Make a form sticky with php session - php

Question

I am trying to create php multipage forms, and I use PHP sessions for this purpose.
However, when there is an error in user input and I want the form to ask user to fill in the form again with correct inputs, the forms field will not hold the data that the user has already put in so the user has to start things all over again.
How to make forms sticky with php session?
Thanks
My code is as bellow
<?php
// Session starts here.
if (!isset($_SESSION)) session_start();
?>
<form action="registration.php" method="post">
<center><h8>Please create your user name and password</h8></center>
<div class="imgcontainer">
<img src="phone.gif" alt="Welcome" class="avatar">
</div>
<div class="container">
<label><b>Username</b></label>
<input type="text" placeholder="Enter Username" name="username" required value="<?php if(isset($_POST['username'])) echo $_POST['username'];?>">
<label><b>Password</b></label>
<input type="Password" placeholder="Enter Password" name="password" required>
<label><b>Confirm Password</b></label>
<input type="Password" placeholder="Confirm Password" name="confirm" required>
<span id="error" width=100%>
<!---- Initializing Session for errors --->
<?php
if (!empty($_SESSION['error'])) {
echo "<error>".$_SESSION['error']."</error>";
unset($_SESSION['error']);
}
if (isset($_POST['username'])){
$_SESSION['username'] = $_POST['username'];
echo $_SESSION['username'];
echo $_POST['username'];
}
?>
</span>
<br>
<input type="reset" value="Reset" />
<input type="submit" value="Next" />
</div>
and the registration php contains
<?php
if (!isset($_SESSION)) session_start();
// Checking first page values for empty,If it finds any blank field then redirected to first page.
if (isset($_POST['username']))
{
if (($_POST['password']) === ($_POST['confirm']))
{
foreach ($_POST as $key => $value)
{
$_SESSION['post'][$key] = $value;
}
}
else
{
$_SESSION['error'] = "Password does not match with Confirm Password.";
if (isset($_POST['username'])){
$_SESSION['username'] = $_POST['username'];
echo $_SESSION['username'];
echo $_POST['username'];
}
header("location: createlogin.php"); //redirecting to first page
}
}

Answer 1

Something like this:
<input name="var" value="<?= isset($_SESSION['var']) ? $_SESSION['var'] : null ?>" />

Answer 2

Try the other way around. Linking the form-action to the current page, and if all fields are valid; redirect it to the next page (registration.php). This way you'd still have all the post-data, you can process everything that needs to be saved in the session- and you can redirect after all of the logic is done.

Answer 3

My two cent would be keep the same page to validate the content and for the form.
You can include other PHP files from a single page depending on if the form is valid.
This way, you keep the same $_POST between both pages and don't need to store the posted data in a session variable.
Otherwise, if you want to keep the same architecture, you need to use the $_SESSION variables instead of the $_POST ones in your input value, such as the answer by delboy.
Replace:
<?php if(isset($_POST['username'])) echo $_POST['username'];?>
With:
<?php if(isset($_SESSION['username'])) echo htmlspecialchars($_SESSION['username']); ?>
^ Note: htmlspecialchars is used to prevent a reflected XSS if the users enters " as username.

Answer 4

The problem is, your data posted to registration.php, so you can't get the posted value in your original file. You are trying to use $SESSION but that's not recommended, and not right. Your whole solution is wrong.
Forget about session and separated files, put everything to registration.php file together.
You can check if user posted or not with $_SERVER['REQUEST_METHOD'] variable.
if($_SERVER['REQUEST_METHOD'] == 'POST'){
print 'Something just posted';
}
PS: Don't forget secure the password before you store it! :)