How do you embed binary data in XML?

Question

I have two applications written in Java that communicate with each other using XML messages over the network. I'm using a SAX parser at the receiving end to get the data back out of the messages. One of the requirements is to embed binary data in an XML message, but SAX doesn't like this. Does anyone know how to do this?

UPDATE: I got this working with the Base64 class from the apache commons codec library, in case anyone else is trying something similar.

Answer 1

Maybe encode them into a known set - something like base 64 is a popular choice.

Answer 2

Try Base64 encoding/decoding your binary data. Also look into CDATA sections

Answer 3

You could encode the binary data using base64 and put it into a Base64 element; the below article is a pretty good one on the subject.

Handling Binary Data in XML Documents

Answer 4

I usually encode the binary data with MIME Base64 or URL encoding.

Answer 5

XML is so versatile...

<DATA>
  <BINARY>
    <BIT index="0">0</BIT>
    <BIT index="1">0</BIT>
    <BIT index="2">1</BIT>
    ...
    <BIT index="n">1</BIT>
  </BINARY>
</DATA>

XML is like violence - If it doesn't solve your problem, you're not using enough of it.

EDIT:

BTW: Base64 + CDATA is probably the best solution

(EDIT2:
Whoever upmods me, please also upmod the real answer. We don't want any poor soul to come here and actually implement my method because it was the highest ranked on SO, right?)

Answer 6

@Mo - XML humour. Nice one. Modded up. :-)

Answer 7

@(whoever downmodded Mo): Lighten up a little, that was hilarious (both the code and the quip). +1

Answer 8

Base64 is indeed the right answer but CDATA is not, that's basically saying: "this could be anything", however it must not be just anything, it has to be Base64 encoded binary data. XML Schema defines Base 64 binary as a primitive datatype which you can use in your xsd.

Answer 9

You can also Uuencode you original binary data. This format is a bit older but it does the same thing as base63 encoding.

Answer 10

Any binary-to-text encoding will do the trick. I use something like that

<data encoding="yEnc>
<![CDATA[ encoded binary data ]]>
</data>

Answer 11

I had this problem just last week. I had to serialize a PDF file and send it, inside an XML file, to a server.

If you're using .NET, you can convert a binary file directly to a base64 string and stick it inside an XML element.

string base64 = Convert.ToBase64String(File.ReadAllBytes(fileName));

Or, there is a method built right into the XmlWriter object. In my particular case, I had to include Microsoft's datatype namespace:

StringBuilder sb = new StringBuilder();
System.Xml.XmlWriter xw = XmlWriter.Create(sb);
xw.WriteStartElement("doc");
xw.WriteStartElement("serialized_binary");
xw.WriteAttributeString("types", "dt", "urn:schemas-microsoft-com:datatypes", "bin.base64");
byte[] b = File.ReadAllBytes(fileName);
xw.WriteBase64(b, 0, b.Length);
xw.WriteEndElement();
xw.WriteEndElement();
string abc = sb.ToString();

The string abc looks something that looks like this:

<?xml version="1.0" encoding="utf-16"?>
<doc>
    <serialized_binary types:dt="bin.base64" xmlns:types="urn:schemas-microsoft-com:datatypes">
        JVBERi0xLjMKJaqrrK0KNCAwIG9iago8PCAvVHlwZSAvSW5mbw...(plus lots more)
    </serialized_binary>
</doc>

Answer 12

Here's a good example of how to proceed XEP-0239

PS: don't forget to read Mo's answer.

PS2: read the NOTICE section on the XEP.