Handling missing mime types gracefully #534

If a key isn't present in the mime_types map, an exception is thrown. This is because mime_types.at() is used at, e.g.,

I propose that the resolution is to search for the provided mime_type within the map using mime_types.find. If it is not found, a warning should be logged, but the content should still be delivered using the following logic:

• Does the provided type look like a MIME type already? I.e. is it one of the IANA-registered types (application, audio, example, font, image, model, text, video), followed by a slash, followed by text? If so, send that verbatim.

• Otherwise send text/plain.

Although this approach isn't quite as lightweight as simply sending text/plain, there are some benefits:

• I'd be able, for example, to send content as text/csv without modifying the mime types map.
• It would also allow people to use the full mime-type format, including parameters (e.g. text/plain;charset=UTF-8)
• Developers coming from other technologies that use full mime types won't be faced with an internal server error for following an old habit.