MultipartGraphQlHttpHandler.readMultipartFiles throws java.lang.IllegalArgumentException

[assens]

When trying to test the file upload form spring boot test, with mock mvc web environment, and having spring security in place, the MultipartGraphQlHttpHandler's method readMultipartFiles throws illegal argument exception.

The assertion is does not allow for wrapped HttpServletRequests to pass.

Assert.isInstanceOf(MultipartHttpServletRequest.class, httpServletRequest,
            "Request should be of type MultipartHttpServletRequest");

When having spring security in the filter chain, the httpServletRequest is of instance SecurityContextHolderAwareRequestWrapper. Instead of using this strict assertion, one could use

WebUtils.getNativeRequest(httpServletRequest, MultipartHttpServletRequest.class);

to obtain the instance of the wrapped MultipartHttpServletRequest.

I'll provide a pull request with a fix. This is just to keep track on the issue.
Below is my unit test, that can be used to reproduce the exception:

 @Test
  void testWithMockMvc() throws Exception {

    // arrange
    final var fileName = "fileName.xlsx";
    final var fileByteArray = new byte[100];

    final var operations = """
        { "query" : "mutation FileUpload($file: Upload!) { uploadFile(file: $file) { fileName size } }" }
        """;

    final var variables = """
        { "file" : ["variables.file"] }
        """;

    final var filePart = new MockMultipartFile("file", fileName, "application/octet-stream", fileByteArray);
    final var operationsPart = new MockPart("operations", operations.getBytes());
    final var variablesPart = new MockPart("map", variables.getBytes());

    // act & assert
    final var asyncMvcResult = mockMvc.perform(MockMvcRequestBuilders
        .multipart("/graphql")
        .file(filePart)
        .part(operationsPart)
        .part(variablesPart)
        .accept(MediaType.APPLICATION_GRAPHQL_RESPONSE_VALUE)
        .with(SecurityMockMvcRequestPostProcessors.jwt().authorities(new SimpleGrantedAuthority("ADMIN"))))
        .andReturn();

    mockMvc.perform(asyncDispatch(asyncMvcResult))
        .andDo(print())
        .andExpect(status().isOk())
        .andExpect(jsonPath("$.data.uploadFile.fileName").value(fileName));

  }