Struct TransformBuf

pub struct TransformBuf<'a, 'b> { /* private fields */ }

A buffer of transformable streaming data.

Overview

A byte buffer, similar to a ReadBuf, with a “fresh” dimension. Fresh data is always a subset of the filled data, filled data is always a subset of initialized data, and initialized data is always a subset of the buffer itself. Both the filled and initialized data sections are guaranteed to be at the start of the buffer, but the fresh subset is likely to begin somewhere inside the filled section.

To visualize this, the diagram below represents a possible state for the byte buffer being tracked. The square [ ] brackets represent the complete buffer, while the curly { } represent the named subset.

[  { !! fresh !! }                                 ]
{ +++ filled +++ }          unfilled               ]
{ ----- initialized ------ }     uninitialized     ]
[                    capacity                      ]

The same buffer represented in its true single dimension is below:

[ ++!!!!!!!!!!!!!!---------xxxxxxxxxxxxxxxxxxxxxxxx]

• +: filled (implies initialized)
• !: fresh (implies filled)
• -: unfilled / initialized (implies initialized)
• x: uninitialized (implies unfilled)

As with ReadBuf, AsyncRead readers fill the initialized portion of a TransformBuf to indicate that data is available. Filling initialized portions of the byte buffers is what increases the size of the filled section. Because a ReadBuf may already be partially filled when a reader adds bytes to it, a mechanism to track where the newly filled portion exists is needed. This is exactly what the “fresh” section tracks.

Implementations

impl TransformBuf<'_, '_>

pub fn fresh(&self) -> &[u8]

Returns a borrow to the fresh data: data filled by the upstream source.

pub fn fresh_mut(&mut self) -> &mut [u8]

Returns a mutable borrow to the fresh data: data filled by the upstream source.

pub fn spoil(&mut self)

Spoils the fresh data by resetting the filled section to its value before any new data was added. As a result, the data will never be seen by any downstream consumer unless it is returned via another mechanism.

Methods from Deref<Target = ReadBuf<'b>>

pub fn capacity(&self) -> usize

Returns the total capacity of the buffer.

pub fn filled(&self) -> &[u8]

Returns a shared reference to the filled portion of the buffer.

pub fn filled_mut(&mut self) -> &mut [u8]

Returns a mutable reference to the filled portion of the buffer.

pub fn take(&mut self, n: usize) -> ReadBuf<'_>

Returns a new ReadBuf comprised of the unfilled section up to n.

pub fn initialized(&self) -> &[u8]

Returns a shared reference to the initialized portion of the buffer.

This includes the filled portion.

pub fn initialized_mut(&mut self) -> &mut [u8]

Returns a mutable reference to the initialized portion of the buffer.

This includes the filled portion.

pub unsafe fn inner_mut(&mut self) -> &mut [MaybeUninit<u8>]

Returns a mutable reference to the entire buffer, without ensuring that it has been fully initialized.

The elements between 0 and self.filled().len() are filled, and those between 0 and self.initialized().len() are initialized (and so can be converted to a &mut [u8]).

The caller of this method must ensure that these invariants are upheld. For example, if the caller initializes some of the uninitialized section of the buffer, it must call assume_init with the number of bytes initialized.

Safety

The caller must not de-initialize portions of the buffer that have already been initialized. This includes any bytes in the region marked as uninitialized by ReadBuf.

pub unsafe fn unfilled_mut(&mut self) -> &mut [MaybeUninit<u8>]

Returns a mutable reference to the unfilled part of the buffer without ensuring that it has been fully initialized.

Safety

The caller must not de-initialize portions of the buffer that have already been initialized. This includes any bytes in the region marked as uninitialized by ReadBuf.

pub fn initialize_unfilled(&mut self) -> &mut [u8]

Returns a mutable reference to the unfilled part of the buffer, ensuring it is fully initialized.

Since ReadBuf tracks the region of the buffer that has been initialized, this is effectively “free” after the first use.

pub fn initialize_unfilled_to(&mut self, n: usize) -> &mut [u8]

Returns a mutable reference to the first n bytes of the unfilled part of the buffer, ensuring it is fully initialized.

Panics

Panics if self.remaining() is less than n.

pub fn remaining(&self) -> usize

Returns the number of bytes at the end of the slice that have not yet been filled.

pub fn clear(&mut self)

Clears the buffer, resetting the filled region to empty.

The number of initialized bytes is not changed, and the contents of the buffer are not modified.

pub fn advance(&mut self, n: usize)

Advances the size of the filled region of the buffer.

The number of initialized bytes is not changed.

Panics

Panics if the filled region of the buffer would become larger than the initialized region.

pub fn set_filled(&mut self, n: usize)

Sets the size of the filled region of the buffer.

The number of initialized bytes is not changed.

Note that this can be used to shrink the filled region of the buffer in addition to growing it (for example, by a AsyncRead implementation that compresses data in-place).

Panics

Panics if the filled region of the buffer would become larger than the initialized region.

pub unsafe fn assume_init(&mut self, n: usize)

Asserts that the first n unfilled bytes of the buffer are initialized.

ReadBuf 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

The caller must ensure that n unfilled bytes of the buffer have already been initialized.

pub fn put_slice(&mut self, buf: &[u8])

Appends data to the buffer, advancing the written position and possibly also the initialized position.

Panics

Panics if self.remaining() is less than buf.len().

Trait Implementations

impl<'a, 'b> Deref for TransformBuf<'a, 'b>

type Target = ReadBuf<'b>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<'a, 'b> DerefMut for TransformBuf<'a, 'b>

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.