Add separate bin for stark2snark conv

goas/host/Cargo.toml

@@ -2,12 +2,16 @@
 name = "host"
 version = "0.1.0"
 edition = "2021"
+default-run = "host"
 
 [dependencies]
 methods = { path = "../methods" }
-risc0-zkvm = { version = "1.0.1" }
+risc0-zkvm = { version = "1.0.1", features = ["prove"] }
+risc0-groth16 = { version = "1.0.1" }
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 serde = "1.0"
 blake2 = "0.10"
 bincode = "1"
-common = { path = "../common" }
+common = { path = "../common" }
+tempfile = "3"
+clap = { version = "4", features = ["derive"] }

goas/host/src/bin/groth16.rs

@@ -0,0 +1,54 @@
+/// Wrapping a STARK proof in groth16 in RISC0 should be as easy as specifying ProverOpts::groth16,
+/// but unfortunately a permission issue seems to get in the way at least in the current machine we're
+/// testing this on.
+/// This workaround manually calls into docker after creating a directory with the required permissions.
+/// In addition, splitting the process in different stages highlights better the different work that
+/// needs to be done which could be split across different actors.
+
+use std::path::PathBuf;
+use clap::Parser;
+use risc0_zkvm::{get_prover_server, ProverOpts, Receipt};
+
+const WORK_DIR_ENV: &str = "RISC0_WORK_DIR";
+
+#[derive(Parser, Debug)]
+#[command(version, about, long_about = None)]
+struct Args {
+    /// Path to the bincode-encoded STARK proof
+    #[arg(short, long, default_value = "proof.stark")]
+    input: PathBuf,
+
+    /// Where to put the output artifacts
+    #[arg(short, long, default_value = "output")]
+    output_dir: PathBuf,
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let args = Args::parse();
+    // Initialize tracing. In order to view logs, run `RUST_LOG=info cargo run`
+    tracing_subscriber::fmt()
+        .with_env_filter(tracing_subscriber::filter::EnvFilter::from_default_env())
+        .init();
+
+    let work_dir = tempfile::tempdir()?;
+    // give permissions to the docker user to write to the work dir
+    let mut perms = std::fs::metadata(&work_dir)?.permissions();
+    // on unix this is for all users
+    perms.set_readonly(false);
+    std::fs::set_permissions(&work_dir, perms)?;
+
+    let proof: Receipt = bincode::deserialize(&std::fs::read(&args.input)?)?;
+
+    let server = get_prover_server(&ProverOpts::groth16())?;
+    let converted = server.identity_p254(proof.inner.succinct()?)?;
+
+    let work_dir_path = work_dir.path();
+    std::env::set_var(WORK_DIR_ENV, work_dir_path);
+    risc0_groth16::docker::stark_to_snark(&converted.get_seal_bytes())?;
+
+    std::fs::create_dir_all(&args.output_dir)?;
+    std::fs::copy(work_dir_path.join("proof.json"), args.output_dir.join("proof.json"))?;
+    std::fs::copy(work_dir_path.join("public.json"), args.output_dir.join("public.json"))?;
+    
+    Ok(())
+   }