How to prevent the form from re-filling when you refresh the page or click the back button

Question

In my form, I allow users to upload files to the database, and I submit them to another page, which is the submission_successful.php, which says "Thanks for submitting." But I noticed that when I click the "Back" button in the file of successful php submission, it returns to the form, and the same information is there and allows a different view. What I want to do is kill the code by clicking the back button or clear everything that was entered by the user. I found a couple of answers, for example, using cache control, but some of them were vague, while others did not work for me. And plus, I don’t want the user to return to the download page when they are on the success page. Therefore, that’s why I’ll create two buttons for “logging out” or “return to page loading”,and if they click the back button, it will crash. I want to showConfirm form resubmission . In another message, they are trying to actually prevent the "Re-Validation of the Application Form", but I would like to receive it for security. Here is my code

developerUpload.php

<?php

session_start();

if(array_key_exists("invalid", $_GET)){

    echo '<br><h3 style="color:red;">File(s) were already submitted! Please re-name file or select a different file...</h3>';
}

if(isset($_COOKIE['username'])){

    if($_SERVER['REQUEST_METHOD'] =="POST"){

        $price = addslashes(trim($_POST['price']));
        $description = addslashes(trim($_POST['description']));

        if(!empty($price) && !empty($description)){

            $userid = $_SESSION['id'];
            $username = $_SESSION['username'];
            echo '<br>'.$userid;
            $pack_id = rand();

            //Check file 1
            if($_FILES['file1']['error'] !== UPLOAD_ERR_OK){

                    $file1 = null;
            }else{

                $target1 = "devFiles/";
                $target_file1 = addslashes(trim($target1 . basename($_FILES["file1"]["name"])));
                $file1 = addslashes(trim($_FILES['file1']['tmp_name']));

            }

            //Check file 2
            if($_FILES['file2']['error'] !== UPLOAD_ERR_OK){

                    $file2 = null;
            }else{

                $target2 = "devFiles/";
                $target_file2 = addslashes(trim($target2 . basename($_FILES["file2"]["name"])));
                $file2 = addslashes(trim($_FILES['file2']['tmp_name']));

            }

            //Check file 3
            if($_FILES['file3']['error'] !== UPLOAD_ERR_OK){

                    $file3 = null;
            }else{

                $target3 = "devFiles/";
                $target_file3 = addslashes(trim($target3 . basename($_FILES["file3"]["name"])));
                $file3 = addslashes(trim($_FILES['file3']['tmp_name']));

            }

            //Check file 4
            if($_FILES['file4']['error'] !== UPLOAD_ERR_OK){

                    $file4 = null;
            }else{

                $target4 = "devFiles/";
                $target_file4 = addslashes(trim($target4 . basename($_FILES["file4"]["name"])));
                $file4 = addslashes(trim($_FILES['file4']['tmp_name']));

            }

            //Check file 5
            if($_FILES['file5']['error'] !== UPLOAD_ERR_OK){

                    $file5 = null;
            }else{

                $target5 = "devFiles/";
                $target_file5 = addslashes(trim($target5 . basename($_FILES["file5"]["name"])));
                $file5 = addslashes(trim($_FILES['file5']['tmp_name']));

            }

            //Check video
            if($_FILES['video']['error'] !== UPLOAD_ERR_OK){

                $video = null;
                $videoName = null;
            }else{

                $target = "devFiles/";
                $target_file = addslashes(trim($target . basename($_FILES["video"]["name"])));
                $video = addslashes(trim($_FILES['video']['tmp_name']));
                $videoName = addslashes(trim($_FILES['video']['name']));

            }

            if(file_exists($target_file1) 
               or file_exists($target_file2) 
               or file_exists($target_file3)
               or file_exists($target_file4) 
               or file_exists($target_file5) 
               or file_exists($target_file)){

                header("Location: developerUpload.php?invalid");
                exit;

            }

            if(move_uploaded_file($_FILES["file1"]["tmp_name"], $target_file1) 
               && move_uploaded_file($_FILES["file2"]["tmp_name"], $target_file2)
               && move_uploaded_file($_FILES["file3"]["tmp_name"], $target_file3)
               && move_uploaded_file($_FILES["file4"]["tmp_name"], $target_file4)
               && move_uploaded_file($_FILES["file5"]["tmp_name"], $target_file5)
               && move_uploaded_file($_FILES["video"]["tmp_name"], $target_file)){

                try{

                    // new php data object 
                    $handler = new PDO('mysql:host=127.0.0.1;dbname=magicsever', 'root', '');
                    //ATTR_ERRMODE set to exception
                    $handler->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

                }catch(PDOException $e){
                    die("There was an error connecting to the database");   

                }

                header("Location: submission_successful.php?");
                die();
            }



        }else{

            echo '<br><h1 style="color:red;">VALUES MISSING!</h1>';

        }
    }
}else {

    header("Location: developerLogin.php");
}



?>

submission_successful.php

<?php
session_start();

    if(array_key_exists("invalid", $_GET)){

        header("Location: developerUpload.php?invalid");

    }
    if(isset($_COOKIE['username'])){
        echo '<br><h1 style="color:red; text_align:center;">Thank You for Submitting!</h1>';

    }else{

        header("Location: developerLogin.php");
    }

?>

Answer 1

I searched for a few days and finally found something. IF you use the HTML command, it will delete any user-entered words when the user returns. Since my problem was when the user returns after the redirect, their information was still there, but if you use

<form method="post" enctype="multipart/form-data" autocomplete="off">

, . , .

Answer 2

, , ( ), . , , () , sth like ( ), ajax, https://es.m.wikipedia.org/wiki/Post/Redirect/Get

Answer 3

,

$_SESSION["post_id"] = "";
if($_POST) {
    if($_POST["post_id"] != $_SESSION["post_id"]) {
        $_SESSION["post_id"] = $_POST["post_id"];
        // do database submission here
    }
}

This sets the session variable, and if they resubmit the form, it will not publish the data twice.