Calling a PHP class from AJAX responder-script

Question

I'm trying to reach a PHP-File via AJAX.

When I'm using a simple PHP-File like this:

<?php

header('Content-Type: text/html; charset=utf-8');
header('Cache-Control: must-revalidate, pre-check=0, no-store, no-cache, max-age=0, post-check=0');

$mode = $_POST['ajax_mode'];

switch ($mode) {
    case "test":
        if (isset($_POST['...'])) {
            $test = $_POST['...'];
            echo $test;
        }
        break;
}
?>

It's working fine. But if I try to use other classes, like a sql-class im getting a internal Server Error.

Here is my AJAX-Script:

function ajax(test, test1)
    {
        if (typeof test!== "undefined")
        {
            test_set = true;
            if (window.XMLHttpRequest) {
                request = new XMLHttpRequest();
            } else if (window.ActiveXObject) {
                try {
                    request = new ActiveXObject('Msxml2.XMLHTTP');
                } catch (e) {
                    try {
                        request = new ActiveXObject('Microsoft.XMLHTTP');
                    } catch (e) {
                    }
                }
            }
            if (!request) {
                alert("No Chance!");
                return false;
            } else {
                var url = ".../.../.../ajax_responder.php";
                request.open('POST', url, true);
                request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
                request.send('ajax_mode=test' + '&test=' + test);
                request.onreadystatechange = function() {
                    if (request.readyState === 4)
                    {
                        interpretRequest();
                    }
                };
            }
        }
    }

    function interpretRequest() {
        if (request.status != 200) {
            alert("Request-Error: " + request.statusText);
        } else {
            var content = request.responseText;
            var string_collection = content.split("_");
            alert(string_collection[0]);
        }
    }
});

EDIT: Here is the server-side script with the use of classes, with this version i get the Internal Server Errors

<?php

include '../../sql.php';
header('Content-Type: text/html; charset=utf-8');
header('Cache-Control: must-revalidate, pre-check=0, no-store, no-cache, max-age=0, post-check=0');
$mode = $_POST['ajax_mode'];
switch ($mode) {
    case "test":
        if (isset($_POST['...'])) {
            $ace = $_POST['...'];
            $sql = new sql_();
            echo $sql->execute();
        }
        break;
}
?>

Answer 1

I found an answer :D

the sql-class that i uncluded into my ajax responder calls another class, but the class is not known because i dont included the file of that class.

I included the new file and everything works just as fine :)

Answer 2

my suggestion and possible answer - place your include after your headers:

<?php

header('Content-Type: text/html; charset=utf-8');
header('Cache-Control: must-revalidate, pre-check=0, no-store, no-cache, max-age=0, post-check=0');

include '../../sql.php';

$mode = $_POST['ajax_mode'];
switch ($mode) {
    case "test":
        if (isset($_POST['...'])) {
            $ace = $_POST['...'];
            $sql = new sql_();
            echo $sql->execute();
        }
        break;
}
?>

it could cause problems if you first include a file (which possibly produces error-messages) and then send your headers. as a rule of thumb, headers in PHP should be always set before any output occurs or could occur (unless you are using output-buffering, but that's another story).

if this doesn't help - have you tried to completely leave out your headers already?