@fastify/reply-from - Reply was already sent, did you forget to "return reply"

[paymog]

💬 Question here

I'm getting the following error in production in unpredictable ways

Reply was already sent, did you forget to "return reply" in "<my url>" (POST)?

Here is the declaration of the fastify handler

  fastify.post<ProxyMessageType>(
    "/:project_id/subgraphs/:name/:version_label/gn*",
    {
      schema: ProxyMessageSchema,
    },
    async (req, reply) => {
      const deployment = await req.deploymentCache.get(
        {
          projectId: req.params.project_id,
          name: req.params.name,
          versionLabel: req.params.version_label,
        },
        async () => req.goldskyDbClient,
        req.log
      );

      if (!deployment) {
        req.log.warn("deployment not found");

        reply.status(404);
        reply.send({
          error: "reach out to support pls",
        });
        return;
      }

      const subgraphUtils = getSubgraphUtils(deployment.project, req.opts);
      const subgraphProxyUrl = subgraphUtils
        .getSubgraphHttpApiUrl(deployment.deploymentId)
        .toString();

      const replyFromUrl = `${subgraphProxyUrl}${req.params["*"]}`;

      requestCounter.inc(
        {
          projectId: req.params.project_id,
          subgraphName: req.params.name,
          versionLabel: req.params.version_label,
        },
        1
      );
      const endTimer = requestGauge.startTimer({
        projectId: req.params.project_id,
        subgraphName: req.params.name,
        versionLabel: req.params.version_label,
      });

      return reply.from(replyFromUrl, {
        onResponse: (_, reply, res) => {
          res.on("end", () => {
            endTimer();
          });

          reply.send(res);
        },
      });
    }
  );

I see in the announcement doc that I should return reply if I call reply.send after the handler has finished. I suspect that's what I should do here but even when I switch to

      reply.from(replyFromUrl, {
        onResponse: (_, reply, res) => {
          res.on("end", () => {
            endTimer();
          });

          reply.send(res);
        },
      });
      return reply

I still see the warning log line get printed.

Your Environment

• node version: 18
• fastify version: ~4.23.2
• os: Linux
• fastify reply-from: ^9.4.0

[mcollina]

Thanks for reporting!

Can you provide steps to reproduce? We often need a reproducible example, e.g. some code that allows someone else to recreate your problem by just copying and pasting it. If it involves more than a couple of different file, create a new repository on GitHub and add a link to that.

[jv-castify]

I believe you need to also return the 404 response you have.

if (!deployment) {
  req.log.warn("deployment not found");

  return reply //   Return this statement.
    .code(404)
    .send({
      error: "reach out to support pls",
    });
}

Also this:

return reply.from(replyFromUrl, {
  onResponse: (_, reply, res) => {
    res.on("end", () => {
      endTimer();
    });

    return reply.send(res); // Return this statement.
  },
});