feat: auto-download .wasm and .zkey while building

Author: KimiWu123

Cargo.lock

@@ -12,6 +12,8 @@ ruint = "1.14.0"
 num-traits = "0.2.19"
 ethers-core = "2.0.14"
 anyhow = "1.0.97"
+reqwest = { version = "0.12.15", features = ["blocking", "json"] } 
+tokio = { version = "1", features = ["full"] }
 
 # arkworks
 ark-ec = { version = "=0.5.0", default-features = false }
@@ -40,3 +42,4 @@ serde = [
 
 [build-dependencies]
 rust-witness = "0.1"
+reqwest = { version = "0.12.15", features = ["blocking", "json"] } 

Cargo.toml

@@ -1,3 +1,62 @@
+use reqwest::blocking::Client;
+use std::error::Error;
+use std::fs::{File, create_dir_all};
+use std::io::copy;
+use std::path::{Path, PathBuf};
+
+/// download semaphore artifacts by required tree depth
+fn download_semaphore_artifacts(depth: usize) -> Result<(), Box<dyn Error>> {
+    let base_url = "https://snark-artifacts.pse.dev/semaphore/latest/";
+    let remote_filenames = [
+        format!("semaphore-{}.wasm", depth),
+        format!("semaphore-{}.zkey", depth),
+    ];
+    let local_filenames = ["semaphore.wasm", "semaphore.zkey"];
+
+    let client = Client::new();
+    let target_dir = Path::new("./zkey");
+
+    // Verify if those files have been downloaded or not. Skip downloading if yes.
+    let version_path = target_dir.join("depth");
+    if version_path.exists() {
+        let current_version = std::fs::read_to_string(&version_path)?.trim().to_string();
+        if current_version == depth.to_string() {
+            println!(
+                "Artifacts for depth {} already downloaded, skipping.",
+                depth
+            );
+            return Ok(());
+        }
+    }
+    // create ./zkey folder
+    create_dir_all(target_dir)?;
+
+    // download artifacts
+    for (remote, local) in remote_filenames.iter().zip(local_filenames.iter()) {
+        let url = format!("{}{}", base_url, remote);
+        let dest_path: PathBuf = target_dir.join(local);
+
+        eprintln!("Downloading {}...", url);
+        let mut resp = client.get(&url).send()?.error_for_status()?;
+        let mut out = File::create(&dest_path)?;
+        copy(&mut resp, &mut out)?;
+        eprintln!("Saved as {}", dest_path.display());
+    }
+
+    // update depth info
+    std::fs::write(&version_path, depth.to_string())?;
+
+    Ok(())
+}
+
 fn main() {
+    // Default depth is 10 for testing purposes; can be overridden via SEMAPHORE_DEPTH environment variable
+    let depth: usize = std::env::var("SEMAPHORE_DEPTH")
+        .unwrap_or_else(|_| "10".to_string())
+        .parse()
+        .expect("SEMAPHORE_DEPTH must be a valid usize");
+
+    download_semaphore_artifacts(depth).expect("Failed to download artifacts");
+
     rust_witness::transpile::transpile_wasm("./zkey".to_string());
 }