Consensus: block batch prepper (#151)

* add block batch prepper

* Apply suggestions from code review

Co-authored-by: hinto-janai <hinto.janai@protonmail.com>

* review comments

* review comments

* fix doc

---------

Co-authored-by: hinto-janai <hinto.janai@protonmail.com>

consensus/src/block.rs

@@ -7,27 +7,91 @@ use std::{
     task::{Context, Poll},
 };
 
-use cuprate_helper::asynch::rayon_spawn_async;
 use futures::FutureExt;
-use monero_serai::{block::Block, transaction::Input};
+use monero_serai::{
+    block::Block,
+    transaction::{Input, Transaction},
+};
+use rayon::prelude::*;
 use tower::{Service, ServiceExt};
+use tracing::instrument;
 
 use cuprate_consensus_rules::{
-    blocks::{calculate_pow_hash, check_block, check_block_pow, BlockError, RandomX},
+    blocks::{
+        calculate_pow_hash, check_block, check_block_pow, is_randomx_seed_height,
+        randomx_seed_height, BlockError, RandomX,
+    },
     miner_tx::MinerTxError,
     ConsensusError, HardFork,
 };
+use cuprate_helper::asynch::rayon_spawn_async;
 use cuprate_types::{VerifiedBlockInformation, VerifiedTransactionInformation};
 
 use crate::{
-    context::{BlockChainContextRequest, BlockChainContextResponse},
+    context::{
+        rx_vms::RandomXVM, BlockChainContextRequest, BlockChainContextResponse,
+        RawBlockChainContext,
+    },
     transactions::{TransactionVerificationData, VerifyTxRequest, VerifyTxResponse},
     Database, ExtendedConsensusError,
 };
 
+/// A pre-prepared block with all data needed to verify it, except the block's proof of work.
+#[derive(Debug)]
+pub struct PreparedBlockExPow {
+    /// The block.
+    pub block: Block,
+    /// The serialised block's bytes.
+    pub block_blob: Vec<u8>,
+
+    /// The block's hard-fork vote.
+    pub hf_vote: HardFork,
+    /// The block's hard-fork version.
+    pub hf_version: HardFork,
+
+    /// The block's hash.
+    pub block_hash: [u8; 32],
+    /// The height of the block.
+    pub height: u64,
+
+    /// The weight of the block's miner transaction.
+    pub miner_tx_weight: usize,
+}
+
+impl PreparedBlockExPow {
+    /// Prepare a new block.
+    ///
+    /// # Errors
+    /// This errors if either the `block`'s:
+    /// - Hard-fork values are invalid
+    /// - Miner transaction is missing a miner input
+    pub fn new(block: Block) -> Result<PreparedBlockExPow, ConsensusError> {
+        let (hf_version, hf_vote) =
+            HardFork::from_block_header(&block.header).map_err(BlockError::HardForkError)?;
+
+        let Some(Input::Gen(height)) = block.miner_tx.prefix.inputs.first() else {
+            Err(ConsensusError::Block(BlockError::MinerTxError(
+                MinerTxError::InputNotOfTypeGen,
+            )))?
+        };
+
+        Ok(PreparedBlockExPow {
+            block_blob: block.serialize(),
+            hf_vote,
+            hf_version,
+
+            block_hash: block.hash(),
+            height: *height,
+
+            miner_tx_weight: block.miner_tx.weight(),
+            block,
+        })
+    }
+}
+
 /// A pre-prepared block with all data needed to verify it.
 #[derive(Debug)]
-pub struct PrePreparedBlock {
+pub struct PreparedBlock {
     /// The block
     pub block: Block,
     /// The serialised blocks bytes
@@ -47,15 +111,15 @@ pub struct PrePreparedBlock {
     pub miner_tx_weight: usize,
 }
 
-impl PrePreparedBlock {
-    /// Creates a new [`PrePreparedBlock`].
+impl PreparedBlock {
+    /// Creates a new [`PreparedBlock`].
     ///
     /// The randomX VM must be Some if RX is needed or this will panic.
     /// The randomX VM must also be initialised with the correct seed.
     fn new<R: RandomX>(
         block: Block,
         randomx_vm: Option<&R>,
-    ) -> Result<PrePreparedBlock, ConsensusError> {
+    ) -> Result<PreparedBlock, ConsensusError> {
         let (hf_version, hf_vote) =
             HardFork::from_block_header(&block.header).map_err(BlockError::HardForkError)?;
 
@@ -65,7 +129,7 @@ impl PrePreparedBlock {
             )))?
         };
 
-        Ok(PrePreparedBlock {
+        Ok(PreparedBlock {
             block_blob: block.serialize(),
             hf_vote,
             hf_version,
@@ -82,6 +146,36 @@ impl PrePreparedBlock {
             block,
         })
     }
+
+    /// Creates a new [`PreparedBlock`] from a [`PreparedBlockExPow`].
+    ///
+    /// This function will give an invalid PoW hash if `randomx_vm` is not initialised
+    /// with the correct seed.
+    ///
+    /// # Panics
+    /// This function will panic if `randomx_vm` is
+    /// [`None`] even though RandomX is needed.
+    fn new_prepped<R: RandomX>(
+        block: PreparedBlockExPow,
+        randomx_vm: Option<&R>,
+    ) -> Result<PreparedBlock, ConsensusError> {
+        Ok(PreparedBlock {
+            block_blob: block.block_blob,
+            hf_vote: block.hf_vote,
+            hf_version: block.hf_version,
+
+            block_hash: block.block_hash,
+            pow_hash: calculate_pow_hash(
+                randomx_vm,
+                &block.block.serialize_hashable(),
+                block.height,
+                &block.hf_version,
+            )?,
+
+            miner_tx_weight: block.block.miner_tx.weight(),
+            block: block.block,
+        })
+    }
 }
 
 /// A request to verify a block.
@@ -91,12 +185,28 @@ pub enum VerifyBlockRequest {
         block: Block,
         prepared_txs: HashMap<[u8; 32], TransactionVerificationData>,
     },
+    /// Verifies a prepared block.
+    MainChainPrepped {
+        /// The already prepared block.
+        block: PreparedBlock,
+        /// The full list of transactions for this block, in the order given in `block`.
+        txs: Vec<Arc<TransactionVerificationData>>,
+    },
+    /// Batch prepares a list of blocks and transactions for verification.
+    MainChainBatchPrepareBlocks {
+        /// The list of blocks and their transactions (not necessarily in the order given in the block).
+        blocks: Vec<(Block, Vec<Transaction>)>,
+    },
 }
 
 /// A response from a verify block request.
+#[allow(clippy::large_enum_variant)] // The largest variant is most common ([`MainChain`])
 pub enum VerifyBlockResponse {
     /// This block is valid.
     MainChain(VerifiedBlockInformation),
+    /// A list of prepared blocks for verification, you should call [`VerifyBlockRequest::MainChainPrepped`] on each of the returned
+    /// blocks to fully verify them.
+    MainChainBatchPrepped(Vec<(PreparedBlock, Vec<Arc<TransactionVerificationData>>)>),
 }
 
 /// The block verifier service.
@@ -178,17 +288,188 @@ where
                 } => {
                     verify_main_chain_block(block, prepared_txs, context_svc, tx_verifier_svc).await
                 }
+                VerifyBlockRequest::MainChainBatchPrepareBlocks { blocks } => {
+                    batch_prepare_main_chain_block(blocks, context_svc).await
+                }
+                VerifyBlockRequest::MainChainPrepped { block, txs } => {
+                    verify_prepped_main_chain_block(block, txs, context_svc, tx_verifier_svc, None)
+                        .await
+                }
             }
         }
         .boxed()
     }
 }
 
+/// Batch prepares a list of blocks for verification.
+#[instrument(level = "debug", name = "batch_prep_blocks", skip_all, fields(amt = blocks.len()))]
+async fn batch_prepare_main_chain_block<C>(
+    blocks: Vec<(Block, Vec<Transaction>)>,
+    mut context_svc: C,
+) -> Result<VerifyBlockResponse, ExtendedConsensusError>
+where
+    C: Service<
+            BlockChainContextRequest,
+            Response = BlockChainContextResponse,
+            Error = tower::BoxError,
+        > + Send
+        + 'static,
+    C::Future: Send + 'static,
+{
+    let (blocks, txs): (Vec<_>, Vec<_>) = blocks.into_iter().unzip();
+
+    tracing::debug!("Calculating block hashes.");
+    let blocks: Vec<PreparedBlockExPow> = rayon_spawn_async(|| {
+        blocks
+            .into_iter()
+            .map(PreparedBlockExPow::new)
+            .collect::<Result<Vec<_>, _>>()
+    })
+    .await?;
+
+    // A Vec of (timestamp, HF) for each block to calculate the expected difficulty for each block.
+    let mut timestamps_hfs = Vec::with_capacity(blocks.len());
+    let mut new_rx_vm = None;
+
+    tracing::debug!("Checking blocks follow each other.");
+
+    // For every block make sure they have the correct height and previous ID
+    for window in blocks.windows(2) {
+        let block_0 = &window[0];
+        let block_1 = &window[1];
+
+        if block_0.block_hash != block_1.block.header.previous
+            || block_0.height != block_1.height - 1
+        {
+            tracing::debug!("Blocks do not follow each other, verification failed.");
+            Err(ConsensusError::Block(BlockError::PreviousIDIncorrect))?;
+        }
+
+        // Cache any potential RX VM seeds as we may need them for future blocks in the batch.
+        if is_randomx_seed_height(block_0.height) {
+            new_rx_vm = Some((block_0.height, block_0.block_hash));
+        }
+
+        timestamps_hfs.push((block_0.block.header.timestamp, block_0.hf_version))
+    }
+
+    // Get the current blockchain context.
+    let BlockChainContextResponse::Context(checked_context) = context_svc
+        .ready()
+        .await?
+        .call(BlockChainContextRequest::GetContext)
+        .await
+        .map_err(Into::<ExtendedConsensusError>::into)?
+    else {
+        panic!("Context service returned wrong response!");
+    };
+
+    // Calculate the expected difficulties for each block in the batch.
+    let BlockChainContextResponse::BatchDifficulties(difficulties) = context_svc
+        .ready()
+        .await?
+        .call(BlockChainContextRequest::BatchGetDifficulties(
+            timestamps_hfs,
+        ))
+        .await
+        .map_err(Into::<ExtendedConsensusError>::into)?
+    else {
+        panic!("Context service returned wrong response!");
+    };
+
+    let context = checked_context.unchecked_blockchain_context().clone();
+
+    // Make sure the blocks follow the main chain.
+
+    if context.chain_height != blocks[0].height {
+        tracing::debug!("Blocks do not follow main chain, verification failed.");
+
+        Err(ConsensusError::Block(BlockError::MinerTxError(
+            MinerTxError::InputsHeightIncorrect,
+        )))?;
+    }
+
+    if context.top_hash != blocks[0].block.header.previous {
+        tracing::debug!("Blocks do not follow main chain, verification failed.");
+
+        Err(ConsensusError::Block(BlockError::PreviousIDIncorrect))?;
+    }
+
+    let mut rx_vms = context.rx_vms;
+
+    // If we have a RX seed in the batch calculate it.
+    if let Some((new_vm_height, new_vm_seed)) = new_rx_vm {
+        tracing::debug!("New randomX seed in batch, initialising VM");
+
+        let new_vm = rayon_spawn_async(move || {
+            Arc::new(RandomXVM::new(&new_vm_seed).expect("RandomX VM gave an error on set up!"))
+        })
+        .await;
+
+        context_svc
+            .ready()
+            .await?
+            .call(BlockChainContextRequest::NewRXVM((
+                new_vm_seed,
+                new_vm.clone(),
+            )))
+            .await
+            .map_err(Into::<ExtendedConsensusError>::into)?;
+
+        rx_vms.insert(new_vm_height, new_vm);
+    }
+
+    tracing::debug!("Calculating PoW and prepping transaction");
+
+    let blocks = rayon_spawn_async(move || {
+        blocks
+            .into_par_iter()
+            .zip(difficulties)
+            .zip(txs)
+            .map(|((block, difficultly), txs)| {
+                // Calculate the PoW for the block.
+                let height = block.height;
+                let block = PreparedBlock::new_prepped(
+                    block,
+                    rx_vms.get(&randomx_seed_height(height)).map(AsRef::as_ref),
+                )?;
+
+                // Check the PoW
+                check_block_pow(&block.pow_hash, difficultly).map_err(ConsensusError::Block)?;
+
+                // Now setup the txs.
+                let mut txs = txs
+                    .into_par_iter()
+                    .map(|tx| {
+                        let tx = TransactionVerificationData::new(tx)?;
+                        Ok::<_, ConsensusError>((tx.tx_hash, tx))
+                    })
+                    .collect::<Result<HashMap<_, _>, _>>()?;
+
+                // Order the txs correctly.
+                let mut ordered_txs = Vec::with_capacity(txs.len());
+
+                for tx_hash in &block.block.txs {
+                    let tx = txs
+                        .remove(tx_hash)
+                        .ok_or(ExtendedConsensusError::TxsIncludedWithBlockIncorrect)?;
+                    ordered_txs.push(Arc::new(tx));
+                }
+
+                Ok((block, ordered_txs))
+            })
+            .collect::<Result<Vec<_>, ExtendedConsensusError>>()
+    })
+    .await?;
+
+    Ok(VerifyBlockResponse::MainChainBatchPrepped(blocks))
+}
+
 /// Verifies a prepared block.
 async fn verify_main_chain_block<C, TxV>(
     block: Block,
     mut txs: HashMap<[u8; 32], TransactionVerificationData>,
-    context_svc: C,
+    mut context_svc: C,
     tx_verifier_svc: TxV,
 ) -> Result<VerifyBlockResponse, ExtendedConsensusError>
 where
@@ -201,8 +482,85 @@ where
     C::Future: Send + 'static,
     TxV: Service<VerifyTxRequest, Response = VerifyTxResponse, Error = ExtendedConsensusError>,
 {
-    tracing::debug!("getting blockchain context");
+    let BlockChainContextResponse::Context(checked_context) = context_svc
+        .ready()
+        .await?
+        .call(BlockChainContextRequest::GetContext)
+        .await?
+    else {
+        panic!("Context service returned wrong response!");
+    };
 
+    let context = checked_context.unchecked_blockchain_context().clone();
+    tracing::debug!("got blockchain context: {:?}", context);
+
+    tracing::debug!(
+        "Preparing block for verification, expected height: {}",
+        context.chain_height
+    );
+
+    // Set up the block and just pass it to [`verify_prepped_main_chain_block`]
+
+    let rx_vms = context.rx_vms.clone();
+
+    let height = context.chain_height;
+    let prepped_block = rayon_spawn_async(move || {
+        PreparedBlock::new(
+            block,
+            rx_vms.get(&randomx_seed_height(height)).map(AsRef::as_ref),
+        )
+    })
+    .await?;
+
+    check_block_pow(&prepped_block.pow_hash, context.next_difficulty)
+        .map_err(ConsensusError::Block)?;
+
+    // Check that the txs included are what we need and that there are not any extra.
+
+    let mut ordered_txs = Vec::with_capacity(txs.len());
+
+    tracing::debug!("Ordering transactions for block.");
+
+    if !prepped_block.block.txs.is_empty() {
+        for tx_hash in &prepped_block.block.txs {
+            let tx = txs
+                .remove(tx_hash)
+                .ok_or(ExtendedConsensusError::TxsIncludedWithBlockIncorrect)?;
+            ordered_txs.push(Arc::new(tx));
+        }
+        drop(txs);
+    }
+
+    verify_prepped_main_chain_block(
+        prepped_block,
+        ordered_txs,
+        context_svc,
+        tx_verifier_svc,
+        Some(context),
+    )
+    .await
+}
+
+async fn verify_prepped_main_chain_block<C, TxV>(
+    prepped_block: PreparedBlock,
+    txs: Vec<Arc<TransactionVerificationData>>,
+    context_svc: C,
+    tx_verifier_svc: TxV,
+    cached_context: Option<RawBlockChainContext>,
+) -> Result<VerifyBlockResponse, ExtendedConsensusError>
+where
+    C: Service<
+            BlockChainContextRequest,
+            Response = BlockChainContextResponse,
+            Error = tower::BoxError,
+        > + Send
+        + 'static,
+    C::Future: Send + 'static,
+    TxV: Service<VerifyTxRequest, Response = VerifyTxResponse, Error = ExtendedConsensusError>,
+{
+    let context = if let Some(context) = cached_context {
+        context
+    } else {
         let BlockChainContextResponse::Context(checked_context) = context_svc
             .oneshot(BlockChainContextRequest::GetContext)
             .await
@@ -212,52 +570,42 @@ where
         };
 
         let context = checked_context.unchecked_blockchain_context().clone();
-    tracing::debug!("got blockchain context: {:?}", context);
 
-    // Set up the block and just pass it to [`verify_main_chain_block_prepared`]
+        tracing::debug!("got blockchain context: {context:?}");
 
-    let rx_vms = context.rx_vms.clone();
-
-    let height = context.chain_height;
-    let prepped_block = rayon_spawn_async(move || {
-        PrePreparedBlock::new(block, rx_vms.get(&height).map(AsRef::as_ref))
-    })
-    .await?;
+        context
+    };
 
     tracing::debug!("verifying block: {}", hex::encode(prepped_block.block_hash));
 
     check_block_pow(&prepped_block.pow_hash, context.next_difficulty)
         .map_err(ConsensusError::Block)?;
 
-    // Check that the txs included are what we need and that there are not any extra.
-
-    let mut ordered_txs = Vec::with_capacity(txs.len());
-
-    tracing::debug!("Checking we have correct transactions for block.");
-
-    for tx_hash in &prepped_block.block.txs {
-        let tx = txs
-            .remove(tx_hash)
-            .ok_or(ExtendedConsensusError::TxsIncludedWithBlockIncorrect)?;
-        ordered_txs.push(Arc::new(tx));
+    if prepped_block.block.txs.len() != txs.len() {
+        return Err(ExtendedConsensusError::TxsIncludedWithBlockIncorrect);
     }
-    drop(txs);
 
-    tracing::debug!("Verifying transactions for block.");
+    if !prepped_block.block.txs.is_empty() {
+        for (expected_tx_hash, tx) in prepped_block.block.txs.iter().zip(txs.iter()) {
+            if expected_tx_hash != &tx.tx_hash {
+                return Err(ExtendedConsensusError::TxsIncludedWithBlockIncorrect);
+            }
+        }
 
         tx_verifier_svc
             .oneshot(VerifyTxRequest::Prepped {
-            txs: ordered_txs.clone(),
+                txs: txs.clone(),
                 current_chain_height: context.chain_height,
                 top_hash: context.top_hash,
                 time_for_time_lock: context.current_adjusted_timestamp_for_time_lock(),
                 hf: context.current_hf,
             })
             .await?;
+    }
 
     let block_weight =
-        prepped_block.miner_tx_weight + ordered_txs.iter().map(|tx| tx.tx_weight).sum::<usize>();
-    let total_fees = ordered_txs.iter().map(|tx| tx.fee).sum::<u64>();
+        prepped_block.miner_tx_weight + txs.iter().map(|tx| tx.tx_weight).sum::<usize>();
+    let total_fees = txs.iter().map(|tx| tx.fee).sum::<u64>();
 
     tracing::debug!("Verifying block header.");
     let (_, generated_coins) = check_block(
@@ -273,7 +621,7 @@ where
         block_hash: prepped_block.block_hash,
         block: prepped_block.block,
         block_blob: prepped_block.block_blob,
-        txs: ordered_txs
+        txs: txs
             .into_iter()
             .map(|tx| {
                 // Note: it would be possible for the transaction verification service to hold onto the tx after the call