From 4e2d96fe88745fb4438da8b3a490d43c8cef6703 Mon Sep 17 00:00:00 2001
From: Justin Starry <justin@solana.com>
Date: Wed, 27 Apr 2022 12:57:18 +0800
Subject: [PATCH] explorer: display slot leaders on block details page (#24727)

---
 .../components/block/BlockOverviewCard.tsx    | 52 ++++++++++++++-----
 explorer/src/providers/block.tsx              | 45 +++++++++++++---
 2 files changed, 76 insertions(+), 21 deletions(-)

diff --git a/explorer/src/components/block/BlockOverviewCard.tsx b/explorer/src/components/block/BlockOverviewCard.tsx
index f129bc98c706d7..9be7cf0fae5282 100644
--- a/explorer/src/components/block/BlockOverviewCard.tsx
+++ b/explorer/src/components/block/BlockOverviewCard.tsx
@@ -14,6 +14,7 @@ import { BlockProgramsCard } from "./BlockProgramsCard";
 import { BlockAccountsCard } from "./BlockAccountsCard";
 import { displayTimestamp, displayTimestampUtc } from "utils/date";
 import { Epoch } from "components/common/Epoch";
+import { Address } from "components/common/Address";
 
 export function BlockOverviewCard({
   slot,
@@ -43,7 +44,8 @@ export function BlockOverviewCard({
     return <ErrorCard retry={refresh} text={`Block ${slot} was not found`} />;
   }
 
-  const block = confirmedBlock.data.block;
+  const { block, blockLeader, childSlot, childLeader, parentLeader } =
+    confirmedBlock.data;
   const committedTxs = block.transactions.filter((tx) => tx.meta?.err === null);
   const epoch = clusterInfo?.epochSchedule.getEpoch(slot);
 
@@ -57,17 +59,25 @@ export function BlockOverviewCard({
         </div>
         <TableCardBody>
           <tr>
-            <td className="w-100">Slot</td>
+            <td className="w-100">Blockhash</td>
             <td className="text-lg-end font-monospace">
-              <Slot slot={slot} />
+              <span>{block.blockhash}</span>
             </td>
           </tr>
           <tr>
-            <td className="w-100">Blockhash</td>
+            <td className="w-100">Slot</td>
             <td className="text-lg-end font-monospace">
-              <span>{block.blockhash}</span>
+              <Slot slot={slot} />
             </td>
           </tr>
+          {blockLeader !== undefined && (
+            <tr>
+              <td className="w-100">Slot Leader</td>
+              <td className="text-lg-end">
+                <Address pubkey={blockLeader} alignRight link />
+              </td>
+            </tr>
+          )}
           {block.blockTime ? (
             <>
               <tr>
@@ -93,12 +103,6 @@ export function BlockOverviewCard({
               <td className="text-lg-end">Unavailable</td>
             </tr>
           )}
-          <tr>
-            <td className="w-100">Parent Slot</td>
-            <td className="text-lg-end font-monospace">
-              <Slot slot={block.parentSlot} link />
-            </td>
-          </tr>
           {epoch !== undefined && (
             <tr>
               <td className="w-100">Epoch</td>
@@ -113,11 +117,33 @@ export function BlockOverviewCard({
               <span>{block.previousBlockhash}</span>
             </td>
           </tr>
-          {confirmedBlock.data.child && (
+          <tr>
+            <td className="w-100">Parent Slot</td>
+            <td className="text-lg-end font-monospace">
+              <Slot slot={block.parentSlot} link />
+            </td>
+          </tr>
+          {parentLeader !== undefined && (
+            <tr>
+              <td className="w-100">Parent Slot Leader</td>
+              <td className="text-lg-end">
+                <Address pubkey={parentLeader} alignRight link />
+              </td>
+            </tr>
+          )}
+          {childSlot !== undefined && (
             <tr>
               <td className="w-100">Child Slot</td>
               <td className="text-lg-end font-monospace">
-                <Slot slot={confirmedBlock.data.child} link />
+                <Slot slot={childSlot} link />
+              </td>
+            </tr>
+          )}
+          {childLeader !== undefined && (
+            <tr>
+              <td className="w-100">Child Slot Leader</td>
+              <td className="text-lg-end">
+                <Address pubkey={childLeader} alignRight link />
               </td>
             </tr>
           )}
diff --git a/explorer/src/providers/block.tsx b/explorer/src/providers/block.tsx
index 724132bb25411f..fa1b564950ddfc 100644
--- a/explorer/src/providers/block.tsx
+++ b/explorer/src/providers/block.tsx
@@ -1,7 +1,7 @@
 import React from "react";
 import * as Sentry from "@sentry/react";
 import * as Cache from "providers/cache";
-import { Connection, BlockResponse } from "@solana/web3.js";
+import { Connection, BlockResponse, PublicKey } from "@solana/web3.js";
 import { useCluster, Cluster } from "./cluster";
 
 export enum FetchStatus {
@@ -17,7 +17,10 @@ export enum ActionType {
 
 type Block = {
   block?: BlockResponse;
-  child?: number;
+  blockLeader?: PublicKey;
+  childSlot?: number;
+  childLeader?: PublicKey;
+  parentLeader?: PublicKey;
 };
 
 type State = Cache.State<Block>;
@@ -59,12 +62,12 @@ export async function fetchBlock(
   dispatch: Dispatch,
   url: string,
   cluster: Cluster,
-  key: number
+  slot: number
 ) {
   dispatch({
     type: ActionType.Update,
     status: FetchStatus.Fetching,
-    key,
+    key: slot,
     url,
   });
 
@@ -73,13 +76,39 @@ export async function fetchBlock(
 
   try {
     const connection = new Connection(url, "confirmed");
-    const block = await connection.getBlock(key);
-    const child = (await connection.getBlocks(key + 1, key + 100)).shift();
+    const block = await connection.getBlock(slot);
     if (block === null) {
       data = {};
       status = FetchStatus.Fetched;
     } else {
-      data = { block, child };
+      const childSlot = (
+        await connection.getBlocks(slot + 1, slot + 100)
+      ).shift();
+      const firstLeaderSlot = block.parentSlot;
+
+      let leaders: PublicKey[] = [];
+      try {
+        const lastLeaderSlot = childSlot !== undefined ? childSlot : slot;
+        const slotLeadersLimit = lastLeaderSlot - block.parentSlot + 1;
+        leaders = await connection.getSlotLeaders(
+          firstLeaderSlot,
+          slotLeadersLimit
+        );
+      } catch (err) {
+        // ignore errors
+      }
+
+      const getLeader = (slot: number) => {
+        return leaders.at(slot - firstLeaderSlot);
+      };
+
+      data = {
+        block,
+        blockLeader: getLeader(slot),
+        childSlot,
+        childLeader: childSlot !== undefined ? getLeader(childSlot) : undefined,
+        parentLeader: getLeader(block.parentSlot),
+      };
       status = FetchStatus.Fetched;
     }
   } catch (err) {
@@ -92,7 +121,7 @@ export async function fetchBlock(
   dispatch({
     type: ActionType.Update,
     url,
-    key,
+    key: slot,
     status,
     data,
   });