register_routes() plugin hook (#819)

Fixes #215

datasette/app.py

@@ -39,6 +39,7 @@ from .renderer import json_renderer
 from .database import Database, QueryInterrupted
 
 from .utils import (
+    async_call_with_supported_arguments,
     escape_css_string,
     escape_sqlite,
     format_bytes,
@@ -783,6 +784,10 @@ class Datasette:
         "Returns an ASGI app function that serves the whole of Datasette"
         routes = []
 
+        for routes_to_add in pm.hook.register_routes():
+            for regex, view_fn in routes_to_add:
+                routes.append((regex, wrap_view(view_fn, self)))
+
         def add_route(view, regex):
             routes.append((regex, view))
 
@@ -1048,3 +1053,19 @@ def _cleaner_task_str(task):
     # running at /Users/simonw/Dropbox/Development/datasette/venv-3.7.5/lib/python3.7/site-packages/uvicorn/main.py:361>
     # Clean up everything up to and including site-packages
     return _cleaner_task_str_re.sub("", s)
+
+
+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)
+
+    return asgi_view_fn

datasette/hookspecs.py

@@ -60,6 +60,11 @@ def register_facet_classes():
     "Register Facet subclasses"
 
 
+@hookspec
+def register_routes():
+    "Register URL routes: return a list of (regex, view_function) pairs"
+
+
 @hookspec
 def actor_from_request(datasette, request):
     "Return an actor dictionary based on the incoming request"

datasette/utils/__init__.py

@@ -842,7 +842,7 @@ def parse_metadata(content):
             raise BadMetadataError("Metadata is not valid JSON or YAML")
 
 
-def call_with_supported_arguments(fn, **kwargs):
+def _gather_arguments(fn, kwargs):
     parameters = inspect.signature(fn).parameters.keys()
     call_with = []
     for parameter in parameters:
@@ -853,9 +853,19 @@ def call_with_supported_arguments(fn, **kwargs):
                 )
             )
         call_with.append(kwargs[parameter])
+    return call_with
+
+
+def call_with_supported_arguments(fn, **kwargs):
+    call_with = _gather_arguments(fn, kwargs)
     return fn(*call_with)
 
 
+async def async_call_with_supported_arguments(fn, **kwargs):
+    call_with = _gather_arguments(fn, kwargs)
+    return await fn(*call_with)
+
+
 def actor_matches_allow(actor, allow):
     actor = actor or {}
     if allow is None:

datasette/utils/asgi.py

@@ -399,7 +399,7 @@ class Response:
     @classmethod
     def text(cls, body, status=200, headers=None):
         return cls(
-            body,
+            str(body),
             status=status,
             headers=headers,
             content_type="text/plain; charset=utf-8",