut task::Context, buf: &[u8])
-> Poll<usize, Error>
{
(**self).poll_write(cx, buf)
}
fn poll_vectored_write(&mut self, cx: &mut task::Context, vec: &[&IoVec])
-> Poll<usize, Error>
{
(**self).poll_vectored_write(cx, vec)
}
fn poll_flush(&mut self, cx: &mut task::Context) -> Poll<(), Error> {
(**self).poll_flush(cx)
}
fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Error> {
(**self).poll_close(cx)
}
}
}
impl<T: ?Sized + AsyncWrite> AsyncWrite for Box<T> {
deref_async_write!();
}
impl<'a, T: ?Sized + AsyncWrite> AsyncWrite for &'a mut T {
deref_async_write!();
}
macro_rules! delegate_async_write_to_stdio {
() => {
fn poll_write(&mut self, _: &mut task::Context, buf: &[u8])
-> Poll<usize, Error>
{
Ok(Async::Ready(StdIo::Write::write(self, buf)?))
}
fn poll_flush(&mut self, _: &mut task::Context) -> Poll<(), Error> {
Ok(Async::Ready(StdIo::Write::flush(self)?))
}
fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Error> {
self.poll_flush(cx)
}
}
}
impl<'a> AsyncWrite for StdIo::Cursor<&'a mut [u8]> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for StdIo::Cursor<Vec<u8>> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for StdIo::Cursor<Box<[u8]>> {
delegate_async_write_to_stdio!();
}
impl AsyncWrite for StdIo::Sink {
delegate_async_write_to_stdio!();
}
}