async-std/src/io/read/mod.rs

mod bytes;
mod chain;
mod read;
mod read_exact;
mod read_to_end;
mod read_to_string;
mod read_vectored;
mod take;

use read::ReadFuture;
use read_exact::ReadExactFuture;
use read_to_end::{read_to_end_internal, ReadToEndFuture};
use read_to_string::ReadToStringFuture;
use read_vectored::ReadVectoredFuture;

use std::mem;

use crate::io::IoSliceMut;

pub use bytes::Bytes;
pub use chain::Chain;
pub use take::Take;

extension_trait! {
    use std::pin::Pin;
    use std::ops::{Deref, DerefMut};

    use crate::io;
    use crate::task::{Context, Poll};

    #[doc = r#"
        Allows reading from a byte stream.

        This trait is a re-export of [`futures::io::AsyncRead`] and is an async version of
        [`std::io::Read`].

        Methods other than [`poll_read`] and [`poll_read_vectored`] do not really exist in the
        trait itself, but they become available when [`ReadExt`] from the [prelude] is imported:

        ```
        # #[allow(unused_imports)]
        use async_std::prelude::*;
        ```

        [`std::io::Read`]: https://doc.rust-lang.org/std/io/trait.Read.html
        [`futures::io::AsyncRead`]:
        https://docs.rs/futures/0.3/futures/io/trait.AsyncRead.html
        [`poll_read`]: #tymethod.poll_read
        [`poll_read_vectored`]: #method.poll_read_vectored
        [`ReadExt`]: ../io/prelude/trait.ReadExt.html
        [prelude]: ../prelude/index.html
    "#]
    pub trait Read {
        #[doc = r#"
            Attempt to read from the `AsyncRead` into `buf`.
        "#]
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut [u8],
        ) -> Poll<io::Result<usize>>;

        #[doc = r#"
            Attempt to read from the `AsyncRead` into `bufs` using vectored IO operations.
        "#]
        fn poll_read_vectored(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            bufs: &mut [IoSliceMut<'_>],
        ) -> Poll<io::Result<usize>> {
            unreachable!("this impl only appears in the rendered docs")
        }
    }

    #[doc = r#"
        Extension methods for [`Read`].

        [`Read`]: ../trait.Read.html
    "#]
    pub trait ReadExt: futures_io::AsyncRead {
        #[doc = r#"
            Reads some bytes from the byte stream.

            Returns the number of bytes read from the start of the buffer.

            If the return value is `Ok(n)`, then it must be guaranteed that
            `0 <= n <= buf.len()`. A nonzero `n` value indicates that the buffer has been
            filled in with `n` bytes of data. If `n` is `0`, then it can indicate one of two
            scenarios:

            1. This reader has reached its "end of file" and will likely no longer be able to
               produce bytes. Note that this does not mean that the reader will always no
               longer be able to produce bytes.
            2. The buffer specified was 0 bytes in length.

            # Examples

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::fs::File;
            use async_std::prelude::*;

            let mut file = File::open("a.txt").await?;

            let mut buf = vec![0; 1024];
            let n = file.read(&mut buf).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn read<'a>(
            &'a mut self,
            buf: &'a mut [u8],
        ) -> impl Future<Output = io::Result<usize>> + 'a [ReadFuture<'a, Self>]
        where
            Self: Unpin
        {
            ReadFuture { reader: self, buf }
        }

        #[doc = r#"
            Like [`read`], except that it reads into a slice of buffers.

            Data is copied to fill each buffer in order, with the final buffer written to
            possibly being only partially filled. This method must behave as a single call to
            [`read`] with the buffers concatenated would.

            The default implementation calls [`read`] with either the first nonempty buffer
            provided, or an empty one if none exists.

            [`read`]: #tymethod.read
        "#]
        fn read_vectored<'a>(
            &'a mut self,
            bufs: &'a mut [IoSliceMut<'a>],
        ) -> impl Future<Output = io::Result<usize>> + 'a [ReadVectoredFuture<'a, Self>]
        where
            Self: Unpin,
        {
            ReadVectoredFuture { reader: self, bufs }
        }

        #[doc = r#"
            Reads all bytes from the byte stream.

            All bytes read from this stream will be appended to the specified buffer `buf`.
            This function will continuously call [`read`] to append more data to `buf` until
            [`read`] returns either `Ok(0)` or an error.

            If successful, this function will return the total number of bytes read.

            [`read`]: #tymethod.read

            # Examples

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::fs::File;
            use async_std::prelude::*;

            let mut file = File::open("a.txt").await?;

            let mut buf = Vec::new();
            file.read_to_end(&mut buf).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn read_to_end<'a>(
            &'a mut self,
            buf: &'a mut Vec<u8>,
        ) -> impl Future<Output = io::Result<usize>> + 'a [ReadToEndFuture<'a, Self>]
        where
            Self: Unpin,
        {
            let start_len = buf.len();
            ReadToEndFuture {
                reader: self,
                buf,
                start_len,
            }
        }

        #[doc = r#"
            Reads all bytes from the byte stream and appends them into a string.

            If successful, this function will return the number of bytes read.

            If the data in this stream is not valid UTF-8 then an error will be returned and
            `buf` will be left unmodified.

            # Examples

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::fs::File;
            use async_std::prelude::*;

            let mut file = File::open("a.txt").await?;

            let mut buf = String::new();
            file.read_to_string(&mut buf).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn read_to_string<'a>(
            &'a mut self,
            buf: &'a mut String,
        ) -> impl Future<Output = io::Result<usize>> + 'a [ReadToStringFuture<'a, Self>]
        where
            Self: Unpin,
        {
            let start_len = buf.len();
            ReadToStringFuture {
                reader: self,
                bytes: unsafe { mem::replace(buf.as_mut_vec(), Vec::new()) },
                buf,
                start_len,
            }
        }

        #[doc = r#"
            Reads the exact number of bytes required to fill `buf`.

            This function reads as many bytes as necessary to completely fill the specified
            buffer `buf`.

            No guarantees are provided about the contents of `buf` when this function is
            called, implementations cannot rely on any property of the contents of `buf` being
            true. It is recommended that implementations only write data to `buf` instead of
            reading its contents.

            If this function encounters an "end of file" before completely filling the buffer,
            it returns an error of the kind [`ErrorKind::UnexpectedEof`].  The contents of
            `buf` are unspecified in this case.

            If any other read error is encountered then this function immediately returns. The
            contents of `buf` are unspecified in this case.

            If this function returns an error, it is unspecified how many bytes it has read,
            but it will never read more than would be necessary to completely fill the buffer.

            [`ErrorKind::UnexpectedEof`]: enum.ErrorKind.html#variant.UnexpectedEof

            # Examples

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::fs::File;
            use async_std::prelude::*;

            let mut file = File::open("a.txt").await?;

            let mut buf = vec![0; 10];
            file.read_exact(&mut buf).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn read_exact<'a>(
            &'a mut self,
            buf: &'a mut [u8],
        ) -> impl Future<Output = io::Result<()>> + 'a [ReadExactFuture<'a, Self>]
        where
            Self: Unpin,
        {
            ReadExactFuture { reader: self, buf }
        }

        #[doc = r#"
            Creates an adaptor which will read at most `limit` bytes from it.

            This function returns a new instance of `Read` which will read at most
            `limit` bytes, after which it will always return EOF ([`Ok(0)`]). Any
            read errors will not count towards the number of bytes read and future
            calls to [`read`] may succeed.

            # Examples

            [`File`]s implement `Read`:

            [`File`]: ../fs/struct.File.html
            [`Ok(0)`]: ../../std/result/enum.Result.html#variant.Ok
            [`read`]: tymethod.read

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::io::prelude::*;
            use async_std::fs::File;

            let f = File::open("foo.txt").await?;
            let mut buffer = [0; 5];

            // read at most five bytes
            let mut handle = f.take(5);

            handle.read(&mut buffer).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn take(self, limit: u64) -> Take<Self>
        where
            Self: Sized,
        {
            Take { inner: self, limit }
        }

        #[doc = r#"
            Creates a "by reference" adaptor for this instance of `Read`.

            The returned adaptor also implements `Read` and will simply borrow this
            current reader.

            # Examples

            [`File`][file]s implement `Read`:

            [file]: ../fs/struct.File.html

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::prelude::*;
            use async_std::fs::File;

            let mut f = File::open("foo.txt").await?;
            let mut buffer = Vec::new();
            let mut other_buffer = Vec::new();

            {
                let reference = f.by_ref();

                // read at most 5 bytes
                reference.take(5).read_to_end(&mut buffer).await?;

            } // drop our &mut reference so we can use f again

            // original file still usable, read the rest
            f.read_to_end(&mut other_buffer).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn by_ref(&mut self) -> &mut Self where Self: Sized { self }


        #[doc = r#"
            Transforms this `Read` instance to a `Stream` over its bytes.

            The returned type implements `Stream` where the `Item` is
            `Result<u8, io::Error>`.
            The yielded item is `Ok` if a byte was successfully read and `Err`
            otherwise. EOF is mapped to returning `None` from this iterator.

            # Examples

            [`File`][file]s implement `Read`:

            [file]: ../fs/struct.File.html

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::prelude::*;
            use async_std::fs::File;

            let f = File::open("foo.txt").await?;
            let mut s = f.bytes();

            while let Some(byte) = s.next().await {
                println!("{}", byte.unwrap());
            }
            #
            # Ok(()) }) }
            ```
        "#]
        fn bytes(self) -> Bytes<Self> where Self: Sized {
            Bytes { inner: self }
        }

        #[doc = r#"
            Creates an adaptor which will chain this stream with another.

            The returned `Read` instance will first read all bytes from this object
            until EOF is encountered. Afterwards the output is equivalent to the
            output of `next`.

            # Examples

            [`File`][file]s implement `Read`:

            [file]: ../fs/struct.File.html

            ```no_run
            # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
            #
            use async_std::prelude::*;
            use async_std::fs::File;

            let f1 = File::open("foo.txt").await?;
            let f2 = File::open("bar.txt").await?;

            let mut handle = f1.chain(f2);
            let mut buffer = String::new();

            // read the value into a String. We could use any Read method here,
            // this is just one example.
            handle.read_to_string(&mut buffer).await?;
            #
            # Ok(()) }) }
            ```
        "#]
        fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized {
            Chain { first: self, second: next, done_first: false }
        }

    }

    impl<T: Read + Unpin + ?Sized> Read for Box<T> {
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut [u8],
        ) -> Poll<io::Result<usize>> {
            unreachable!("this impl only appears in the rendered docs")
        }
    }

    impl<T: Read + Unpin + ?Sized> Read for &mut T {
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut [u8],
        ) -> Poll<io::Result<usize>> {
            unreachable!("this impl only appears in the rendered docs")
        }
    }

    impl<P> Read for Pin<P>
    where
        P: DerefMut + Unpin,
        <P as Deref>::Target: Read,
    {
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut [u8],
        ) -> Poll<io::Result<usize>> {
            unreachable!("this impl only appears in the rendered docs")
        }
    }

    impl Read for &[u8] {
        fn poll_read(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
            buf: &mut [u8],
        ) -> Poll<io::Result<usize>> {
            unreachable!("this impl only appears in the rendered docs")
        }
    }
}

/// Initializes a buffer if necessary.
///
/// Currently, a buffer is always initialized because `read_initializer`
/// feature is not stable.
#[inline]
unsafe fn initialize<R: futures_io::AsyncRead>(_reader: &R, buf: &mut [u8]) {
    std::ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len())
}

#[cfg(test)]
mod tests {
    use crate::io;
    use crate::prelude::*;

    #[test]
    fn test_read_by_ref() {
        crate::task::block_on(async {
            let mut f = io::Cursor::new(vec![0u8, 1, 2, 3, 4, 5, 6, 7, 8]);
            let mut buffer = Vec::new();
            let mut other_buffer = Vec::new();

            {
                let reference = f.by_ref();

                // read at most 5 bytes
                assert_eq!(reference.take(5).read_to_end(&mut buffer).await.unwrap(), 5);
                assert_eq!(&buffer, &[0, 1, 2, 3, 4])
            } // drop our &mut reference so we can use f again

            // original file still usable, read the rest
            assert_eq!(f.read_to_end(&mut other_buffer).await.unwrap(), 4);
            assert_eq!(&other_buffer, &[5, 6, 7, 8]);
        });
    }
}