ASP.NET Pass non-printable barcode character from a web.form to server side

Question

I've been developing a web app that accepts input from a barcode scanner. I need to pass scanned barcodes (GS1-128) from client-side to server-side. By standard, GS1-128 may contain one or several group separator <GS> characters (characters with ASCII code 29). Thus, "123<GS>45", "12<GS>345" are DIFFERENT inputs. I have a textbox and a submit button to get the input. For some reason, ASP.NET does not include non-printable characters in the postback and in both cases I receive "12345" instead.

Is there any way to overcome this issue?

P.S. When I'm using a WinForm (for testing) everything is OK and I get the character, but with ASP.NET this doesn't work.

Answer 1

After some digging up I've found out that most barcode scanners actually transmit a series of keystrokes as if they were from the keyboard. As this happens, the <GS> symbol is transmitted as two keystrokes CTRL+] with keycodes values of 17 and 229 correspondingly.

Since it has no printable representation, the Textbox I was using for the input simply ignored it.

What I ended up with was this keyDown event handler placed on the textbox. It simply substitutes '^]' with '|'.

    <script type="text/javascript">
        var ctrlReceived = false;
        function handleStroke(event) {
          if (ctrlReceived && 221 == event.keyCode)
              document.getElementById('txtScanBoxBarcode').value += '|';
          ctrlReceived = (17 == event.keyCode);
          return null;
        };
    </script>

On the server side I simply change it back:

    string barcode = this.txtScanBoxBarcode.Text.Replace('|', (char)29);

Everything works so far. I wonder if there's a better way to handle the problem though.