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// Copyright 2021 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Rewindable (but still readonly) view of a PMMR.
//! Only supports non-pruneable backends (i.e. kernel MMR backend).
use std::marker;
use crate::core::pmmr::{round_up_to_leaf_pos, Backend, ReadonlyPMMR};
use crate::ser::PMMRable;
/// Rewindable (but still readonly) view of a PMMR.
pub struct RewindablePMMR<'a, T, B>
where
T: PMMRable,
B: Backend<T>,
{
/// The last position in the PMMR
last_pos: u64,
/// The backend for this readonly PMMR
backend: &'a B,
// only needed to parameterise Backend
_marker: marker::PhantomData<T>,
}
impl<'a, T, B> RewindablePMMR<'a, T, B>
where
T: PMMRable,
B: 'a + Backend<T>,
{
/// Build a new readonly PMMR.
pub fn new(backend: &'a B) -> RewindablePMMR<'_, T, B> {
RewindablePMMR {
backend,
last_pos: 0,
_marker: marker::PhantomData,
}
}
/// Build a new readonly PMMR pre-initialized to
/// last_pos with the provided backend.
pub fn at(backend: &'a B, last_pos: u64) -> RewindablePMMR<'_, T, B> {
RewindablePMMR {
backend,
last_pos,
_marker: marker::PhantomData,
}
}
/// Note: We only rewind the last_pos, we do not rewind the (readonly) backend.
/// Prunable backends are not supported here.
pub fn rewind(&mut self, position: u64) -> Result<(), String> {
// Identify which actual position we should rewind to as the provided
// position is a leaf. We traverse the MMR to include any parent(s) that
// need to be included for the MMR to be valid.
self.last_pos = round_up_to_leaf_pos(position);
Ok(())
}
/// Allows conversion of a "rewindable" PMMR into a "readonly" PMMR.
/// Intended usage is to create a rewindable PMMR, rewind it,
/// then convert to "readonly" and read from it.
pub fn as_readonly(&self) -> ReadonlyPMMR<'a, T, B> {
ReadonlyPMMR::at(&self.backend, self.last_pos)
}
}