php: session disappears after page navigation - php

Question

I've read all the posts I could find about this issue, but, to date, none of the solutions have worked for me. Obviously, I'm overlooking something important. I also don't know how to debug sessions. I read one article, PHP session Debugging, but it was over my head.
So, much like the other issues, when I navigate to another page in my app, whether through a link or a form submit, my session disappears. I have no idea why my session vanishes. If someone has the time to help me investigate, it would be greatly appreciated.
These are my php.ini settings
; Name of the session (used as cookie name).
session.name = PHPSESSID
; The path for which the cookie is valid.
session.cookie_path = /
This is the first view to display
<?php
session_start();
if (!isset($_SESSION['session_id'])) {
$_SESSION['session_id'] = session_id();
}
if (!isset($_SESSION['invoices'])) {
$_SESSION['invoices'] = $invoices;
}
if (isset($_SESSION['session_id'])) {
print_r($_SESSION['session_id'] . " in invoiceList.<br />");
} else {
echo 'No session ID set in invoiceList <br />';
}
?>
<div>
<table>
<tr>
<th>Customer Name</th>
<th>Invoice Date</th>
<th>Invoice Number</th>
</tr>
<tr>
<?php
include_once 'form/editInvoice.php';
if (isset($invoices)) {
foreach ($invoices as $invoice) {
?>
<tr>
<td><?php echo $invoice['customer_name'] ?></td>
<td><?php echo $invoice['invoice_date'] ?></td>
<td><?php echo $invoice['invoice_number'] ?></td>
<td><a href='<?php echo $_SERVER['SCRIPT_NAME']; ?>/retrieve?class=InvoiceLineItems&id=<?php echo $invoice['invoice_id']; ?>'><?php echo $invoice['invoice_id']; ?></a></td>
</tr>
<?php
}
} else {
echo 'No invoices retrieved.';
}
?>
</tr>
</table>
</div>
Here is the included form:
<?php
session_start();
if (isset($_SESSION['session_id'])) {
print_r($_SESSION['session_id'] . "in editForm<br />");
} else {
echo 'No session ID set in editForm <br />';
}
if (!$_POST) {
?>
<form action="<?php $_SERVER['PHP_SELF'] ?>" method="post">
<fieldset>
<legend>Enter Updated PO Number</legend>
<li>PO Number: <input type="text" name="po_number"/></li>
</fieldset>
<input type="submit" value="Submit" />
<input type="button" onclick="alert('Changes Canceled.')" value="Cancel"/>
</form>
<?php }
?>
And finally, the detail page for when the user clicks a link in the main page.
<?php
session_start();
if (isset($_SESSION['session_id'])) {
print_r($_SESSION['session_id'] . "<br />");
} else {
echo 'No session ID set invoice<br />';
}
?>
<h1>Invoice Detail</h1>
<div>
<?php
foreach ($partnerInfo as $info) {
switch ($info['role_indicator']) {
case 'remit_to':
?>
<div id="remit">
<ul>
<li>PLEASE REMIT TO:</li>
<li><?php echo $info['partner_name']; ?></li>
<li><?php echo $info['street_name']; ?></li>
<li><?php echo $info['city_name']; ?>, <?php echo $info['state']; ?> <?php echo $info['postal_code']; ?></li>
</ul>
</div>
<?php break; ?>
<?php case 'seller': ?>
<div id = "seller" >
<ul>
<li>Service Site:</li>
<li><?php echo $info['partner_name']; ?></li>
<?php
if ($info['partner_aux_info'] !== NULL) {
?><li><?php echo $info['partner_aux_info']; ?>
<?php }
?>
</li>
<li><?php echo $info['street_name']; ?></li>
<li><?php echo $info['city_name']; ?>, <?php echo $info['state']; ?> <?php echo $info['postal_code']; ?></li>
<li>[phone]</li>
</ul>
</div>
<?php break; ?>
<?php case 'sold_to': ?>
<div id="buyer">
<ul>
<li>Bill To: </li>
<li><?php echo $info['partner_name']; ?></li>
<li><?php echo $info['street_name']; ?></li>
<?php
if ($info['suite_info'] !== NULL) {
?><li><?php echo $info['suite_info']; ?>
<?php }
?>
</li>
<li><?php echo $info['city_name']; ?>, <?php echo $info['state']; ?> <?php echo $info['postal_code']; ?></li>
</ul>
</div>
<?php break; ?>
<?php
}
}
?>
<h1>Line Items</h1>
<table>
<th>PO Number</th>
<th>PO Issued Date</th>
<th>Description</th>
<th>Service Start Date</th>
<th>Service End Date</th>
<th>Shipped Date</th>
<?php foreach ($invoiceLineItems as $lineItem) { ?>
<tr>
<td><?php echo $lineItem['po_number']; ?></td>
<td><?php echo $lineItem['po_issued_date']; ?></td>
<td><?php echo $lineItem['line_item_name']; ?></td>
<td><?php echo $lineItem['service_period_start']; ?></td>
<td><?php echo $lineItem['service_period_end']; ?></td>
<td><?php echo $lineItem['request_for_delivery']; ?></td>
</tr>
<?php
}
?>
</table>
</div>
Edit: I've removed the session checks and updated the code sample. I've added session_start() before my <head> tag in index.php. I've verified that I can write to the session temp folder.
When i execute this code in my controller to update the invoices with the new PO number, I reach the model's function, but the session is gone.
//If form is posted, update line items with PO number and date.
if (isset($_POST['po_number'])) {
$this->invoice->update();
}
By the time I reach the session variable assignment, I have no session data:
public function update() {
$con = $this->_getLocalConn();
$invoices = $_SESSION['invoices'];
try {
$sqlUpdate = $con->prepare("UPDATE invoices
SET po_number = ?, po_issued_date = ?
WHERE invoice_id = ?");
foreach ($invoices as $record) {
$sqlUpdate->execute(array(
$_POST['po_number'],
getdate(),
$record['invoice_id']
));
}
} catch (PDOException $e) {
print $e->getMessage();
}
//get the PO number being used to update the records
//perform db update where po_number = input
//notify user of success and display updated records.
}

Answer 1

Each PHP file should start with session_start(); regardless of $_SESSION being set or not. This function will create a new session OR take up the existing one.

Answer 2

No $_SESSION is started to begin with when you check it with your first if. Therefore, it will always FAIL. You must call session_start() PRIOR to doing anything with a $_SESSION variable. Correct your code.
First page:
<?php
session_start();
/* Don't need this unless you really need the debugging
Previously you where assigning variables that did not
exist to the the $_SESSION variables. Not what you want
I imagine.
if (!isset($_SESSION)) {
var_dump($_SESSION);
}
*/
...
Include form:
<?php
session_start();
if (isset($_SESSION['session_id'])) {
print_r($_SESSION['session_id'] . "in editForm<br />");
} else {
echo 'No session ID set in editForm <br />';
}
...
Detail page:
<?php
session_start(); //Notice a pattern here??
if (isset($_SESSION['session_id'])) {
print_r($_SESSION['session_id'] . "<br />");
} else {
echo 'No session ID set invoice<br />';
}
?>

Answer 3

All of your code that needs the session information should start with session_start(). session_start() needs to happen before any headers or other output would be written.
Setup and teardown are then handled for you.
I do this:
session_start();
$s = &$_SESSION;
Then you can use read/write $s just like it was $_SESSION
If you are doing self referencing image downloads or other code that may end up wanting to execute in parallel, NOT starting a session or closing it as soon as possible with session_write_close() will give you a significant performance boost.
Without this, sessions essentially make your code run single threaded.
Edit: Saying single threaded was perhaps a bad choice of words.
Lets say you had a page with three iframes in it, each one loading a different (or the same) php script. If you are using sessions, the result would be the iframes loading one at a time instead of all at once. Each one would get a lock on the session and the others would wait at session_start() until the session was available again.