createAssets fails in case of broken JSON in fetch cache

[grabmateusz]

There is an issue in code:
https://github.com/opennextjs/opennextjs-aws/blob/main/packages/open-next/src/build/createAssets.ts
Code like:

  Object.entries(cacheFilesPath).forEach(([cacheFilePath, files]) => {
    const cacheFileMeta = files.meta
      ? JSON.parse(fs.readFileSync(files.meta, "utf8"))
      : undefined;
  //...
  });

is failing because of unsafe JSON parsing - whenever Next.js creates a file in cache that is not valid JSON file, deployment of OpenNext fails with:

SyntaxError: Unexpected non-whitespace character after JSON at position 34335
    at JSON.parse (<anonymous>)
    at file:///app/node_modules/@opennextjs/aws/dist/build/createAssets.js:141:35
    at file:///app/node_modules/@opennextjs/aws/dist/build/helper.js:159:13
    at Array.forEach (<anonymous>)
    at Module.traverseFiles (file:///app/node_modules/@opennextjs/aws/dist/build/helper.js:151:51)
    at createCacheAssets (file:///app/node_modules/@opennextjs/aws/dist/build/createAssets.js:139:21)
    at build (file:///app/node_modules/@opennextjs/cloudflare/dist/cli/build/build.js:59:44)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async buildCommand (file:///app/node_modules/@opennextjs/cloudflare/dist/cli/commands/build.js:13:5)

(The fact that Next.js generates incorrect JSON file in data cache is other problem, but not a subject of this ticket).
The goal of this ticket is to request fix in the way JSON is being parsed in mentioned createAssets.ts file.

[khuezy]

Interesting, do you have an example of the incorrect JSON? We can forward it to the vercel team for them to look at if that's not expected.

[sommeeeer]

Yeah, and also what version of Next is this happening on? A reproduction would be awesome!

[grabmateusz]

Hi, I will submit incorrect JSON example later when I reproduce the issue again (it is reproducible very often, but not in 100% cases).
Regarding Next.js version at the moment it's 15.3.4, but it has been reproducible on multiple previous 15.x versions.
Regarding reproduction steps I would have to create standalone repository, I will try to do that.
Our current setup is next@15.3.4 + @opennextjs/cloudflare@1.6.5 + @opennextjs/aws@3.7.4 used under the hood by @opennextjs/cloudflare@1.6.5.

Anyway, as I've reported in this ticket (and as I've proposed in pull request) issue I try to resolve via this ticket is the fact that incorrect json in fetch cache completely breaks deployment, which shouldn't be the case.

[grabmateusz]

@khuezy this is how broken JSON looks like:

{
  "kind": "FETCH",
  "data": {
    "headers": {
      "header-name": "header-value"
    },
    "body": "<Base64-encoded-response-body>",
    "status": 200,
    "url": "<url-of-requested-resource>"
  },
  "revalidate": 300,
  "tags": [
    "name-of-the-cache-key"
  ]
}"name-of-the-cache-key"]
}

I have:

• removed headers and replaced with:

"header-name": "header-value"

• Replaced body content with:

<Base64-encoded-response-body>

• Replaced url with:

<url-of-requested-resource>
Let me know if I can provide more details.

[khuezy]

Cool thanks! I pinged the team.