84 lines
3.0 KiB
Rust
84 lines
3.0 KiB
Rust
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//! Checkpoint lists for checkpoint-based block verification
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//!
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//! Each checkpoint consists of a coinbase height and block header hash.
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//!
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//! Checkpoints can be used to verify their ancestors, by chaining backwards
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//! to another checkpoint, via each block's parent block hash.
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use std::{collections::BTreeMap, error, ops::RangeBounds};
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use zebra_chain::block::BlockHeaderHash;
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use zebra_chain::types::BlockHeight;
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/// The inner error type for CheckpointVerifier.
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// TODO(jlusby): Error = Report ?
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type Error = Box<dyn error::Error + Send + Sync + 'static>;
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/// Checkpoint lists are implemented using a BTreeMap.
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///
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/// Checkpoints should be chosen to avoid forks or chain reorganizations,
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/// which only happen in the last few hundred blocks in the chain.
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/// (zcashd allows chain reorganizations up to 99 blocks, and prunes
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/// orphaned side-chains after 288 blocks.)
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///
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/// There must be a checkpoint for the genesis block at BlockHeight 0.
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/// (All other checkpoints are optional.)
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#[derive(Debug)]
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pub struct CheckpointList(BTreeMap<BlockHeight, BlockHeaderHash>);
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impl CheckpointList {
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/// Create a new checkpoint list from `checkpoint_list`.
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pub fn new(
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checkpoint_list: impl IntoIterator<Item = (BlockHeight, BlockHeaderHash)>,
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) -> Result<Self, Error> {
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let checkpoints: BTreeMap<BlockHeight, BlockHeaderHash> =
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checkpoint_list.into_iter().collect();
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// An empty checkpoint list can't actually verify any blocks.
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match checkpoints.keys().next() {
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Some(BlockHeight(0)) => {}
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None => Err("there must be at least one checkpoint, for the genesis block")?,
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_ => Err("checkpoints must start at the genesis block height 0")?,
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};
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Ok(CheckpointList(checkpoints))
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}
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/// Is there a checkpoint at `height`?
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///
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/// See `BTreeMap::contains_key()` for details.
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pub fn contains(&self, height: BlockHeight) -> bool {
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self.0.contains_key(&height)
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}
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/// Returns the hash corresponding to the checkpoint at `height`,
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/// or None if there is no checkpoint at that height.
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///
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/// See `BTreeMap::get()` for details.
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pub fn hash(&self, height: BlockHeight) -> Option<BlockHeaderHash> {
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self.0.get(&height).cloned()
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}
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/// Return the block height of the highest checkpoint in the checkpoint list.
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///
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/// If there is only a single checkpoint, then the maximum height will be
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/// zero. (The genesis block.)
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///
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/// The maximum height is constant for each checkpoint list.
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pub fn max_height(&self) -> BlockHeight {
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self.0
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.keys()
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.cloned()
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.next_back()
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.expect("checkpoint lists must have at least one checkpoint")
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}
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/// Return the block height of the highest checkpoint in a sub-range.
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pub fn max_height_in_range<R>(&self, range: R) -> Option<BlockHeight>
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where
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R: RangeBounds<BlockHeight>,
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{
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self.0.range(range).map(|(height, _)| *height).next_back()
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}
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}
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