set charset in shareddatamiddleware

[bastidest]

Description

UTF-8 Javascript files served by the SharedDataMiddleware do not contain a charset in the Content-Type response header. This leads to issues of javascript interpreted as US-ASCII by browsers (posativ/isso#607).

Current

Content-Type: application/javascript

Expected

Content-Type: application/javascript; charset=UTF-8

The mime type is deducted by using python's mimetypes module and the filename:

werkzeug/src/werkzeug/middleware/shared_data.py

Lines 256 to 257 in aa9676f

	guessed_type = mimetypes.guess_type(real_filename)
	mime_type = guessed_type[0] or self.fallback_mimetype

It is sent without appending an encoding:

werkzeug/src/werkzeug/middleware/shared_data.py

Line 281 in aa9676f

("Content-Type", mime_type),

Other usages seem to suggest that a call to get_content_type is necessary to append the charset, if applicable:

werkzeug/src/werkzeug/wrappers/common_descriptors.py

Line 146 in e76aac8

self.headers["Content-Type"] = get_content_type(value, self.charset)

Possible solutions

I am not familiar with the codebase, but would it be possible to call get_content_type? I tried to modify it myself, but I don't know where to get the encoding from inside SharedDataMiddleware.

My problem is solved when I hardcode 'utf-8' as charset:

("Content-Type", get_content_type(mime_type, 'utf-8'))