Spring NoHandlerFoundException mistakenly returns request headers from ErrorResponse#getHeaders

I found an inconsistency in 404 handling using the new ProblemDetails feature of Spring 6 (6.0.2).

My example application is:

@SpringBootApplication
@RestController
public class ProblemDetailsApplication {

    @GetMapping("/hello")
    public String hello() {
        return "World";
    }

    public static void main(String[] args) {
        SpringApplication.run(ProblemDetailsApplication.class, args);
    }

}

In order to enable ProblemDetails handling, I configured this in my application.properties:

spring.mvc.problemdetails.enabled = true
spring.mvc.throw-exception-if-no-handler-found = true
spring.web.resources.add-mappings = false

And the CLI interaction:

curl http://localhost:8080/hello
World

curl http://localhost:8080/non-existent
{"type":"about:blank","title":"Not Found","status":404,"detail":"No endpoint GET /non-existent.","instance":"/non-existent"}

curl -X POST -d '{"foo":"bar"}' http://localhost:8080/non-existent
{"timestamp":"2022-12-02T18:48:36.587+00:00","status":404,"error":"Not Found","path":"/non-existent"}

The last request did not result in a problem details report as I would expect.

Comment From: osiegmar

I figured out that a part of the problem is caused by the Content-Type. The command

curl -X POST -d '{"foo":"bar"}' http://localhost:8080/non-existent
{"timestamp":"2022-12-02T18:48:36.587+00:00","status":404,"error":"Not Found","path":"/non-existent"}

sends a Content-Type of application/x-www-form-urlencoded which causes an exception:

org.springframework.http.converter.HttpMessageNotWritableException: No converter for [class org.springframework.http.ProblemDetail] with preset Content-Type 'application/x-www-form-urlencoded;charset=UTF-8'
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:319) ~[spring-webmvc-6.0.2.jar:6.0.2]

But sending a Content-Type of application/json makes things even worse:

curl -v -H "Content-Type: application/json" -d '{"foo":"bar"}' http://localhost:8080/non-existent
*   Trying 127.0.0.1:8080...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> POST /non-existent HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.84.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 13
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 404
< host: localhost:8080
< user-agent: curl/7.84.0
< accept: */*
< Content-Type: application/json;charset=UTF-8
< Content-Length: 13
< Date: Fri, 02 Dec 2022 20:13:00 GMT
<
* Connection #0 to host localhost left intact
{"type":"abou

The response body is truncated and no exception is logged! I also noted that the Content-Length of the response is identical to the one of the request. If I change the size of the request, the size of the response changes accordingly.

Comment From: rstoyanchev

NoHandlerFoundException already had getHeaders() which returns request headers, but in 6.0 that ends up overriding getHeaders() from ErrorResponse, and as a result the request "Content-Type" ends up being used for the response.