datasette.add_message() doesn't work inside plugins

[simonw]

Similar problem to #863 - calling datasette.add_message() in a view registered using the register_routes() plugin hook doesn't work, because the code that writes accumulated messages to the ds_messages signed cookie lives in the BaseView class here:

datasette/datasette/views/base.py

Lines 94 to 97 in 28bb1c5

	response = await super().dispatch_request(request, *args, **kwargs)
	if self.ds:
	self.ds._write_messages_to_response(request, response)
	return response

[simonw]

Urgh, fixing this is going to be a bit of a pain.

Here's where I added that custom dispatch_request() method - it was to implement flash messaging in #790: https://github.com/simonw/datasette/blame/1a5b7d318fa923edfcefd3df8f64dae2e9c49d3f/datasette/views/base.py#L85

If I want this to be made available to register_routes() views as well, I'm going to have to move the logic somewhere else. In particular I need to make sure that the request object is created once and used throughout the whole request cycle.

Currently register_routes() view functions get their own separate request object which is created here:

datasette/datasette/app.py

Lines 1057 to 1068 in 1a5b7d3

	def wrap_view(view_fn, datasette):
	async def asgi_view_fn(scope, receive, send):
	response = await async_call_with_supported_arguments(
	view_fn,
	scope=scope,
	receive=receive,
	send=send,
	request=Request(scope, receive),
	datasette=datasette,
	)
	if response is not None:
	await response.asgi_send(send)

So I'm going to have to refactor this quite a bit to get that shared request object which can be passed both to register_routes views and to my various BaseView subclasses.

[simonw]

The ideal fix here would be to rework my BaseView subclass mechanism to work with register_routes() so that those views don't have any special privileges above plugin-provided views.

[simonw]

I've made enough progress on this to be able to solve the messages issue in #864. I may still complete this overall goal (registering internal views with register_routes()) as part of Datasette 0.45 but it would be OK if it slipped to a later release.
#870 (comment)

[simonw]

Re-opening: plugins may get to set messages but they don't display them, even if they render a template that extends base.html. For example, this code in a plugin:

        return Response.html(
            await datasette.render_template(
                "write.html",
                {"databases": databases, "sql": request.args.get("sql") or ""},
                request=request,
            )
        )

This won't display messages. The reason is that the messages are made available to the template context in the BaseView.render() method here:

datasette/datasette/views/base.py

Lines 87 to 95 in 7ac4936

	async def render(self, templates, request, context=None):
	context = context or {}
	template = self.ds.jinja_env.select_template(templates)
	template_context = {
	**context,
	**{
	"database_url": self.database_url,
	"database_color": self.database_color,
	"show_messages": lambda: self.ds._show_messages(request),

[simonw]

I think the fix is to move the "show_messages" variable to here:

datasette/datasette/app.py

Lines 735 to 748 in 7ac4936

	template_context = {
	**context,
	**{
	"app_css_hash": self.app_css_hash(),
	"zip": zip,
	"body_scripts": body_scripts,
	"format_bytes": format_bytes,
	"extra_css_urls": self._asset_urls("extra_css_urls", template, context),
	"extra_js_urls": self._asset_urls("extra_js_urls", template, context),
	"base_url": self.config("base_url"),
	"csrftoken": request.scope["csrftoken"] if request else lambda: "",
	},
	**extra_template_vars,
	}

[simonw]

To test this I'll need a plugin test that renders a custom template. Here's an example I can imitate:

datasette/tests/test_plugins.py

Lines 588 to 596 in 7ac4936

	def test_register_routes_csrftoken(restore_working_directory, tmpdir_factory):
	templates = tmpdir_factory.mktemp("templates")
	(templates / "csrftoken_form.html").write_text(
	"CSRFTOKEN: {{ csrftoken() }}", "utf-8"
	)
	with make_app_client(template_dir=templates) as client:
	response = client.get("/csrftoken-form/")
	expected_token = client.ds._last_request.scope["csrftoken"]()
	assert "CSRFTOKEN: {}".format(expected_token) == response.text