From 4ae90c294453829ad663a5c9fd9d0a3f4d94aa20 Mon Sep 17 00:00:00 2001
From: Tyera Eulberg <tyera@solana.com>
Date: Thu, 26 Sep 2019 14:13:57 -0600
Subject: [PATCH] fix: add api for getMinimumBalanceForRentExemption

---
 web3.js/src/connection.js       | 22 ++++++++++++++++++++++
 web3.js/test/connection.test.js | 19 +++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/web3.js/src/connection.js b/web3.js/src/connection.js
index 77e70dd225..02b4d12e41 100644
--- a/web3.js/src/connection.js
+++ b/web3.js/src/connection.js
@@ -294,6 +294,11 @@ const GetTransactionCountRpcResult = jsonRpcResult('number');
  */
 const GetTotalSupplyRpcResult = jsonRpcResult('number');
 
+/**
+ * Expected JSON RPC response for the "getMinimumBalanceForRentExemption" message
+ */
+const GetMinimumBalanceForRentExemptionRpcResult = jsonRpcResult('number');
+
 /**
  * Expected JSON RPC response for the "getRecentBlockhash" message
  */
@@ -683,6 +688,23 @@ export class Connection {
     return GetInflationResult(res.result);
   }
 
+  /**
+   * Fetch the minimum balance needed to exempt an account of `dataLength`
+   * size from rent
+   */
+  async getMinimumBalanceForRentExemption(dataLength: number): Promise<number> {
+    const unsafeRes = await this._rpcRequest(
+      'getMinimumBalanceForRentExemption',
+      [dataLength],
+    );
+    const res = GetMinimumBalanceForRentExemptionRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error(res.error.message);
+    }
+    assert(typeof res.result !== 'undefined');
+    return Number(res.result);
+  }
+
   /**
    * Fetch a recent blockhash from the cluster
    */
diff --git a/web3.js/test/connection.test.js b/web3.js/test/connection.test.js
index ec3898be21..2ec2320b2e 100644
--- a/web3.js/test/connection.test.js
+++ b/web3.js/test/connection.test.js
@@ -330,6 +330,25 @@ test('get total supply', async () => {
   expect(count).toBeGreaterThanOrEqual(0);
 });
 
+test('get minimum balance for rent exemption', async () => {
+  const connection = new Connection(url);
+
+  mockRpc.push([
+    url,
+    {
+      method: 'getMinimumBalanceForRentExemption',
+      params: [512],
+    },
+    {
+      error: null,
+      result: 1000000,
+    },
+  ]);
+
+  const count = await connection.getMinimumBalanceForRentExemption(512);
+  expect(count).toBeGreaterThanOrEqual(0);
+});
+
 test('get recent blockhash', async () => {
   const connection = new Connection(url);