mod.rs

//! no-std io replacement
use crate::{cmp, convert::TryInto, mem, vec::Vec};

mod error;
pub use error::*;

pub mod prelude {
    pub use super::{Read, Result, Write};
}

/// The `Read` trait allows for reading bytes from a source.
///
/// Implementors of the `Read` trait are called 'readers'.
///
/// Readers are defined by one required method, [`read()`]. Each call to [`read()`]
/// will attempt to pull bytes from this source into a provided buffer. A
/// number of other methods are implemented in terms of [`read()`], giving
/// implementors a number of ways to read bytes while only needing to implement
/// a single method.
///
/// Readers are intended to be composable with one another. Many implementors
/// throughout [`ark_std::io`] take and provide types which implement the `Read`
/// trait.
///
/// Please note that each call to [`read()`] may involve a system call, and
/// therefore, using something that implements [`BufRead`], such as
/// [`BufReader`], will be more efficient.
///
///
/// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
///
/// ```no_run
/// # use ark_std::io;
/// use ark_std::io::prelude::*;
///
/// fn main() -> Result<()> {
///     let mut b = "This string will be read".as_bytes();
///     let mut buffer = [0; 10];
///
///     // read up to 10 bytes
///     b.read(&mut buffer)?;
///
///     Ok(())
/// }
/// ```
///
/// [`read()`]: trait.Read.html#tymethod.read
/// [`ark_std::io`]: ../../std/io/index.html
/// [`BufRead`]: trait.BufRead.html
/// [`BufReader`]: struct.BufReader.html
/// [`&str`]: ../../std/primitive.str.html
/// [slice]: ../../std/primitive.slice.html
pub trait Read {
    /// Pull some bytes from this source into the specified buffer, returning
    /// how many bytes were read.
    ///
    /// This function does not provide any guarantees about whether it blocks
    /// waiting for data, but if an object needs to block for a read but cannot
    /// it will typically signal this via an [`Err`] return value.
    ///
    /// If the return value of this method is [`Ok(n)`], then it must be
    /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
    /// that the buffer `buf` has been filled in with `n` bytes of data from this
    /// source. If `n` is `0`, then it can indicate that the the buffer
    /// specified was 0 bytes in length.
    ///
    /// 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.
    ///
    /// # Errors
    ///
    /// If this function encounters any form of I/O or other error, an error
    /// variant will be returned. If an error is returned then it must be
    /// guaranteed that no bytes were read.
    ///
    /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the read
    /// operation should be retried if there is nothing else to do.
    ///
    fn read(&mut self, buf: &mut [u8]) -> Result<usize>;

    /// Read 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.
    ///
    /// # Errors
    ///
    /// If this function encounters an error of the kind
    /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
    /// will continue.
    ///
    /// 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.
    fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
        while !buf.is_empty() {
            match self.read(buf) {
                Ok(0) => break,
                Ok(n) => {
                    let tmp = buf;
                    buf = &mut tmp[n..];
                },
                Err(ref e) if e.kind() == ErrorKind::Interrupted => {},
                Err(e) => return Err(e),
            }
        }
        if !buf.is_empty() {
            Err(Error::new(
                ErrorKind::UnexpectedEof,
                "failed to fill whole buffer",
            ))
        } else {
            Ok(())
        }
    }

    /// Creates a "by reference" adaptor for this instance of `Read`.
    ///
    /// The returned adaptor also implements `Read` and will simply borrow this
    /// current reader.
    fn by_ref(&mut self) -> &mut Self
    where
        Self: Sized,
    {
        self
    }
}

pub trait Write {
    /// Write a buffer into this writer, returning how many bytes were written.
    ///
    /// This function will attempt to write the entire contents of `buf`, but
    /// the entire write may not succeed, or the write may also generate an
    /// error. A call to `write` represents *at most one* attempt to write to
    /// any wrapped object.
    ///
    /// Calls to `write` are not guaranteed to block waiting for data to be
    /// written, and a write which would otherwise block can be indicated through
    /// an [`Err`] variant.
    ///
    /// If the return value is [`Ok(n)`] then it must be guaranteed that
    /// `0 <= n <= buf.len()`. A return value of `0` typically means that the
    /// underlying object is no longer able to accept bytes and will likely not
    /// be able to in the future as well, or that the buffer provided is empty.
    ///
    /// # Errors
    ///
    /// Each call to `write` may generate an I/O error indicating that the
    /// operation could not be completed. If an error is returned then no bytes
    /// in the buffer were written to this writer.
    ///
    /// It is **not** considered an error if the entire buffer could not be
    /// written to this writer.
    ///
    /// An error of the [`ErrorKind::Interrupted`] kind is non-fatal and the
    /// write operation should be retried if there is nothing else to do.
    ///
    /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
    /// [`Ok(n)`]:  ../../std/result/enum.Result.html#variant.Ok
    /// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
    fn write(&mut self, buf: &[u8]) -> Result<usize>;

    /// Flush this output stream, ensuring that all intermediately buffered
    /// contents reach their destination.
    ///
    /// # Errors
    ///
    /// It is considered an error if not all bytes could be written due to
    /// I/O errors or EOF being reached.
    ///
    fn flush(&mut self) -> Result<()>;

    /// Attempts to write an entire buffer into this writer.
    ///
    /// This method will continuously call [`write`] until there is no more data
    /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
    /// returned. This method will not return until the entire buffer has been
    /// successfully written or such an error occurs. The first error that is
    /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
    /// returned.
    ///
    /// # Errors
    ///
    /// This function will return the first error of
    /// non-[`ErrorKind::Interrupted`] kind that [`write`] returns.
    ///
    /// [`ErrorKind::Interrupted`]: ../../std/io/enum.ErrorKind.html#variant.Interrupted
    /// [`write`]: #tymethod.write
    fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
        while !buf.is_empty() {
            match self.write(buf) {
                Ok(0) => {
                    return Err(Error::new(
                        ErrorKind::WriteZero,
                        "failed to write whole buffer",
                    ))
                },
                Ok(n) => buf = &buf[n..],
                Err(ref e) if e.kind() == ErrorKind::Interrupted => {},
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }

    /// Creates a "by reference" adaptor for this instance of `Write`.
    ///
    /// The returned adaptor also implements `Write` and will simply borrow this
    /// current writer.
    fn by_ref(&mut self) -> &mut Self
    where
        Self: Sized,
    {
        self
    }
}

impl<R: Read + ?Sized> Read for &mut R {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        (**self).read(buf)
    }

    #[inline]
    fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
        (**self).read_exact(buf)
    }
}

impl Read for &[u8] {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let amt = cmp::min(buf.len(), self.len());
        let (a, b) = self.split_at(amt);

        // First check if the amount of bytes we want to read is small:
        // `copy_from_slice` will generally expand to a call to `memcpy`, and
        // for a single byte the overhead is significant.
        if amt == 1 {
            buf[0] = a[0];
        } else {
            buf[..amt].copy_from_slice(a);
        }

        *self = b;
        Ok(amt)
    }

    #[inline]
    fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
        if buf.len() > self.len() {
            return Err(Error::new(
                ErrorKind::UnexpectedEof,
                "failed to fill whole buffer",
            ));
        }
        let (a, b) = self.split_at(buf.len());

        // First check if the amount of bytes we want to read is small:
        // `copy_from_slice` will generally expand to a call to `memcpy`, and
        // for a single byte the overhead is significant.
        if buf.len() == 1 {
            buf[0] = a[0];
        } else {
            buf.copy_from_slice(a);
        }

        *self = b;
        Ok(())
    }
}

impl<W: Write + ?Sized> Write for &mut W {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        (**self).write(buf)
    }

    #[inline]
    fn flush(&mut self) -> Result<()> {
        (**self).flush()
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> Result<()> {
        (**self).write_all(buf)
    }
}

impl Write for &mut [u8] {
    fn write(&mut self, data: &[u8]) -> Result<usize> {
        let amt = cmp::min(data.len(), self.len());
        let (a, b) = mem::replace(self, &mut []).split_at_mut(amt);
        a.copy_from_slice(&data[..amt]);
        *self = b;
        Ok(amt)
    }

    #[inline]
    fn write_all(&mut self, data: &[u8]) -> Result<()> {
        if self.write(data)? == data.len() {
            Ok(())
        } else {
            Err(Error::new(
                ErrorKind::WriteZero,
                "failed to write whole buffer",
            ))
        }
    }

    #[inline]
    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

impl Write for Vec<u8> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        self.extend_from_slice(buf);
        Ok(buf.len())
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> Result<()> {
        self.extend_from_slice(buf);
        Ok(())
    }

    #[inline]
    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

/////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////

/// This data structure is used as a workaround for current design of `ToBytes`
/// which does not allow multiple writes to `&mut [u8]`.
pub struct Cursor<T> {
    inner: T,
    pos: u64,
}

impl<T> Cursor<T> {
    /// Creates a new cursor wrapping the provided underlying in-memory buffer.
    ///
    /// Cursor initial position is `0` even if underlying buffer (e.g., `Vec`)
    /// is not empty. So writing to cursor starts with overwriting `Vec`
    /// content, not with appending to it.
    ///
    /// # Examples
    ///
    /// ```
    /// use ark_std::io::Cursor;
    ///
    /// let buff = Cursor::new(Vec::new());
    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
    /// # force_inference(&buff);
    /// ```
    pub fn new(inner: T) -> Self {
        Cursor { inner, pos: 0 }
    }

    /// Consumes this cursor, returning the underlying value.
    ///
    /// # Examples
    ///
    /// ```
    /// use ark_std::io::Cursor;
    ///
    /// let buff = Cursor::new(Vec::new());
    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
    /// # force_inference(&buff);
    ///
    /// let vec = buff.into_inner();
    /// ```
    pub fn into_inner(self) -> T {
        self.inner
    }

    /// Gets a reference to the underlying value in this cursor.
    ///
    /// # Examples
    ///
    /// ```
    /// use ark_std::io::Cursor;
    ///
    /// let buff = Cursor::new(Vec::new());
    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
    /// # force_inference(&buff);
    ///
    /// let reference = buff.get_ref();
    /// ```
    pub fn get_ref(&self) -> &T {
        &self.inner
    }

    /// Gets a mutable reference to the underlying value in this cursor.
    ///
    /// Care should be taken to avoid modifying the internal I/O state of the
    /// underlying value as it may corrupt this cursor's position.
    ///
    /// # Examples
    ///
    /// ```
    /// use ark_std::io::Cursor;
    ///
    /// let mut buff = Cursor::new(Vec::new());
    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
    /// # force_inference(&buff);
    ///
    /// let reference = buff.get_mut();
    /// ```
    pub fn get_mut(&mut self) -> &mut T {
        &mut self.inner
    }

    /// Returns the current position of this cursor.
    pub fn position(&self) -> u64 {
        self.pos
    }

    /// Sets the position of this cursor.
    ///
    /// # Examples
    ///
    /// ```
    /// use ark_std::io::Cursor;
    ///
    /// let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
    ///
    /// assert_eq!(buff.position(), 0);
    ///
    /// buff.set_position(2);
    /// assert_eq!(buff.position(), 2);
    ///
    /// buff.set_position(4);
    /// assert_eq!(buff.position(), 4);
    /// ```
    pub fn set_position(&mut self, pos: u64) {
        self.pos = pos;
    }
}

impl<T> Read for Cursor<T>
where
    T: AsRef<[u8]>,
{
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let n = Read::read(&mut self.get_buf()?, buf)?;
        self.pos += n as u64;
        Ok(n)
    }

    fn read_exact(&mut self, buf: &mut [u8]) -> Result<()> {
        let n = buf.len();
        Read::read_exact(&mut self.get_buf()?, buf)?;
        self.pos += n as u64;
        Ok(())
    }
}

impl<T> Cursor<T>
where
    T: AsRef<[u8]>,
{
    fn get_buf(&mut self) -> Result<&[u8]> {
        let amt = cmp::min(self.pos, self.inner.as_ref().len() as u64);
        Ok(&self.inner.as_ref()[(amt as usize)..])
    }
}

impl Write for Cursor<&mut [u8]> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        slice_write(&mut self.pos, self.inner, buf)
    }

    #[inline]
    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

impl Write for Cursor<Vec<u8>> {
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        vec_write(&mut self.pos, &mut self.inner, buf)
    }

    #[inline]
    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

// Non-resizing write implementation
#[inline]
fn slice_write(pos_mut: &mut u64, slice: &mut [u8], buf: &[u8]) -> Result<usize> {
    let pos = cmp::min(*pos_mut, slice.len() as u64);
    let amt = (&mut slice[(pos as usize)..]).write(buf)?;
    *pos_mut += amt as u64;
    Ok(amt)
}

fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> Result<usize> {
    let pos: usize = (*pos_mut).try_into().map_err(|_| {
        Error::new(
            ErrorKind::InvalidInput,
            "cursor position exceeds maximum possible vector length",
        )
    })?;
    // Make sure the internal buffer is as least as big as where we
    // currently are
    let len = vec.len();
    if len < pos {
        // use `resize` so that the zero filling is as efficient as possible
        vec.resize(pos, 0);
    }
    // Figure out what bytes will be used to overwrite what's currently
    // there (left), and what will be appended on the end (right)
    {
        let space = vec.len() - pos;
        let (left, right) = buf.split_at(cmp::min(space, buf.len()));
        vec[pos..pos + left.len()].copy_from_slice(left);
        vec.extend_from_slice(right);
    }

    // Bump us forward
    *pos_mut = (pos + buf.len()) as u64;
    Ok(buf.len())
}