Allow for customizable recent genesis window

beacon_node/beacon_chain/src/beacon_chain_builder.rs

@@ -22,8 +22,13 @@ pub struct BeaconChainBuilder<T: BeaconChainTypes> {
 }
 
 impl<T: BeaconChainTypes> BeaconChainBuilder<T> {
-    pub fn recent_genesis(validator_count: usize, spec: ChainSpec, log: Logger) -> Self {
-        Self::quick_start(recent_genesis_time(), validator_count, spec, log)
+    pub fn recent_genesis(
+        validator_count: usize,
+        minutes: u64,
+        spec: ChainSpec,
+        log: Logger,
+    ) -> Self {
+        Self::quick_start(recent_genesis_time(minutes), validator_count, spec, log)
     }
 
     pub fn quick_start(
@@ -123,12 +128,12 @@ fn genesis_block<T: EthSpec>(genesis_state: &BeaconState<T>, spec: &ChainSpec) -
 /// Returns the system time, mod 30 minutes.
 ///
 /// Used for easily creating testnets.
-fn recent_genesis_time() -> u64 {
+fn recent_genesis_time(minutes: u64) -> u64 {
     let now = SystemTime::now()
         .duration_since(SystemTime::UNIX_EPOCH)
         .unwrap()
         .as_secs();
-    let secs_after_last_period = now.checked_rem(30 * 60).unwrap_or(0);
-    // genesis is now the last 30 minute block.
+    let secs_after_last_period = now.checked_rem(minutes * 60).unwrap_or(0);
+    // genesis is now the last 15 minute block.
     now - secs_after_last_period
 }

beacon_node/client/src/config.rs

@@ -42,7 +42,10 @@ pub enum BeaconChainStartMethod {
     /// Create a new beacon chain that can connect to mainnet.
     ///
     /// Set the genesis time to be the start of the previous 30-minute window.
-    RecentGenesis { validator_count: usize },
+    RecentGenesis {
+        validator_count: usize,
+        minutes: u64,
+    },
     /// Create a new beacon chain with `genesis_time` and `validator_count` validators, all with well-known
     /// secret keys.
     Generated {

beacon_node/client/src/lib.rs

@@ -88,9 +88,15 @@ where
                 crit!(log, "No mainnet beacon chain startup specification.");
                 return Err("Mainnet is not yet specified. We're working on it.".into());
             }
-            BeaconChainStartMethod::RecentGenesis { validator_count } => {
-                BeaconChainBuilder::recent_genesis(*validator_count, spec.clone(), log.clone())
-            }
+            BeaconChainStartMethod::RecentGenesis {
+                validator_count,
+                minutes,
+            } => BeaconChainBuilder::recent_genesis(
+                *validator_count,
+                *minutes,
+                spec.clone(),
+                log.clone(),
+            ),
             BeaconChainStartMethod::Generated {
                 validator_count,
                 genesis_time,

beacon_node/src/config.rs

@@ -120,8 +120,15 @@ fn process_testnet_subcommand(
                 .parse::<usize>()
                 .map_err(|e| format!("Unable to parse validator_count: {:?}", e))?;
 
+            let minutes = cli_args
+                .value_of("minutes")
+                .ok_or_else(|| "No recent genesis minutes supplied")?
+                .parse::<u64>()
+                .map_err(|e| format!("Unable to parse minutes: {:?}", e))?;
+
             builder.set_beacon_chain_start_method(BeaconChainStartMethod::RecentGenesis {
                 validator_count,
+                minutes,
             })
         }
         _ => return Err("No testnet method specified. See 'testnet --help'.".into()),

beacon_node/src/main.rs

@@ -259,11 +259,17 @@ fn main() {
              */
             .subcommand(SubCommand::with_name("recent")
                 .about("Creates a new genesis state where the genesis time was at the previous \
-                       30-minute boundary (e.g., 12:00, 12:30, 13:00, etc.)")
+                       MINUTES boundary (e.g., when MINUTES == 30; 12:00, 12:30, 13:00, etc.)")
                 .arg(Arg::with_name("validator_count")
                     .value_name("VALIDATOR_COUNT")
                     .required(true)
                     .help("The number of validators in the genesis state"))
+                .arg(Arg::with_name("minutes")
+                    .short("m")
+                    .value_name("MINUTES")
+                    .required(true)
+                    .default_value("15")
+                    .help("The maximum number of minutes that will have elapsed before genesis"))
             )
             .subcommand(SubCommand::with_name("yaml-genesis-state")
                 .about("Creates a new datadir where the genesis state is read from YAML. Will fail to parse \