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//! Pivot hint provides validation support during blockchain synchronization and
//! historical data execution by leveraging trusted pivot chain information from
//! authoritative sources.
//!
//! During the synchronization process of archive nodes, when processing
//! historical data, pivot hints help prevent execution on forked branches and
//! protect against problematic historical states that occurred on
//! mainnet/testnet chains.
//!
//! # File Structure
//! The pivot hint file consists of three main parts:
//! * Header Part (28 bytes): Contains configuration parameters
//! * Page Digests Part: A list of keccak hashes for each page
//! * Pages Part: Sequential storage of all pages
//!
//! # Page Organization
//! Blocks are organized into pages based on several configurable parameters:
//! * `range_max`: Upper bound (exclusive) of block heights for stored hashes
//! * `page_interval`: Number of consecutive blocks in each page
//! * Each page contains:
//! - Major section: Full hashes for blocks every `major_interval` heights
//! - Minor section: Hash prefixes (in length of `minor_hash_length``) for
//! blocks every `minor_interval` heights
//!
//! # Parameter Constraints
//! The following parameters must maintain integer multiple relationships:
//! * `range_max` must be a multiple of `page_interval`
//! * `page_interval` must be a multiple of `major_interval`
//! * `major_interval` must be a multiple of `minor_interval`
//!
//! # Fork Validation
//! During fork validation, when the consensus layer attempts to switch the
//! pivot chain from branch A to branch B, it must provide:
//! * `fork_at`: The first block height where branch A and B diverge
//! * `me_height`: The last block height of branch B
//! * A query interface to retrieve block hashes on branch B within range
//! [fork_at, me_height]
//!
//! The validation process follows these rules:
//! * If [fork_at, me_height] covers with major section records, validation uses
//! the last recorded full hash
//! * If no major section records covered but minor section overlap exists,
//! validation uses minor section records (note: this may allow switching to
//! branches that aren't on the final main chain)
//! * If neither major nor minor section overlap exists, the switch is allowed
//!
//! When `fork_at` exceeds `range_max`, it indicates the fork point is beyond
//! the static file records, and the switch is automatically allowed.
//!
//! # Loading Process
//! 1. Load and validate Header Part parameters
//! 2. Load Page Digests Part and verify against predetermined Pivot Hint
//! Checksum
//! 3. Keep Page Digests in memory
//! 4. Verify each page against Page Digests when loading to prevent corruption
mod config;
mod header;
mod page;
#[cfg(test)]
mod tests;
pub use config::PivotHintConfig;
use header::{PivotHintHeader, HEADER_LENGTH};
use page::PivotHintPage;
use std::{
fs::File,
io::{Read, Seek, SeekFrom},
sync::atomic::{AtomicBool, Ordering},
};
use crate::hash::{keccak, H256};
use lru_time_cache::LruCache;
use parking_lot::RwLock;
/// Manages pivot block hash records for chain fork validation during sync
/// process.
pub struct PivotHint {
/// Path to the pivot hint file
file_path: String,
/// Module status flag. Set to false if error occurs, disabling the module
/// without thread panic.
active: AtomicBool,
/// Pivot hint header with configuration parameters
header: PivotHintHeader,
/// LRU cache storing loaded pivot hint pages
pages: RwLock<LruCache<u64, PivotHintPage>>,
/// Keccak hashes of all pages, kept in memory for integrity verification
page_digests: Vec<H256>,
}
impl PivotHint {
/// Creates a new PivotHint instance by loading and validating the pivot
/// hint file.
///
/// # Steps
/// 1. Loads and validates the header
/// 2. Loads page digests and verifies against provided checksum
/// 3. Initializes LRU cache for page data
///
/// # Arguments
/// * `conf` - Configuration containing file path and expected checksum
///
/// # Errors
/// * File open/read errors
/// * Header parsing errors
/// * Checksum mismatch
pub fn new(conf: &PivotHintConfig) -> Result<Self, String> {
let mut file = File::open(&conf.file_path)
.map_err(|e| format!("Cannot open file: {:?}", e))?;
let mut raw_header = [0u8; HEADER_LENGTH];
file.read_exact(&mut raw_header)
.map_err(|e| format!("Cannot load header: {:?}", e))?;
let header = PivotHintHeader::from_raw(raw_header)
.map_err(|e| format!("Cannot parse and check header: {}", e))?;
let mut raw_page_digests = vec![0u8; header.page_number() * 32];
file.read_exact(&mut raw_page_digests)
.map_err(|e| format!("Cannot load page digests: {:?}", e))?;
let file_checksum = keccak(&raw_page_digests);
if file_checksum != conf.checksum {
return Err("Incorrect checksum".into());
}
let page_digests = raw_page_digests
.chunks_exact(32)
.map(H256::from_slice)
.collect();
Ok(Self {
file_path: conf.file_path.clone(),
active: AtomicBool::new(true),
header,
pages: RwLock::new(LruCache::with_capacity(5)),
page_digests,
})
}
/// Validates if switching to a target branch is allowed based on pivot hint
/// records.
///
/// # Arguments
/// * `fork_at` - First block height where the current chain and target
/// branch diverge
/// * `me_height` - Last block height of the target branch
/// * `ancestor_hash_at` - Callback to retrieve block hash at specified
/// height on target branch
///
/// # Returns
/// Returns whether switching to the fork branch is allowed.
pub fn allow_switch(
&self, fork_at: u64, me_height: u64,
ancestor_hash_at: impl FnOnce(u64) -> H256,
) -> bool {
if !self.active.load(Ordering::Acquire) {
return true;
}
if fork_at >= self.header.range_max {
return true;
}
let check_height = if let Some(check_height) =
self.header.compute_check_height(fork_at, me_height)
{
check_height
} else {
return true;
};
let actual_hash = ancestor_hash_at(check_height);
let result = self.check_hash(check_height, actual_hash);
debug!("Pivot hint check switch result {result}. fork_at: {fork_at}, me_height: {me_height}, check_height: {check_height}, fetch_hash: {actual_hash:?}");
result
}
pub fn allow_extend(&self, height: u64, hash: H256) -> bool {
if !self.active.load(Ordering::Acquire) {
return true;
}
if height >= self.header.range_max {
return true;
}
if height % self.header.minor_interval != 0 {
return true;
}
let page_number = height / self.header.page_interval;
let page_offset = height % self.header.page_interval;
let result = self.check_with_page(page_number, |page| {
page.check_hash_at_height(page_offset, hash)
});
debug!("Pivot hint check extend result {result}. me_height: {height}, fetch_hash: {hash:?}");
result
}
pub fn is_active(&self) -> bool { self.active.load(Ordering::Acquire) }
fn check_hash(&self, height: u64, hash: H256) -> bool {
let page_number = height / self.header.page_interval;
let page_offset = height % self.header.page_interval;
self.check_with_page(page_number, |page| {
page.check_hash_at_height(page_offset, hash)
})
}
fn check_with_page(
&self, page_number: u64, check: impl Fn(&PivotHintPage) -> bool,
) -> bool {
let mut guard = self.pages.write();
if let Some(page) = guard.get(&page_number) {
check(page)
} else {
info!("Loading pivot hint page {}", page_number);
let page = match self.load_page(page_number) {
Ok(page) => page,
Err(e) => {
warn!(
"Failed to load pivot hint page {}, pivot hint check disabled: {}",
page_number, e
);
self.active.store(false, Ordering::Release);
return true;
}
};
let result = check(&page);
guard.insert(page_number, page);
result
}
}
fn load_page(&self, page_number: u64) -> Result<PivotHintPage, String> {
let page_bytes = self.header.page_bytes();
let start_pos = HEADER_LENGTH as u64
+ self.page_digests.len() as u64 * 32
+ page_number * page_bytes as u64;
let mut file = File::open(&self.file_path)
.map_err(|e| format!("Cannot open pivot hint file: {:?}", e))?;
file.seek(SeekFrom::Start(start_pos))
.map_err(|e| format!("Cannot seek to start position: {:?}", e))?;
let mut page_content = vec![0u8; page_bytes];
file.read_exact(&mut page_content[..])
.map_err(|e| format!("Cannot load the page: {:?}", e))?;
let expected_page_checksum =
if let Some(hash) = self.page_digests.get(page_number as usize) {
hash
} else {
return Err("Empty page checksum".into());
};
let actual_page_checksum = keccak(&page_content);
if expected_page_checksum != &actual_page_checksum {
return Err("Incorrect checksum".into());
}
Ok(PivotHintPage::new(page_content, self.header))
}
}