Spring Netflix Zuul: API-Gateway - Transforming a JSON request - json

Question

I am currently building an API gateway for a new microservices system, using the Spring Netflix Zuul library.
So far my gateway contains PRE and POST filters that intercept the requests and perform the required logic, etc.
One thing that I see is that REST calls to specific microservices require invoking an API endpoint (either GET or POST) containing JSON payload data that is very complex.
For an end-user sending a request to a microservice containing this JSON would not be user friendly.
I had an idea such that the API gateway act as a mediator, where the user can submit a more "simplified/ user-friendly" JSON to the API gateway, which will transform the JSON payload with the correct "complex" JSON structure that the target microservice can understand in order to handle the request efficiently.
My understanding of how Netflix Zuul is that this can be done by creating a RouteFilter and then including this logic here.
Can anyone explain if (or how) this transformation could be done using Netflix Zuul?
Any advice is appreciated.
Thanks.

Answer 1

No doubt you can do it with Zuul, i am currently trying to do almost the same. i'd suggest you take a look at this repo :
sample-zuul-filters
and the official doc on github.
Filters have to extend ZuulFilter and implement the following methods :
/**
*return a string defining when your filter must execute during zuul's
*lyfecyle ('pre'/'post' routing
**/
#Override
public String filterType(){
return 'pre'; // run this filter before sending the final request
}
/**
* return an int describing the order that the filter should run on,
* (relative to the other filters and the current 'pre' or 'post' context)
**/
#Override
public int filterOrder {
return 1; //this filter runs first in a pre-request context
}
/**
* return a boolean indicating if the filter should run or not
**/
#Override
public boolean shouldFilter() {
RequestContext ctx = RequestContext.getCurrentContext();
if(ctx.getRequest().getRequestURI().equals("/theRouteIWantToFilter"))
{
return true;
}
else {
return false;
}
}
/**
* After all the config stuffs you can set what your filter actually does
* here. This is where your json logic goes.
*/
#Override
public Object run() {
try {
RequestContext ctx = RequestContext.getCurrentContext();
HttpServletRequest request = ctx.getRequest();
InputStream stream = ctx.getResponseDataStream();
String body = StreamUtils.copyToString(stream, Charset.forName("UTF-8"));
// transform your json and send it to the api.
ctx.setResponseBody(" Modified body : " + body);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
I am not sure my answer is 100% accurate since i am working on it but it's a start.

Answer 2

I've done payload conversion in pre filter but this should work in route filter as well. Use com.netflix.zuul.http.HttpServletRequestWrapper to capture and modify the original request payload before forwarding the request to target microservice.
Sample code:
package com.sample.zuul.filters.pre;
import com.google.common.io.CharStreams;
import com.netflix.zuul.ZuulFilter;
import com.netflix.zuul.context.RequestContext;
import com.netflix.zuul.http.HttpServletRequestWrapper;
import com.netflix.zuul.http.ServletInputStreamWrapper;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
public class JsonConverterFilter extends ZuulFilter {
#Override
public String filterType() {
return "pre";
}
#Override
public int filterOrder() {
return 0; // Set it to whatever the order of your filter is
}
#Override
public boolean shouldFilter() {
return true;
}
#Override
public Object run() {
RequestContext context = RequestContext.getCurrentContext();
HttpServletRequest request = new HttpServletRequestWrapper(context.getRequest());
String requestData = null;
JSONParser jsonParser = new JSONParser();
JSONObject requestJson = null;
try {
if (request.getContentLength() > 0) {
requestData = CharStreams.toString(request.getReader());
}
if (requestData == null) {
return null;
}
requestJson = (JSONObject) jsonParser.parse(requestData);
} catch (Exception e) {
//Add your exception handling code here
}
JSONObject modifiedRequest = modifyJSONRequest(requestJson);
final byte[] newRequestDataBytes = modifiedRequest.toJSONString().getBytes();
request = getUpdatedHttpServletRequest(request, newRequestDataBytes);
context.setRequest(request);
return null;
}
private JSONObject modifyJSONRequest(JSONObject requestJSON) {
JSONObject jsonObjectDecryptedPayload = null;
try {
jsonObjectDecryptedPayload = (JSONObject) new JSONParser()
.parse("Your new complex json");
} catch (ParseException e) {
e.printStackTrace();
}
return jsonObjectDecryptedPayload;
}
private HttpServletRequest getUpdatedHttpServletRequest(HttpServletRequest request, final byte[] newRequestDataBytes) {
request = new javax.servlet.http.HttpServletRequestWrapper(request) {
#Override
public BufferedReader getReader() throws IOException {
return new BufferedReader(
new InputStreamReader(new ByteArrayInputStream(newRequestDataBytes)));
}
#Override
public ServletInputStream getInputStream() throws IOException {
return new ServletInputStreamWrapper(newRequestDataBytes);
}
/*
* Forcing any calls to HttpServletRequest.getContentLength to return the accurate length of bytes
* from a modified request
*/
#Override
public int getContentLength() {
return newRequestDataBytes.length;
}
};
return request;
}
}