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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(); } }