PHP inserting meaningless characters into string

Question

I'm working on an application where I need to be able to send a string from JavaScript to PHP. At first I had just sent it through $_POST variable, but I noticed that it was inserting values into the string.

Then I recoded both parts to use base 64 to send the data because I assumed that the data was being mangled in transmission. The string was being transferred just fine with no mistakes, but then when I converted it back from base 64 to base 16, it had the exact same mistakes as before!

Here is a comparison of the two strings (hex dumps). There are two meaningful chunks of data in each string, and it seems PHP is making mistakes only near those areas. The first line is how PHP is interpreting the string, and the second line is how I'm sending it from JavaScript.

c2 b0 c2 a7 c3 9a 7a 00 00 00 c2 bb 30 4d 61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
b0 a7 da 7a 00 00 00 00 00 00 bb 30 4d 61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Why are these phantom bytes appearing?

EDIT: Here's the code I'm using.

JavaScript:

function sendRequest(body)
{
    var url = "../update/index.php";
    $.post(url,{msg:body},function(data,status,jqx)
    {
        $("#response").html(data);
    });
}

body is a string whose beginning is hard-coded as "\u00b0\u00a7\u00da\u007a".

Then in PHP:

$msg =$_POST['msg'];
plain_hex_dump($msg);

plain_hex_dump simply outputs the string as hex, resulting in the first of the two hex dumps above.

I've updated the post. However, I think the problem might come from some encoding concept I don't understand. I'm fairly certain that my JavaScript code generates no characters that use more than one byte. — Ryan Kennedy
– Ryan Kennedy, Commented May 9, 2012 at 18:03

Andrew Leach · Accepted Answer · 2012-05-09 18:06:36Z

3

This is UTF-8 encoding.

b0 is encoded as c2 b0. a7 becomes c2 a7. da becomes c3 9a. 7a is not changed.

Thus your b0 a7 da 7a is represented in UTF-8 as c2 b0 c2 a7 c3 9a 7a.

It appears that Javascript is UTF-8-encoding your body variable. You could try using the utf8_decode function in PHP.

answered May 9, 2012 at 18:06

Andrew Leach

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1 Comment

Ryan Kennedy Over a year ago

Thanks so much, that solved it! I've been bashing my head over that one all day.

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