From 3f988493622ab0221649b91682e4ad8296f86542 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Sun, 10 Mar 2019 08:55:45 +1100
Subject: [PATCH] Optimise attester slashing processing.

---
 .../src/per_block_processing.rs               | 32 ++++++++++++++++---
 .../src/per_block_processing/errors.rs        |  9 ++++++
 .../verify_attester_slashing.rs               | 11 ++++---
 3 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/eth2/state_processing/src/per_block_processing.rs b/eth2/state_processing/src/per_block_processing.rs
index d871914d9..7b5aafa7f 100644
--- a/eth2/state_processing/src/per_block_processing.rs
+++ b/eth2/state_processing/src/per_block_processing.rs
@@ -13,6 +13,7 @@ pub use verify_deposit::{
     build_public_key_hashmap, get_existing_validator_index, verify_deposit, verify_deposit_index,
 };
 pub use verify_exit::verify_exit;
+pub use verify_slashable_attestation::verify_slashable_attestation;
 pub use verify_transfer::{execute_transfer, verify_transfer};
 
 pub mod errors;
@@ -264,19 +265,40 @@ pub fn process_attester_slashings(
         Invalid::MaxAttesterSlashingsExceed
     );
 
-    // Verify attester slashings in parallel.
-    attester_slashings
+    // Verify the `SlashableAttestation`s in parallel (these are the resource-consuming objects, not
+    // the `AttesterSlashing`s themselves).
+    let mut slashable_attestations: Vec<&SlashableAttestation> =
+        Vec::with_capacity(attester_slashings.len() * 2);
+    for attester_slashing in attester_slashings {
+        slashable_attestations.push(&attester_slashing.slashable_attestation_1);
+        slashable_attestations.push(&attester_slashing.slashable_attestation_2);
+    }
+
+    // Verify slashable attestations in parallel.
+    slashable_attestations
         .par_iter()
         .enumerate()
-        .try_for_each(|(i, attester_slashing)| {
-            verify_attester_slashing(&state, &attester_slashing, spec)
+        .try_for_each(|(i, slashable_attestation)| {
+            verify_slashable_attestation(&state, slashable_attestation, spec)
                 .map_err(|e| e.into_with_index(i))
         })?;
+    let all_slashable_attestations_have_been_checked = true;
 
-    // Gather the slashable indices and update the state in series.
+    // Gather the slashable indices and preform the final verification and update the state in series.
     for (i, attester_slashing) in attester_slashings.iter().enumerate() {
+        let should_verify_slashable_attestations = !all_slashable_attestations_have_been_checked;
+
+        verify_attester_slashing(
+            &state,
+            &attester_slashing,
+            should_verify_slashable_attestations,
+            spec,
+        )
+        .map_err(|e| e.into_with_index(i))?;
+
         let slashable_indices = gather_attester_slashing_indices(&state, &attester_slashing)
             .map_err(|e| e.into_with_index(i))?;
+
         for i in slashable_indices {
             state.slash_validator(i as usize, spec)?;
         }
diff --git a/eth2/state_processing/src/per_block_processing/errors.rs b/eth2/state_processing/src/per_block_processing/errors.rs
index f64a3f8aa..a3e3ebad1 100644
--- a/eth2/state_processing/src/per_block_processing/errors.rs
+++ b/eth2/state_processing/src/per_block_processing/errors.rs
@@ -76,6 +76,10 @@ pub enum BlockInvalid {
     MaxExitsExceeded,
     MaxTransfersExceed,
     AttestationInvalid(usize, AttestationInvalid),
+    /// A `SlashableAttestation` inside an `AttesterSlashing` was invalid.
+    ///
+    /// To determine the offending `AttesterSlashing` index, divide the error message `usize` by two.
+    SlashableAttestationInvalid(usize, SlashableAttestationInvalid),
     AttesterSlashingInvalid(usize, AttesterSlashingInvalid),
     ProposerSlashingInvalid(usize, ProposerSlashingInvalid),
     DepositInvalid(usize, DepositInvalid),
@@ -235,6 +239,11 @@ impl Into<SlashableAttestationInvalid> for SlashableAttestationValidationError {
     }
 }
 
+impl_into_with_index_without_beacon_error!(
+    SlashableAttestationValidationError,
+    SlashableAttestationInvalid
+);
+
 /*
  * `ProposerSlashing` Validation
  */
diff --git a/eth2/state_processing/src/per_block_processing/verify_attester_slashing.rs b/eth2/state_processing/src/per_block_processing/verify_attester_slashing.rs
index 2970712c5..d126849b6 100644
--- a/eth2/state_processing/src/per_block_processing/verify_attester_slashing.rs
+++ b/eth2/state_processing/src/per_block_processing/verify_attester_slashing.rs
@@ -11,6 +11,7 @@ use types::*;
 pub fn verify_attester_slashing(
     state: &BeaconState,
     attester_slashing: &AttesterSlashing,
+    should_verify_slashable_attestations: bool,
     spec: &ChainSpec,
 ) -> Result<(), Error> {
     let slashable_attestation_1 = &attester_slashing.slashable_attestation_1;
@@ -26,10 +27,12 @@ pub fn verify_attester_slashing(
         Invalid::NotSlashable
     );
 
-    verify_slashable_attestation(state, &slashable_attestation_1, spec)
-        .map_err(|e| Error::Invalid(Invalid::SlashableAttestation1Invalid(e.into())))?;
-    verify_slashable_attestation(state, &slashable_attestation_2, spec)
-        .map_err(|e| Error::Invalid(Invalid::SlashableAttestation2Invalid(e.into())))?;
+    if should_verify_slashable_attestations {
+        verify_slashable_attestation(state, &slashable_attestation_1, spec)
+            .map_err(|e| Error::Invalid(Invalid::SlashableAttestation1Invalid(e.into())))?;
+        verify_slashable_attestation(state, &slashable_attestation_2, spec)
+            .map_err(|e| Error::Invalid(Invalid::SlashableAttestation2Invalid(e.into())))?;
+    }
 
     Ok(())
 }