Capitalizing Response Header Names

Falcon always renders WSGI response header names in lower case; see also: Why is Falcon changing my header names to lowercase?

While this should normally never be an issue for standards-conformant HTTP clients, it is possible to override HTTP headers using generic WSGI middleware:

class CustomHeadersMiddleware:

    def __init__(self, app, title_case=True, custom_capitalization=None):
        self._app = app
        self._title_case = title_case
        self._capitalization = custom_capitalization or {}

    def __call__(self, environ, start_response):
        def start_response_wrapper(status, response_headers, exc_info=None):
            if self._title_case:
                headers = [
                    (self._capitalization.get(name, name.title()), value)
                    for name, value in response_headers]
            else:
                headers = [
                    (self._capitalization.get(name, name), value)
                    for name, value in response_headers]
            start_response(status, headers, exc_info)

        return self._app(environ, start_response_wrapper)

We can now use this middleware to wrap a Falcon app:

import falcon

# Import or define CustomHeadersMiddleware from the above snippet...


class FunkyResource:

    def on_get(self, req, resp):
        resp.set_header('X-Funky-Header', 'test')
        resp.media = {'message': 'Hello'}


app = falcon.App()
app.add_route('/test', FunkyResource())

app = CustomHeadersMiddleware(
    app,
    custom_capitalization={'x-funky-header': 'X-FuNkY-HeADeR'},
)

As a bonus, this recipe applies to non-Falcon WSGI applications too.