Start implementing BeaconChainBuilder

beacon_node/beacon_chain/Cargo.toml

@@ -13,6 +13,7 @@ log = "0.4"
 operation_pool = { path = "../../eth2/operation_pool" }
 serde = "1.0"
 serde_derive = "1.0"
+serde_yaml = "0.8"
 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

@@ -0,0 +1,68 @@
+use crate::BeaconChainTypes;
+use std::fs::File;
+use std::path::PathBuf;
+use std::time::SystemTime;
+use types::{
+    test_utils::TestingBeaconStateBuilder, BeaconBlock, BeaconState, ChainSpec, EthSpec, Hash256,
+};
+
+pub struct BeaconChainBuilder<T: BeaconChainTypes> {
+    genesis_state: BeaconState<T::EthSpec>,
+    genesis_block: BeaconBlock<T::EthSpec>,
+    spec: ChainSpec,
+}
+
+impl<T: BeaconChainTypes> BeaconChainBuilder<T> {
+    pub fn recent_genesis(validator_count: usize, spec: ChainSpec) -> Self {
+        Self::quick_start(recent_genesis_time(), validator_count, spec)
+    }
+
+    pub fn quick_start(genesis_time: u64, validator_count: usize, spec: ChainSpec) -> Self {
+        let (mut genesis_state, _keypairs) =
+            TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(validator_count, &spec)
+                .build();
+
+        genesis_state.genesis_time = genesis_time;
+
+        Self::from_genesis_state(genesis_state, spec)
+    }
+
+    pub fn yaml_state(file: PathBuf, spec: ChainSpec) -> Result<Self, String> {
+        let file = File::open(file.clone())
+            .map_err(|e| format!("Unable to open YAML genesis state file {:?}: {:?}", file, e))?;
+
+        let genesis_state = serde_yaml::from_reader(file)
+            .map_err(|e| format!("Unable to parse YAML genesis state file: {:?}", e))?;
+
+        Ok(Self::from_genesis_state(genesis_state, spec))
+    }
+
+    pub fn from_genesis_state(genesis_state: BeaconState<T::EthSpec>, spec: ChainSpec) -> Self {
+        Self {
+            genesis_block: genesis_block(&genesis_state, &spec),
+            genesis_state,
+            spec,
+        }
+    }
+}
+
+fn genesis_block<T: EthSpec>(genesis_state: &BeaconState<T>, spec: &ChainSpec) -> BeaconBlock<T> {
+    let mut genesis_block = BeaconBlock::empty(&spec);
+
+    genesis_block.state_root = genesis_state.canonical_root();
+
+    genesis_block
+}
+
+/// Returns the system time, mod 30 minutes.
+///
+/// Used for easily creating testnets.
+fn recent_genesis_time() -> 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.
+    now - secs_after_last_period
+}

beacon_node/beacon_chain/src/lib.rs

@@ -3,6 +3,7 @@
 extern crate lazy_static;
 
 mod beacon_chain;
+mod beacon_chain_builder;
 mod checkpoint;
 mod errors;
 mod fork_choice;
@@ -16,6 +17,7 @@ pub use self::beacon_chain::{
 };
 pub use self::checkpoint::CheckPoint;
 pub use self::errors::{BeaconChainError, BlockProductionError};
+pub use beacon_chain_builder::BeaconChainBuilder;
 pub use lmd_ghost;
 pub use metrics::scrape_for_metrics;
 pub use parking_lot;