Revert "Merge pull request #200 from sigp/new-structure"

This reverts commit d7a3545be1, reversing
changes made to 1da06c156c.

eth2/fork_choice/src/slow_lmd_ghost.rs

@@ -0,0 +1,223 @@
+// Copyright 2019 Sigma Prime Pty Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+extern crate db;
+
+use crate::{ForkChoice, ForkChoiceError};
+use db::{
+    stores::{BeaconBlockStore, BeaconStateStore},
+    ClientDB,
+};
+use std::collections::HashMap;
+use std::sync::Arc;
+use types::{
+    readers::{BeaconBlockReader, BeaconStateReader},
+    slot_epoch_height::Slot,
+    validator_registry::get_active_validator_indices,
+    BeaconBlock, Hash256,
+};
+
+//TODO: Pruning and syncing
+
+//TODO: Sort out global constants
+const GENESIS_SLOT: u64 = 0;
+const FORK_CHOICE_BALANCE_INCREMENT: u64 = 1e9 as u64;
+const MAX_DEPOSIT_AMOUNT: u64 = 32e9 as u64;
+const EPOCH_LENGTH: u64 = 64;
+
+pub struct SlowLMDGhost<T: ClientDB + Sized> {
+    /// The latest attestation targets as a map of validator index to block hash.
+    //TODO: Could this be a fixed size vec
+    latest_attestation_targets: HashMap<u64, Hash256>,
+    /// Stores the children for any given parent.
+    children: HashMap<Hash256, Vec<Hash256>>,
+    /// Block storage access.
+    block_store: Arc<BeaconBlockStore<T>>,
+    /// State storage access.
+    state_store: Arc<BeaconStateStore<T>>,
+}
+
+impl<T> SlowLMDGhost<T>
+where
+    T: ClientDB + Sized,
+{
+    pub fn new(block_store: BeaconBlockStore<T>, state_store: BeaconStateStore<T>) -> Self {
+        SlowLMDGhost {
+            latest_attestation_targets: HashMap::new(),
+            children: HashMap::new(),
+            block_store: Arc::new(block_store),
+            state_store: Arc::new(state_store),
+        }
+    }
+
+    /// Finds the latest votes weighted by validator balance. Returns a hashmap of block_hash to
+    /// weighted votes.
+    pub fn get_latest_votes(
+        &self,
+        state_root: &Hash256,
+        block_slot: Slot,
+    ) -> Result<HashMap<Hash256, u64>, ForkChoiceError> {
+        // get latest votes
+        // Note: Votes are weighted by min(balance, MAX_DEPOSIT_AMOUNT) //
+        // FORK_CHOICE_BALANCE_INCREMENT
+        // build a hashmap of block_hash to weighted votes
+        let mut latest_votes: HashMap<Hash256, u64> = HashMap::new();
+        // gets the current weighted votes
+        let current_state = self
+            .state_store
+            .get_deserialized(&state_root)?
+            .ok_or_else(|| ForkChoiceError::MissingBeaconState(*state_root))?;
+
+        let active_validator_indices = get_active_validator_indices(
+            &current_state.validator_registry,
+            block_slot.epoch(EPOCH_LENGTH),
+        );
+
+        for index in active_validator_indices {
+            let balance =
+                std::cmp::min(current_state.validator_balances[index], MAX_DEPOSIT_AMOUNT)
+                    / FORK_CHOICE_BALANCE_INCREMENT;
+            if balance > 0 {
+                if let Some(target) = self.latest_attestation_targets.get(&(index as u64)) {
+                    *latest_votes.entry(*target).or_insert_with(|| 0) += balance;
+                }
+            }
+        }
+
+        Ok(latest_votes)
+    }
+
+    /// Get the total number of votes for some given block root.
+    ///
+    /// The vote count is incremented each time an attestation target votes for a block root.
+    fn get_vote_count(
+        &self,
+        latest_votes: &HashMap<Hash256, u64>,
+        block_root: &Hash256,
+    ) -> Result<u64, ForkChoiceError> {
+        let mut count = 0;
+        let block_slot = self
+            .block_store
+            .get_deserialized(&block_root)?
+            .ok_or_else(|| ForkChoiceError::MissingBeaconBlock(*block_root))?
+            .slot();
+
+        for (target_hash, votes) in latest_votes.iter() {
+            let (root_at_slot, _) = self
+                .block_store
+                .block_at_slot(&block_root, block_slot)?
+                .ok_or(ForkChoiceError::MissingBeaconBlock(*block_root))?;
+            if root_at_slot == *target_hash {
+                count += votes;
+            }
+        }
+        Ok(count)
+    }
+}
+
+impl<T: ClientDB + Sized> ForkChoice for SlowLMDGhost<T> {
+    /// Process when a block is added
+    fn add_block(
+        &mut self,
+        block: &BeaconBlock,
+        block_hash: &Hash256,
+    ) -> Result<(), ForkChoiceError> {
+        // build the children hashmap
+        // add the new block to the children of parent
+        (*self
+            .children
+            .entry(block.parent_root)
+            .or_insert_with(|| vec![]))
+        .push(block_hash.clone());
+
+        // complete
+        Ok(())
+    }
+
+    fn add_attestation(
+        &mut self,
+        validator_index: u64,
+        target_block_root: &Hash256,
+    ) -> Result<(), ForkChoiceError> {
+        // simply add the attestation to the latest_attestation_target if the block_height is
+        // larger
+        let attestation_target = self
+            .latest_attestation_targets
+            .entry(validator_index)
+            .or_insert_with(|| *target_block_root);
+        // if we already have a value
+        if attestation_target != target_block_root {
+            // get the height of the target block
+            let block_height = self
+                .block_store
+                .get_deserialized(&target_block_root)?
+                .ok_or_else(|| ForkChoiceError::MissingBeaconBlock(*target_block_root))?
+                .slot()
+                .height(Slot::from(GENESIS_SLOT));
+
+            // get the height of the past target block
+            let past_block_height = self
+                .block_store
+                .get_deserialized(&attestation_target)?
+                .ok_or_else(|| ForkChoiceError::MissingBeaconBlock(*attestation_target))?
+                .slot()
+                .height(Slot::from(GENESIS_SLOT));
+            // update the attestation only if the new target is higher
+            if past_block_height < block_height {
+                *attestation_target = *target_block_root;
+            }
+        }
+        Ok(())
+    }
+
+    /// A very inefficient implementation of LMD ghost.
+    fn find_head(&mut self, justified_block_start: &Hash256) -> Result<Hash256, ForkChoiceError> {
+        let start = self
+            .block_store
+            .get_deserialized(&justified_block_start)?
+            .ok_or_else(|| ForkChoiceError::MissingBeaconBlock(*justified_block_start))?;
+
+        let start_state_root = start.state_root();
+
+        let latest_votes = self.get_latest_votes(&start_state_root, start.slot())?;
+
+        let mut head_hash = Hash256::zero();
+
+        loop {
+            let mut head_vote_count = 0;
+
+            let children = match self.children.get(&head_hash) {
+                Some(children) => children,
+                // we have found the head, exit
+                None => break,
+            };
+
+            for child_hash in children {
+                let vote_count = self.get_vote_count(&latest_votes, &child_hash)?;
+
+                if vote_count > head_vote_count {
+                    head_hash = *child_hash;
+                    head_vote_count = vote_count;
+                }
+            }
+        }
+        Ok(head_hash)
+    }
+}