350 lines
13 KiB
Rust
350 lines
13 KiB
Rust
//! The scanner task and scanning APIs.
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use std::{collections::HashMap, sync::Arc, time::Duration};
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use color_eyre::{eyre::eyre, Report};
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use itertools::Itertools;
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use tower::{buffer::Buffer, util::BoxService, Service, ServiceExt};
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use tracing::info;
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use zcash_client_backend::{
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data_api::ScannedBlock,
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encoding::decode_extended_full_viewing_key,
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proto::compact_formats::{
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ChainMetadata, CompactBlock, CompactSaplingOutput, CompactSaplingSpend, CompactTx,
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},
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scanning::{ScanError, ScanningKey},
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};
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use zcash_primitives::{
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constants::*,
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sapling::SaplingIvk,
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zip32::{AccountId, DiversifiableFullViewingKey, Scope},
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};
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use zebra_chain::{
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block::Block,
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chain_tip::ChainTip,
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diagnostic::task::WaitForPanics,
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parameters::Network,
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serialization::ZcashSerialize,
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transaction::{self, Transaction},
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};
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use zebra_state::{ChainTipChange, SaplingScannedResult};
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use crate::storage::{SaplingScanningKey, Storage};
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/// The generic state type used by the scanner.
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pub type State = Buffer<
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BoxService<zebra_state::Request, zebra_state::Response, zebra_state::BoxError>,
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zebra_state::Request,
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>;
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/// Wait a few seconds at startup for some blocks to get verified.
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///
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/// But sometimes the state might be empty if the network is slow.
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const INITIAL_WAIT: Duration = Duration::from_secs(15);
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/// The amount of time between checking for new blocks and starting new scans.
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///
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/// This is just under half the target block interval.
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const CHECK_INTERVAL: Duration = Duration::from_secs(30);
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/// We log an info log with progress after this many blocks.
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const INFO_LOG_INTERVAL: u32 = 100_000;
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/// Start a scan task that reads blocks from `state`, scans them with the configured keys in
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/// `storage`, and then writes the results to `storage`.
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pub async fn start(
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mut state: State,
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chain_tip_change: ChainTipChange,
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storage: Storage,
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) -> Result<(), Report> {
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let network = storage.network();
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let mut height = storage.min_sapling_birthday_height();
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// Read keys from the storage on disk, which can block async execution.
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let key_storage = storage.clone();
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let key_birthdays = tokio::task::spawn_blocking(move || key_storage.sapling_keys())
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.wait_for_panics()
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.await;
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// Parse and convert keys once, then use them to scan all blocks.
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// There is some cryptography here, but it should be fast even with thousands of keys.
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let parsed_keys: HashMap<
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SaplingScanningKey,
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(Vec<DiversifiableFullViewingKey>, Vec<SaplingIvk>),
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> = key_birthdays
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.keys()
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.map(|key| {
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let parsed_keys = sapling_key_to_scan_block_keys(key, network)?;
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Ok::<_, Report>((key.clone(), parsed_keys))
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})
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.try_collect()?;
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// Give empty states time to verify some blocks before we start scanning.
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tokio::time::sleep(INITIAL_WAIT).await;
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loop {
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// Get a block from the state.
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// We can't use ServiceExt::oneshot() here, because it causes lifetime errors in init().
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let block = state
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.ready()
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.await
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.map_err(|e| eyre!(e))?
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.call(zebra_state::Request::Block(height.into()))
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.await
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.map_err(|e| eyre!(e))?;
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let block = match block {
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zebra_state::Response::Block(Some(block)) => block,
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zebra_state::Response::Block(None) => {
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// If we've reached the tip, sleep for a while then try and get the same block.
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tokio::time::sleep(CHECK_INTERVAL).await;
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continue;
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}
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_ => unreachable!("unmatched response to a state::Tip request"),
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};
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// Only log at info level every 100,000 blocks
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let is_info_log =
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height == storage.min_sapling_birthday_height() || height.0 % INFO_LOG_INTERVAL == 0;
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// TODO: add debug logs?
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if is_info_log {
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info!(
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"Scanning the blockchain: now at block {:?}, current tip {:?}",
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height,
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chain_tip_change
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.latest_chain_tip()
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.best_tip_height_and_hash(),
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);
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}
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for (key_num, (sapling_key, birthday_height)) in key_birthdays.iter().enumerate() {
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// # Security
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//
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// We can't log `sapling_key` here because it is a private viewing key. Anyone who reads
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// the logs could use the key to view those transactions.
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if is_info_log {
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info!(
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"Scanning the blockchain for key {}, started at block {:?}",
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key_num, birthday_height,
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);
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}
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// Get the pre-parsed keys for this configured key.
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let (dfvks, ivks) = parsed_keys.get(sapling_key).cloned().unwrap_or_default();
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// Scan the block, which blocks async execution until the scan is complete.
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//
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// TODO: skip scanning before birthday height (#8022)
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// TODO: scan each key in parallel (after MVP?)
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let sapling_key = sapling_key.clone();
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let block = block.clone();
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let mut storage = storage.clone();
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// We use a dummy size of the Sapling note commitment tree.
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//
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// We can't set the size to zero, because the underlying scanning function would return
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// `zcash_client_backeng::scanning::ScanError::TreeSizeUnknown`.
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//
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// And we can't set them close to 0, because the scanner subtracts the number of notes
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// in the block, and panics with "attempt to subtract with overflow". The number of
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// notes in a block must be less than this value, this is a consensus rule.
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let sapling_tree_size = 1 << 16;
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tokio::task::spawn_blocking(move || {
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let dfvk_res =
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scan_block(network, &block, sapling_tree_size, &dfvks).map_err(|e| eyre!(e))?;
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let ivk_res =
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scan_block(network, &block, sapling_tree_size, &ivks).map_err(|e| eyre!(e))?;
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let dfvk_res = scanned_block_to_db_result(dfvk_res);
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let ivk_res = scanned_block_to_db_result(ivk_res);
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storage.add_sapling_result(sapling_key.clone(), height, dfvk_res);
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storage.add_sapling_result(sapling_key, height, ivk_res);
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Ok::<_, Report>(())
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})
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.wait_for_panics()
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.await?;
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}
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height = height
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.next()
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.expect("a valid blockchain never reaches the max height");
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}
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}
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/// Returns transactions belonging to the given `ScanningKey`. This list of keys should come from
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/// a single configured `SaplingScanningKey`.
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///
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/// # Performance / Hangs
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///
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/// This method can block while reading database files, so it must be inside spawn_blocking()
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/// in async code.
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///
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/// TODO:
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/// - Remove the `sapling_tree_size` parameter or turn it into an `Option` once we have access to
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/// Zebra's state, and we can retrieve the tree size ourselves.
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/// - Add prior block metadata once we have access to Zebra's state.
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pub fn scan_block<K: ScanningKey>(
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network: Network,
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block: &Arc<Block>,
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sapling_tree_size: u32,
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scanning_keys: &[K],
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) -> Result<ScannedBlock<K::Nf>, ScanError> {
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// TODO: Implement a check that returns early when the block height is below the Sapling
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// activation height.
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let network: zcash_primitives::consensus::Network = network.into();
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let chain_metadata = ChainMetadata {
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sapling_commitment_tree_size: sapling_tree_size,
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// Orchard is not supported at the moment so the tree size can be 0.
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orchard_commitment_tree_size: 0,
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};
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// Use a dummy `AccountId` as we don't use accounts yet.
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let dummy_account = AccountId::from(0);
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let scanning_keys: Vec<_> = scanning_keys
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.iter()
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.map(|key| (&dummy_account, key))
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.collect();
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zcash_client_backend::scanning::scan_block(
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&network,
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block_to_compact(block, chain_metadata),
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scanning_keys.as_slice(),
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// Ignore whether notes are change from a viewer's own spends for now.
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&[],
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// Ignore previous blocks for now.
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None,
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)
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}
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/// Converts a Zebra-format scanning key into some `scan_block()` keys.
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///
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/// Currently only accepts extended full viewing keys, and returns both their diversifiable full
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/// viewing key and their individual viewing key, for testing purposes.
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///
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/// TODO: work out what string format is used for SaplingIvk, if any, and support it here
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/// performance: stop returning both the dfvk and ivk for the same key
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pub fn sapling_key_to_scan_block_keys(
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sapling_key: &SaplingScanningKey,
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network: Network,
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) -> Result<(Vec<DiversifiableFullViewingKey>, Vec<SaplingIvk>), Report> {
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let hrp = if network.is_a_test_network() {
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// Assume custom testnets have the same HRP
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//
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// TODO: add the regtest HRP here
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testnet::HRP_SAPLING_EXTENDED_FULL_VIEWING_KEY
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} else {
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mainnet::HRP_SAPLING_EXTENDED_FULL_VIEWING_KEY
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};
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let efvk = decode_extended_full_viewing_key(hrp, sapling_key).map_err(|e| eyre!(e))?;
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// Just return all the keys for now, so we can be sure our code supports them.
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let dfvk = efvk.to_diversifiable_full_viewing_key();
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let eivk = dfvk.to_ivk(Scope::External);
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let iivk = dfvk.to_ivk(Scope::Internal);
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Ok((vec![dfvk], vec![eivk, iivk]))
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}
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/// Converts a zebra block and meta data into a compact block.
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pub fn block_to_compact(block: &Arc<Block>, chain_metadata: ChainMetadata) -> CompactBlock {
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CompactBlock {
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height: block
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.coinbase_height()
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.expect("verified block should have a valid height")
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.0
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.into(),
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// TODO: performance: look up the block hash from the state rather than recalculating it
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hash: block.hash().bytes_in_display_order().to_vec(),
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prev_hash: block
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.header
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.previous_block_hash
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.bytes_in_display_order()
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.to_vec(),
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time: block
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.header
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.time
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.timestamp()
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.try_into()
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.expect("unsigned 32-bit times should work until 2105"),
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header: block
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.header
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.zcash_serialize_to_vec()
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.expect("verified block should serialize"),
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vtx: block
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.transactions
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.iter()
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.cloned()
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.enumerate()
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.map(transaction_to_compact)
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.collect(),
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chain_metadata: Some(chain_metadata),
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// The protocol version is used for the gRPC wire format, so it isn't needed here.
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proto_version: 0,
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}
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}
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/// Converts a zebra transaction into a compact transaction.
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fn transaction_to_compact((index, tx): (usize, Arc<Transaction>)) -> CompactTx {
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CompactTx {
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index: index
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.try_into()
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.expect("tx index in block should fit in u64"),
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// TODO: performance: look up the tx hash from the state rather than recalculating it
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hash: tx.hash().bytes_in_display_order().to_vec(),
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// `fee` is not checked by the `scan_block` function. It is allowed to be unset.
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// <https://docs.rs/zcash_client_backend/latest/zcash_client_backend/proto/compact_formats/struct.CompactTx.html#structfield.fee>
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fee: 0,
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spends: tx
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.sapling_nullifiers()
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.map(|nf| CompactSaplingSpend {
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nf: <[u8; 32]>::from(*nf).to_vec(),
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})
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.collect(),
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// > output encodes the cmu field, ephemeralKey field, and a 52-byte prefix of the encCiphertext field of a Sapling Output
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//
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// <https://docs.rs/zcash_client_backend/latest/zcash_client_backend/proto/compact_formats/struct.CompactSaplingOutput.html>
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outputs: tx
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.sapling_outputs()
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.map(|output| CompactSaplingOutput {
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cmu: output.cm_u.to_bytes().to_vec(),
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ephemeral_key: output
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.ephemeral_key
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.zcash_serialize_to_vec()
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.expect("verified output should serialize successfully"),
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ciphertext: output
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.enc_ciphertext
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.zcash_serialize_to_vec()
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.expect("verified output should serialize successfully")
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.into_iter()
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.take(52)
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.collect(),
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})
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.collect(),
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// `actions` is not checked by the `scan_block` function.
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actions: vec![],
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}
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}
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/// Convert a scanned block to a list of scanner database results.
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fn scanned_block_to_db_result<Nf>(scanned_block: ScannedBlock<Nf>) -> Vec<SaplingScannedResult> {
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scanned_block
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.transactions()
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.iter()
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.map(|tx| transaction::Hash::from_bytes_in_display_order(tx.txid.as_ref()))
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.collect()
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}
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