We make a REST call (POST) where we build the request as form data, to submit a survey (a specialization of System.FileDocument). This goes without problems in Mendix 8.5.0. However, the functionality broke in 8.6. The error is: Failed to parse multipart servlet request the request was rejected because no multipart boundary was found The REST call has stayed broken till 8.8 (tested it yesterday). Mendix support is aware of the issue (ticket 96483), but says that "considering the complexity of the issue, it is unlikely that the fix will be released with Mendix 8.9". What could be a workaround to fix the problem and still convert to 8.8? Can we add the multipart boundary manually?
A workaround could be that you send the file as Base64 encoded string instead of multipart request.
I also have issues with multipart/form-data when sending a FileDocument in Mendix 8.7.
When the server is receiving the Content-Type header, it is not able to parse the boundary. It looks like Mendix puts an extra line break in the boundary and therefore malform the header.
I reported an issue with Mendix two weeks ago (#98364), there is no solution yet.
EDIT: Mendix reported that they’re fixing this in 8.9.