request.post_vars() method obliterates form keys with multiple values

[simonw]

datasette/datasette/utils/asgi.py

Lines 137 to 139 in 452a587

	async def post_vars(self):
	body = await self.post_body()
	return dict(parse_qsl(body.decode("utf-8"), keep_blank_values=True))

In GET requests you can do ?foo=1&foo=2 - you can do the same in POST requests, but the dict() call here eliminates those duplicates.

You can't even try calling post_body() and implement your own custom parsing because of:

• request.post_body() can only be called once #2204

[simonw]

I found this problem while trying to use WTForms with this pattern:

choices = [(col, col) for col in await db.table_columns(table)]

class ConfigForm(Form):
    template = TextAreaField("Template")
    api_token = PasswordField("OpenAI API token")
    columns = MultiCheckboxField('Columns', choices=choices)

[simonw]

It should return a MultiParams:

datasette/datasette/utils/__init__.py

Lines 900 to 917 in 452a587

	class MultiParams:
	def __init__(self, data):
	# data is a dictionary of key => [list, of, values] or a list of [["key", "value"]] pairs
	if isinstance(data, dict):
	for key in data:
	assert isinstance(
	data[key], (list, tuple)
	), "dictionary data should be a dictionary of key => [list]"
	self._data = data
	elif isinstance(data, list) or isinstance(data, tuple):
	new_data = {}
	for item in data:
	assert (
	isinstance(item, (list, tuple)) and len(item) == 2
	), "list data should be a list of [key, value] pairs"
	key, value = item
	new_data.setdefault(key, []).append(value)
	self._data = new_data

Change needs to be made before 1.0.

return MultiParams(urllib.parse.parse_qs(body.decode("utf-8")))

Need to remember why I was using keep_blank_values=True there and check that using MultiParams doesn't conflict with that reason.

[simonw]

That keep_blank_values=True is from 0934844

Commit message:

request.post_vars() no longer discards empty values

Relevant test:

datasette/tests/test_internals_request.py

Lines 19 to 27 in 452a587

	async def receive():
	return {
	"type": "http.request",
	"body": b"foo=bar&baz=1&empty=",
	"more_body": False,
	}
	request = Request(scope, receive)
	assert {"foo": "bar", "baz": "1", "empty": ""} == await request.post_vars()