feat: add getBlockTime method

web3.js/src/connection.js

@@ -356,6 +356,16 @@ const GetEpochScheduleRpcResult = struct({
  */
 const GetBalanceAndContextRpcResult = jsonRpcResultAndContext('number?');
 
+/**
+ * Expected JSON RPC response for the "getBlockTime" message
+ */
+const GetBlockTimeRpcResult = struct({
+  jsonrpc: struct.literal('2.0'),
+  id: 'string',
+  error: 'any?',
+  result: struct.union(['null', 'number']),
+});
+
 /**
  * Expected JSON RPC response for the "getVersion" message
  */
@@ -942,6 +952,21 @@ export class Connection {
       });
   }
 
+  /**
+   * Fetch the estimated production time of a block
+   */
+  async getBlockTime(slot: number): Promise<number | null> {
+    const unsafeRes = await this._rpcRequest('getBlockTime', [slot]);
+    const res = GetBlockTimeRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error(
+        'failed to get block time for slot ' + slot + ': ' + res.error.message,
+      );
+    }
+    assert(typeof res.result !== 'undefined');
+    return res.result;
+  }
+
   /**
    * Fetch all the account info for the specified public key, return with context
    */