MTOM+XOP How to get the binary part in WCF and prevent it from being encoded to Base64

Question

I am implementing a client that receives SOAP MTOM+XOP messages. (XDS.b Consumer to retrieve documents)

I know that for small attachments the attached file will be base64 encoded into the body and for big ones the binary data will be attached in a separate MIME part and a as my Client proxy class. After I get the Message, the binary data already been encoded into the body as base64, so I implemented CustomEncoded and IncommingInspector and I was able to see the buffer and dumping the message before returning it to the client.

My question: I would like to prevent the process of Encoding/Decoding to Base64 if possible. I would like to get the binary part, write it to the file (for example) and if possible to return a file location in the message body instead of the huge base64 encoded string.

Is this possible?

Following is a sample of message I am trying to process (binary part replaced with ...)

HTTP/1.1 200 OK
Date: Tue, 02 Dec 2014 11:07:55 GMT
Server: Apache
Set-Cookie: JSESSIONID=005193579FC6F91CC7BD0B671E616CB6; Path=/um
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: multipart/related; start-info="application/soap+xml"; type="application/xop+xml"; boundary="----=_Part_178_590817.1417518476024"

1ff8
------=_Part_178_590817.1417518476024
Content-Type: application/xop+xml; charset=utf-8; type="application/soap+xml"
Content-Id: <http://corp.com/xds_source>
Content-Transfer-Encoding: 8bit

<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">
    <env:Header>
        <wsa:Action xmlns:wsa="http://www.w3.org/2005/08/addressing">urn:ihe:iti:2007:RetrieveDocumentSetResponse</wsa:Action>
            <wsa:RelatesTo xmlns:wsa="http://www.w3.org/2005/08/addressing">urn:uuid:123503ce-fba9-4bed-a77f-0cf6d9a51744</wsa:RelatesTo>
    </env:Header>
    <env:Body>
        <xdsb:RetrieveDocumentSetResponse xmlns:xdsb="urn:ihe:iti:xds-b:2007">
            <RegistryResponse xmlns="urn:oasis:names:tc:ebxml-regrep:xsd:rs:3.0" status="urn:oasis:names:tc:ebxml-regrep:ResponseStatusType:Success"/>
            <xdsb:DocumentResponse><xdsb:RepositoryUniqueId>SAMPLE:12345678</xdsb:RepositoryUniqueId>
            <xdsb:DocumentUniqueId>1.2.840.113704.7.1.0.14117819932881.1416384260.2</xdsb:DocumentUniqueId>
            <xdsb:mimeType>application/vnd.openxmlformats-officedocument.wordprocessingml.document</xdsb:mimeType>
            <xdsb:Document><xop:Include xmlns:xop="http://www.w3.org/2004/08/xop/include" href="cid:1.urn:uuid:[email protected]"/>
            </xdsb:Document>
            </xdsb:DocumentResponse>
        </xdsb:RetrieveDocumentSetResponse>
    </env:Body>
</env:Envelope>
------=_Part_178_590817.1417518476024
Content-Type: application/octet-stream
Content-ID: <1.urn:uuid:[email protected]>
Content-Transfer-Encoding: binary
...
------=_Part_178_590817.1417518476024--