From f654704169fd54ec3633ff92491b6e2fd4ce7b49 Mon Sep 17 00:00:00 2001
From: mononaut <mononaut@mempool.space>
Date: Wed, 17 Jun 2026 11:59:54 +0000
Subject: [PATCH] fix missing canonical hash on stale block responses

---
 backend/src/repositories/BlocksRepository.ts | 28 ++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/backend/src/repositories/BlocksRepository.ts b/backend/src/repositories/BlocksRepository.ts
index 3a34e3a20..bb0e4f6c5 100644
--- a/backend/src/repositories/BlocksRepository.ts
+++ b/backend/src/repositories/BlocksRepository.ts
@@ -575,6 +575,31 @@ class BlocksRepository {
     }
   }
 
+  /**
+   * Get the canonical block hash at a given height
+   * @asyncSafe
+   */
+  public async $getCanonicalBlockHashByHeight(height: number): Promise<string | null> {
+    try {
+      const [rows]: any[] = await DB.query(`
+        SELECT hash
+        FROM blocks
+        WHERE height = ? AND stale = 0
+        LIMIT 1`,
+        [height]
+      );
+
+      if (rows.length <= 0) {
+        return null;
+      }
+
+      return rows[0].hash;
+    } catch (e) {
+      logger.err(`Cannot get canonical block hash at height ${height}. Reason: ` + (e instanceof Error ? e.message : e));
+      throw e;
+    }
+  }
+
   /**
    * Get one block by hash
    * @asyncSafe
@@ -1258,6 +1283,9 @@ class BlocksRepository {
     blk.mediantime = dbBlk.mediantime;
     blk.indexVersion = dbBlk.index_version;
     blk.stale = dbBlk.stale;
+    if (dbBlk.stale) {
+      blk.canonical = await this.$getCanonicalBlockHashByHeight(dbBlk.height) || undefined;
+    }
     // BlockExtension
     extras.totalFees = dbBlk.totalFees;
     extras.medianFee = dbBlk.medianFee;