consensus: add stub groth16::Verifier

Co-authored-by: Deirdre Connolly <deirdre@zfnd.org>

zebra-consensus/Cargo.toml

@@ -8,6 +8,8 @@ edition = "2018"
 [dependencies]
 chrono = "0.4.19"
 color-eyre = "0.5"
+displaydoc = "0.1.7"
+jubjub = "0.5.1"
 once_cell = "1.4"
 rand = "0.7"
 redjubjub = "0.2"
@@ -28,7 +30,6 @@ tower-batch = { path = "../tower-batch/" }
 zebra-chain = { path = "../zebra-chain" }
 zebra-state = { path = "../zebra-state" }
 zebra-script = { path = "../zebra-script" }
-displaydoc = "0.1.7"
 
 [dev-dependencies]
 rand = "0.7"

zebra-consensus/src/primitives.rs

@@ -1,5 +1,6 @@
 //! Asynchronous verification of cryptographic primitives.
 
+pub mod groth16;
 pub mod redjubjub;
 
 /// The maximum batch size for any of the batch verifiers.

zebra-consensus/src/primitives/groth16.rs

@@ -0,0 +1,55 @@
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use tower::Service;
+
+use zebra_chain::primitives::Groth16Proof;
+
+use crate::BoxError;
+
+/// Provides verification of Groth16 proofs for a specific statement.
+///
+/// Groth16 proofs require a proof verification key; the [`Verifier`] type is
+/// responsible for ownership of the PVK.
+pub struct Verifier {
+    // XXX this needs to hold on to a verification key
+}
+
+impl Verifier {
+    /// Create a new Groth16 verifier, supplying the encoding of the verification key.
+    pub fn new(_encoded_verification_key: &[u8]) -> Result<Self, BoxError> {
+        // parse and turn into a bellman type,
+        // so that users don't have to have the entire bellman api
+        unimplemented!();
+    }
+}
+
+// XXX this is copied from the WIP batch bellman impl,
+// in the future, replace with a re export
+
+pub struct Item {
+    pub proof: Groth16Proof,
+    pub public_inputs: Vec<jubjub::Fr>,
+}
+
+// XXX in the future, Verifier will implement
+// Service<BatchControl<Item>>> and be wrapped in a Batch
+// to get a Service<Item>
+// but for now, just implement Service<Item> and do unbatched verif.
+//impl Service<BatchControl<Item>> for Verifier {
+impl Service<Item> for Verifier {
+    type Response = ();
+    type Error = BoxError;
+    type Future = Pin<Box<dyn Future<Output = Result<(), BoxError>> + Send + 'static>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, _req: Item) -> Self::Future {
+        unimplemented!()
+    }
+}