Partinfo field "partFileName" is a Maybe, but is never Nothing?

[ghost]

When you submit a form that contains a file input element, and have not selected a file, you get a PartInfo containing: partFileName = Just "" instead of Nothing.

[dbp]

I just ran into this, and it seems very wrong... This issue has obviously been open for a while - is there a specific design reason for this, or is it a bug (that should be fixed)?

[gregorycollins]

It's probably a bug -- please send a minimal server exhibiting the problem along with instructions for reproduction.

[dbp]

@gregorycollins Here's a repository containing a server that exhibits the problem:

https://github.com/dbp/snap-upload-blank-example

To reproduce, build and run the server, then visit the index, and hit submit without setting a file. It will print, to the console:

PartInfo {partFieldName = "f", partFileName = Just "", partContentType = "application/octet-stream"}

Which I believe should instead be:

PartInfo {partFieldName = "f", partFileName = Nothing, partContentType = "application/octet-stream"}

[emhoracek]

I think this is fixed in Digestive Functors since https://github.com/jaspervdj/digestive-functors/pull/125/files (0.8.1.0), in that they changed the type from a Maybe to a list in order to support multiple file upload.

[mightybyte]

@emhoracek Sorry I missed your comment until just now. Are you saying that the issue is gone and we should close this ticket, or just that digestive-functors worked around it and it's less important?

[emhoracek]

@mightybyte I found this issue while debugging a problem with Fn and just wanted to share what I found for any other googlers. If Snap is using the latest digestive functors it should be fixed, but I haven't actually tried it.

[mightybyte]

@emhoracek Ok, thanks. It sounds like this might still be considered a bug in snap-core or potentially snap-server, so I'll leave this open for now.

[k0001]

I just encountered this issue.

This is what Firefox sends:

-----------------------------8290905687149505892030108654
Content-Disposition: form-data; name="file"; filename=""
Content-Type: application/octet-stream

I don't think the difference between Nothing and Just "" is relevant here: They both signify a lack of filename. I think having partFileName :: ByteString rather than partFileName :: Maybe ByteString would be better.

[gregorycollins]

Should we treat filename="" as Nothing instead of Just ""? It's a major version bump but I agree that current behavior violates principle of least surprise

[gregorycollins]

...and P.S. I'd prefer this to changing the type, since a correct user program will probably not be broken by that change.