Struct domain_core::bits::compose::Compressor

pub struct Compressor { /* fields omitted */ }

A buffer for composing a compressed DNS message.

This type wraps a BytesMut value into which it composes a message, growing it as necessary. It provides an implementation for BufMut allowing it to be used like any other buffer. In addition, it provides special handling for types that implement Compose via the compose method, appending them if there’s enough space.

The whole point of this type is, of course, name compression. This is being provided via the compress_name method which appends any domain name. Since compression is actually rather expensive as we need to keep track of names that have been written so far, it needs to be explicitely enabled via the enable_compression method.

Two more methods for tweaking the behaviour of Compressor are available. The maximum size of a message can be set via the set_limit. A value will grow its underlying buffer as needed up to at most this size. It will re-allocate memory if necessary by the amount set through set_page_size. By default, or if the page size is set to 0, it will only allocate exactly once to have enough space to reach the current limit.

Once you are done composing your message, you can either extract the underlying BytesMut via unwrap or get it as a frozen Bytes directly via freeze.

Note: Name compression is currently implemented in a rather naive way by simply storing each compressed name’s position in a hash map (also considering all its parents). This can probably be optimized. In addition, this approach doesn’t consider non-compressed names (since they are appended via their Compose implementation).

Methods

impl Compressor

pub fn from_buf(buf: BytesMut) -> Self

Creates a compressor from the given bytes buffer.

The compressor will have a default limit equal to the buffer’s current capacity and a page size of 0.

pub fn new() -> Self

Creates a new compressor with a default capacity and limit.

The compressor will be created atop a new buffer which will use its default capacity. This is the largest capacity it can use without having to allocate. The compressor will start out with a limit equal to this capacity and a page size of 0.

pub fn with_capacity(capacity: usize) -> Self

Creates a new compressor with the given capacity.

The compressor will be created atop a new buffer with at least the given capacity. The compressor’s initial limit will be the actual capacity of the buffer which may be larger than capacity. The initial page size will be 0.

pub fn enable_compression(&mut self)

Enable name compression.

By default, a compressor will not actually compress domain names, but rather append them like any other data. Instead, compression needs to be enable once via this method.

pub fn set_limit(&mut self, limit: usize)

Sets the size limit for the compressor.

This limit only regards the part of the underlying buffer that is being built by the compressor. That is, if the compressor was created on top of a buffer that already contained data, the buffer will never exceed that amount of data plus limit.

If you try to set the limit to a value smaller than what has already been added so far, the limit will silently be increased to that amount.

A new compressor starts out with a size limit equal to the remaining capacity of the buffer it is being created with.

pub fn set_page_size(&mut self, page_size: usize)

Sets the number of bytes by which the buffer should be grown.

Each time the buffer runs out of capacity and is still below its size limit, it will be grown by page_size bytes. This may result in a buffer with more capacity than the limit.

If page_size is set to 0, the buffer will be expanded only once to match the size limit.

A new compressor starts out with this specia page size of 0.

pub fn unwrap(self) -> BytesMut

Trades in the compressor for its underlying bytes buffer.

pub fn freeze(self) -> Bytes

Trades in the compressor for the frozen underlying buffer.

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

Returns a reference to the bytes that have been assembled so far.

This differs from as_slice if the compressor was created atop an existing buffer in that the slice does not contain the data that was in the buffer before.

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

Returns a mutable reference to the data assembled so far.

This differs from as_slice_mut if the compressor was created atop an existing buffer in that the slice does not contain the data that was in the buffer before.

pub fn compress_name<N: ToDname>(&mut self, name: &N) -> Result<(), ShortBuf>

Composes a the given name compressed into the buffer.

If compression hasn’t been enable yet via enable_compression, the name will be appended without compression. It will also not be remembered as a compression target for later names.

pub fn compose<C: ?Sized>(&mut self, what: &C) -> Result<(), ShortBuf> where
    C: Compose, 

Appends something composable to the end of the buffer.

This method can be used to append something and short circuit via the question mark operator if it doesn’t fit. This is most helpful when implementing the Compress trait for a composite type.

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

Returns a reference to the complete data of the underlying buffer.

This may be more than the assembled data if the compressor was created atop a buffer that already contained data.

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

Returns a mutable reference to the data of the underlying buffer.

This may be more than the assembled data if the compressor was created atop a buffer that already contained data.

Methods from Deref<Target = BytesMut>

pub fn len(&self) -> usize

Returns the number of bytes contained in this BytesMut.

Examples

use bytes::BytesMut;

let b = BytesMut::from(&b"hello"[..]);
assert_eq!(b.len(), 5);

pub fn is_empty(&self) -> bool

Returns true if the BytesMut has a length of 0.

Examples

use bytes::BytesMut;

let b = BytesMut::with_capacity(64);
assert!(b.is_empty());

pub fn capacity(&self) -> usize

Returns the number of bytes the BytesMut can hold without reallocating.

Examples

use bytes::BytesMut;

let b = BytesMut::with_capacity(64);
assert_eq!(b.capacity(), 64);

pub fn split_off(&mut self, at: usize) -> BytesMut

Splits the bytes into two at the given index.

Afterwards self contains elements [0, at), and the returned BytesMut contains elements [at, capacity).

This is an O(1) operation that just increases the reference count and sets a few indices.

Examples

use bytes::BytesMut;

let mut a = BytesMut::from(&b"hello world"[..]);
let mut b = a.split_off(5);

a[0] = b'j';
b[0] = b'!';

assert_eq!(&a[..], b"jello");
assert_eq!(&b[..], b"!world");

Panics

Panics if at > capacity.

pub fn take(&mut self) -> BytesMut

Removes the bytes from the current view, returning them in a new BytesMut handle.

Afterwards, self will be empty, but will retain any additional capacity that it had before the operation. This is identical to self.split_to(self.len()).

This is an O(1) operation that just increases the reference count and sets a few indices.

Examples

use bytes::{BytesMut, BufMut};

let mut buf = BytesMut::with_capacity(1024);
buf.put(&b"hello world"[..]);

let other = buf.take();

assert!(buf.is_empty());
assert_eq!(1013, buf.capacity());

assert_eq!(other, b"hello world"[..]);

pub fn split_to(&mut self, at: usize) -> BytesMut

Splits the buffer into two at the given index.

Afterwards self contains elements [at, len), and the returned BytesMut contains elements [0, at).

This is an O(1) operation that just increases the reference count and sets a few indices.

Examples

use bytes::BytesMut;

let mut a = BytesMut::from(&b"hello world"[..]);
let mut b = a.split_to(5);

a[0] = b'!';
b[0] = b'j';

assert_eq!(&a[..], b"!world");
assert_eq!(&b[..], b"jello");

Panics

Panics if at > len.

pub fn truncate(&mut self, len: usize)

Shortens the buffer, keeping the first len bytes and dropping the rest.

If len is greater than the buffer's current length, this has no effect.

The split_off method can emulate truncate, but this causes the excess bytes to be returned instead of dropped.

Examples

use bytes::BytesMut;

let mut buf = BytesMut::from(&b"hello world"[..]);
buf.truncate(5);
assert_eq!(buf, b"hello"[..]);

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

Shortens the buffer, dropping the first cnt bytes and keeping the rest.

This is the same function as Buf::advance, and in the next breaking release of bytes, this implementation will be removed in favor of having BytesMut implement Buf.

Panics

This function panics if cnt is greater than self.len()

pub fn clear(&mut self)

Clears the buffer, removing all data.

Examples

use bytes::BytesMut;

let mut buf = BytesMut::from(&b"hello world"[..]);
buf.clear();
assert!(buf.is_empty());

pub fn resize(&mut self, new_len: usize, value: u8)

Resizes the buffer so that len is equal to new_len.

If new_len is greater than len, the buffer is extended by the difference with each additional byte set to value. If new_len is less than len, the buffer is simply truncated.

Examples

use bytes::BytesMut;

let mut buf = BytesMut::new();

buf.resize(3, 0x1);
assert_eq!(&buf[..], &[0x1, 0x1, 0x1]);

buf.resize(2, 0x2);
assert_eq!(&buf[..], &[0x1, 0x1]);

buf.resize(4, 0x3);
assert_eq!(&buf[..], &[0x1, 0x1, 0x3, 0x3]);

pub unsafe fn set_len(&mut self, len: usize)

Sets the length of the buffer.

This will explicitly set the size of the buffer without actually modifying the data, so it is up to the caller to ensure that the data has been initialized.

Examples

use bytes::BytesMut;

let mut b = BytesMut::from(&b"hello world"[..]);

unsafe {
    b.set_len(5);
}

assert_eq!(&b[..], b"hello");

unsafe {
    b.set_len(11);
}

assert_eq!(&b[..], b"hello world");

Panics

This method will panic if len is out of bounds for the underlying slice or if it comes after the end of the configured window.

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more bytes to be inserted into the given BytesMut.

More than additional bytes may be reserved in order to avoid frequent reallocations. A call to reserve may result in an allocation.

Before allocating new buffer space, the function will attempt to reclaim space in the existing buffer. If the current handle references a small view in the original buffer and all other handles have been dropped, and the requested capacity is less than or equal to the existing buffer's capacity, then the current view will be copied to the front of the buffer and the handle will take ownership of the full buffer.

Examples

In the following example, a new buffer is allocated.

use bytes::BytesMut;

let mut buf = BytesMut::from(&b"hello"[..]);
buf.reserve(64);
assert!(buf.capacity() >= 69);

In the following example, the existing buffer is reclaimed.

use bytes::{BytesMut, BufMut};

let mut buf = BytesMut::with_capacity(128);
buf.put(&[0; 64][..]);

let ptr = buf.as_ptr();
let other = buf.take();

assert!(buf.is_empty());
assert_eq!(buf.capacity(), 64);

drop(other);
buf.reserve(128);

assert_eq!(buf.capacity(), 128);
assert_eq!(buf.as_ptr(), ptr);

Panics

Panics if the new capacity overflows usize.

pub fn extend_from_slice(&mut self, extend: &[u8])

Appends given bytes to this object.

If this BytesMut object has not enough capacity, it is resized first. So unlike put_slice operation, extend_from_slice does not panic.

Examples

use bytes::BytesMut;

let mut buf = BytesMut::with_capacity(0);
buf.extend_from_slice(b"aaabbb");
buf.extend_from_slice(b"cccddd");

assert_eq!(b"aaabbbcccddd", &buf[..]);

pub fn unsplit(&mut self, other: BytesMut)

Combine splitted BytesMut objects back as contiguous.

If BytesMut objects were not contiguous originally, they will be extended.

Examples

use bytes::BytesMut;

let mut buf = BytesMut::with_capacity(64);
buf.extend_from_slice(b"aaabbbcccddd");

let splitted = buf.split_off(6);
assert_eq!(b"aaabbb", &buf[..]);
assert_eq!(b"cccddd", &splitted[..]);

buf.unsplit(splitted);
assert_eq!(b"aaabbbcccddd", &buf[..]);

Trait Implementations

impl Clone for Compressor

fn clone(&self) -> Compressor

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl AsMut<BytesMut> for Compressor

fn as_mut(&mut self) -> &mut BytesMut

Performs the conversion.

impl AsMut<[u8]> for Compressor

fn as_mut(&mut self) -> &mut [u8]

Performs the conversion.

impl AsRef<BytesMut> for Compressor

fn as_ref(&self) -> &BytesMut

Performs the conversion.

impl AsRef<[u8]> for Compressor

fn as_ref(&self) -> &[u8]

Performs the conversion.

impl Default for Compressor

fn default() -> Self

Returns the "default value" for a type.

impl DerefMut for Compressor

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

Mutably dereferences the value.

impl Deref for Compressor

type Target = BytesMut

The resulting type after dereferencing.

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

Dereferences the value.

impl Debug for Compressor

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl BufMut for Compressor

fn remaining_mut(&self) -> usize

Returns the number of bytes that can be written from the current position until the end of the buffer is reached.

unsafe fn advance_mut(&mut self, cnt: usize)

Advance the internal cursor of the BufMut

unsafe fn bytes_mut(&mut self) -> &mut [u8]

Returns a mutable slice starting at the current BufMut position and of length between 0 and BufMut::remaining_mut(). Note that this can be shorter than the whole remainder of the buffer (this allows non-continuous implementation).

fn has_remaining_mut(&self) -> bool

Returns true if there is space in self for more bytes.

unsafe fn bytes_vec_mut(&'a mut self, dst: &mut [&'a mut IoVec]) -> usize

Fills dst with potentially multiple mutable slices starting at self's current position.

fn put<T>(&mut self, src: T) where
    T: IntoBuf, 

Transfer bytes into self from src and advance the cursor by the number of bytes written.

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

Transfer bytes into self from src and advance the cursor by the number of bytes written.

fn put_u8(&mut self, n: u8)

Writes an unsigned 8 bit integer to self.

fn put_i8(&mut self, n: i8)

Writes a signed 8 bit integer to self.

fn put_u16_be(&mut self, n: u16)

Writes an unsigned 16 bit integer to self in big-endian byte order.

fn put_u16_le(&mut self, n: u16)

Writes an unsigned 16 bit integer to self in little-endian byte order.

fn put_i16_be(&mut self, n: i16)

Writes a signed 16 bit integer to self in big-endian byte order.

fn put_i16_le(&mut self, n: i16)

Writes a signed 16 bit integer to self in little-endian byte order.

fn put_u32_be(&mut self, n: u32)

Writes an unsigned 32 bit integer to self in big-endian byte order.

fn put_u32_le(&mut self, n: u32)

Writes an unsigned 32 bit integer to self in little-endian byte order.

fn put_i32_be(&mut self, n: i32)

Writes a signed 32 bit integer to self in big-endian byte order.

fn put_i32_le(&mut self, n: i32)

Writes a signed 32 bit integer to self in little-endian byte order.

fn put_u64_be(&mut self, n: u64)

Writes an unsigned 64 bit integer to self in the big-endian byte order.

fn put_u64_le(&mut self, n: u64)

Writes an unsigned 64 bit integer to self in little-endian byte order.

fn put_i64_be(&mut self, n: i64)

Writes a signed 64 bit integer to self in the big-endian byte order.

fn put_i64_le(&mut self, n: i64)

Writes a signed 64 bit integer to self in little-endian byte order.

fn put_uint_be(&mut self, n: u64, nbytes: usize)

Writes an unsigned n-byte integer to self in big-endian byte order.

fn put_uint_le(&mut self, n: u64, nbytes: usize)

Writes an unsigned n-byte integer to self in the little-endian byte order.

fn put_int_be(&mut self, n: i64, nbytes: usize)

Writes a signed n-byte integer to self in big-endian byte order.

fn put_int_le(&mut self, n: i64, nbytes: usize)

Writes a signed n-byte integer to self in little-endian byte order.

fn put_f32_be(&mut self, n: f32)

Writes an IEEE754 single-precision (4 bytes) floating point number to self in big-endian byte order.

fn put_f32_le(&mut self, n: f32)

Writes an IEEE754 single-precision (4 bytes) floating point number to self in little-endian byte order.

fn put_f64_be(&mut self, n: f64)

Writes an IEEE754 double-precision (8 bytes) floating point number to self in big-endian byte order.

fn put_f64_le(&mut self, n: f64)

Writes an IEEE754 double-precision (8 bytes) floating point number to self in little-endian byte order.

fn by_ref(&mut self) -> &mut Self

Creates a "by reference" adaptor for this instance of BufMut.

fn writer(self) -> Writer<Self>

Creates an adaptor which implements the Write trait for self.