From f9fd6ac39272053f7b1334486aa113d3f7560033 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Mon, 27 Sep 2021 16:05:19 +1000
Subject: [PATCH] Add search for TTD block

---
 beacon_node/execution_layer/src/engine_api.rs | 26 +++++++++++++++-
 .../execution_layer/src/engine_api/http.rs    | 27 +++++++++++++++++
 beacon_node/execution_layer/src/lib.rs        | 30 +++++++++++++++++++
 3 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/beacon_node/execution_layer/src/engine_api.rs b/beacon_node/execution_layer/src/engine_api.rs
index 7362c52eee..e03a9e6dae 100644
--- a/beacon_node/execution_layer/src/engine_api.rs
+++ b/beacon_node/execution_layer/src/engine_api.rs
@@ -2,7 +2,9 @@ use async_trait::async_trait;
 use eth1::http::RpcError;
 use serde::{Deserialize, Serialize};
 
-pub use types::{Address, EthSpec, ExecutionPayload, Hash256};
+pub const LATEST_TAG: &str = "latest";
+
+pub use types::{Address, EthSpec, ExecutionPayload, Hash256, Uint256};
 
 pub mod http;
 
@@ -37,6 +39,13 @@ impl From<serde_json::Error> for Error {
 pub trait EngineApi {
     async fn upcheck(&self) -> Result<(), Error>;
 
+    async fn get_block_by_number<'a>(
+        &self,
+        block_by_number: BlockByNumberQuery<'a>,
+    ) -> Result<ExecutionBlock, Error>;
+
+    async fn get_block_by_hash<'a>(&self, block_hash: Hash256) -> Result<ExecutionBlock, Error>;
+
     async fn prepare_payload(
         &self,
         parent_hash: Hash256,
@@ -82,3 +91,18 @@ pub enum ConsensusStatus {
     Valid,
     Invalid,
 }
+
+#[derive(Clone, Copy, Debug, PartialEq, Serialize)]
+#[serde(untagged)]
+pub enum BlockByNumberQuery<'a> {
+    Tag(&'a str),
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecutionBlock {
+    pub block_hash: Hash256,
+    pub block_number: u64,
+    pub parent_hash: Hash256,
+    pub total_difficulty: Uint256,
+}
diff --git a/beacon_node/execution_layer/src/engine_api/http.rs b/beacon_node/execution_layer/src/engine_api/http.rs
index 976cca2102..5dce3500b0 100644
--- a/beacon_node/execution_layer/src/engine_api/http.rs
+++ b/beacon_node/execution_layer/src/engine_api/http.rs
@@ -13,6 +13,12 @@ pub use reqwest::Client;
 const STATIC_ID: u32 = 1;
 const JSONRPC_VERSION: &str = "2.0";
 
+const ETH_GET_BLOCK_BY_NUMBER: &str = "eth_getBlockByNumber";
+const ETH_GET_BLOCK_BY_NUMBER_TIMEOUT: Duration = Duration::from_secs(1);
+
+const ETH_GET_BLOCK_BY_HASH: &str = "eth_getBlockByHash";
+const ETH_GET_BLOCK_BY_HASH_TIMEOUT: Duration = Duration::from_secs(1);
+
 const ETH_SYNCING: &str = "eth_syncing";
 const ETH_SYNCING_TIMEOUT: Duration = Duration::from_millis(250);
 
@@ -103,6 +109,27 @@ impl EngineApi for HttpJsonRpc {
         }
     }
 
+    async fn get_block_by_number<'a>(
+        &self,
+        query: BlockByNumberQuery<'a>,
+    ) -> Result<ExecutionBlock, Error> {
+        let params = json!([query]);
+
+        self.rpc_request(
+            ETH_GET_BLOCK_BY_NUMBER,
+            params,
+            ETH_GET_BLOCK_BY_NUMBER_TIMEOUT,
+        )
+        .await
+    }
+
+    async fn get_block_by_hash<'a>(&self, block_hash: Hash256) -> Result<ExecutionBlock, Error> {
+        let params = json!([block_hash]);
+
+        self.rpc_request(ETH_GET_BLOCK_BY_HASH, params, ETH_GET_BLOCK_BY_HASH_TIMEOUT)
+            .await
+    }
+
     async fn prepare_payload(
         &self,
         parent_hash: Hash256,
diff --git a/beacon_node/execution_layer/src/lib.rs b/beacon_node/execution_layer/src/lib.rs
index 5862a5cb12..da58853a78 100644
--- a/beacon_node/execution_layer/src/lib.rs
+++ b/beacon_node/execution_layer/src/lib.rs
@@ -30,6 +30,7 @@ impl From<ApiError> for Error {
 
 struct Inner {
     engines: Engines<HttpJsonRpc>,
+    total_terminal_difficulty: Uint256,
     executor: TaskExecutor,
     log: Logger,
 }
@@ -42,6 +43,7 @@ pub struct ExecutionLayer {
 impl ExecutionLayer {
     pub fn from_urls(
         urls: Vec<SensitiveUrl>,
+        total_terminal_difficulty: Uint256,
         executor: TaskExecutor,
         log: Logger,
     ) -> Result<Self, Error> {
@@ -59,6 +61,7 @@ impl ExecutionLayer {
                 engines,
                 log: log.clone(),
             },
+            total_terminal_difficulty,
             executor,
             log,
         };
@@ -78,6 +81,10 @@ impl ExecutionLayer {
         &self.inner.executor
     }
 
+    fn total_terminal_difficulty(&self) -> Uint256 {
+        self.inner.total_terminal_difficulty
+    }
+
     fn log(&self) -> &Logger {
         &self.inner.log
     }
@@ -218,4 +225,27 @@ impl ExecutionLayer {
             ))
         }
     }
+
+    pub async fn find_ttd_block_hash(&self) -> Result<Option<Hash256>, Error> {
+        self.engines()
+            .first_success(|engine| async move {
+                let mut ttd_exceeding_block = None;
+                let mut block = engine
+                    .api
+                    .get_block_by_number(BlockByNumberQuery::Tag(LATEST_TAG))
+                    .await?;
+
+                loop {
+                    if block.total_difficulty >= self.total_terminal_difficulty() {
+                        ttd_exceeding_block = Some(block.block_hash);
+
+                        block = engine.api.get_block_by_hash(block.parent_hash).await?;
+                    } else {
+                        return Ok::<_, ApiError>(ttd_exceeding_block);
+                    }
+                }
+            })
+            .await
+            .map_err(Error::EngineErrors)
+    }
 }