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

User · Accepted Answer

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

User · Answer

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

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If you have control over the XML format  you should turn the problem inside out  Rather than attaching the binary XML you should think about how to enclose a document that has multiple parts  one of which contains XML   The traditional solution to this is an archive  e g  tar   But if you want to keep your enclosing document in a text-based format or if you don t have access to an file archiving library  there is also a standardized scheme that is used heavily in email and HTTP which is multipart   MIME with Content-Transfer-Encoding  binary    For example if your servers communicate through HTTP and you want to send a multipart document  the primary being an XML document which refers to a binary data  the HTTP communication might look something like this   POST   HTTP 1 1 Content-Type  multipart related  boundary  qd43hdi34udh34id344      other headers elided      --qd43hdi34udh34id344 Content-Type  application xml   lt myxml gt       lt data href  cid data bin   gt   lt  myxml gt  --qd43hdi34udh34id344 Content-Id   lt data bin gt  Content-type  application octet-stream Content-Transfer-Encoding  binary      binary data     --qd43hdi34udh34id344--   As in above example  the XML refer to the binary data in the enclosing multipart by using a cid URI scheme which is an identifier to the Content-Id header  The overhead of this scheme would be just the MIME header  A similar scheme can also be used for HTTP response  Of course in HTTP protocol  you also have the option of sending a multipart document into separate request response   If you want to avoid wrapping your data in a multipart is to use data URI    lt myxml gt       lt data href  data application something charset utf-8 base64 dGVzdGRhdGE    gt   lt  myxml gt    But this has the base64 overhead

User · Answer

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

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XML is so versatile      lt DATA gt     lt BINARY gt       lt BIT index  0  gt 0 lt  BIT gt       lt BIT index  1  gt 0 lt  BIT gt       lt BIT index  2  gt 1 lt  BIT gt               lt BIT index  n  gt 1 lt  BIT gt     lt  BINARY gt   lt  DATA gt    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

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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    lt  xml version  1 0  encoding  utf-16   gt   lt doc gt       lt serialized binary types dt  bin base64  xmlns types  urn schemas-microsoft-com datatypes  gt          JVBERi0xLjMKJaqrrK0KNCAwIG9iago8PCAvVHlwZSAvSW5mbw    plus lots more       lt  serialized binary gt   lt  doc gt

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Any binary-to-text encoding will do the trick  I use something like that   lt data encoding  yEnc gt   lt   CDATA  encoded binary data    gt   lt  data gt

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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

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

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Base64 overhead is 33    BaseXML for XML1 0 overhead is only 20   But it s not a standard and only have a C implementation yet  Check it out if you re concerned with data size  Note that however browsers tends to implement compression so that it is less needed   I developed it after the discussion in this thread  Encoding binary data within XML   alternatives to base64

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While the other answers are mostly fine  you could try another  more space-efficient  encoding method like yEnc   yEnc wikipedia link   With yEnc also get checksum capability right  out of the box   Read and links below  Of course  because XML does not have a native yEnc type your XML schema should be updated to properly describe the encoded node   Why  Due to the encoding strategies base64 63  uuencode et al  encodings increase the amount of data  overhead  you need to store and transfer by roughly 40   vs  yEnc s 1-2    Depending on what you re encoding  40  overhead could be become an issue      yEnc - Wikipedia abstract  https   en wikipedia org wiki YEnc yEnc is a binary-to-text encoding scheme for transferring binary files in messages on Usenet or via e-mail      An additional advantage of yEnc over previous encoding methods  such as uuencode and Base64  is the inclusion of a CRC checksum to verify that the decoded file has been delivered intact

User · Answer

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

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