From 5179de150046ec5d441163fa2065c6f18ad66845 Mon Sep 17 00:00:00 2001
From: David Murdoch <david@davidmurdoch.com>
Date: Wed, 24 Nov 2021 18:44:15 -0500
Subject: [PATCH] fix: don't return an error from miner_start if aleady started

---
 src/chains/ethereum/ethereum/src/api.ts               | 11 ++++++++---
 .../ethereum/ethereum/tests/api/miner/miner.test.ts   |  8 ++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/chains/ethereum/ethereum/src/api.ts b/src/chains/ethereum/ethereum/src/api.ts
index 59b91880aa..58ae4cda06 100644
--- a/src/chains/ethereum/ethereum/src/api.ts
+++ b/src/chains/ethereum/ethereum/src/api.ts
@@ -592,9 +592,14 @@ export default class EthereumApi implements Api {
   @assertArgLength(0, 1)
   async miner_start(threads: number = 1) {
     if (this.#options.miner.legacyInstamine === true) {
-      const { transactions } = await this.#blockchain.resume(threads);
-      if (transactions != null && this.#options.chain.vmErrorsOnRPCResponse) {
-        assertExceptionalTransactions(transactions);
+      const resumption = await this.#blockchain.resume(threads);
+      // resumption can be undefined if the blockchain isn't currently paused
+      if (
+        resumption &&
+        resumption.transactions != null &&
+        this.#options.chain.vmErrorsOnRPCResponse
+      ) {
+        assertExceptionalTransactions(resumption.transactions);
       }
     } else {
       this.#blockchain.resume(threads);
diff --git a/src/chains/ethereum/ethereum/tests/api/miner/miner.test.ts b/src/chains/ethereum/ethereum/tests/api/miner/miner.test.ts
index f72caf104d..2f274ff128 100644
--- a/src/chains/ethereum/ethereum/tests/api/miner/miner.test.ts
+++ b/src/chains/ethereum/ethereum/tests/api/miner/miner.test.ts
@@ -67,6 +67,14 @@ describe("api", () => {
         const provider = await getProvider({ miner: { blockTime: 1 } });
         await testStopStartMining(provider);
       }).timeout(4000);
+
+      it("should not throw an error when miner was already started when calling miner_start", async () => {
+        const provider = await getProvider({
+          miner: { blockTime: 1, legacyInstamine: true }
+        });
+        await assert.doesNotReject(provider.send("miner_start"));
+        await assert.doesNotReject(provider.send("miner_start"));
+      }).timeout(4000);
     });
 
     describe("miner_setEtherbase", () => {