feat: txpool block building fallback

crates/rpc/rpc/src/eth/api/block.rs

@@ -10,10 +10,13 @@ use crate::{
 use reth_primitives::{BlockId, BlockNumberOrTag, TransactionMeta};
 use reth_provider::{BlockReaderIdExt, EvmEnvProvider, StateProviderFactory};
 use reth_rpc_types::{Block, Index, RichBlock, TransactionReceipt};
+use reth_transaction_pool::TransactionPool;
 
 impl<Provider, Pool, Network> EthApi<Provider, Pool, Network>
 where
     Provider: BlockReaderIdExt + StateProviderFactory + EvmEnvProvider + 'static,
+    Pool: TransactionPool + Clone + 'static,
+    Network: Send + Sync + 'static,
 {
     /// Returns the uncle headers of the given block
     ///
@@ -121,7 +124,12 @@ where
 
         if block_id.is_pending() {
             // Pending block can be fetched directly without need for caching
-            return Ok(self.provider().pending_block()?)
+            let maybe_pending = self.provider().pending_block()?;
+            return if maybe_pending.is_some() {
+                return Ok(maybe_pending)
+            } else {
+                self.local_pending_block().await
+            }
         }
 
         let block_hash = match self.provider().block_hash_for_id(block_id)? {

crates/rpc/rpc/src/eth/api/mod.rs

@@ -12,22 +12,27 @@ use crate::eth::{
 use async_trait::async_trait;
 use reth_interfaces::Result;
 use reth_network_api::NetworkInfo;
-use reth_primitives::{Address, BlockId, BlockNumberOrTag, ChainInfo, H256, U256, U64};
+use reth_primitives::{
+    Address, BlockId, BlockNumberOrTag, ChainInfo, SealedBlock, H256, U256, U64,
+};
 use reth_provider::{BlockReaderIdExt, EvmEnvProvider, StateProviderBox, StateProviderFactory};
 use reth_rpc_types::{SyncInfo, SyncStatus};
 use reth_tasks::{TaskSpawner, TokioTaskExecutor};
 use reth_transaction_pool::TransactionPool;
-use std::{future::Future, sync::Arc};
-use tokio::sync::oneshot;
+use revm_primitives::{BlockEnv, CfgEnv};
+use std::{future::Future, sync::Arc, time::Instant};
+use tokio::sync::{oneshot, Mutex};
 
 mod block;
 mod call;
 mod fees;
+mod pending_block;
 mod server;
 mod sign;
 mod state;
 mod transactions;
 
+use crate::eth::api::pending_block::{PendingBlock, PendingBlockEnv, PendingBlockEnvOrigin};
 pub use transactions::{EthTransactions, TransactionSource};
 
 /// `Eth` API trait.
@@ -115,6 +120,7 @@ where
             gas_oracle,
             starting_block: U256::from(latest_block),
             task_spawner,
+            pending_block: Default::default(),
         };
         Self { inner: Arc::new(inner) }
     }
@@ -201,6 +207,74 @@ where
     }
 }
 
+impl<Provider, Pool, Network> EthApi<Provider, Pool, Network>
+where
+    Provider: BlockReaderIdExt + StateProviderFactory + EvmEnvProvider + 'static,
+    Pool: TransactionPool + Clone + 'static,
+    Network: Send + Sync + 'static,
+{
+    /// Configures the [CfgEnv] and [BlockEnv] for the pending block
+    ///
+    /// If no pending block is available, this will derive it from the `latest` block
+    pub(crate) fn pending_block_env_and_cfg(&self) -> EthResult<PendingBlockEnv> {
+        let origin = if let Some(pending) = self.provider().pending_block()? {
+            PendingBlockEnvOrigin::ActualPending(pending)
+        } else {
+            // no pending block from the CL yet, so we use the latest block and modify the env
+            // values that we can
+            let mut latest =
+                self.provider().latest_header()?.ok_or_else(|| EthApiError::UnknownBlockNumber)?;
+
+            // child block
+            latest.number += 1;
+            // assumed child block is in the next slot
+            latest.timestamp += 12;
+            // base fee of the child block
+            latest.base_fee_per_gas = latest.next_block_base_fee();
+
+            PendingBlockEnvOrigin::DerivedFromLatest(latest)
+        };
+
+        let mut cfg = CfgEnv::default();
+        let mut block_env = BlockEnv::default();
+        self.provider().fill_block_env_with_header(&mut block_env, origin.header())?;
+        self.provider().fill_cfg_env_with_header(&mut cfg, origin.header())?;
+
+        Ok(PendingBlockEnv { cfg, block_env, origin })
+    }
+
+    /// Returns the locally built pending block
+    pub(crate) async fn local_pending_block(&self) -> EthResult<Option<SealedBlock>> {
+        let pending = self.pending_block_env_and_cfg()?;
+        if pending.origin.is_actual_pending() {
+            return Ok(pending.origin.into_actual_pending())
+        }
+
+        // no pending block from the CL yet, so we need to build it ourselves via txpool
+        self.on_blocking_task(|this| async move {
+            let PendingBlockEnv { cfg: _, block_env, origin } = pending;
+            let lock = this.inner.pending_block.lock().await;
+            let now = Instant::now();
+            // this is guaranteed to be the `latest` header
+            let parent_header = origin.into_header();
+
+            // check if the block is still good
+            if let Some(pending) = lock.as_ref() {
+                if block_env.number.to::<u64>() == pending.block.number &&
+                    pending.block.parent_hash == parent_header.parent_hash &&
+                    now <= pending.expires_at
+                {
+                    return Ok(Some(pending.block.clone()))
+                }
+            }
+
+            // TODO(mattsse): actually build the pending block
+            Ok(None)
+        })
+        .await
+    }
+}
+
 impl<Provider, Pool, Events> std::fmt::Debug for EthApi<Provider, Pool, Events> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("EthApi").finish_non_exhaustive()
@@ -284,4 +358,6 @@ struct EthApiInner<Provider, Pool, Network> {
     starting_block: U256,
     /// The type that can spawn tasks which would otherwise block.
     task_spawner: Box<dyn TaskSpawner>,
+    /// Cached pending block if any
+    pending_block: Mutex<Option<PendingBlock>>,
 }

crates/rpc/rpc/src/eth/api/pending_block.rs

@@ -0,0 +1,67 @@
+//! Support for building a pending block via local txpool.
+
+use reth_primitives::{SealedBlock, SealedHeader};
+use revm_primitives::{BlockEnv, CfgEnv};
+use std::time::Instant;
+
+/// Configured [BlockEnv] and [CfgEnv] for a pending block
+#[derive(Debug, Clone)]
+pub(crate) struct PendingBlockEnv {
+    /// Configured [CfgEnv] for the pending block.
+    pub(crate) cfg: CfgEnv,
+    /// Configured [BlockEnv] for the pending block.
+    pub(crate) block_env: BlockEnv,
+    /// Origin block for the config
+    pub(crate) origin: PendingBlockEnvOrigin,
+}
+
+/// The origin for a configured [PendingBlockEnv]
+#[derive(Clone, Debug)]
+pub(crate) enum PendingBlockEnvOrigin {
+    /// The pending block as received from the CL.
+    ActualPending(SealedBlock),
+    /// The header of the latest block
+    DerivedFromLatest(SealedHeader),
+}
+
+impl PendingBlockEnvOrigin {
+    /// Returns true if the origin is the actual pending block as received from the CL.
+    pub(crate) fn is_actual_pending(&self) -> bool {
+        matches!(self, PendingBlockEnvOrigin::ActualPending(_))
+    }
+
+    /// Consumes the type and returns the actual pending block.
+    pub(crate) fn into_actual_pending(self) -> Option<SealedBlock> {
+        match self {
+            PendingBlockEnvOrigin::ActualPending(block) => Some(block),
+            _ => None,
+        }
+    }
+
+    /// Returns the header this pending block is based on.
+    pub(crate) fn header(&self) -> &SealedHeader {
+        match self {
+            PendingBlockEnvOrigin::ActualPending(block) => &block.header,
+            PendingBlockEnvOrigin::DerivedFromLatest(header) => header,
+        }
+    }
+
+    /// Consumes the type and returns the header this pending block is based on.
+    pub(crate) fn into_header(self) -> SealedHeader {
+        match self {
+            PendingBlockEnvOrigin::ActualPending(block) => block.header,
+            PendingBlockEnvOrigin::DerivedFromLatest(header) => header,
+        }
+    }
+}
+
+/// In memory pending block for `pending` tag
+#[derive(Debug)]
+pub(crate) struct PendingBlock {
+    /// The cached pending block
+    pub(crate) block: SealedBlock,
+    /// Timestamp when the pending block is considered outdated
+    pub(crate) expires_at: Instant,
+}
+
+impl PendingBlock {}

crates/rpc/rpc/src/eth/api/transactions.rs

@@ -1,6 +1,7 @@
 //! Contains RPC handler implementations specific to transactions
 use crate::{
     eth::{
+        api::pending_block::PendingBlockEnv,
         error::{EthApiError, EthResult, SignError},
         revm_utils::{
             inspect, inspect_and_return_db, prepare_call_env, replay_transactions_until, transact,
@@ -239,31 +240,8 @@ where
 
     async fn evm_env_at(&self, at: BlockId) -> EthResult<(CfgEnv, BlockEnv, BlockId)> {
         if at.is_pending() {
-            let header = if let Some(pending) = self.provider().pending_header()? {
-                pending
-            } else {
-                // no pending block from the CL yet, so we use the latest block and modify the env
-                // values that we can
-                let mut latest = self
-                    .provider()
-                    .latest_header()?
-                    .ok_or_else(|| EthApiError::UnknownBlockNumber)?;
-
-                // child block
-                latest.number += 1;
-                // assumed child block is in the next slot
-                latest.timestamp += 12;
-                // base fee of the child block
-                latest.base_fee_per_gas = latest.next_block_base_fee();
-
-                latest
-            };
-
-            let mut cfg = CfgEnv::default();
-            let mut block_env = BlockEnv::default();
-            self.provider().fill_block_env_with_header(&mut block_env, &header)?;
-            self.provider().fill_cfg_env_with_header(&mut cfg, &header)?;
-            return Ok((cfg, block_env, header.hash.into()))
+            let PendingBlockEnv { cfg, block_env, origin } = self.pending_block_env_and_cfg()?;
+            Ok((cfg, block_env, origin.header().hash.into()))
         } else {
             //  Use cached values if there is no pending block
             let block_hash = self
@@ -652,6 +630,7 @@ where
 impl<Provider, Pool, Network> EthApi<Provider, Pool, Network>
 where
     Provider: BlockReaderIdExt + StateProviderFactory + EvmEnvProvider + 'static,
+    Network: 'static,
 {
     /// Helper function for `eth_getTransactionReceipt`
     ///
@@ -675,7 +654,7 @@ impl<Provider, Pool, Network> EthApi<Provider, Pool, Network>
 where
     Pool: TransactionPool + 'static,
     Provider: BlockReaderIdExt + StateProviderFactory + EvmEnvProvider + 'static,
-    Network: 'static,
+    Network: Send + Sync + 'static,
 {
     pub(crate) fn sign_request(
         &self,