From 09d16aa199b24bfa9ab7cb23e955d155d2b298b4 Mon Sep 17 00:00:00 2001
From: Cho Young-Hwi <cyh76507707@gmail.com>
Date: Fri, 20 Mar 2026 09:17:11 +0000
Subject: [PATCH] [#376] Fall back to provided content on IPFS hash mismatch

Previously, fallback content was only used when IPFS fetch failed.
If IPFS returned content whose hash didn't match the on-chain hash
(e.g. dummy CIDs pointing to unrelated IPFS content), the indexer
returned 400 with no way to override.

Now both storyline and plot routes:
1. Try IPFS content first, verify hash
2. If hash mismatches, try fallback content and verify its hash
3. Only fail if neither source provides hash-matching content

Fixes #376

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/app/api/index/plot/route.ts      | 25 ++++++++++++++++---------
 src/app/api/index/storyline/route.ts | 28 ++++++++++++++++------------
 2 files changed, 32 insertions(+), 21 deletions(-)

diff --git a/src/app/api/index/plot/route.ts b/src/app/api/index/plot/route.ts
index 5c6a479c..650ce342 100644
--- a/src/app/api/index/plot/route.ts
+++ b/src/app/api/index/plot/route.ts
@@ -74,24 +74,31 @@ export async function POST(req: Request) {
     decoded.args;
 
   // 4. Fetch content from IPFS (with fallback)
-  let content: string;
+  let content: string | null = null;
   try {
     const ipfsRes = await fetch(`${IPFS_GATEWAY}${contentCID}`, {
       signal: AbortSignal.timeout(IPFS_TIMEOUT_MS),
     });
     if (!ipfsRes.ok) throw new Error(`IPFS status ${ipfsRes.status}`);
-    content = await ipfsRes.text();
+    const ipfsContent = await ipfsRes.text();
+    // Verify IPFS content hash matches on-chain hash
+    if (hashContent(ipfsContent) === contentHash) {
+      content = ipfsContent;
+    }
+    // If hash mismatches, fall through to fallback content below
   } catch {
-    if (!fallbackContent) {
-      return error("IPFS fetch failed and no fallback content provided", 502);
+    // IPFS fetch failed — fall through to fallback content below
+  }
+
+  // 5. Try fallback content if IPFS content was unavailable or hash-mismatched
+  if (!content && fallbackContent) {
+    if (hashContent(fallbackContent) === contentHash) {
+      content = fallbackContent;
     }
-    content = fallbackContent;
   }
 
-  // 5. Verify content hash
-  const computedHash = hashContent(content);
-  if (computedHash !== contentHash) {
-    return error("Content hash mismatch");
+  if (!content) {
+    return error("Content hash mismatch (IPFS and fallback both failed)");
   }
 
   // 6. Get block timestamp
diff --git a/src/app/api/index/storyline/route.ts b/src/app/api/index/storyline/route.ts
index 97b90eb6..fd125e18 100644
--- a/src/app/api/index/storyline/route.ts
+++ b/src/app/api/index/storyline/route.ts
@@ -100,27 +100,31 @@ export async function POST(req: Request) {
   const writerType = await detectWriterType(writer);
 
   // 6. Fetch genesis plot content from IPFS (with fallback)
-  let genesisContent: string;
+  let genesisContent: string | null = null;
   try {
     const ipfsRes = await fetch(`${IPFS_GATEWAY}${openingCID}`, {
       signal: AbortSignal.timeout(IPFS_TIMEOUT_MS),
     });
     if (!ipfsRes.ok) throw new Error(`IPFS status ${ipfsRes.status}`);
-    genesisContent = await ipfsRes.text();
+    const ipfsContent = await ipfsRes.text();
+    // Verify IPFS content hash matches on-chain hash
+    if (hashContent(ipfsContent) === openingHash) {
+      genesisContent = ipfsContent;
+    }
+    // If hash mismatches, fall through to fallback content below
   } catch {
-    if (!fallbackContent) {
-      return error(
-        "IPFS fetch failed and no fallback content provided",
-        502
-      );
+    // IPFS fetch failed — fall through to fallback content below
+  }
+
+  // 7. Try fallback content if IPFS content was unavailable or hash-mismatched
+  if (!genesisContent && fallbackContent) {
+    if (hashContent(fallbackContent) === openingHash) {
+      genesisContent = fallbackContent;
     }
-    genesisContent = fallbackContent;
   }
 
-  // 7. Verify genesis content hash
-  const computedHash = hashContent(genesisContent);
-  if (computedHash !== openingHash) {
-    return error("Genesis content hash mismatch");
+  if (!genesisContent) {
+    return error("Genesis content hash mismatch (IPFS and fallback both failed)");
   }
 
   // 8. Upsert storyline to Supabase