Fix endpoints with HttpServletResponse parameters causing empty produces

[uuf6429]

Setup information

hikaku version: 2.2.0
specification converter: OpenApi
implementation converter: Spring
build tool and version: gradle 5, kotlin 1.3.21
test framework: junit 5.1

Describe the bug

Modifying response passed as method parameter (and thus not requiring a method return type) causes Hikaku to ignore produces in @XXXMapping annotation.

Expected behavior

Hikaku Spring converter should probably check that result is not void and there is no parameter of type HttpServletResponse.

Code samples

The following PoC produces this issue:

    @GetMapping("v1/test", produces = ["application/pdf"])
    fun invoke(response: HttpServletResponse)
    {
        try {
            val inputStream = fileStreamer.stream("s3://some-endpoint/test.pdf")
            IoUtils.copy(inputStream, response.outputStream)
        } catch (ex: NoSuchKeyException) {
            response.status = 404
        }
    }

The root cause is the this.value.method.hasNoReturnType() part here:
https://github.com/codecentric/hikaku/blob/master/spring/src/main/kotlin/de/codecentric/hikaku/converters/spring/extensions/ProducesSpringExtension.kt#L20

    if (isNotErrorPath && ((hasNoResponseBodyAnnotation && hasNoRestControllerAnnotation) || this.value.method.hasNoReturnType())) {
        return emptySet()
    }

Potential solution

Off the top of my mind, this might fix the problem:

    val isNotErrorPath = !this.key.patternsCondition.patterns.contains("/error")
    val hasNoResponseBodyAnnotation = !this.value.providesResponseBodyAnnotation()
    val hasNoRestControllerAnnotation = !this.value.providesRestControllerAnnotation()
    val hasHttpServletResponseParam = this.value.hasHttpServletResponseParam()

    if (isNotErrorPath && (hasNoResponseBodyAnnotation && hasNoRestControllerAnnotation)) {
        return emptySet()
    }

    if (isNotErrorPath && (this.value.method.hasNoReturnType() && !hasHttpServletResponseParam)) {
        return emptySet()
    }

    // ...

    private fun HandlerMethod.hasHttpServletResponseParam() = this.methodParameters
        .any { it.parameterType.isAssignableFrom(HttpServletResponse::class.java) }

[lmller]

Hey, thanks for reaching out! If you like, you can provide a PR (with unit tests) :-) . Otherwise, I'll take a look at it some time later.