Port Datasette from Sanic to ASGI + Uvicorn (#518)

Datasette now uses ASGI internally, and no longer depends on Sanic.

It now uses Uvicorn as the underlying HTTP server.

This was thirteen months in the making... for full details see the issue:

https://github.com/simonw/datasette/issues/272

And for a full sequence of commits plus commentary, see the pull request:

https://github.com/simonw/datasette/pull/518

tests/fixtures.py

@@ -1,5 +1,7 @@
 from datasette.app import Datasette
 from datasette.utils import sqlite3
+from asgiref.testing import ApplicationCommunicator
+from asgiref.sync import async_to_sync
 import itertools
 import json
 import os
@@ -10,16 +12,82 @@ import sys
 import string
 import tempfile
 import time
+from urllib.parse import unquote
+
+
+class TestResponse:
+    def __init__(self, status, headers, body):
+        self.status = status
+        self.headers = headers
+        self.body = body
+
+    @property
+    def json(self):
+        return json.loads(self.text)
+
+    @property
+    def text(self):
+        return self.body.decode("utf8")
 
 
 class TestClient:
-    def __init__(self, sanic_test_client):
-        self.sanic_test_client = sanic_test_client
+    max_redirects = 5
 
-    def get(self, path, allow_redirects=True):
-        return self.sanic_test_client.get(
-            path, allow_redirects=allow_redirects, gather_request=False
+    def __init__(self, asgi_app):
+        self.asgi_app = asgi_app
+
+    @async_to_sync
+    async def get(self, path, allow_redirects=True, redirect_count=0, method="GET"):
+        return await self._get(path, allow_redirects, redirect_count, method)
+
+    async def _get(self, path, allow_redirects=True, redirect_count=0, method="GET"):
+        query_string = b""
+        if "?" in path:
+            path, _, query_string = path.partition("?")
+            query_string = query_string.encode("utf8")
+        instance = ApplicationCommunicator(
+            self.asgi_app,
+            {
+                "type": "http",
+                "http_version": "1.0",
+                "method": method,
+                "path": unquote(path),
+                "raw_path": path.encode("ascii"),
+                "query_string": query_string,
+                "headers": [[b"host", b"localhost"]],
+            },
         )
+        await instance.send_input({"type": "http.request"})
+        # First message back should be response.start with headers and status
+        messages = []
+        start = await instance.receive_output(2)
+        messages.append(start)
+        assert start["type"] == "http.response.start"
+        headers = dict(
+            [(k.decode("utf8"), v.decode("utf8")) for k, v in start["headers"]]
+        )
+        status = start["status"]
+        # Now loop until we run out of response.body
+        body = b""
+        while True:
+            message = await instance.receive_output(2)
+            messages.append(message)
+            assert message["type"] == "http.response.body"
+            body += message["body"]
+            if not message.get("more_body"):
+                break
+        response = TestResponse(status, headers, body)
+        if allow_redirects and response.status in (301, 302):
+            assert (
+                redirect_count < self.max_redirects
+            ), "Redirected {} times, max_redirects={}".format(
+                redirect_count, self.max_redirects
+            )
+            location = response.headers["Location"]
+            return await self._get(
+                location, allow_redirects=True, redirect_count=redirect_count + 1
+            )
+        return response
 
 
 def make_app_client(
@@ -32,6 +100,7 @@ def make_app_client(
     is_immutable=False,
     extra_databases=None,
     inspect_data=None,
+    static_mounts=None,
 ):
     with tempfile.TemporaryDirectory() as tmpdir:
         filepath = os.path.join(tmpdir, filename)
@@ -73,9 +142,10 @@ def make_app_client(
             plugins_dir=plugins_dir,
             config=config,
             inspect_data=inspect_data,
+            static_mounts=static_mounts,
         )
         ds.sqlite_functions.append(("sleep", 1, lambda n: time.sleep(float(n))))
-        client = TestClient(ds.app().test_client)
+        client = TestClient(ds.app())
         client.ds = ds
         yield client
 
@@ -88,7 +158,7 @@ def app_client():
 @pytest.fixture(scope="session")
 def app_client_no_files():
     ds = Datasette([])
-    client = TestClient(ds.app().test_client)
+    client = TestClient(ds.app())
     client.ds = ds
     yield client