에러

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at new NodeError (node:internal/errors:393:5)
    at ServerResponse.setHeader (node:_http_outgoing:644:11)
    at ServerResponse.header (/home/cloudcoke/my/nodejs/practice/221215/node_modules/express/lib/response.js:794:10)
    at ServerResponse.send (/home/cloudcoke/my/nodejs/practice/221215/node_modules/express/lib/response.js:174:12)
    at done (/home/cloudcoke/my/nodejs/practice/221215/node_modules/express/lib/response.js:1035:10)
    at /home/cloudcoke/my/nodejs/practice/221215/node_modules/nunjucks/src/environment.js:41:5
    at RawTask.call (/home/cloudcoke/my/nodejs/practice/221215/node_modules/asap/asap.js:40:19)
    at flush (/home/cloudcoke/my/nodejs/practice/221215/node_modules/asap/raw.js:50:29)
    at process.processTicksAndRejections (node:internal/process/task_queues:77:11) {
  code: 'ERR_HTTP_HEADERS_SENT'
}

에러 원인

• 이미 응답을 보냈는데 다시 또 응답을 보내려고 해서 에러가 발생했다.

문제 코드

app.get("/", (req, res) => {
  const user = app.get("login");
  console.log(user);
  if (user !== undefined) {
    const nickname = user["nickname"];
    res.render("index", { nickname: `${nickname}님 안녕하세요` });
  }
  res.render("index");
});

app.post("/login", (req, res) => {
  const { id, pw } = req.body;
  if (isIdPwCorrect(id, pw)) {
    res.redirect("/");
  }
  res.render("login");
});

해결

• if ... else 문으로 true일 경우와 false일 경우에 할 동작을 명확히 해주었다.

app.get("/", (req, res) => {
  const user = app.get("login");
  if (user !== undefined) {
    const nickname = user["nickname"];
    res.render("index", { nickname: `${nickname}님 안녕하세요` });
  } else {
    res.render("index");
  }
});

app.post("/login", (req, res) => {
  const { id, pw } = req.body;
  if (isIdPwCorrect(id, pw)) {
    res.redirect("/");
  } else {
    res.render("login");
  }
});

참고

• [node] code: ERR_HTTP_HEADERS_SENT 에러