PHP会话变量未在其他页面上显示

Question

I have a page a to which I am posting the data from a python script. I am processing that data, storing the data into SQL. I want to store the time when this post request is made. Note that the post request is made continuously. So the session variable keeps on changing. Well here is the little code for that-

<?PHP
session_start();
include 'db.inc.php';

if(isset($_POST['data']){
$data_decode = (array)json_decode($_POST['data']);
$data_var1 = $data_decode['var1'];
$data_var2 = $data_decode['var2'];
$data_var3 = $data_decode['var3'];
$date = date('Y-m-d H:i:s');
$_SESSION['time'] = $date;  //Set the session with current time
$sql = "UPDATE `table` SET row1=$data_var1, row2=$data_var2 WHERE row3=$data_var3";
$result = mysqli_query($db,$link) or die('Table could not be updated');
echo "Following data inserted: row1=$data_var1, row2=$data_var2, at $_SESSION['time']"; //Echoing the data and time as expected
?>

Now, I have another page on the same domain, which makes the ajax request and fetches out the data every second from the SQL table I just inserted the data into. So here is the whole scenario- The client python script makes the post request to the webpage, which updates the sql with the received data, sets the session variable. Another page simultaneously fetches that data out using ajax and shows it.

Now I am calling the session variable on another page as shown-

<?php
session_start();
if(isset($_SESSION['time']){ echo $_SESSION['time']; } //Didn't echoes anything
?>

I used <?php print_r($_SESSION) ?> to check whether the session variable is set or not, it echoed "Array()", which means my session variable is not set. So my question is, What I am doing wrong and how can I correct it?

Answer 1

I am trying to reconstruct which components are acting in your scenario.

So first you mention a Python script. How does it work together with PHP? Does it actually emit a HTTP request itself, or does it only send HTML to a browser that is then going to PHP? If Python is acting like a HTTP client, this is important, because PHP sessions use cookies, so your Python script has to be able to accept the "Set-cookie" HTTP header and deal with it, especially send it back on later requests.

Second info is that there is some Ajax going on. This points to a browser and some Javascript as a client, and this combo is clearly able to accept any cookie that is set by PHP.

But how do the browser and the Python script communicate? How does the browser know which cookie the Python script got back from PHP so that the session data can be loaded?

I hope you see the hole in your approach. Posting data from Python into the database is one thing, saving the time of this event probably is a global information (date of last DB update), and not a session information (is different per Python client). As such, the session is the wrong location for storage. And the other obstacle is that your Ajax client cannot share the session ID from your Python client! And the last downside to sessions: If it would work, you would constantly interfere with both requests, because sessions use locking to prevent two requests deleting each others data. This is especially bad because a hanging Ajax request might prevent the Python script from writing to the database, and vice versa.

Find a way to store a global information on your server. You already have a database, why not use it for this?