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Allow querying all keys with a prefix through storage queries (#576)
* Add trie_node_info function * Allow passing nibbles for the node info * Add a `prefix_proof` module * Comment and fmt * Finish changes * Build fix * Fix doc * Verbose panic message * More docfix * Add comment Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
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| // Smoldot | ||
| // Copyright (C) 2019-2021 Parity Technologies (UK) Ltd. | ||
| // SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0 | ||
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| // This program is free software: you can redistribute it and/or modify | ||
| // it under the terms of the GNU General Public License as published by | ||
| // the Free Software Foundation, either version 3 of the License, or | ||
| // (at your option) any later version. | ||
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| // This program is distributed in the hope that it will be useful, | ||
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| // GNU General Public License for more details. | ||
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| // You should have received a copy of the GNU General Public License | ||
| // along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
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| //! Scanning, through trie proofs, the list of all keys that share a certain prefix. | ||
| //! | ||
| //! This module is a helper whose objective is to find out the list of all keys that start with | ||
| //! a certain prefix by performing storage proofs. | ||
| //! | ||
| //! The total number of storage proofs required is equal to the maximum depth of the tree below | ||
| //! the requested prefix, plus one. For example, if a tree has the nodes `[1, 5]`, `[1, 5, 8, 9]`, | ||
| //! and `[1, 5, 8, 9, 2]`, then four queries are necessary to find all the keys whose prefix | ||
| //! is `[1]`. | ||
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| // TODO: usage example | ||
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| // TODO: this code is entirely untested; no idea if it works | ||
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| use super::{nibble, proof_verify}; | ||
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| use alloc::{vec, vec::Vec}; | ||
| use core::{fmt, iter}; | ||
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| /// Configuration to pass to [`prefix_scan`]. | ||
| pub struct Config<'a> { | ||
| /// Prefix that all the keys must share. | ||
| pub prefix: &'a [u8], | ||
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| /// Merkle value (or node value) of the root node of the trie. | ||
| /// | ||
| /// > **Note**: The Merkle value and node value are always the same for the root node. | ||
| pub trie_root_hash: [u8; 32], | ||
| } | ||
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| /// Start a new scanning process. | ||
| pub fn prefix_scan(config: Config<'_>) -> PrefixScan { | ||
| PrefixScan { | ||
| trie_root_hash: config.trie_root_hash, | ||
| next_queries: vec![nibble::bytes_to_nibbles(config.prefix.iter().copied()).collect()], | ||
| final_result: Vec::with_capacity(32), | ||
| } | ||
| } | ||
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| /// Scan of a prefix in progress. | ||
| pub struct PrefixScan { | ||
| trie_root_hash: [u8; 32], | ||
| // TODO: we have lots of Vecs here; maybe find a way to optimize | ||
| next_queries: Vec<Vec<nibble::Nibble>>, | ||
| // TODO: we have lots of Vecs here; maybe find a way to optimize | ||
| final_result: Vec<Vec<u8>>, | ||
| } | ||
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| impl PrefixScan { | ||
| /// Returns the list of keys whose storage proof must be queried. | ||
| pub fn requested_keys( | ||
| &'_ self, | ||
| ) -> impl Iterator<Item = impl Iterator<Item = nibble::Nibble> + '_> + '_ { | ||
| self.next_queries.iter().map(|l| l.iter().copied()) | ||
| } | ||
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| /// Injects the proof presumably containing the keys returned by [`PrefixScan::requested_keys`]. | ||
| /// | ||
| /// Returns an error if the proof is invalid. In that case, `self` isn't modified. | ||
| pub fn resume<'a>( | ||
| mut self, | ||
| proof: impl Iterator<Item = &'a [u8]> + Clone + 'a, | ||
| ) -> Result<ResumeOutcome, proof_verify::Error> { | ||
| // The entire body is executed as long as verifying at least one proof succeeds. | ||
| for is_first_iteration in iter::once(true).chain(iter::repeat(false)) { | ||
| // Filled with the queries to perform at the next iteration. | ||
| // Capacity assumes a maximum of 2 children per node on average. This value was chosen | ||
| // completely arbitrarily. | ||
| let mut next = Vec::with_capacity(self.next_queries.len() * 2); | ||
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| // True if any proof verification has succeeded during this iteration. | ||
| // Controls whether we continue iterating. | ||
| let mut any_successful_proof = false; | ||
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| for query in &self.next_queries { | ||
| let info = match proof_verify::trie_node_info(proof_verify::TrieNodeInfoConfig { | ||
| requested_key: query.iter().cloned(), | ||
| trie_root_hash: &self.trie_root_hash, | ||
| proof: proof.clone(), | ||
| }) { | ||
| Ok(info) => info, | ||
| Err(err) if is_first_iteration => return Err(err), | ||
| Err(_) => continue, | ||
| }; | ||
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| any_successful_proof = true; | ||
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| if info.node_value.is_some() { | ||
| // Trie nodes with a value are always aligned to "bytes-keys". In other words, the | ||
| // number of nibbles is always even. | ||
| debug_assert_eq!(query.len() % 2, 0); | ||
| let key = query | ||
| .chunks(2) | ||
| .map(|n| (u8::from(n[0]) << 4) | u8::from(n[1])) | ||
| .collect::<Vec<_>>(); | ||
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| // Insert in final results, making sure we check for duplicates. | ||
| debug_assert!(!self.final_result.iter().any(|n| *n == key)); | ||
| self.final_result.push(key); | ||
| } | ||
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| for child_nibble in info.children.next_nibbles() { | ||
| let mut next_query = Vec::with_capacity(query.len() + 1); | ||
| next_query.extend_from_slice(&query); | ||
| next_query.push(child_nibble); | ||
| next.push(next_query); | ||
| } | ||
| } | ||
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| // Finished when nothing more to request. | ||
| if next.is_empty() { | ||
| return Ok(ResumeOutcome::Success { | ||
| keys: self.final_result, | ||
| }); | ||
| } | ||
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| // Update `next_queries` for the next iteration. | ||
| self.next_queries = next; | ||
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| if !any_successful_proof { | ||
| break; | ||
| } | ||
| } | ||
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| Ok(ResumeOutcome::InProgress(self)) | ||
| } | ||
| } | ||
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| impl fmt::Debug for PrefixScan { | ||
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| f.debug_struct("PrefixScan").finish() | ||
| } | ||
| } | ||
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| /// Outcome of calling [`PrefixScan::resume`]. | ||
| #[derive(Debug)] | ||
| pub enum ResumeOutcome { | ||
| /// Scan must continue with the next storage proof query. | ||
| InProgress(PrefixScan), | ||
| /// Scan has succeeded. | ||
| Success { | ||
| /// List of keys with the requested prefix. | ||
| keys: Vec<Vec<u8>>, | ||
| }, | ||
| } |
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