Add file submission to problem page

[alexwaeseperlman]

• Changed the button labelled "Submit!" on the problem page to say "Go to editor"
• Added a small form beneath the "Go to editor" button, initially hidden behind a chevron, that allows users to submit a file. I tried to make the changes as unobtrusive as possible.

Notes:

• The file submission form goes to /problem/<problem-code>/submit, which means that error messages, for example when submitting a file with length greater than 65535, show up in the editor. This isn't amazing UX but it might be acceptable.
• It might be worth adding a button to submit files from the editor page
• If a user selects a file and then clicks "Go to editor", should it load that file into their editor?

[ehhthing]

Perhaps it would be be much less code if this was just implemented client side with JS so there would be no need for any kind of server code changes.

[alexwaeseperlman]

I added 16 lines of server side code. It's possible that using client side JS would take less but it won't be a huge difference. Unless there is a better reason to switch I think we can leave things as they are.

[ehhthing]

I added 16 lines of server side code. It's possible that using client side JS would take less but it won't be a huge difference. Unless there is a better reason to switch I think we can leave things as they are.

The main issue is that handling file uploads on the server side is much more prone to issues than simply using a text field.

For example, your code is vulnerable to memory DoS attacks if the user uploads a very large file composed of only 0s since it decodes line-by-line. In addition, it would cause a 500 if you were to upload a file that included invalid UTF-8 because it tries to decode without a try-except.

Typically, Django does most of the validation work for you if you use a normal text field, but it provides much less built in protection against these bugs if you want to handle file uploads.

Moving the processing to the client side significantly reduces the bug surface simply because handling file uploads on the server side is nontrivial.

[alexwaeseperlman]

The main issue is that handling file uploads on the server side is much more prone to issues than simply using a text field.

I removed all modifications to server side code. Thanks for looking at this.

Just a general comment: I think we should move this to the Submit Solution page rather than at the bottom of the problem statement page. This centralizes the location where a user can submit a solution.

In my opinion the main benefit of this feature is that it creates a shortcut for submitting from the problem page. I'm open to moving it around though.

Here are some screenshots of the "Submit solution"/"Go to editor" button in case anyone wants to look at the changes without setting them up:

Old:

New with dropdown closed:

New with dropdown open: