Allow starting testnet from JSON state

beacon_node/beacon_chain/Cargo.toml

@@ -18,6 +18,7 @@ rayon = "1.0"
 serde = "1.0"
 serde_derive = "1.0"
 serde_yaml = "0.8"
+serde_json = "^1.0"
 slog = { version = "^2.2.3" , features = ["max_level_trace"] }
 sloggers = { version = "^0.3" }
 slot_clock = { path = "../../eth2/utils/slot_clock" }

beacon_node/beacon_chain/src/beacon_chain_builder.rs

@@ -76,6 +76,16 @@ impl<T: BeaconChainTypes> BeaconChainBuilder<T> {
         Ok(Self::from_genesis_state(genesis_state, spec, log))
     }
 
+    pub fn json_state(file: &PathBuf, spec: ChainSpec, log: Logger) -> Result<Self, String> {
+        let file = File::open(file.clone())
+            .map_err(|e| format!("Unable to open JSON genesis state file {:?}: {:?}", file, e))?;
+
+        let genesis_state = serde_json::from_reader(file)
+            .map_err(|e| format!("Unable to parse JSON genesis state file: {:?}", e))?;
+
+        Ok(Self::from_genesis_state(genesis_state, spec, log))
+    }
+
     pub fn http_bootstrap(server: &str, spec: ChainSpec, log: Logger) -> Result<Self, String> {
         let bootstrapper = Bootstrapper::from_server_string(server.to_string())
             .map_err(|e| format!("Failed to initialize bootstrap client: {}", e))?;

beacon_node/client/src/config.rs

@@ -56,6 +56,8 @@ pub enum BeaconChainStartMethod {
     Yaml { file: PathBuf },
     /// Create a new beacon chain by loading a SSZ-encoded genesis state from a file.
     Ssz { file: PathBuf },
+    /// Create a new beacon chain by loading a JSON-encoded genesis state from a file.
+    Json { file: PathBuf },
     /// Create a new beacon chain by using a HTTP server (running our REST-API) to load genesis and
     /// finalized states and blocks.
     HttpBootstrap { server: String, port: Option<u16> },

beacon_node/client/src/lib.rs

@@ -147,6 +147,15 @@ where
                 );
                 BeaconChainBuilder::ssz_state(file, spec.clone(), log.clone())?
             }
+            BeaconChainStartMethod::Json { file } => {
+                info!(
+                    log,
+                    "Starting beacon chain";
+                    "file" => format!("{:?}", file),
+                    "method" => "json"
+                );
+                BeaconChainBuilder::json_state(file, spec.clone(), log.clone())?
+            }
             BeaconChainStartMethod::HttpBootstrap { server, port } => {
                 info!(
                     log,

beacon_node/src/config.rs

@@ -186,6 +186,7 @@ fn process_testnet_subcommand(
             let start_method = match format {
                 "yaml" => BeaconChainStartMethod::Yaml { file },
                 "ssz" => BeaconChainStartMethod::Ssz { file },
+                "json" => BeaconChainStartMethod::Json { file },
                 other => return Err(format!("Unknown genesis file format: {}", other)),
             };
 

beacon_node/src/main.rs

@@ -318,7 +318,7 @@ fn main() {
                 .arg(Arg::with_name("format")
                     .value_name("FORMAT")
                     .required(true)
-                    .possible_values(&["yaml", "ssz"])
+                    .possible_values(&["yaml", "ssz", "json"])
                     .help("The encoding of the state in the file."))
                 .arg(Arg::with_name("file")
                     .value_name("YAML_FILE")
@@ -344,7 +344,7 @@ fn main() {
         _ => unreachable!("guarded by clap"),
     };
 
-    let mut log = slog::Logger::root(drain.fuse(), o!());
+    let log = slog::Logger::root(drain.fuse(), o!());
 
     warn!(
         log,