Question

When I urlEncode a string (namely a xml file) in some ocassions it adds %00 character at the end of the file. I’d like to know why it happens this and if it can be prevented (i can always erase the %00 characters). The xml file was created using xmlwriter. Weird thing is I use the same code to create other xml files and after encoding them it doesn’t add %00 characters.

Example:

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE peticion >
<peticion>
    <nombre>Info hotel</nombre>
    <agencia>HOTUSA</agencia>
    <tipo>15</tipo>
</peticion>

Edit: to create the xml this is what I do.

Dim xmlWriterSettings As New System.Xml.XmlWriterSettings
        With xmlWriterSettings
            .Encoding = Encoding.GetEncoding("iso-8859-1")
            .OmitXmlDeclaration = False
            .Indent = True
        End With

        Dim ms As New IO.MemoryStream

        Using writer As System.Xml.XmlWriter = System.Xml.XmlWriter.Create(ms, xmlWriterSettings)
            With writer
                .WriteDocType("peticion", Nothing, Nothing, Nothing)
                .WriteStartElement("peticion")
                .WriteElementString("nombre", "Info hotel")
                .WriteElementString("agencia", "HOTUSA")
                .WriteElementString("tipo", "15")
                .WriteEndElement()
            End With
        End Using

        Dim xml As String = Encoding.GetEncoding("iso-8859-1").GetString(ms.GetBuffer)

Dim XmlEncoded As String = HttpUtility.UrlEncode(xml)

XmlEncoded contains:

%3c%3fxml+version%3d%221.0%22+encoding%3d%22iso-8859-1%22%3f%3e%0d%0a%3c!DOCTYPE+peticion+%3e%0d%
0a%3cpeticion%3e%0d%0a++%3cnombre%3eInfo+hotel%3c%2fnombre%3e%0d%0a++%3cagencia%3eHOTUSA%3c%
2fagencia%3e%0d%0a++%3ctipo%3e15%3c%2ftipo%3e%0d%0a%3c%2fpeticion%3e%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%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%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

Where all these %00 come from?

Answer 1

The remarks on MemoryStream.GetBuffer provide the appropriate guidance:

Note that the buffer contains allocated bytes which might be unused. For example, if the string “test” is written into the MemoryStream object, the length of the buffer returned from GetBuffer is 256, not 4, with 252 bytes unused. To obtain only the data in the buffer, use the ToArray method; however, ToArray creates a copy of the data in memory.

Modify your code like so:

Dim xml As String = Encoding.GetEncoding("iso-8859-1").GetString(ms.ToArray)

In fact, a better option in this case would be to use a StringBuilder:

Dim sb As New StringBuilder
Using writer As XmlWriter = XmlWriter.Create(sb, xmlWriterSettings)
    ' ...
End Using        

Dim xml as String = sb.ToString()