Server Side Redirect Returns ERR_HTTP_HEADERS_SENT

[simonuvarov]

Hi,

I'm trying to use a redirect from getServerSideProps and I get Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client in some cases. I have seen that this problem was covered in issues many times and the solution was to use res.end() like this.

However, the following code fails for me when used with Link or Router.push():

export const getServerSideProps = async ({ req, res }) => {
  const session = await getCurrentSession({ req });
  if (!session) {
    res.setHeader('location', '/signin');
    res.statusCode = 302;
    res.end();
    return { props: {} };
  }

  return { props: {} };
};

while this one works:

export const getServerSideProps = async ({ req, res }) => {
  res.setHeader('location', '/signin');
  res.statusCode = 302;
  res.end();
  return { props: {} };
};

So, my first guess was that this happens because the first code returns the same props (?) for both paths, but I tried to return { props: { foo: 'bar' } };, and it gave me the same result.

It would be super helpful if somebody could help me understand the cause of this behavior.

I've also gone through all links at this RFC

Thanks,
Simon

[simonuvarov]

This code does not work as well:

export const getServerSideProps = async ({ req, res }) => {
  res.setHeader('location', '/signin');
  res.statusCode = 302;
  res.end();
  return { props: {} };
  const session = await getCurrentSession({ req });
  if (!session) {
    res.setHeader('location', '/signin');
    res.statusCode = 302;
    res.end();
    return;
  }

  return { props: {} };
};

and to make sure that getCurrentSession does not touch res, I tried this:

export const getServerSideProps = async ({ req, res }) => {
  const session = false;
  if (!session) {
    res.setHeader('location', '/signin');
    res.statusCode = 302;
    res.end();
    return { props: {} };
  }
  return { props: {} };
};

[paambaati]

Can you check if this happens on the canary version?

[simonuvarov]

I have updated next to v9.4.5-canary.38 and it still returns the same error.

[simonuvarov]

Seems like this code works:

export const getServerSideProps = async ({ req, res }) => {
  const session = false;
  if (!session) {
    res.setHeader('location', '/signin');
    res.statusCode = 302;
    res.end();
    return;
  }
  return { props: {} };
};

So, I assume that return { props: {} }; is writing in res after res.end().

However, when I use return, I get the error Your getServerSideProps function did not return an object. Did you forget to add a return?

With return {} I get SerializableError: Error serializing props returned from getServerSideProps in "/{redacted}".

[simonuvarov]

Weird, but this code works when deployed on Vercel.