ASP.NET File Upload Validation

UPDATE:

You could probably adapt the regex instead to allow for backslashes up to the filename and disallow them in the filename, but the complexity of such a beast would not likely be worth the time and effort to construct it.

Since the original regex was for validating a textbox where the user was typing a filename (and not a file input where the name is generated by the OS), I think the better course of action would be to use an <asp:CustomValidator> control instead and split the value on \ to get more easily parseable chunks.

The primary advantage of this approach is that you can break that complex regex down into multiple simpler (and more easily understood) regexes and test them one at a time against the filename.

    <script type="text/javascript">
        var validateFile = function validateFile(sender, args) {
            'use strict';
            var fileWithPath, //split on backslash
                fileName = fileWithPath[fileWithPath.length - 1], //grab the last element
                containsInvalidChars = /["#%&*:<>?\/{|}~]/g, //no reason to include \ as we split on that.
                containsSequentialDots = /[.][.]+/g, //literal .. or ... or .... (etc.)
                endsWithDot = /[.]$/g, // . at end of string
                startsWithDot = /^[.]/g, // . at start of string
                notValid = false, //boolean for flagging not valid
                valid = fileName.length > 0 && fileName.length <= 128;
            notValid = containsInvalidChars.test(fileName);
            notValid = notValid || containsSequentialDots.test(fileName);
            notValid = notValid || endsWithDot.test(fileName);
            notValid = notValid || startsWithDot.test(fileName);
            args.IsValid = valid && !notValid;
        };
    </script>
    <asp:FileUpload ID="InputFile" runat="server" />
    <asp:RequiredFieldValidator ID="rqfvInputFile" runat="server" ControlToValidate="InputFile" ErrorMessage="File is required"></asp:RequiredFieldValidator>
    <asp:CustomValidator ID="cstvInputFile" runat="server" ControlToValidate="InputFile" ClientValidationFunction="validateFile" ErrorMessage="File is not a sharepoint file"></asp:CustomValidator>
    <asp:Button ID="Button1" runat="server" Text="Button" />

One caveat to the above is that the filename chunks are split on \, which is not likely to be the path separator for Unix or Mac systems. If you need this to run on those clients as well, you'll likely have to split on either \ or / which you should be able to do with this:

var filePath = args.Value.split(/\\|\//g); //not tested.

ORIGINAL:

Add in an <asp:RegularExpressionValidator> control and set the ControlToValidate property to your file uploader control.

You can have as many validator controls as you like pointed towards a single input.

Just set the appropriate properties (such as the ValidationExpression in the <asp:RegularExpressionValidator>) and make sure the ControlToValidate property is pointed towards the input to validate.

Example:

<asp:Button id="btnUploadFile" class="ms-ButtonHeightWidth" runat="server" OnClick="UploadFile_Click" Text="Upload File"></asp:Button>
<asp:RequiredFieldValidator runat="server" ID="RequiredInputFileValidator" ControlToValidate="InputFile" Text="You must specify a value for the required field" />
<asp:RegularExpressionValidator runat="server" ID="RegexInputFileValidator" ControlToValidate="InputFile" ErrorMessage="Only valid SharePoint files are allowed."
    ValidationExpression="^(?!..)(?!...)(?=.[^.]$)[^\"#%&:<>?\/{|}~]{1,128}$" />

You may also want to look into Validation groups