Support Multiple Files for One Form Field in multipart/form-data

[dschulten]

Affects Version(s): 5.1.3

---

Bug

The multipart/form-data RFC states:

multiple files MUST be sent
by supplying each file in a separate part but all with the same
"name" parameter

However, when I send a multipart message with three parts named data, only one makes it into the message.

Sample request (with Intellij's http client)

### Send a form with the text and file fields
POST http://localhost:8091/conversion
Content-Type: multipart/form-data; boundary=WebAppBoundary

--WebAppBoundary
Content-Disposition: form-data; name="data"; filename="data.tiff"
Content-Type: image/tiff

< ../resources/inputSamples/data.tiff
--WebAppBoundary
Content-Disposition: form-data; name="data"; filename="data2.tiff"
Content-Type: image/tiff

< ../resources/inputSamples/data2.tiff
--WebAppBoundary
Content-Disposition: form-data; name="data"; filename="data3.tiff"
Content-Type: image/tiff

< ../resources/inputSamples/data3.tiff
--WebAppBoundary--

The reason is that MultipartAwareFormHttpMessageConverter#readMultipart uses multipartRequest.getFileMap()to access the files:

private MultiValueMap<String, ?> readMultipart(MultipartHttpInputMessage multipartRequest) throws IOException {
	MultiValueMap<String, Object> resultMap = new LinkedMultiValueMap<String, Object>();
	Map<?, ?> parameterMap = multipartRequest.getParameterMap();
	for (Entry<?, ?> entry : parameterMap.entrySet()) {
		resultMap.add((String) entry.getKey(), entry.getValue());
	}
	for (Map.Entry<String, MultipartFile> entry : multipartRequest
            .getFileMap().entrySet()) { //                               <== problematic
		MultipartFile multipartFile = entry.getValue();
		if (multipartFile.isEmpty()) {
			continue;
		}
		resultMap.add(entry.getKey(), this.multipartFileReader.readMultipartFile(multipartFile));
	}
	return resultMap;
}

which ultimately comes to AbstractMutlipartHttpServletRequest:

public Map<String, MultipartFile> getFileMap() {
    return getMultipartFiles().toSingleValueMap();
}

Here it loses all but the first files.

Possible solution: Use MultipartHttpInputMessage#getMultiFileMap instead of getFileMap. I suggest to treat this as a bug because it really seems that getFileMap was used inadvertently.

Workaround: use different names for all multipart files (pretty ugly, though).

[dschulten]

👍