标头未被发送但没有给出错误消息

Question

我已经使用php和myqli进行了oop登录，我还使用jquery动态检查用户输入，当用户详细信息正确时，我的代码会记录用户但是没有发送头重定向但没有错误给出了消息，它可能与我有关，我正在使用json数组将值返回给用户。任何帮助都将受到赞赏。

登录类

<?php
require "db_config.php";

class login
{


    public function user_exists($username) {
     $sql="SELECT * FROM users WHERE  username='$username'";    
     //checking if the email is available in db
        $check = Database::getInstance()->getConnection()->query($sql);
    $count_row = $check->num_rows;

    if ($count_row == 1) {
        return true;
    } else {
        return false;
    }
    }
    public function check_login($username,$password){
        $sql2="SELECT user_id FROM users WHERE username='$username' and password='$password'";    
        //checking if the username is available in the table
    $check = Database::getInstance()->getConnection()->query($sql2);
    $count_row = $check->num_rows;
    if ($count_row == 1) {
            $_SESSION['username'] = $username;
      return true;
    }
    else {
        return false;
        }
  }
     public function is_loggedin()
     {
          if(isset($_SESSION['user_session']))
          {
             return true;
          }
     }
   public function redirect($url)
   {
       header("Location: $url");
   }
}
?>

登录脚本

<?php
require '../includes/class/login.php';
$login = new login();
$username_error=' ';
$password_error=' ';
$result=' ';

if (isset($_POST['login'])&& $_POST['login'] !== "") 
{ 
    $log = $login->check_login($username,$password);
    if ($log) 
    {
        $login->redirect('home.php');
    } 
    else
    {
        // Registration Failed
        $password_error='Wrong username or password';
    }
}

if(isset($_POST['username']) && $_POST['username'] !== "")
{
    $username = $_POST['username'];
    $username = trim($username);
    $user_exists = $login->user_exists($username);
    if ($user_exists) {
        $username_error = '';
    } 
    else {
        $username_error = 'username not found';
    }
}

if(isset($_POST['password']) && $_POST['password'] !== "") {

    $password = $_POST['password'];
    $password = trim($password);
    $password_check = $login->check_login($username,$password);
    if ($password_check) {
        $password_error = '';
    } 
    else {
        $password_error = 'password not found';
    }
}

$return_data=array('username'=> $username_error, 'password'=> $password_error ,'user_session'=>$_SESSION['username']);
header('Content-Type: application/json');
echo json_encode($return_data);
?>

登录js代码

<?
function validate(username, password, login)
{
    $.post('includes/login.php', {username: username,password: password,login: login,}, 
  function(data){
        $('#username_feedback').text(data.username);
        $('#password_feedback').text(data.password);
        $('#login_feedback').text(data.user_session); },'json');
}

/////////////////////////////////username jquery///////////////////////////////////

$('#username').focusin(function(){ 
  if($('#username').val() ==='') {
$('#username_feedback').text('requried field');
} else {
validate($('#username').val(),"","");
}
}).blur(function() { 
$('#username_feedback').text('');
validate($('#username').val(),"","");
}).keyup(function(){
validate($('#username').val(),"","");
});

/////////////////////////////////password jquery///////////////////////////////////

$('#password').focusin(function(){ 
  if($('#password').val() ==='') {
$('#password_feedback').text('requried field');
} else {
validate( $('#username').val(), $('#password').val(),"");
}
}).blur(function() { 
$('#password_feedback').text('');
validate( $('#username').val(), $('#password').val(),"");
}).keyup(function(){
validate( $('#username').val(), $('#password').val(),"");
});
$( "#login" ).click(function() {
validate($('#username').val(),$('#password').val(),$('#login').val());
});