From aa50b4cfad5d47dcdbcd7fa62d31b7bc55ea23e0 Mon Sep 17 00:00:00 2001
From: Noah Citron <noah@jeff.org>
Date: Sat, 27 Aug 2022 16:43:27 -0400
Subject: [PATCH] add eth_estimateGas

---
 src/client/client.rs |  6 ++++++
 src/client/rpc.rs    | 14 ++++++++++++++
 src/execution/evm.rs | 19 +++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/src/client/client.rs b/src/client/client.rs
index 4befbaa..0252b08 100644
--- a/src/client/client.rs
+++ b/src/client/client.rs
@@ -42,6 +42,12 @@ impl Client {
         evm.call(to, calldata, value)
     }
 
+    pub async fn estimate_gas(&self, to: &Address, calldata: &Vec<u8>, value: U256) -> Result<u64> {
+        let payload = self.consensus.get_execution_payload().await?;
+        let mut evm = Evm::new(self.execution.clone(), payload);
+        evm.estimate_gas(to, calldata, value)
+    }
+
     pub async fn get_balance(&self, address: &Address) -> Result<U256> {
         let payload = self.consensus.get_execution_payload().await?;
         let account = self.execution.get_account(&address, None, &payload).await?;
diff --git a/src/client/rpc.rs b/src/client/rpc.rs
index c2058ed..8d9142c 100644
--- a/src/client/rpc.rs
+++ b/src/client/rpc.rs
@@ -49,6 +49,8 @@ trait EthRpc {
     async fn get_code(&self, address: &str, block: &str) -> Result<String, Error>;
     #[method(name = "call")]
     async fn call(&self, opts: CallOpts, block: &str) -> Result<String, Error>;
+    #[method(name = "estimateGas")]
+    async fn estimate_gas(&self, opts: CallOpts) -> Result<String, Error>;
     #[method(name = "chainId")]
     fn chain_id(&self) -> Result<String, Error>;
 }
@@ -112,6 +114,18 @@ impl EthRpcServer for RpcInner {
         }
     }
 
+    async fn estimate_gas(&self, opts: CallOpts) -> Result<String, Error> {
+        let to = convert_err(Address::from_str(&opts.to))?;
+        let data = convert_err(hex_str_to_bytes(&opts.data.unwrap_or("0x".to_string())))?;
+        let value = convert_err(U256::from_str_radix(
+            &opts.value.unwrap_or("0x0".to_string()),
+            16,
+        ))?;
+
+        let gas = convert_err(self.client.estimate_gas(&to, &data, value).await)?;
+        Ok(u64_to_hex_string(gas))
+    }
+
     fn chain_id(&self) -> Result<String, Error> {
         let id = self.client.chain_id();
         Ok(u64_to_hex_string(id))
diff --git a/src/execution/evm.rs b/src/execution/evm.rs
index 0d26f80..0769d74 100644
--- a/src/execution/evm.rs
+++ b/src/execution/evm.rs
@@ -44,6 +44,25 @@ impl Evm {
             TransactOut::Call(bytes) => Ok(bytes.to_vec()),
         }
     }
+
+    pub fn estimate_gas(&mut self, to: &Address, calldata: &Vec<u8>, value: U256) -> Result<u64> {
+        let mut env = Env::default();
+        let mut tx = revm::TxEnv::default();
+        tx.transact_to = TransactTo::Call(*to);
+        tx.data = Bytes::from(calldata.clone());
+        tx.value = value;
+        env.tx = tx;
+
+        self.evm.env = env;
+
+        let gas = self.evm.transact().2;
+
+        if let Some(err) = &self.evm.db.as_ref().unwrap().error {
+            return Err(eyre::eyre!(err.clone()));
+        }
+
+        Ok(gas)
+    }
 }
 
 struct ProofDB {