feat: add getLeaderSchedule api

web3.js/src/connection.js

@@ -288,6 +288,21 @@ const GetEpochScheduleResult = struct({
   firstNormalSlot: 'number',
 });
 
+/**
+ * Leader schedule
+ * (see https://docs.solana.com/terminology#leader-schedule)
+ *
+ * @typedef {Object} LeaderSchedule
+ */
+type LeaderSchedule = {
+  [address: string]: number[],
+};
+
+const GetLeaderScheduleResult = struct.record([
+  'string',
+  struct.array(['number']),
+]);
+
 /**
  * Transaction error or null
  */
@@ -424,6 +439,13 @@ const GetEpochScheduleRpcResult = struct({
   result: GetEpochScheduleResult,
 });
 
+/**
+ * Expected JSON RPC response for the "getLeaderSchedule" message
+ */
+const GetLeaderScheduleRpcResult = jsonRpcResult(
+  GetLeaderScheduleResult,
+);
+
 /**
  * Expected JSON RPC response for the "getBalance" message
  */
@@ -1476,6 +1498,20 @@ export class Connection {
     return GetEpochScheduleResult(res.result);
   }
 
+  /**
+   * Fetch the leader schedule for the current epoch
+   * @return {Promise<RpcResponseAndContext<LeaderSchedule>>}
+   */
+  async getLeaderSchedule(): Promise<LeaderSchedule> {
+    const unsafeRes = await this._rpcRequest('getLeaderSchedule', []);
+    const res = GetLeaderScheduleRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error('failed to get leader schedule: ' + res.error.message);
+    }
+    assert(typeof res.result !== 'undefined');
+    return res.result;
+  }
+
   /**
    * Fetch the minimum balance needed to exempt an account of `dataLength`
    * size from rent