mysql_real_escape_string() just makes an empty string?

Question

I am using a jQuery AJAX request to a page called like.php that connects to my database and inserts a row. This is the like.php code:

<?php

// Some config stuff
define(DB_HOST, 'localhost');
define(DB_USER, 'root');
define(DB_PASS, '');
define(DB_NAME, 'quicklike');

$link = mysql_connect(DB_HOST, DB_USER, DB_PASS) or die('ERROR: ' . mysql_error());
$sel = mysql_select_db(DB_NAME, $link) or die('ERROR: ' . mysql_error());

$likeMsg = mysql_real_escape_string(trim($_POST['likeMsg']));
$timeStamp = time();

if(empty($likeMsg))
    die('ERROR: Message is empty');

$sql = "INSERT INTO `likes` (like_message, timestamp)
        VALUES ('$likeMsg', $timeStamp)";

$result = mysql_query($sql, $link) or die('ERROR: ' . mysql_error());

echo mysql_insert_id();

mysql_close($link);

?>

The problematic line is $likeMsg = mysql_real_escape_string(trim($_POST['likeMsg']));. It seems to just return an empty string, and in my database under the like_message column all I see is blank entries. If I remove mysql_real_escape_string() though, it works fine.

Here's my jQuery code if it helps.

$('#like').bind('keydown', function(e) {
    if(e.keyCode == 13) {
        var likeMessage = $('#changer p').html();

        if(likeMessage) {
            $.ajax({
                cache: false,
                url: 'like.php',
                type: 'POST',
                data: { likeMsg: likeMessage },
                success: function(data) {
                    $('#like').unbind();
                    writeLikeButton(data);
                }
            });
        } else {
            $('#button_container').html('');
        }
    }
});

All this jQuery code works fine, I've tested it myself independently.

Any help is greatly appreciated, thanks.

Answer 1

Are you 1000% sure that $_POST["likeMsg"] actually contains something?

As for mysql_real_escape_string() returning an empty value, the manual says there is only one situation where that can happen:

Note: A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MySQL connection is used.

this doesn't seem to be the case here though, as you do have a connection open. Strange.