feat(payload): add support for stack of payload builders

crates/payload/basic/src/builder_stack.rs

@@ -0,0 +1,320 @@
+use crate::{
+    BuildArguments, BuildOutcome, PayloadBuilder, PayloadBuilderError,
+    PayloadConfig, PayloadBuilderAttributes
+};
+
+use alloy_primitives::{Address, B256};
+use reth_payload_builder::PayloadId;
+use reth_payload_primitives::BuiltPayload;
+use reth_primitives::{SealedBlock, Withdrawals, U256};
+
+use std::fmt;
+use std::error::Error;
+
+/// hand rolled Either enum to handle two builder types
+#[derive(Debug, Clone)]
+pub enum Either<L, R> {
+    /// left variant
+    Left(L),
+    /// right variant
+    Right(R),
+}
+
+impl<L, R> fmt::Display for Either<L, R>
+where
+    L: fmt::Display,
+    R: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Either::Left(l) => write!(f, "Left: {}", l),
+            Either::Right(r) => write!(f, "Right: {}", r),
+        }
+    }
+}
+
+impl<L, R> Error for Either<L, R>
+where
+    L: Error + 'static,
+    R: Error + 'static,
+{
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            Either::Left(l) => Some(l),
+            Either::Right(r) => Some(r),
+        }
+    }
+}
+
+impl<L, R> PayloadBuilderAttributes for Either<L, R>
+   where
+       L: PayloadBuilderAttributes,
+       R: PayloadBuilderAttributes,
+       L::Error: Error + 'static, 
+       R::Error: Error + 'static,
+   {
+       type RpcPayloadAttributes = Either<L::RpcPayloadAttributes, R::RpcPayloadAttributes>;
+       type Error = Either<L::Error, R::Error>;
+
+       fn try_new(
+           parent: B256,
+           rpc_payload_attributes: Self::RpcPayloadAttributes,
+       ) -> Result<Self, Self::Error> {
+           match rpc_payload_attributes {
+               Either::Left(attr) => L::try_new(parent, attr).map(Either::Left).map_err(Either::Left),
+               Either::Right(attr) => R::try_new(parent, attr).map(Either::Right).map_err(Either::Right),
+           }
+       }
+
+       fn payload_id(&self) -> PayloadId {
+           match self {
+               Either::Left(l) => l.payload_id(),
+               Either::Right(r) => r.payload_id(),
+           }
+       }
+
+       fn parent(&self) -> B256 {
+           match self {
+               Either::Left(l) => l.parent(),
+               Either::Right(r) => r.parent(),
+           }
+       }
+
+       fn timestamp(&self) -> u64 {
+           match self {
+               Either::Left(l) => l.timestamp(),
+               Either::Right(r) => r.timestamp(),
+           }
+       }
+
+       fn parent_beacon_block_root(&self) -> Option<B256> {
+            match self {
+                Either::Left(l) => l.parent_beacon_block_root(),
+                Either::Right(r) => r.parent_beacon_block_root(),   
+            }
+       }
+
+       fn suggested_fee_recipient(&self) -> Address {
+            match self {
+                Either::Left(l) => l.suggested_fee_recipient(),
+                Either::Right(r) => r.suggested_fee_recipient(),
+            }
+       }
+
+       fn prev_randao(&self) -> B256 {
+            match self {
+                Either::Left(l) => l.prev_randao(),
+                Either::Right(r) => r.prev_randao(),
+            }
+       }
+
+       fn withdrawals(&self) -> &Withdrawals {
+            match self {
+                Either::Left(l) => l.withdrawals(),
+                Either::Right(r) => r.withdrawals(),
+            }
+       }
+   }
+
+/// this structure enables the chaining of multiple `PayloadBuilder` implementations,
+/// creating a hierarchical fallback system. It's designed to be nestable, allowing
+/// for complex builder arrangements like `Stack<Stack<A, B>, C>` with different
+#[derive(Debug)]
+pub struct PayloadBuilderStack<L, R> {
+    left: L,
+    right: R,
+}
+
+impl<L, R> PayloadBuilderStack<L, R> {
+    /// Creates a new `PayloadBuilderStack` with the given left and right builders.
+    pub const fn new(left: L, right: R) -> Self {
+        Self { left, right }
+    }
+}
+
+impl<L, R> Clone for PayloadBuilderStack<L, R>
+where
+    L: Clone,
+    R: Clone,
+{
+    fn clone(&self) -> Self {
+        Self::new(self.left.clone(), self.right.clone())
+    }
+}
+
+impl<L, R> BuiltPayload for Either<L, R>
+where
+    L: BuiltPayload,
+    R: BuiltPayload,
+{
+    fn block(&self) -> &SealedBlock {
+        match self {
+            Either::Left(l) => l.block(),
+            Either::Right(r) => r.block(),
+        }
+    }
+
+    fn fees(&self) -> U256 {
+        match self {
+            Either::Left(l) => l.fees(),
+            Either::Right(r) => r.fees(),
+        }
+    }
+}
+
+impl<B> BuildOutcome<B> {
+    fn map_payload<F, B2>(self, f: F) -> BuildOutcome<B2>
+    where
+        F: FnOnce(B) -> B2,
+    {
+        match self {
+            BuildOutcome::Better { payload, cached_reads } => BuildOutcome::Better {
+                payload: f(payload),
+                cached_reads,
+            },
+            BuildOutcome::Aborted { fees, cached_reads } => BuildOutcome::Aborted { fees, cached_reads },
+            BuildOutcome::Cancelled => BuildOutcome::Cancelled,
+        }
+    }
+}
+
+impl<L, R, Pool, Client> PayloadBuilder<Pool, Client> for PayloadBuilderStack<L, R>
+where
+    L: PayloadBuilder<Pool, Client> + Unpin + 'static,
+    R: PayloadBuilder<Pool, Client> + Unpin + 'static,
+    Client: Clone,
+    Pool: Clone,
+    L::Attributes: Unpin + Clone,
+    R::Attributes: Unpin + Clone,
+    L::BuiltPayload: Unpin + Clone,
+    R::BuiltPayload: Unpin + Clone,
+    <<L as PayloadBuilder<Pool, Client>>::Attributes as PayloadBuilderAttributes>::Error: 'static,
+    <<R as PayloadBuilder<Pool, Client>>::Attributes as PayloadBuilderAttributes>::Error: 'static,
+{
+    type Attributes = Either<L::Attributes, R::Attributes>;
+    type BuiltPayload = Either<L::BuiltPayload, R::BuiltPayload>;
+
+    fn try_build(
+        &self,
+        args: BuildArguments<Pool, Client, Self::Attributes, Self::BuiltPayload>,
+    ) -> Result<BuildOutcome<Self::BuiltPayload>, PayloadBuilderError> {
+        match args.config.attributes {
+            Either::Left(ref left_attr) => {
+                let left_args:  BuildArguments<Pool, Client, L::Attributes, L::BuiltPayload> = BuildArguments {
+                    client: args.client.clone(),
+                    pool: args.pool.clone(),
+                    cached_reads: args.cached_reads.clone(),
+                    config: PayloadConfig {
+                        parent_block: args.config.parent_block.clone(),
+                        extra_data: args.config.extra_data.clone(),
+                        attributes: left_attr.clone(),
+                    },
+                    cancel: args.cancel.clone(),
+                    best_payload: args.best_payload.clone().and_then(|payload| {
+                        if let Either::Left(p) = payload {
+                            Some(p)
+                        } else {
+                            None
+                        }
+                    }),
+                };
+
+                match self.left.try_build(left_args) {
+                    Ok(BuildOutcome::Better { payload, cached_reads }) => {
+                        return Ok(BuildOutcome::Better {
+                            payload: Either::Left(payload),
+                            cached_reads,
+                        })
+                    }
+                    Ok(other) => {
+                        return Ok(other.map_payload(Either::Left))
+                    }
+                    Err(_) => {
+                    }
+                }
+            }
+            Either::Right(ref right_attr) => {
+                let right_args = BuildArguments {
+                    client: args.client.clone(),
+                    pool: args.pool.clone(),
+                    cached_reads: args.cached_reads.clone(),
+                    config: PayloadConfig {
+                        parent_block: args.config.parent_block.clone(),
+                        extra_data: args.config.extra_data.clone(),
+                        attributes: right_attr.clone(),
+                    },
+                    cancel: args.cancel.clone(),
+                    best_payload: args.best_payload.clone().and_then(|payload| {
+                        if let Either::Right(p) = payload {
+                            Some(p)
+                        } else {
+                            None
+                        }
+                    }),
+                };
+
+                match self.right.try_build(right_args) {
+                    Ok(BuildOutcome::Better { payload, cached_reads }) => {
+                        return Ok(BuildOutcome::Better {
+                            payload: Either::Right(payload),
+                            cached_reads,
+                        })
+                    }
+                    Ok(other) => {
+                        return Ok(other.map_payload(Either::Right))
+                    }
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+        }
+        Err(PayloadBuilderError::Other(Box::new(std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "Both left and right builders failed to build the payload"
+        ))))
+    }
+
+    fn build_empty_payload(
+        &self,
+        client: &Client,
+        config: PayloadConfig<Self::Attributes>,
+    ) -> Result<Self::BuiltPayload, PayloadBuilderError> {
+        match config.attributes {
+            Either::Left(left_attr) => {
+                let left_config = PayloadConfig {
+                    attributes: left_attr,
+                    parent_block: config.parent_block.clone(),
+                    extra_data: config.extra_data.clone(),
+                };
+
+                match self.left.build_empty_payload(client, left_config) {
+                    Ok(payload_left) => { 
+                        return Ok(Either::Left(payload_left))
+                    },
+                    Err(_) => {}
+                }
+            },
+            Either::Right(right_attr) => {
+                let right_config = PayloadConfig {
+                    parent_block: config.parent_block.clone(),
+                    extra_data: config.extra_data.clone(),
+                    attributes: right_attr.clone(),
+                };
+
+                match self.right.build_empty_payload(client, right_config) {
+                    Ok(payload_right) => { 
+                        return Ok(Either::Right(payload_right))
+                    },
+                    Err(e) => {
+                        return Err(e);
+                    }
+                }
+            }
+        }
+        Err(PayloadBuilderError::Other(Box::new(std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "Failed to build empty payload with both left and right builders"
+        ))))
+    }
+}

crates/payload/basic/src/lib.rs

@@ -44,6 +44,9 @@ use tokio::{
 use tracing::{debug, trace, warn};
 
 mod metrics;
+mod builder_stack;
+
+pub use builder_stack::PayloadBuilderStack;
 
 /// The [`PayloadJobGenerator`] that creates [`BasicPayloadJob`]s.
 #[derive(Debug)]