404's should display an error page and not redirect

[brassy-endomorph]

Is your feature request related to a problem? Please describe.

When a user access a resource that isn't found (not authorized, missing, whatever), they should land on an actual missing page that displays a generic "not found" error message whose status code is 404. No flashed message should be displayed.

Why?

We have some non-standard code that has already led me to confusion as to why abort(404) (a typical pattern) wasn't working as expected.

Affected endpoint:

hushline/hushline/routes.py

Lines 553 to 562 in 4552cb0

	@app.route("/info")
	def personal_server_info() -> Response:
	if app.config.get("IS_PERSONAL_SERVER"):
	ip_address = get_ip_address()
	return make_response(
	render_template(
	"personal_server_info.html", is_personal_server=True, ip_address=ip_address
	)
	)
	return Response(status=404)

Affected error handler:

hushline/hushline/__init__.py

Lines 95 to 98 in 4552cb0

	@app.errorhandler(404)
	def page_not_found(e: Exception) -> Response:
	flash("⛓️‍💥 That page doesn't exist.", "warning")
	return redirect(url_for("index"))

Also, this will make it possible for tests to check that a missing/unauthorized entity actually returns 404 (a clear sign of missing) instead of redirects to / and then doesn't have some heading (User 123) present in the response body.