Support file input in form

[hezhenxing]

Please support file input type in form. There is no File type in InputType, and manually adding an input filed of file type does not get the value set in formData.

[seanhess]

Anyone have thoughts on how should we design the interface to this? It's quite different than an InputType: it will upload the file to a temporary location on the server somewhere. We could require the use of WAI middleware, but it might make sense to configure it directly using liveAppWith in the ServerOptions.

[seanhess]

Draft Design: Submit all forms via fetch() instead of the socket. The WAI endpoint is still working on the backend. Use Network.Wai.Parse.parseRequestBodyEx to handle uploads.

(Network.Wai.Parser puts files into memory by default, which allows us to avoid many security issues from automatically storing files. We are still vulnerable to memory-based denial of service attacks)

• Submit all forms via fetch() instead of socket
• Refactor WAI body parsing to use Network.Wai.parser.parseRequestBodyEx
• Allow configuration of backend and file upload limits via ServerOptions. Or perhaps the entire parser? "Serious" apps need a way to control this
• Needs to be configurable to handle large files that don't fit in memory? Maybe you have no business uploading files that big via HTTP :)