spring-proxy-multipart

Spike to test a bug in Zuul

• cd spring-tomcat-server

• ./gradlew bootRun

• curl --location --request POST 'localhost:8080/upload' \ --form 'file=@"/path/to/large/file"'

• cd spring-zuul

• ./gradlew bootRun

• curl --location --request POST 'localhost:4000/upload' \ --form 'file=@"/path/to/large/file"'

Behaviour of embedded-tomcat

Embedded tomcat will immediately reject the request based on the header if the content-length too large

Behaviour of Zuul in Spring with Embedded Tomcat

(Zuul (Tomcat))

We've used Zuul with Spring so the embedded tomcat will do the same

Zuul starts to proxy the request, Tomcat rejects it and throws an exception because of the file size, however Zuul needs to return a response so it hits /error in the downstream

The rabbit hole goes deeper

If the requested request in POST then the downstream /error is also a POST call

Let's go even deeper in this hole

@ExceptionHandler(MaxUploadSizeExceededException.class)
public String handleFileSizeException(MaxUploadSizeExceededException err) {
  log.error("File is too large", err);
  return "upload-error";
}

If I add an ExceptionControllerAdvice to handle MaxUploadSizeExceededException then the downstream error endpoint becomes POST upload-error

@ExceptionHandler(MaxUploadSizeExceededException.class)
public String handleFileSizeException(MaxUploadSizeExceededException err) {
  log.error("File is too large", err);
  return "unable to upload error";
}

So now Zuul tries to hit the endpoint /unable to upload error

2021-01-07 22:42:02.755  WARN 39467 --- [nio-4000-exec-1] o.s.c.n.z.f.pre.PreDecorationFilter      : No route found for uri: /unable to upload error