How to encrypt payload file streamingly via WSO2 ESB - wso2-esb

Question

I have to implement a scenario by using WSO2 ESB, as encrypting the binary payload streamingly while response to the client side (I assume the content-type in the case is Application/Octet-Stream), below is some details by my thought:
An Endpoint like "http://myhost/backend/" which provides business functionality;
A proxy which pass messages through the endpoint;
I attempt to write an OutSequence to check the Content-type: if the Content-Type matches Application/Octet-Stream, invoke my customized class mediator to encrypt the fileStream Streamingly and response.
I have no idea on how to write the class mediator to make it implemented? How could I get/read the file stream from the message as well as how to put the outputStream back to the response while I could only see mc.getEnvelope().getBody() in mediation method? Below is my current mediator which doesn't work.
public boolean mediate(MessageContext mc) {
org.apache.axis2.context.MessageContext amc = ((Axis2MessageContext) mc).getAxis2MessageContext();
try {
String contentID = amc.getAttachmentMap().getAllContentIDs()[0];
DataHandler dh = amc.getAttachment(contentID);
dh.getDataSource().getName();
InputStream is = null;
try {
is = dh.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line = null;
while ((line = br.readLine()) != null) {
System.out.println("client read:" + line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
return true;
}
Many thanks if anybody with experience would kindly help.

Answer 1

Pasted my current solution for anyone else who confronts similar issue.
In the mediator, I read the file content from response stream via OMText.InputStream and use net.lingala.zip4j package to write a zip file(in memory) with the raw file encrypted; Finally I write the zip file content as ByteArray back to the OMElement of the soap message.
public boolean mediate(MessageContext mc) {
System.out.println("========================Mediator log start================================");
org.apache.axis2.context.MessageContext amc = ((Axis2MessageContext) mc).getAxis2MessageContext();
try {
#SuppressWarnings("unchecked")
Map<String, String> responseHeaders = (Map<String, String>) amc.getProperty("TRANSPORT_HEADERS");
String rawFileName = "";
String[] contentDisps = responseHeaders.get("Content-Disposition").split(";");
for (String item : contentDisps) {
System.out.println("item::" + item);
if (item.trim().startsWith(CONTENT_DISPOSITION_FILENAME)) {
rawFileName = item.substring(item.indexOf("\"") + 1, item.length() - 1);
break;
}
}
responseHeaders.put(
"Content-Disposition",
responseHeaders.get("Content-Disposition").replace(rawFileName,
rawFileName.substring(0, rawFileName.lastIndexOf(".")) + ".myzip"));
OMElement binaryPayload =
amc.getEnvelope().getBody()
.getFirstChildWithName(new QName("http://ws.apache.org/commons/ns/payload", "binary"));
OMText binaryNode = (OMText) binaryPayload.getFirstOMChild();
DataHandler dataHandler = (DataHandler) binaryNode.getDataHandler();
InputStream is = dataHandler.getInputStream();
ByteArrayOutputStream responseOutputStream = new ByteArrayOutputStream();
ZipOutputStream zipOutputStream = getZipOutputStreamInstance(responseOutputStream, rawFileName);
// write to zipOutputStream
byte data[] = new byte[BUFFER_SIZE];
int count;
while ((count = is.read(data, 0, BUFFER_SIZE)) != -1) {
zipOutputStream.write(data, 0, count);
zipOutputStream.flush();
}
zipOutputStream.closeEntry();
zipOutputStream.finish();
InputStream in = new ByteArrayInputStream(responseOutputStream.toByteArray());
DataHandler zipDataHandler = new DataHandler(new StreamingOnRequestDataSource(in));
OMFactory factory = OMAbstractFactory.getOMFactory();
OMText zipData = factory.createOMText(zipDataHandler, true);
zipData.setBinary(true);
binaryPayload.getFirstOMChild().detach();
binaryPayload.addChild(zipData);
amc.setProperty("TRANSPORT_HEADERS", responseHeaders);
System.out.println("========================Mediator end==================================");
} catch (Exception ex) {
System.out.println("exception found here:");
ex.printStackTrace();
}
return true;
}