What needs to be awaited?

[gajus]

I wish documentation made it clearer as to when fastify methods like setCookie, code, send, etc. need to awaited or if their output can be just voided, e.g.

export const authenticatedCookieFastifyPlugin = fastifyPlugin(
  async (instance) => {
    instance.addHook('onRequest', async (request, reply) => {
      const userAccountId = request.session.get('userAccountId');

      if (userAccountId) {
        // The only purpose this serve is to determine whether https://contra.com/
        // serves the landing pages or the contra-web-app.
        void reply.setCookie('contra_authenticated', 'true', {
          httpOnly: true,
          maxAge: ONE_DAY,
          path: '/',
        });
      } else if (request.cookies.contra_authenticated) {
        void reply.clearCookie('contra_authenticated');
      }
    });
  },
  {
    name: 'authenticated-cookie',
  },
);

Do reply.setCookie and reply.clearCookie need to be awaited?

  app.get<{ Params: { domain: string } }>(
    '/domains/validate/:domain',
    async (request, reply) => {
      const domain = request.params.domain;

      const status = await services.customDomain.getCustomDomainStatus({
        domain,
      });

      if (status === 'ACTIVE') {
        void reply.code(204).send();
      } else {
        void reply.code(404).send();
      }
    },
  );

Does reply.send need to be awaited/returned?

Reading examples from documentation it is not clear.

[mcollina]

Do reply.setCookie and reply.clearCookie need to be awaited?

No, this is just an odd rule added by some validator.

[gajus]

For context, the reason this question came up is because after upgrading to Node.js v20 we started getting error:

Error: Cannot write headers after they are sent to the client
 ❯ new NodeError node:internal/errors:399:5
 ❯ ServerResponse.writeHead node:_http_server:342:11
 ❯ onSendEnd ../../node_modules/.pnpm/fastify@4.17.0/node_modules/fastify/lib/reply.js:579:9
 ❯ wrapOnSendEnd ../../node_modules/.pnpm/fastify@4.17.0/node_modules/fastify/lib/reply.js:545:5
 ❯ next ../../node_modules/.pnpm/fastify@4.17.0/node_modules/fastify/lib/hooks.js:224:7
 ❯ handleResolve ../../node_modules/.pnpm/fastify@4.17.0/node_modules/fastify/lib/hooks.js:241:5
 ❯ processTicksAndRejections node:internal/process/task_queues:95:5

Turns out it was this code:

for (const { name, value } of result.headers) {
  void reply.header(name, value);
}

void reply.code(result.status).send(result.payload);

Refactoring to the following code fixed the issue:

const headers: Record<string, string> = {};

for (const { name, value } of result.headers) {
  headers[name] = value;
}

void reply.headers(headers).code(result.status).send(result.payload);

If anyone runs into this, the way I tracked down what causes the issue is by monkey-patching ../../node_modules/.pnpm/fastify@4.17.0/node_modules/fastify/lib/reply.js file to add console.trace to send and header funcitons.

[mcollina]

app.get<{ Params: { domain: string } }>(
    '/domains/validate/:domain',
    async (request, reply) => {
      const domain = request.params.domain;

      const status = await services.customDomain.getCustomDomainStatus({
        domain,
      });

      if (status === 'ACTIVE') {
        return reply.code(204).send();
      } else {
        return reply.code(404).send();
      }
    },
  );

or

app.get<{ Params: { domain: string } }>(
    '/domains/validate/:domain',
    async (request, reply) => {
      const domain = request.params.domain;

      const status = await services.customDomain.getCustomDomainStatus({
        domain,
      });

      if (status === 'ACTIVE') {
        reply.code(204).send();
      } else {
        reply.code(404).send();
      }
      await reply;
      //// or
      // return reply
    },
  );

[gajus]

The problem in my example was that headers are being sent after send, despite header being called before send.

[gajus]

@mcollina https://www.loom.com/share/2333cf06a2cc44a7a4647cc43396618e

[mcollina]

The problem in my example was that headers are being sent after send, despite header being called before send.

if that's the case, then this is sent in a previous hook or something similar.

I would recommend creating a minimal reproduction.

[mcollina]

(I'll watch the loom whenever I can).