add initial attestation validation structure

lighthouse/state/mod.rs

@@ -15,3 +15,4 @@ pub mod crosslink_record;
 pub mod shard_and_committee;
 pub mod transition;
 pub mod validator_record;
+pub mod validation;

lighthouse/state/validation/attestation_validation.rs

@@ -0,0 +1,66 @@
+use super::super::crystallized_state::CrystallizedState;
+use super::super::active_state::ActiveState;
+use super::super::attestation_record::AttestationRecord;
+use super::super::block::Block;
+use super::super::chain_config::ChainConfig;
+
+use ::utils::errors::AttestationValidationError;
+
+// implementation of validate_attestation in the v2.1 python reference implementation
+// see: https://github.com/ethereum/beacon_chain/blob/a79ab2c6f03cbdabf2b6d9d435c26e2b216e09a5/beacon_chain/state/state_transition.py#L61
+pub fn validate_attestation(
+    crystallized_state: &CrystallizedState, 
+    active_state: &ActiveState,
+    attestation: &AttestationRecord,
+    block: &Block,
+    chain_config: &ChainConfig) 
+    -> Result<bool, AttestationValidationError> { 
+
+        if !(attestation.slot < block.slot_number) {
+            return Err(AttestationValidationError::SlotTooHigh);
+        }
+
+        if !(attestation.slot > (block.slot_number - chain_config.cycle_length as u64)) {
+            return Err(AttestationValidationError::SlotTooLow(format!("Attestation slot number too low\n\tFound: {:?}, Needed greater than: {:?}", attestation.slot, block.slot_number - chain_config.cycle_length as u64)));
+        }
+
+        return Ok(true);
+    }
+
+
+#[cfg(test)]
+mod tests { 
+
+    use super::*;
+    // test helper functions
+     
+    fn generate_standard_state() -> (
+         CrystallizedState,
+         ActiveState,
+         AttestationRecord,
+         Block,
+         ChainConfig) { 
+
+        let mut crystallized_state = CrystallizedState::zero(); 
+        let mut active_state = ActiveState::zero();
+        let mut attestation_record = AttestationRecord::zero();
+        let mut block = Block::zero();
+        let chain_config = ChainConfig::standard();
+
+        return (crystallized_state, active_state, attestation_record, block, chain_config);
+
+    }
+    
+
+    #[test]
+    fn test_attestation_validation_slot_high() { 
+        // generate standard state
+        let (mut crystallized_state, mut active_state, mut attestation_record, mut block, mut chain_config) = generate_standard_state();
+        // set slot too high
+        attestation_record.slot = 30;
+        block.slot_number = 10;
+
+        let result = validate_attestation(&crystallized_state, &active_state, &attestation_record, &block, &chain_config);
+        assert_eq!(result, Err(AttestationValidationError::SlotTooHigh));
+    }
+}

lighthouse/state/validation/mod.rs

@@ -0,0 +1 @@
+mod attestation_validation;

lighthouse/utils/errors.rs

@@ -0,0 +1,12 @@
+// Collection of custom errors 
+
+#[derive(Debug,PartialEq)]
+pub enum AttestationValidationError { 
+    SlotTooHigh,
+    SlotTooLow(String),
+    IncorrectBitField,
+    NonZeroTrailingBits,
+    AggregateSignatureFail
+}
+
+

lighthouse/utils/mod.rs

@@ -7,3 +7,4 @@ pub mod types;
 pub mod bls;
 pub mod test_helpers;
 pub mod logging;
+pub mod errors;