Storing Special Characters in Windows Azure Blob Metadata

Question

I have an app that is storing images in a Windows Azure Block Blob. I'm adding meta data to each blob that gets uploaded. The metadata may include some special characters. For instance, the registered trademark symbol (®). How do I add this value to meta data in Windows Azure?

Currently, when I try, I get a 400 (Bad Request) error anytime I try to upload a file that uses a special character like this.

Thank you!

Answer 1

You might use HttpUtility to encode/decode the string:

blob.Metadata["Description"] = HttpUtility.HtmlEncode(model.Description);
Description = HttpUtility.HtmlDecode(blob.Metadata["Description"]);

http://lvbernal.blogspot.com/2013/02/metadatos-de-azure-vs-caracteres.html

Answer 2

The supported characters in the blob metadata must be ASCII characters. To work around this you can either escape the string ( percent encode), base64 encode etc.

joe

Answer 3

HttpUtility.HtmlEncode may not work; if Unicode characters are in your string (ie &#8217), it will fail. So far, I have found Uri.EscapeDataString does handle this edge case and others. However, there are a number of characters that get encoded unnecessarily, such as space (' '=chr(32)=%20).

I mapped the illegal ascii characters metadata will not accept and built this to restore the characters:

    static List<string> illegals = new List<string> { "%1", "%2", "%3", "%4", "%5", "%6", "%7", "%8", "%A", "%B", "%C", "%D", "%E", "%F", "%10", "%11", "%12", "%13", "%14", "%15", "%16", "%17", "%18", "%19", "%1A", "%1B", "%1C", "%1D", "%1E", "%1F", "%7F", "%80", "%81", "%82", "%83", "%84", "%85", "%86", "%87", "%88", "%89", "%8A", "%8B", "%8C", "%8D", "%8E", "%8F", "%90", "%91", "%92", "%93", "%94", "%95", "%96", "%97", "%98", "%99", "%9A", "%9B", "%9C", "%9D", "%9E", "%9F", "%A0", "%A1", "%A2", "%A3", "%A4", "%A5", "%A6", "%A7", "%A8", "%A9", "%AA", "%AB", "%AC", "%AD", "%AE", "%AF", "%B0", "%B1", "%B2", "%B3", "%B4", "%B5", "%B6", "%B7", "%B8", "%B9", "%BA", "%BB", "%BC", "%BD", "%BE", "%BF", "%C0", "%C1", "%C2", "%C3", "%C4", "%C5", "%C6", "%C7", "%C8", "%C9", "%CA", "%CB", "%CC", "%CD", "%CE", "%CF", "%D0", "%D1", "%D2", "%D3", "%D4", "%D5", "%D6", "%D7", "%D8", "%D9", "%DA", "%DB", "%DC", "%DD", "%DE", "%DF", "%E0", "%E1", "%E2", "%E3", "%E4", "%E5", "%E6", "%E7", "%E8", "%E9", "%EA", "%EB", "%EC", "%ED", "%EE", "%EF", "%F0", "%F1", "%F2", "%F3", "%F4", "%F5", "%F6", "%F7", "%F8", "%F9", "%FA", "%FB", "%FC", "%FD", "%FE" };
    private static string MetaDataEscape(string value)
    {
        //CDC%20Guideline%20for%20Prescribing%20Opioids%20Module%206%3A%20%0Ahttps%3A%2F%2Fwww.cdc.gov%2Fdrugoverdose%2Ftraining%2Fdosing%2F
        var x = HttpUtility.HtmlEncode(value);

        var sz = value.Trim();
        sz = Uri.EscapeDataString(sz);

        for (int i = 1; i < 255; i++)
        {
            var hex = "%" + i.ToString("X");
            if (!illegals.Contains(hex))
            {
                sz = sz.Replace(hex, Uri.UnescapeDataString(hex));
            }
        }

        return sz;
    }

The result is:

• Before ==> "1080x1080 Facebook Images"
• Uri.EscapeDataString => "1080x1080%20Facebook%20Images"
• After => "1080x1080 Facebook Images"

I am sure there is a more efficient way, but the hit seems negligible for my needs.