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//! Variable-sized output digest support
use crate::{InvalidOutputSize, Reset};
#[cfg(feature = "alloc")]
use alloc::boxed::Box;
/// Trait for returning digest result with the variable size
pub trait VariableOutput: Sized {
/// Create new hasher instance with the given output size.
///
/// It will return `Err(InvalidOutputSize)` in case if hasher can not return
/// specified output size. It will always return an error if output size
/// equals to zero.
fn new(output_size: usize) -> Result<Self, InvalidOutputSize>;
/// Get output size of the hasher instance provided to the `new` method
fn output_size(&self) -> usize;
/// Retrieve result via closure and consume hasher.
///
/// Closure is guaranteed to be called, length of the buffer passed to it
/// will be equal to `output_size`.
fn finalize_variable(self, f: impl FnOnce(&[u8]));
/// Retrieve result via closure and reset the hasher state.
///
/// Closure is guaranteed to be called, length of the buffer passed to it
/// will be equal to `output_size`.
fn finalize_variable_reset(&mut self, f: impl FnOnce(&[u8]));
/// Retrieve result into a boxed slice and consume hasher.
///
/// `Box<[u8]>` is used instead of `Vec<u8>` to save stack space, since
/// they have size of 2 and 3 words respectively.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
fn finalize_boxed(self) -> Box<[u8]> {
let n = self.output_size();
let mut buf = vec![0u8; n].into_boxed_slice();
self.finalize_variable(|res| buf.copy_from_slice(res));
buf
}
/// Retrieve result into a boxed slice and reset hasher state.
///
/// `Box<[u8]>` is used instead of `Vec<u8>` to save stack space, since
/// they have size of 2 and 3 words respectively.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
fn finalize_boxed_reset(&mut self) -> Box<[u8]> {
let n = self.output_size();
let mut buf = vec![0u8; n].into_boxed_slice();
self.finalize_variable_reset(|res| buf.copy_from_slice(res));
buf
}
}
/// Trait for variable-sized output digest implementations to use to retrieve
/// the hash output.
///
/// Usage of this trait in user code is discouraged. Instead use the
/// [`VariableOutput::finalize_variable`] or
/// [`VariableOutput::finalize_variable_reset`] methods.
///
/// Types which impl this trait along with [`Reset`] will receive a blanket
/// impl of [`VariableOutput`].
pub trait VariableOutputDirty: Sized {
/// Create new hasher instance with the given output size.
///
/// It will return `Err(InvalidOutputSize)` in case if hasher can not return
/// specified output size. It will always return an error if output size
/// equals to zero.
fn new(output_size: usize) -> Result<Self, InvalidOutputSize>;
/// Get output size of the hasher instance provided to the `new` method
fn output_size(&self) -> usize;
/// Retrieve result into provided buffer and leave hasher in a dirty state.
///
/// This method is expected to only be called once unless
/// [`Reset::reset`] is called, after which point it can be
/// called again and reset again (and so on).
fn finalize_variable_dirty(&mut self, f: impl FnOnce(&[u8]));
}
impl<D: VariableOutputDirty + Reset> VariableOutput for D {
fn new(output_size: usize) -> Result<Self, InvalidOutputSize> {
<Self as VariableOutputDirty>::new(output_size)
}
fn output_size(&self) -> usize {
<Self as VariableOutputDirty>::output_size(self)
}
#[inline]
fn finalize_variable(mut self, f: impl FnOnce(&[u8])) {
self.finalize_variable_dirty(f);
}
#[inline]
fn finalize_variable_reset(&mut self, f: impl FnOnce(&[u8])) {
self.finalize_variable_dirty(f);
self.reset();
}
}