v4 -> v5 migration. Is the change of reply payload check somewhere documented?

[globalexport]

💬 Change introduced in v5.0.0-alpha.4 is crashing my application

In fastify/lib/reply.js this part was removed:

  // Response
  if (isResponse) {
    // https://developer.mozilla.org/en-US/docs/Web/API/Response/headers
    if (typeof payload.headers === 'object' && typeof payload.headers.forEach === 'function') {
      for (const [headerName, headerValue] of payload.headers) {
        reply.header(headerName, headerValue)
      }
    }

    // https://developer.mozilla.org/en-US/docs/Web/API/Response/body
    if (payload.body != null) {
      if (payload.bodyUsed) {
        throw new FST_ERR_REP_RESPONSE_BODY_CONSUMED()
      }
      // Response.body always a ReadableStream
      sendWebStream(payload.body, res, reply)
    }
    return
  }

Instead of the above, the process is running into

  if (typeof payload !== 'string' && !Buffer.isBuffer(payload)) {
    throw new FST_ERR_REP_INVALID_PAYLOAD_TYPE(typeof payload)
  }

I failed to find documentation regarding this breaking change in the migration documentations. Maybe I am missing something?
https://fastify.dev/docs/v5.0.x/Guides/Migration-Guide-V5/
https://fastify.dev/docs/v5.1.x/Guides/Migration-Guide-V5/

/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/reply.js:642
    throw new FST_ERR_REP_INVALID_PAYLOAD_TYPE(typeof payload)
          ^
FastifyError [Error]: Attempted to send payload of invalid type 'object'. Expected a string or Buffer.
    at onSendEnd (/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/reply.js:642:11)
    at wrapOnSendEnd (/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/reply.js:536:5)
    at next (/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/hooks.js:289:7)
    at handleResolve (/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/hooks.js:306:5)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  code: 'FST_ERR_REP_INVALID_PAYLOAD_TYPE',
  statusCode: 500
}
Node.js v20.16.0
[nodemon] app crashed - waiting for file changes before starting...

Environment

• node version: 20
• fastify version: >=v5.0.0-alpha.4
• os: Mac, Linux

[metcoder95]

Noup, it stills here: https://github.com/fastify/fastify/blob/8f3eab6dd7d3524a684f83f5c49d5795f2babe83/lib/reply.js#L573-L594

Can you try with latest version?

[globalexport]

Hi @metcoder95 !

Thank you for your help.

The stacktrace above was created with the latest version v5.1.0 (/path-to-project/node_modules/.pnpm/fastify@5.1.0/node_modules/fastify/lib/reply.js:642)

[jsumners]

Please provide a minimal reproducible example, written in JavaScript. Doing so will help us diagnose your issue. It should be the bare minimum code needed to trigger the issue, and easily runnable without any changes or extra code.

You may use a GitHub repository to host the code if it is too much to fit in a code block (or two).

[globalexport]

Hi @jsumners !

Thank you. I will need some time to compile a reproducible setup. The error is occuring during a rather complex single-sign-on process which is involving different dependencies (e.g., grant, @fastify/http-proxy).
Hope to get it done before Christmas, but can't say for sure.