No originalFilename in MockMultipartFile now leads to add it just as part

[markusheiden]

When using MockMultipartFile with an empty originalFilename (""), it now gets added to multi part requests just as a part, not as a file. When migrating from Spring Boot 2.3 to 2.4.1, this made my MockMvc test fail for a controller using a @RequestPart MultipartFile parameter causing a longer debugging session :-) It would be nice, if there had been a check (exception), that empty originalFilenames are no longer supported for MockMultipartFiles.

If the nullability of the originalFilename in MultipartFile is intended, org.springframework.web.multipart.support.StandardMultipartHttpServletRequest#parseRequest seems to be broken as it recognizes parts without filename not as files, so that they don't match MultipartFile parameters.

[jhoeller]

This seems to be a consequence of #25602. I'll revisit the assertions in MockMultipartFile, we should indeed reject empty filenames there then. It's just not entirely clear to me yet where specifically we're evaluating MockMultipartFile-specified empty original filenames to plain parts...

[rstoyanchev]

This is likely impacted by the more recent change in #26166. There is also a separate new report https://github.com/spring-projects/spring-boot/issues/24483.

[jhoeller]

Good catch, @rstoyanchev - so that effect seems to come from the intermediate MockPart handling since there is filename differentiation being made for Part (but not for MultipartFile which is always clearly a file, never a parameter). I guess this is to be treated as a regression then...