Make loading of Sprout key optional in zcash_proofs API

librustzcash/src/rustzcash.rs

@@ -210,8 +210,8 @@ fn init_zksnark_params(
         spend_hash,
         output_path,
         output_hash,
-        sprout_path,
-        sprout_hash,
+        Some(sprout_path),
+        Some(sprout_hash),
     );
 
     // Caller is responsible for calling this function once, so
@@ -223,7 +223,7 @@ fn init_zksnark_params(
 
         SAPLING_SPEND_VK = Some(spend_vk);
         SAPLING_OUTPUT_VK = Some(output_vk);
-        SPROUT_GROTH16_VK = Some(sprout_vk);
+        SPROUT_GROTH16_VK = Some(sprout_vk.unwrap());
     }
 }
 

zcash_proofs/src/lib.rs

@@ -20,25 +20,26 @@ pub fn load_parameters(
     spend_hash: &str,
     output_path: &Path,
     output_hash: &str,
-    sprout_path: &Path,
-    sprout_hash: &str,
+    sprout_path: Option<&Path>,
+    sprout_hash: Option<&str>,
 ) -> (
     Parameters<Bls12>,
     PreparedVerifyingKey<Bls12>,
     Parameters<Bls12>,
     PreparedVerifyingKey<Bls12>,
-    PreparedVerifyingKey<Bls12>,
+    Option<PreparedVerifyingKey<Bls12>>,
 ) {
     // Load from each of the paths
     let spend_fs = File::open(spend_path).expect("couldn't load Sapling spend parameters file");
     let output_fs = File::open(output_path).expect("couldn't load Sapling output parameters file");
-    let sprout_fs = File::open(sprout_path).expect("couldn't load Sprout groth16 parameters file");
+    let sprout_fs =
+        sprout_path.map(|p| File::open(p).expect("couldn't load Sprout groth16 parameters file"));
 
     let mut spend_fs = hashreader::HashReader::new(BufReader::with_capacity(1024 * 1024, spend_fs));
     let mut output_fs =
         hashreader::HashReader::new(BufReader::with_capacity(1024 * 1024, output_fs));
     let mut sprout_fs =
-        hashreader::HashReader::new(BufReader::with_capacity(1024 * 1024, sprout_fs));
+        sprout_fs.map(|fs| hashreader::HashReader::new(BufReader::with_capacity(1024 * 1024, fs)));
 
     // Deserialize params
     let spend_params = Parameters::<Bls12>::read(&mut spend_fs, false)
@@ -49,8 +50,10 @@ pub fn load_parameters(
     // We only deserialize the verifying key for the Sprout parameters, which
     // appears at the beginning of the parameter file. The rest is loaded
     // during proving time.
-    let sprout_vk = VerifyingKey::<Bls12>::read(&mut sprout_fs)
-        .expect("couldn't deserialize Sprout Groth16 verifying key");
+    let sprout_vk = sprout_fs.as_mut().map(|mut fs| {
+        VerifyingKey::<Bls12>::read(&mut fs)
+            .expect("couldn't deserialize Sprout Groth16 verifying key")
+    });
 
     // There is extra stuff (the transcript) at the end of the parameter file which is
     // used to verify the parameter validity, but we're not interested in that. We do
@@ -61,8 +64,10 @@ pub fn load_parameters(
         .expect("couldn't finish reading Sapling spend parameter file");
     io::copy(&mut output_fs, &mut sink)
         .expect("couldn't finish reading Sapling output parameter file");
-    io::copy(&mut sprout_fs, &mut sink)
-        .expect("couldn't finish reading Sprout groth16 parameter file");
+    if let Some(mut sprout_fs) = sprout_fs.as_mut() {
+        io::copy(&mut sprout_fs, &mut sink)
+            .expect("couldn't finish reading Sprout groth16 parameter file");
+    }
 
     if spend_fs.into_hash() != spend_hash {
         panic!("Sapling spend parameter file is not correct, please clean your `~/.zcash-params/` and re-run `fetch-params`.");
@@ -72,14 +77,14 @@ pub fn load_parameters(
         panic!("Sapling output parameter file is not correct, please clean your `~/.zcash-params/` and re-run `fetch-params`.");
     }
 
-    if sprout_fs.into_hash() != sprout_hash {
+    if sprout_fs.map(|fs| fs.into_hash()) != sprout_hash.map(|h| h.to_owned()) {
         panic!("Sprout groth16 parameter file is not correct, please clean your `~/.zcash-params/` and re-run `fetch-params`.");
     }
 
     // Prepare verifying keys
     let spend_vk = prepare_verifying_key(&spend_params.vk);
     let output_vk = prepare_verifying_key(&output_params.vk);
-    let sprout_vk = prepare_verifying_key(&sprout_vk);
+    let sprout_vk = sprout_vk.map(|vk| prepare_verifying_key(&vk));
 
     (spend_params, spend_vk, output_params, output_vk, sprout_vk)
 }