zebra_consensus/primitives/
sapling.rs

1//! Async Sapling batch verifier service
2
3use core::fmt;
4use std::{
5    future::Future,
6    mem,
7    pin::Pin,
8    task::{Context, Poll},
9};
10
11use futures::{future::BoxFuture, FutureExt, TryFutureExt};
12use once_cell::sync::Lazy;
13use rand::thread_rng;
14use tokio::sync::watch;
15use tower::{util::ServiceFn, Service};
16use tower_batch_control::{Batch, BatchControl, RequestWeight};
17use tower_fallback::Fallback;
18
19use sapling_crypto::{bundle::Authorized, BatchValidator, Bundle};
20use zcash_protocol::value::ZatBalance;
21use zebra_chain::transaction::SigHash;
22
23use crate::groth16::SAPLING;
24
25#[derive(Clone)]
26pub struct Item {
27    /// The bundle containing the Sapling shielded data to verify.
28    bundle: Bundle<Authorized, ZatBalance>,
29    /// The sighash of the transaction that contains the Sapling shielded data.
30    sighash: SigHash,
31}
32
33impl Item {
34    /// Creates a new [`Item`] from a Sapling bundle and sighash.
35    pub fn new(bundle: Bundle<Authorized, ZatBalance>, sighash: SigHash) -> Self {
36        Self { bundle, sighash }
37    }
38}
39
40impl RequestWeight for Item {}
41
42/// A service that verifies Sapling shielded data in batches.
43///
44/// Handles batching incoming requests, driving batches to completion, and reporting results.
45#[derive(Default)]
46pub struct Verifier {
47    /// A batch verifier for Sapling shielded data.
48    batch: BatchValidator,
49
50    /// A channel for broadcasting the verification result of the batch.
51    ///
52    /// Each batch gets a newly created channel, so there is only ever one result sent per channel.
53    /// Tokio doesn't have a oneshot multi-consumer channel, so we use a watch channel.
54    tx: watch::Sender<Option<bool>>,
55}
56
57impl fmt::Debug for Verifier {
58    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
59        f.debug_struct("Verifier")
60            .field("batch", &"..")
61            .field("tx", &self.tx)
62            .finish()
63    }
64}
65
66impl Drop for Verifier {
67    // Flush the current batch in case there are still any pending futures.
68    //
69    // Flushing the batch means we need to validate it. This function fires off the validation and
70    // returns immediately, usually before the validation finishes.
71    fn drop(&mut self) {
72        let batch = mem::take(&mut self.batch);
73        let tx = mem::take(&mut self.tx);
74
75        // The validation is CPU-intensive; do it on a dedicated thread so it does not block.
76        rayon::spawn_fifo(move || {
77            let (spend_vk, output_vk) = SAPLING.verifying_keys();
78
79            // Validate the batch and send the result through the channel.
80            let res = batch.validate(&spend_vk, &output_vk, thread_rng());
81            let _ = tx.send(Some(res));
82        });
83    }
84}
85
86impl Service<BatchControl<Item>> for Verifier {
87    type Response = ();
88    type Error = Box<dyn std::error::Error + Send + Sync>;
89    type Future = Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>>;
90
91    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
92        Poll::Ready(Ok(()))
93    }
94
95    fn call(&mut self, req: BatchControl<Item>) -> Self::Future {
96        match req {
97            BatchControl::Item(item) => {
98                let mut rx = self.tx.subscribe();
99
100                let bundle_check = self
101                    .batch
102                    .check_bundle(item.bundle, item.sighash.into())
103                    .then_some(())
104                    .ok_or("invalid Sapling bundle");
105
106                async move {
107                    bundle_check?;
108
109                    rx.changed()
110                        .await
111                        .map_err(|_| "verifier was dropped without flushing")
112                        .and_then(|_| {
113                            // We use a new channel for each batch, so we always get the correct
114                            // batch result here.
115                            rx.borrow()
116                                .ok_or("threadpool unexpectedly dropped channel sender")?
117                                .then(|| {
118                                    metrics::counter!("proofs.groth16.verified").increment(1);
119                                })
120                                .ok_or_else(|| {
121                                    metrics::counter!("proofs.groth16.invalid").increment(1);
122                                    "batch verification of Sapling shielded data failed"
123                                })
124                        })
125                        .map_err(Self::Error::from)
126                }
127                .boxed()
128            }
129
130            BatchControl::Flush => {
131                let batch = mem::take(&mut self.batch);
132                let tx = mem::take(&mut self.tx);
133
134                async move {
135                    tokio::task::spawn_blocking(move || {
136                        let (spend_vk, output_vk) = SAPLING.verifying_keys();
137
138                        let res = batch.validate(&spend_vk, &output_vk, thread_rng());
139                        tx.send(Some(res))
140                    })
141                    .await?
142                    .map_err(Self::Error::from)
143                }
144                .boxed()
145            }
146        }
147    }
148}
149
150/// Verifies a single [`Item`].
151pub fn verify_single(
152    item: Item,
153) -> Pin<Box<dyn Future<Output = Result<(), Box<dyn std::error::Error + Send + Sync>>> + Send>> {
154    async move {
155        let mut verifier = Verifier::default();
156
157        let check = verifier
158            .batch
159            .check_bundle(item.bundle, item.sighash.into())
160            .then_some(())
161            .ok_or("invalid Sapling bundle");
162        check?;
163
164        tokio::task::spawn_blocking(move || {
165            let (spend_vk, output_vk) = SAPLING.verifying_keys();
166
167            mem::take(&mut verifier.batch).validate(&spend_vk, &output_vk, thread_rng())
168        })
169        .await
170        .map_err(|_| "Sapling bundle validation thread panicked")?
171        .then_some(())
172        .ok_or("invalid proof or sig in Sapling bundle")
173    }
174    .map_err(Box::from)
175    .boxed()
176}
177
178/// Global batch verification context for Sapling shielded data.
179pub static VERIFIER: Lazy<
180    Fallback<
181        Batch<Verifier, Item>,
182        ServiceFn<
183            fn(Item) -> BoxFuture<'static, Result<(), Box<dyn std::error::Error + Send + Sync>>>,
184        >,
185    >,
186> = Lazy::new(|| {
187    Fallback::new(
188        Batch::new(
189            Verifier::default(),
190            super::MAX_BATCH_SIZE,
191            None,
192            super::MAX_BATCH_LATENCY,
193        ),
194        tower::service_fn(verify_single),
195    )
196});
zebra_consensus/primitives/sapling.rs

zebra_consensus/primitives/
sapling.rs
