Setting session before login throws Error: Can’t set headers after they are sent

[Yuripetusko]

I need to have sessionId even before user logs in, to tracks browsing session of user and tie him to it later when he logs in, so I did this:

server.use(async (ctx, next) => {
  if (!ctx.session.sessionId) {
    ctx.session.sessionId = uuid.v4();
  }
  await next();
});

however if I do this I get (despite session id saving no problem)

{ Error: Can't set headers after they are sent.
    at validateHeader (_http_outgoing.js:504:11)
    at ServerResponse.setHeader (_http_outgoing.js:511:3)
    at Cookies.set (/Users/yuri/Sites/bridebook/Bridebook-next/node_modules/cookies/index.js:115:13)
    at ContextSession.save (/Users/yuri/Sites/bridebook/Bridebook-next/node_modules/koa-session/lib/context.js:276:22)
    at ContextSession.commit (/Users/yuri/Sites/bridebook/Bridebook-next/node_modules/koa-session/lib/context.js:220:16)
    at session (/Users/yuri/Sites/bridebook/Bridebook-next/node_modules/koa-session/index.js:46:18)
    at <anonymous> headerSent: true }

Any idea what I am doing wrong?

[davegomez]

I'm getting the exact same error when trying to use koa-session + Next.js with async/await functions.

This is the code I have to write a UUID in the session:

    router.get('/', async ctx => {
      ctx.session.uuid = ctx.session.uuid || uuidv4()
      const params = { uuid: ctx.session.uuid }
      await app.render(ctx.req, ctx.res, '/', params)
      ctx.respond = false
    })

I get the error even if I use it just as a middleware (without routing) unless I write the function as not async.

[Yuripetusko]

@davegomez yes we are on nextJS also

[dead-horse]

koa will send body when all middleware executed. but next.js is not follow this rule for now, it will send body before middleware executed, so when middleware's downstream try to set a header, it will throw this error.

[davegomez]

Any idea how to workaround this @dead-horse?

@timneutkens from Next.js is already looking at the issue.

[dead-horse]

there are lot's of middlewares will not work with next.js if it still use ctx.respond = false, for now, you can't set session in the same controller with next.js.

[dead-horse]

already fixed in new koa version, it will ignore set header if body already sent.

[coler-j]

@dead-horse which version? I am on 2.13.0 (the current version) and this is still happening.