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Add some docs for BorrowBuf

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Signed-off-by: Nick Cameron <nrc@ncameron.org>
This commit is contained in:
Nick Cameron 2022-05-22 20:57:58 -05:00
parent c1aae4d279
commit b56cf67ce1
1 changed files with 60 additions and 24 deletions
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84
library/std/src/io/readbuf.rs
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@ -7,8 +7,7 @@ use crate::cmp;
use crate::fmt::{self, Debug, Formatter};
use crate::mem::MaybeUninit;
// TODO docs
/// A wrapper around a byte buffer that is incrementally filled and initialized.
/// A borrowed byte buffer which is incrementally filled and initialized.
///
/// This type is a sort of "double cursor". It tracks three regions in the buffer: a region at the beginning of the
/// buffer that has been logically filled with data, a region that has been initialized at some point but not yet
@ -21,9 +20,20 @@ use crate::mem::MaybeUninit;
/// [ filled | unfilled ]
/// [ initialized | uninitialized ]
/// ```
///
/// A `BorrowBuf` is created around some existing data (or capacity for data) via a unique reference
/// (`&mut`). The `BorrowBuf` can be configured (e.g., using `clear` or `set_init`), but otherwise
/// is read-only. To write into the buffer, use `unfilled` to create a `BorrowCursor`. The cursor
/// has write-only access to the unfilled portion of the buffer (you can think of it like a
/// write-only iterator).
///
/// The lifetime `'a` is a bound on the lifetime of the underlying data.
pub struct BorrowBuf<'a> {
/// The buffer's underlying data.
buf: &'a mut [MaybeUninit<u8>],
/// The length of `self.buf` which is known to be filled.
filled: usize,
/// The length of `self.buf` which is known to be initialized.
initialized: usize,
}
@ -37,7 +47,7 @@ impl Debug for BorrowBuf<'_> {
}
}
/// Creates a new `BorrowBuf` from a fully initialized slice.
/// Create a new `BorrowBuf` from a fully initialized slice.
impl<'a> From<&'a mut [u8]> for BorrowBuf<'a> {
#[inline]
fn from(slice: &'a mut [u8]) -> BorrowBuf<'a> {
@ -52,7 +62,7 @@ impl<'a> From<&'a mut [u8]> for BorrowBuf<'a> {
}
}
/// Creates a new `BorrowBuf` from a fully uninitialized buffer.
/// Create a new `BorrowBuf` from an uninitialized buffer.
///
/// Use `set_init` if part of the buffer is known to be already initialized.
impl<'a> From<&'a mut [MaybeUninit<u8>]> for BorrowBuf<'a> {
@ -90,7 +100,7 @@ impl<'a> BorrowBuf<'a> {
/// Returns a cursor over the unfilled part of the buffer.
#[inline]
pub fn unfilled<'b>(&'b mut self) -> BorrowCursor<'a, 'b> {
pub fn unfilled<'this>(&'this mut self) -> BorrowCursor<'this, 'a> {
BorrowCursor { start: self.filled, buf: self }
}
@ -118,20 +128,36 @@ impl<'a> BorrowBuf<'a> {
}
}
/// A cursor view of a [`BorrowBuf`](BorrowBuf).
/// A writeable view of the unfilled portion of a [`BorrowBuf`](BorrowBuf).
///
/// Provides mutable access to the unfilled portion (both initialised and uninitialised data) from
/// the buffer.
/// Provides access to the initialized and uninitialized parts of the underlying `BorrowBuf`.
/// Data can be written directly to the cursor by using [`append`](BorrowCursor::append) or
/// indirectly by getting a slice of part or all of the cursor and writing into the slice. In the
/// indirect case, the caller must call [`advance`](BorrowCursor::advance) after writing to inform
/// the cursor how many bytes have been written.
///
/// Once data is written to the cursor, it becomes part of the filled portion of the underlying
/// `BorrowBuf` and can no longer be accessed or re-written by the cursor. I.e., the cursor tracks
/// the unfilled part of the underlying `BorrowBuf`.
///
/// The `'buf` lifetime is a bound on the lifetime of the underlying buffer. `'data` is a bound on
/// that buffer's underlying data.
#[derive(Debug)]
pub struct BorrowCursor<'a, 'b> {
buf: &'b mut BorrowBuf<'a>,
pub struct BorrowCursor<'buf, 'data> {
/// The underlying buffer.
buf: &'buf mut BorrowBuf<'data>,
/// The length of the filled portion of the underlying buffer at the time of the cursor's
/// creation.
start: usize,
}
impl<'a, 'b> BorrowCursor<'a, 'b> {
impl<'buf, 'data> BorrowCursor<'buf, 'data> {
/// Clone this cursor.
///
/// Since a cursor maintains unique access to its underlying buffer, the cloned cursor is not
/// accessible while the clone is alive.
#[inline]
pub fn clone<'c>(&'c mut self) -> BorrowCursor<'a, 'c> {
pub fn clone<'this>(&'this mut self) -> BorrowCursor<'this, 'data> {
BorrowCursor { buf: self.buf, start: self.start }
}
@ -141,14 +167,16 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
self.buf.capacity() - self.buf.filled
}
/// Returns the number of bytes written to this cursor.
// TODO check for reuse uses
/// Returns the number of bytes written to this cursor since it was created from a `BorrowBuf`.
///
/// Note that if this cursor is a clone of another, then the count returned is the count written
/// via either cursor, not the count since the cursor was cloned.
#[inline]
pub fn written(&self) -> usize {
self.buf.filled - self.start
}
/// Returns a shared reference to the initialized portion of the buffer.
/// Returns a shared reference to the initialized portion of the cursor.
#[inline]
pub fn init_ref(&self) -> &[u8] {
//SAFETY: We only slice the initialized part of the buffer, which is always valid
@ -157,7 +185,7 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
}
}
/// Returns a mutable reference to the initialized portion of the buffer.
/// Returns a mutable reference to the initialized portion of the cursor.
#[inline]
pub fn init_mut(&mut self) -> &mut [u8] {
//SAFETY: We only slice the initialized part of the buffer, which is always valid
@ -168,7 +196,7 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
}
}
/// Returns a mutable reference to the uninitialized part of the buffer.
/// Returns a mutable reference to the uninitialized part of the cursor.
///
/// It is safe to uninitialize any of these bytes.
#[inline]
@ -176,17 +204,25 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
&mut self.buf.buf[self.buf.initialized..]
}
/// A view of the cursor as a mutable slice of `MaybeUninit<u8>`.
/// Returns a mutable reference to the whole cursor.
///
/// # Safety
///
/// The caller must not uninitialize any bytes in the initialized portion of the cursor.
#[inline]
pub unsafe fn as_mut(&mut self) -> &mut [MaybeUninit<u8>] {
&mut self.buf.buf[self.buf.filled..]
}
/// Increases the size of the filled region of the buffer.
/// Advance the cursor by asserting that `n` bytes have been filled.
///
/// After advancing, the `n` bytes are no longer accessible via the cursor and can only be
/// accessed via the underlying buffer. I.e., the buffer's filled portion grows by `n` elements
/// and its unfilled portion (and the capacity of this cursor) shrinks by `n` elements.
///
/// # Safety
///
/// The caller must ensure that the first `n` elements of the cursor have been properly
/// The caller must ensure that the first `n` bytes of the cursor have been properly
/// initialised.
#[inline]
pub unsafe fn advance(&mut self, n: usize) -> &mut Self {
@ -195,7 +231,7 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
self
}
/// Initialised all bytes in the cursor.
/// Initializes all bytes in the cursor.
#[inline]
pub fn ensure_init(&mut self) -> &mut Self {
for byte in self.uninit_mut() {
@ -208,8 +244,8 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
/// Asserts that the first `n` unfilled bytes of the cursor are initialized.
///
/// `BorrowBuf` assumes that bytes are never de-initialized, so this method does nothing when called with fewer
/// bytes than are already known to be initialized.
/// `BorrowBuf` assumes that bytes are never de-initialized, so this method does nothing when
/// called with fewer bytes than are already known to be initialized.
///
/// # Safety
///
@ -220,7 +256,7 @@ impl<'a, 'b> BorrowCursor<'a, 'b> {
self
}
/// Appends data to the cursor, advancing the position within its buffer.
/// Appends data to the cursor, advancing position within its buffer.
///
/// # Panics
///