Retry Zcash sprout and sapling parameters download (#3306)

* retry download parameters a few times before giving up

* separate sapling and sprout params download to methods

* simpify the new created methods

* Assert the parameters were downloaded to the expected paths

Co-authored-by: teor <teor@riseup.net>

zebra-consensus/src/primitives/groth16/params.rs

@@ -1,9 +1,12 @@
 //! Downloading, checking, and loading Groth16 Sapling and Sprout parameters.
 
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use bellman::groth16;
 use bls12_381::Bls12;
+use zcash_proofs::SaplingParameterPaths;
+
+use crate::BoxError;
 
 /// The timeout for each parameter file download, in seconds.
 ///
@@ -12,6 +15,12 @@ use bls12_381::Bls12;
 /// But `zebrad start` downloads blocks at the same time, so we allow some extra time.
 pub const PARAMETER_DOWNLOAD_TIMEOUT: u64 = 60 * 60;
 
+/// The maximum number of times to retry download parameters.
+///
+/// Zebra will retry to download Sprout of Sapling parameters only if they
+/// failed for whatever reason.
+pub const PARAMETER_DOWNLOAD_MAX_RETRIES: usize = 3;
+
 lazy_static::lazy_static! {
     /// Groth16 Zero-Knowledge Proof parameters for the Sapling and Sprout circuits.
     ///
@@ -56,43 +65,20 @@ impl Groth16Parameters {
     ///
     /// # Panics
     ///
+    /// If the parameters were downloaded to the wrong path.
+    /// After `PARAMETER_DOWNLOAD_MAX_RETRIES` failed download attempts.
     /// If the downloaded or pre-existing parameter files are invalid.
     fn new() -> Groth16Parameters {
         let params_directory = Groth16Parameters::directory();
         let sapling_spend_path = params_directory.join(zcash_proofs::SAPLING_SPEND_NAME);
         let sapling_output_path = params_directory.join(zcash_proofs::SAPLING_OUTPUT_NAME);
         let sprout_path = params_directory.join(zcash_proofs::SPROUT_NAME);
 
-        // TODO: instead of the path check, add a zcash_proofs argument to skip hashing existing files
-        //       (we check them on load anyway)
-        if !sapling_spend_path.exists() || !sapling_output_path.exists() {
-            tracing::info!("downloading Zcash Sapling parameters");
-            let new_sapling_paths =
-                zcash_proofs::download_sapling_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))
-                    .unwrap_or_else(|error| {
-                        panic!(
-                            "error downloading Sapling parameter files: {:?}. {}",
-                            error,
-                            Groth16Parameters::failure_hint()
-                        )
-                    });
-            assert_eq!(sapling_spend_path, new_sapling_paths.spend);
-            assert_eq!(sapling_output_path, new_sapling_paths.output);
-        }
-
-        if !sprout_path.exists() {
-            tracing::info!("downloading Zcash Sprout parameters");
-            let new_sprout_path =
-                zcash_proofs::download_sprout_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))
-                    .unwrap_or_else(|error| {
-                        panic!(
-                            "error downloading Sprout parameter files: {:?}. {}",
-                            error,
-                            Groth16Parameters::failure_hint()
-                        )
-                    });
-            assert_eq!(sprout_path, new_sprout_path);
-        }
+        Groth16Parameters::retry_download_sapling_parameters(
+            &sapling_spend_path,
+            &sapling_output_path,
+        );
+        Groth16Parameters::retry_download_sprout_parameters(&sprout_path);
 
         // TODO: if loading fails, log a message including `failure_hint`
         tracing::info!("checking and loading Zcash Sapling and Sprout parameters");
@@ -130,4 +116,102 @@ impl Groth16Parameters {
             Groth16Parameters::directory(),
         )
     }
+
+    /// Download Sapling parameters and retry [`PARAMETER_DOWNLOAD_MAX_RETRIES`] if it fails.
+    ///
+    /// # Panics
+    ///
+    /// If the parameters were downloaded to the wrong path.
+    /// After `PARAMETER_DOWNLOAD_MAX_RETRIES` failed download attempts.
+    fn retry_download_sapling_parameters(sapling_spend_path: &Path, sapling_output_path: &Path) {
+        // TODO: instead of the path check, add a zcash_proofs argument to skip hashing existing files
+        //       (we check them on load anyway)
+        if !sapling_spend_path.exists() || !sapling_output_path.exists() {
+            tracing::info!("downloading Zcash Sapling parameters");
+
+            let mut retries = 0;
+            while let Err(error) = Groth16Parameters::download_sapling_parameters_once(
+                sapling_spend_path,
+                sapling_output_path,
+            ) {
+                retries += 1;
+                if retries >= PARAMETER_DOWNLOAD_MAX_RETRIES {
+                    panic!(
+                        "error downloading Sapling parameter files after {} retries. {:?} {}",
+                        PARAMETER_DOWNLOAD_MAX_RETRIES,
+                        error,
+                        Groth16Parameters::failure_hint(),
+                    );
+                } else {
+                    tracing::info!(
+                        ?error,
+                        "error downloading Zcash Sapling parameters, retrying"
+                    );
+                }
+            }
+        }
+    }
+
+    /// Try to download the Sapling parameters once, and return the result.
+    ///
+    /// # Panics
+    ///
+    /// If the parameters were downloaded to different paths to `sapling_spend_path`
+    /// or `sapling_output_path`.
+    fn download_sapling_parameters_once(
+        sapling_spend_path: &Path,
+        sapling_output_path: &Path,
+    ) -> Result<SaplingParameterPaths, BoxError> {
+        let new_sapling_paths =
+            zcash_proofs::download_sapling_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))?;
+
+        assert_eq!(sapling_spend_path, new_sapling_paths.spend);
+        assert_eq!(sapling_output_path, new_sapling_paths.output);
+
+        Ok(new_sapling_paths)
+    }
+
+    /// Download Sprout parameters and retry [`PARAMETER_DOWNLOAD_MAX_RETRIES`] if it fails.
+    ///
+    /// # Panics
+    ///
+    /// If the parameters were downloaded to the wrong path.
+    /// After `PARAMETER_DOWNLOAD_MAX_RETRIES` failed download attempts.
+    fn retry_download_sprout_parameters(sprout_path: &Path) {
+        if !sprout_path.exists() {
+            tracing::info!("downloading Zcash Sprout parameters");
+
+            let mut retries = 0;
+            while let Err(error) = Groth16Parameters::download_sprout_parameters_once(sprout_path) {
+                retries += 1;
+                if retries >= PARAMETER_DOWNLOAD_MAX_RETRIES {
+                    panic!(
+                        "error downloading Sprout parameter files after {} retries. {:?} {}",
+                        PARAMETER_DOWNLOAD_MAX_RETRIES,
+                        error,
+                        Groth16Parameters::failure_hint(),
+                    );
+                } else {
+                    tracing::info!(
+                        ?error,
+                        "error downloading Zcash Sprout parameters, retrying"
+                    );
+                }
+            }
+        }
+    }
+
+    /// Try to download the Sprout parameters once, and return the result.
+    ///
+    /// # Panics
+    ///
+    /// If the parameters were downloaded to a different path to `sprout_path`.
+    fn download_sprout_parameters_once(sprout_path: &Path) -> Result<PathBuf, BoxError> {
+        let new_sprout_path =
+            zcash_proofs::download_sprout_parameters(Some(PARAMETER_DOWNLOAD_TIMEOUT))?;
+
+        assert_eq!(sprout_path, new_sprout_path);
+
+        Ok(new_sprout_path)
+    }
 }