211 lines
7.9 KiB
Rust
211 lines
7.9 KiB
Rust
//! Async Ed25519 batch verifier service
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use std::{
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future::Future,
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mem,
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pin::Pin,
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task::{Context, Poll},
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};
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use futures::{future::BoxFuture, FutureExt};
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use once_cell::sync::Lazy;
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use rand::thread_rng;
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use rayon::prelude::*;
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use tokio::sync::watch;
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use tower::{util::ServiceFn, Service};
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use tower_batch::{Batch, BatchControl};
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use tower_fallback::Fallback;
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use zebra_chain::primitives::ed25519::{batch, *};
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#[cfg(test)]
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mod tests;
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/// The type of the batch verifier.
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type BatchVerifier = batch::Verifier;
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/// The type of verification results.
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type VerifyResult = Result<(), Error>;
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/// The type of the batch sender channel.
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type Sender = watch::Sender<Option<VerifyResult>>;
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/// The type of the batch item.
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/// This is an `Ed25519Item`.
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pub type Item = batch::Item;
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/// Global batch verification context for Ed25519 signatures.
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///
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/// This service transparently batches contemporaneous signature verifications,
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/// handling batch failures by falling back to individual verification.
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///
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/// Note that making a `Service` call requires mutable access to the service, so
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/// you should call `.clone()` on the global handle to create a local, mutable
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/// handle.
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pub static VERIFIER: Lazy<
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Fallback<Batch<Verifier, Item>, ServiceFn<fn(Item) -> BoxFuture<'static, VerifyResult>>>,
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> = Lazy::new(|| {
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Fallback::new(
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Batch::new(
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Verifier::default(),
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super::MAX_BATCH_SIZE,
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None,
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super::MAX_BATCH_LATENCY,
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),
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// We want to fallback to individual verification if batch verification fails,
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// so we need a Service to use.
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//
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// Because we have to specify the type of a static, we need to be able to
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// write the type of the closure and its return value. But both closures and
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// async blocks have unnameable types. So instead we cast the closure to a function
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// (which is possible because it doesn't capture any state), and use a BoxFuture
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// to erase the result type.
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// (We can't use BoxCloneService to erase the service type, because it is !Sync.)
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tower::service_fn(
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(|item: Item| Verifier::verify_single_spawning(item).boxed()) as fn(_) -> _,
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),
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)
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});
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/// Ed25519 signature verifier service
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pub struct Verifier {
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/// A batch verifier for ed25519 signatures.
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batch: BatchVerifier,
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/// A channel for broadcasting the result of a batch to the futures for each batch item.
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///
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/// Each batch gets a newly created channel, so there is only ever one result sent per channel.
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/// Tokio doesn't have a oneshot multi-consumer channel, so we use a watch channel.
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tx: Sender,
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}
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impl Default for Verifier {
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fn default() -> Self {
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let batch = BatchVerifier::default();
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let (tx, _) = watch::channel(None);
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Self { batch, tx }
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}
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}
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impl Verifier {
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/// Returns the batch verifier and channel sender from `self`,
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/// replacing them with a new empty batch.
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fn take(&mut self) -> (BatchVerifier, Sender) {
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// Use a new verifier and channel for each batch.
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let batch = mem::take(&mut self.batch);
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let (tx, _) = watch::channel(None);
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let tx = mem::replace(&mut self.tx, tx);
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(batch, tx)
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}
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/// Synchronously process the batch, and send the result using the channel sender.
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/// This function blocks until the batch is completed.
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fn verify(batch: BatchVerifier, tx: Sender) {
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let result = batch.verify(thread_rng());
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let _ = tx.send(Some(result));
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}
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/// Flush the batch using a thread pool, and return the result via the channel.
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/// This returns immediately, usually before the batch is completed.
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fn flush_blocking(&mut self) {
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let (batch, tx) = self.take();
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// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
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//
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// We don't care about execution order here, because this method is only called on drop.
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tokio::task::block_in_place(|| rayon::spawn_fifo(|| Self::verify(batch, tx)));
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}
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/// Flush the batch using a thread pool, and return the result via the channel.
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/// This function returns a future that becomes ready when the batch is completed.
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fn flush_spawning(batch: BatchVerifier, tx: Sender) -> impl Future<Output = ()> {
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// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
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tokio::task::spawn_blocking(|| {
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// TODO:
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// - spawn batches so rayon executes them in FIFO order
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// possible implementation: return a closure in a Future,
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// then run it using scope_fifo() in the worker task,
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// limiting the number of concurrent batches to the number of rayon threads
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rayon::scope_fifo(|s| s.spawn_fifo(|_s| Self::verify(batch, tx)))
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})
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.map(|join_result| join_result.expect("panic in ed25519 batch verifier"))
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}
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/// Verify a single item using a thread pool, and return the result.
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/// This function returns a future that becomes ready when the item is completed.
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fn verify_single_spawning(item: Item) -> impl Future<Output = VerifyResult> {
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// Correctness: Do CPU-intensive work on a dedicated thread, to avoid blocking other futures.
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tokio::task::spawn_blocking(|| {
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// Rayon doesn't have a spawn function that returns a value,
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// so we use a parallel iterator instead.
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//
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// TODO:
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// - when a batch fails, spawn all its individual items into rayon using Vec::par_iter()
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// - spawn fallback individual verifications so rayon executes them in FIFO order,
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// if possible
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rayon::iter::once(item)
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.map(|item| item.verify_single())
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.collect()
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})
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.map(|join_result| join_result.expect("panic in ed25519 fallback verifier"))
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}
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}
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impl Service<BatchControl<Item>> for Verifier {
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type Response = ();
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type Error = Error;
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type Future = Pin<Box<dyn Future<Output = VerifyResult> + Send + 'static>>;
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fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
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Poll::Ready(Ok(()))
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}
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fn call(&mut self, req: BatchControl<Item>) -> Self::Future {
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match req {
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BatchControl::Item(item) => {
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tracing::trace!("got ed25519 item");
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self.batch.queue(item);
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let mut rx = self.tx.subscribe();
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Box::pin(async move {
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match rx.changed().await {
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Ok(()) => {
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// We use a new channel for each batch,
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// so we always get the correct batch result here.
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let result = rx.borrow().expect("completed batch must send a value");
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if result.is_ok() {
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tracing::trace!(?result, "validated ed25519 signature");
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metrics::counter!("signatures.ed25519.validated", 1);
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} else {
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tracing::trace!(?result, "invalid ed25519 signature");
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metrics::counter!("signatures.ed25519.invalid", 1);
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}
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result
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}
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Err(_recv_error) => panic!("ed25519 verifier was dropped without flushing"),
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}
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})
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}
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BatchControl::Flush => {
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tracing::trace!("got ed25519 flush command");
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let (batch, tx) = self.take();
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Box::pin(Self::flush_spawning(batch, tx).map(Ok))
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}
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}
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}
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}
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impl Drop for Verifier {
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fn drop(&mut self) {
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// We need to flush the current batch in case there are still any pending futures.
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// This returns immediately, usually before the batch is completed.
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self.flush_blocking();
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}
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}
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