startup() plugin hook

[simonw]

It might be useful to have an startup hook which gets passed the datasette object as soon as Datasette has finished initializing.

My initial use-case for this is configuration verification - checking that the "plugins" configuration block for this plugin contains valid details.

I imagine there are plenty of other potential uses for this as well.

[simonw]

Another use-case for this: I want to use the --root option on Glitch but it gives me a 127.0.0.1 URL. Glitch has a PROJECT_DOMAIN environment variable which tells me the URL. A datasette-glitch plugin could use a startup hook to output the correct login URL.

[simonw]

This should be able to optionally return an async function which is then awaited.

[simonw]

Another use-case: plugins that need their own database with the correct tables. They can write to the database on startup to create their tables.

[simonw]

Implementing this is proving surprisingly tricky, because of the need to be able to optionally await the returned value. It's a bit of a fiddle to get this to work within unit tests because they run in non-async functions - due to this cunning async_to_sync usage in the test client:

datasette/tests/fixtures.py

Lines 115 to 133 in b906030

	@async_to_sync
	async def get(
	self, path, allow_redirects=True, redirect_count=0, method="GET", cookies=None
	):
	return await self._request(
	path, allow_redirects, redirect_count, method, cookies
	)
	@async_to_sync
	async def post(
	self,
	path,
	post_data=None,
	allow_redirects=True,
	redirect_count=0,
	content_type="application/x-www-form-urlencoded",
	cookies=None,
	csrftoken_from=None,
	):

I could switch to using async def test_* functions decorated with @pytest.mark.asyncio but I'd rather not re-engineer the entire test suite just for this one feature, so I'll try to find another way.

[simonw]

Documentation: https://datasette.readthedocs.io/en/latest/plugin_hooks.html#startup-datasette