使用明上文将标题发送给客户端后无法设置标题

Question

    const emailaddress = req.body.emailaddress;
const password = req.body.password;
if (emailaddress && password) {
    const query = `SELECT * FROM users where email=? AND password=?`;
    connection.query(
        query,
        [emailaddress, password],
        function (err, results, fields) {
            if (err) {
                res.send({
                    code: 500,
                    failed: "Error ocurred",
                });
            }
            if (results.length > 0) {
                req.session.regenerate(function (err) {
                    // if (err) next(err);
                    req.session.loggedin = true;
                    req.session.emailaddress = req.body.emailaddress;
                    req.session.save(function (err) {
                        // if (err) return next(err);
                        res.redirect("/home");
                    });
                });
            } else {
                res.send("Incorrect email address and/or password!");
            }
            res.end();
        }
    );
} else {
    res.send("Please enter username and/or password");
    res.end();
}

我尝试使用上面的代码使用快递会话来存储会话值。但是它给出以下错误。

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

我怎么避免这种情况。我已经尝试了许多解决方案。我正在遵循他们的文档。请帮忙。谢谢。 “ https://www.npmjs.com/package/package/express-session”

Answer 1

可能的问题：

else block呼叫<代码>发送和在外面的最后一行，否则调用end（）。
因此，如果它属于其他块，send和end将被称为引起该错误。

您还可以多次呼叫next（err），而不知道这是下一个处理程序，我可以肯定地告诉您，但他们也可能正在调用send。这将属于与上述相同的情况。

Answer 2

我看到您回答后的代码进行了一些更改。
让我重试，您不能使用res.send和res.end一起选择一个。另外，您需要确保您仅调用res.send一次。

您的代码应该是这样的：

const emailaddress = req.body.emailaddress;
const password = req.body.password;
if (emailaddress && password) {
    const query = `SELECT * FROM users where email=? AND password=?`;
    connection.query(
        query,
        [emailaddress, password],
        function (err, results, fields) {
            if (err) {
                res.send({
                    code: 500,
                    failed: "Error occurred",
                });
                return; // make sure your function execution stops here, as you already called send();
            }
            if (results.length > 0) {
                req.session.regenerate(function (err) {
                    // if (err) next(err);
                    req.session.loggedin = true;
                    req.session.emailaddress = req.body.emailaddress;
                    req.session.save(function (err) {
                        // if (err) return next(err);
                        res.redirect("/home");
                    });
                });
            } else {
                res.send("Incorrect email address and/or password!");
                return; // same thing, called send() make sure to end the function
            }
            // res.end(); you probably don't need this
        }
    );
} else {
    res.send("Please enter username and/or password");
    // res.end(); you probably don't need this
    return;
}