120 lines
4.2 KiB
Rust
120 lines
4.2 KiB
Rust
//! Async RedJubjub batch verifier service
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#[cfg(test)]
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mod tests;
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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::{ready, Ready};
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use once_cell::sync::Lazy;
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use rand::thread_rng;
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use redjubjub::{batch, *};
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use tokio::sync::broadcast::{channel, RecvError, Sender};
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use tower::Service;
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use tower_batch::{Batch, BatchControl};
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use tower_fallback::Fallback;
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use tower_util::ServiceFn;
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/// Global batch verification context for RedJubjub 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) -> Ready<Result<(), Error>>>>,
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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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super::MAX_BATCH_LATENCY,
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),
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// We want to fallback to individual verification if batch verification
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// fails, so we need a Service to use. The obvious way to do this would
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// be to write a closure that returns an async block. But because we
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// have to specify the type of a static, we need to be able to write the
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// type of the closure and its return value, and both closures and async
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// blocks have eldritch types whose names cannot be written. So instead,
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// we use a Ready to avoid an async block and cast the closure to a
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// function (which is possible because it doesn't capture any state).
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tower::service_fn((|item: Item| ready(item.verify_single())) as fn(_) -> _),
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)
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});
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/// RedJubjub signature verifier service
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pub struct Verifier {
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batch: batch::Verifier,
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// This uses a "broadcast" channel, which is an mpmc channel. Tokio also
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// provides a spmc channel, "watch", but it only keeps the latest value, so
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// using it would require thinking through whether it was possible for
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// results from one batch to be mixed with another.
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tx: Sender<Result<(), Error>>,
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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 = batch::Verifier::default();
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// XXX(hdevalence) what's a reasonable choice here?
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let (tx, _) = channel(10);
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Self { tx, batch }
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}
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}
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/// Type alias to clarify that this batch::Item is a RedJubjubItem
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pub type Item = batch::Item;
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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 = Result<(), Error>> + 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 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.recv().await {
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Ok(result) => result,
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Err(RecvError::Lagged(_)) => {
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tracing::warn!(
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"missed channel updates for the correct signature batch!"
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);
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Err(Error::InvalidSignature)
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}
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Err(RecvError::Closed) => panic!("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 flush command");
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let batch = mem::take(&mut self.batch);
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let _ = self.tx.send(batch.verify(thread_rng()));
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Box::pin(async { 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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let batch = mem::take(&mut self.batch);
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let _ = self.tx.send(batch.verify(thread_rng()));
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}
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}
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