Spring Cloud Zuul - Custom Error Filter - spring

Question

I want to add a custom error Zuul Filter and want to make sure SendErrorFilter does not execute. I have looked at few github links including Spring-cloud/spring-cloud-netflix and various stack-overflow questions:-
Customizing Zuul Exception
Overriding Zuul Filter SendErrorFilter
My code is as follows-
public class CustomErrorFilter extends ZuulFilter {
private static final Logger LOG = LoggerFactory.getLogger(CustomErrorFilter.class);
#Override
public String filterType() {
return "post";
}
#Override
public int filterOrder() {
return -1;
}
#Override
public boolean shouldFilter() {
RequestContext ctx=RequestContext.getCurrentContext();
if(ctx.getThrowable()!=null)
return true;
else
return false;
}
#Override
public Object run() {
RequestContext ctx = RequestContext.getCurrentContext();
ctx.setThrowable(null); // response is not returned unless
throwable is set to null.
ctx.remove("error.status_code");
ctx.setResponseBody(“Error”);
ctx.getResponse().setContentType("text/plain");
ctx.setResponseStatusCode(400);
}
return null;
}
I am having the following issues-
Setting filter order to -1 does not prohibit sendErrorFilter from running.
To stop sendErrorFilter from running, I need to set
zuul.SendErrorFilter.error.disable=true in bootstrap.yml
To get a response body which is set in the custom error filter, i need to set throwable to null as mentioned in the github.
Setting a filter as type "error" does nothing, and the custom filer does not run.
I would like someone to explain, what I am doing wrong and what is the most correct way of handling custom error filters, because there is lot of conflicting information available on the web.
Dependencies-
spring cloud - Edgware.RELEASE
spring cloud netflix starter zuul- 1.4.3.RELEASE

Answer 1

filtertype() should return "error" if you want to handle error scenario
filterOrder() should be -1 to execute before SendErrorFilter
Add the following lines to your filter(CustomErrorFilter )
protected static final String SEND_ERROR_FILTER_RAN = "sendErrorFilter.ran";
and
#Override
public Object run() {
RequestContext ctx = RequestContext.getCurrentContext();
ctx.set(SEND_ERROR_FILTER_RAN);
// rest of your code
return null;
}
ctx.set(SEND_ERROR_FILTER_RAN); will block the SendErrorFilter from running.
Update:
Check shouldFilter() method in SendErrorFilter
#Override
public boolean shouldFilter() {
RequestContext ctx = RequestContext.getCurrentContext();
// only forward to errorPath if it hasn't been forwarded to already
return ctx.getThrowable() != null
&& !ctx.getBoolean(SEND_ERROR_FILTER_RAN, false);
}
For every request a RequestContext gets created, but spring is not setting SEND_ERROR_FILTER_RAN in the context. May be for older version you have to configure from yaml file (zuul.SendErrorFilter.error.disable=true) for newer version(1.4.3.RELEASE) its from code like ctx.set(SEND_ERROR_FILTER_RAN).
By default !ctx.getBoolean(SEND_ERROR_FILTER_RAN, false) this will evaluates to true and run() method of SendErrorFilter will execute.
if you put ctx.set(SEND_ERROR_FILTER_RAN) in your CustomErrorFilter with filterOrder() as -1, your CustomErrorFilter will execute first and we are setting the RequestContext with SEND_ERROR_FILTER_RAN as true. Now when it goes to shouldFilter() method of SendErrorFilter evaluate to false and it won't execute run() method of SendErrorFilter.