Creating a PHP session variable after successful AJAX call

Question

I am having problems creating a PHP session following a successful AJAX call. Here is the AJAX code:

function onSignIn(googleUser) {
 var profile = googleUser.getBasicProfile();
 var id = profile.getId();
 var em = profile.getEmail();
 var name = profile.getName();
 var pic = profile.getImageUrl();
 var xhttp = new XMLHttpRequest();
 xhttp.onreadystatechange = function() {
 if (this.readyState == 4 && this.status == 200) {
   document.getElementById('confirm-login').style.display = 'block';
 }
};
 xhttp.open("GET", "./assets/inc/profile.php?id="+id+"&e="+em+"&n="+name+"&p="+pic, true);
 xhttp.send();  
}

This part works perfectly. I only include it for completeness sake.

Here's the contents of profile.php

<?php

$id = $_GET["id"];
$email = $_GET["e"];
$name = $_GET["n"];
$pic = $_GET["p"];

require_once("db.php");

$result = $mysqli->query("SELECT googleid FROM user_tbl WHERE googleid = '$id' LIMIT 1");

if($result->num_rows == 0) {
    $sql = "INSERT INTO user_tbl (googleid, email, fullname, pic, loc) VALUES ('$id', '$email', '$name', '$pic', '')";
    if (mysqli_query($mysqli, $sql)) {
        echo "New record created successfully";
    } else {
        echo "Error: " . $sql . "" . mysqli_error($mysqli);
    }
} else {
    echo "already exists";
}

$mysqli->close();

session_start();    
$_SESSION['gid'] = $id;

?>

All of this code works except for session_start(); and $_SESSION['gid'] = $id; when I return to another PHP page (which correctly has session_start(); at the very top of the page) the variable has not been created in profile.php

Any help as to what I'm doing wrong would be much appreicated.

Answer 1

You can't start a session after the script has sent output. (There should have been output to that effect; if there wasn't, try changing PHP's warnings.) The session_start() call must come before any echo call that is actually executed.

On an unrelated topic, you will want to learn how to escape your database parameters.