Add missing docs/test to the Risc0 adapter (#920)

* Document risc0 adapter

* add test for adapter

* Update adapters/risc0/README.md

Co-authored-by: Nikolai Golub <nikolai@sovlabs.io>

* Code review feedback

---------

Co-authored-by: Blazej Kolad <blazejkolad@gmail.com>
Co-authored-by: Nikolai Golub <nikolai@sovlabs.io>

adapters/risc0/Cargo.toml

@@ -30,3 +30,7 @@ sov-rollup-interface = { path = "../../rollup-interface", version = "0.2" }
 default = []
 native = ["risc0-zkvm/prove", "dep:risc0-zkp", "dep:risc0-circuit-rv32im"]
 bench = ["once_cell", "parking_lot", "native", "sov-zk-cycle-utils/native"]
+
+[[test]]
+name = "native"
+required-features = ["native"]

adapters/risc0/README.md

@@ -1,11 +1,11 @@
 # Risc0 Adapter
 
-This package adapts Risc0 version 0.14 to work as a ZKVM for the Sovereign SDK.
+This package adapts Risc0 version 0.18 to work as a zkVM for the Sovereign SDK.
 
 ## Limitations
 
-Since recursion is not included in the 0.14 release, this adapter is currently limited - individual "slots" may
-be proven, but those proofs cannot be recursively combined to facilitate bridging or ultra-fast sync.
+Since in-VM recursion is not included in the 0.18 release, this adapter is currently limited. Individual "slots" may
+be proven, but those proofs cannot be recursively combined to facilitate bridging or ultra-fast sync ("user recursion" is not supported).
 
 ## Warning
 

adapters/risc0/src/guest.rs

@@ -1,3 +1,4 @@
+//! This module implements the `ZkvmGuest` trait for the RISC0 VM.
 #[cfg(not(target_os = "zkvm"))]
 use std::ops::DerefMut;
 
@@ -64,6 +65,10 @@ impl WordRead for Hints {
     }
 }
 
+/// A guest for the RISC0 VM. When running in the Risc0 environment, this struct
+/// implements the `ZkvmGuest` trait in terms of Risc0's env::read and env::commit functions.
+/// When running in any other environment, the struct uses interior mutability to emulate
+/// the same functionality.
 #[derive(Default)]
 pub struct Risc0Guest {
     #[cfg(not(target_os = "zkvm"))]
@@ -73,10 +78,14 @@ pub struct Risc0Guest {
 }
 
 impl Risc0Guest {
+    /// Constructs a new Risc0 Guest
     pub fn new() -> Self {
         Self::default()
     }
 
+    /// Constructs a new Risc0 Guest with the provided hints.
+    ///
+    /// This function is only available outside of Risc0's environment.
     #[cfg(not(target_os = "zkvm"))]
     pub fn with_hints(hints: Vec<u32>) -> Self {
         Self {

adapters/risc0/src/host.rs

@@ -1,3 +1,4 @@
+//! This module implements the `ZkvmHost` trait for the RISC0 VM.
 use std::sync::Mutex;
 
 use risc0_zkvm::serde::to_vec;
@@ -13,6 +14,8 @@ use crate::guest::Risc0Guest;
 use crate::metrics::metrics_callback;
 use crate::Risc0MethodId;
 
+/// A Risc0Host stores a binary to execute in the Risc0 VM, and accumulates hints to be
+/// provided to its execution.
 pub struct Risc0Host<'a> {
     env: Mutex<Vec<u32>>,
     elf: &'a [u8],
@@ -36,6 +39,7 @@ fn add_benchmarking_callbacks(mut env: ExecutorEnvBuilder<'_>) -> ExecutorEnvBui
 }
 
 impl<'a> Risc0Host<'a> {
+    /// Create a new Risc0Host to prove the given binary.
     pub fn new(elf: &'a [u8]) -> Self {
         Self {
             env: Default::default(),
@@ -107,6 +111,7 @@ impl<'host> Zkvm for Risc0Host<'host> {
     }
 }
 
+/// A verifier for Risc0 proofs.
 pub struct Risc0Verifier;
 
 impl Zkvm for Risc0Verifier {
@@ -150,6 +155,8 @@ fn verify_from_slice<'a>(
 /// data. This allows us to avoid one unnecessary copy during proof verification.
 #[derive(serde::Serialize, serde::Deserialize)]
 pub struct Risc0Proof<'a> {
+    /// The cryptographic data certifying the execution of the program.
     pub receipt: InnerReceipt,
+    /// The public outputs produced by the program execution.
     pub journal: &'a [u8],
 }

adapters/risc0/src/lib.rs

@@ -1,3 +1,8 @@
+#![deny(missing_docs)]
+//! # RISC0 Adapter
+//!
+//! This crate contains an adapter allowing the Risc0 to be used as a proof system for
+//! Sovereign SDK rollups.
 use risc0_zkvm::sha::Digest;
 use serde::{Deserialize, Serialize};
 use sov_rollup_interface::zk::Matches;
@@ -9,6 +14,8 @@ pub mod host;
 #[cfg(feature = "bench")]
 pub mod metrics;
 
+/// Uniquely identifies a Risc0 binary. Roughly equivalent to
+/// the hash of the ELF file.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Risc0MethodId([u32; 8]);
 

adapters/risc0/src/metrics.rs

@@ -1,14 +1,18 @@
+//! Defines utilities for collecting runtime metrics from inside a Risc0 VM
 use std::collections::HashMap;
 
 use anyhow::Context;
 use once_cell::sync::Lazy;
 use parking_lot::Mutex;
 use risc0_zkvm::Bytes;
 
+/// A global hashmap mapping metric names to their values.
 pub static GLOBAL_HASHMAP: Lazy<Mutex<HashMap<String, (u64, u64)>>> =
     Lazy::new(|| Mutex::new(HashMap::new()));
 
-pub fn add_value(metric: String, value: u64) {
+/// Increments the requested metric by the given value, creating a
+/// new entry in the global map if necessary.
+fn add_value(metric: String, value: u64) {
     let mut hashmap = GLOBAL_HASHMAP.lock();
     hashmap
         .entry(metric)
@@ -19,7 +23,9 @@ pub fn add_value(metric: String, value: u64) {
         .or_insert((value, 1));
 }
 
-pub fn deserialize_custom(serialized: Bytes) -> Result<(String, u64), anyhow::Error> {
+/// Deserialize a `Bytes` into a null-separated `(String, u64)` tuple. This function
+/// expects its arguments to match the format of arguments to Risc0's io callbacks.
+fn deserialize_custom(serialized: Bytes) -> Result<(String, u64), anyhow::Error> {
     let null_pos = serialized
         .iter()
         .position(|&b| b == 0)
@@ -31,6 +37,11 @@ pub fn deserialize_custom(serialized: Bytes) -> Result<(String, u64), anyhow::Er
     Ok((string, size))
 }
 
+/// A custom callback for extracting metrics from the Risc0 zkvm.
+///
+/// When the "bench" feature is enabled, this callback is registered as a syscall
+/// in the Risc0 VM and invoked whenever a function annotated with the [`sov-zk-cycle-utils::cycle_tracker`]
+/// macro is invoked.
 pub fn metrics_callback(input: risc0_zkvm::Bytes) -> Result<Bytes, anyhow::Error> {
     let met_tuple = deserialize_custom(input)?;
     add_value(met_tuple.0, met_tuple.1);

adapters/risc0/tests/native.rs

@@ -0,0 +1,24 @@
+use serde::{Deserialize, Serialize};
+use sov_risc0_adapter::host::Risc0Host;
+use sov_rollup_interface::zk::{ZkvmGuest, ZkvmHost};
+
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
+struct TestStruct {
+    ints: Vec<i32>,
+    string: String,
+}
+
+#[test]
+fn test_hints_roundtrip() {
+    let hint = TestStruct {
+        ints: vec![1, 2, 3, 4, 5],
+        string: "hello".to_string(),
+    };
+    let mut host = Risc0Host::new(&[]);
+
+    host.add_hint(&hint);
+
+    let guest = host.simulate_with_hints();
+    let received = guest.read_from_host();
+    assert_eq!(hint, received);
+}