Handling empty request body (protobuf3 encoded) - spring

Question

I have a Spring Boot application running. Requests/responses are sent protobuf (Protobuf3) encoded.
My (simplified) REST controller:
#RestController
public class ServiceController {
#RequestMapping(value = "/foo/{userId}", method = RequestMethod.POST)
public void doStuff(#PathVariable int userId, #RequestBody(required = false) Stuff.Request pbRequest) {
// Do stuff
}
}
My (simplified) protobuf3 schema:
syntax = "proto3";
message Request {
int32 data = 1;
}
My configuration to have content negotiation available:
#Configuration
public class ProtobufConfig {
#Bean
ProtobufHttpMessageConverter protobufHttpMessageConverter() {
return new ProtobufHttpMessageConverter();
}
}
Everything is working like a charm as long as the request body has some bytes set. BUT protobuf does not write any bytes if just default values are sent. As soon I have a request message which contains data = 0 the generated bytes are just empty. On the app side the request body is null and won't be converted to a protobuf message (it even throws an exception if request body is set to required = true). The HTTP input message isn't processed by the ProtobufHttpMessageConverter at all. Is there a way to handle that?

Answer 1

I found a way of handling it. But it uses reflection which is really something I don't want to have:
#ControllerAdvice
public class RequestBodyAdviceChain implements RequestBodyAdvice {
#Override
public boolean supports(MethodParameter methodParameter, Type type,
Class< ? extends HttpMessageConverter< ? >> aClass) {
return true;
}
#Override
public Object handleEmptyBody(Object body, HttpInputMessage httpInputMessage, MethodParameter methodParameter,
Type type, Class< ? extends HttpMessageConverter< ? >> aClass) {
try {
Class<?> cls = Class.forName(type.getTypeName());
Method m = cls.getMethod("getDefaultInstance");
return m.invoke(null);
} catch (Exception e) {
e.printStackTrace();
}
return body;
}
#Override
public HttpInputMessage beforeBodyRead(HttpInputMessage httpInputMessage, MethodParameter methodParameter,
Type type, Class< ? extends HttpMessageConverter< ? >> aClass) throws IOException {
return httpInputMessage;
}
#Override
public Object afterBodyRead(Object body, HttpInputMessage httpInputMessage, MethodParameter methodParameter, Type type,
Class< ? extends HttpMessageConverter< ? >> aClass) {
return body;
}
}
So in the case of an empty body I create a default instance of the protobuf message object.