Fixed URLRouter root_path handling. (#1954)

* Add tests for handling root_path in URLRouting
* Handle root_path in URLRouter

If we have a scope["root_path"], raise if it does not prefix
scope["path"], and strip it from scope["path"] if it does. Do this
only if we're in an outermost URLRouter.

Signed-off-by: Alejandro R. Sedeño <asedeno@mit.edu>
Signed-off-by: Alejandro R Sedeño <asedeno@google.com>

channels/routing.py

@@ -107,6 +107,15 @@ async def __call__(self, scope, receive, send):
         path = scope.get("path_remaining", scope.get("path", None))
         if path is None:
             raise ValueError("No 'path' key in connection scope, cannot route URLs")
+
+        if "path_remaining" not in scope:
+            # We are the outermost URLRouter, so handle root_path if present.
+            root_path = scope.get("root_path", "")
+            if root_path and not path.startswith(root_path):
+                # If root_path is present, path must start with it.
+                raise ValueError("No route found for path %r." % path)
+            path = path[len(root_path) :]
+
         # Remove leading / to match Django's handling
         path = path.lstrip("/")
         # Run through the routes we have until one matches

tests/test_routing.py

@@ -107,6 +107,23 @@ async def test_url_router():
         "args": tuple(),
         "kwargs": {"default": 42},
     }
+    # Valid root_path in scope
+    assert (
+        await router(
+            {"type": "http", "path": "/root/", "root_path": "/root"}, None, None
+        )
+        == 1
+    )
+    assert (
+        await router(
+            {"type": "http", "path": "/root/foo/", "root_path": "/root"}, None, None
+        )
+        == 2
+    )
+
+    # Unmatched root_path in scope
+    with pytest.raises(ValueError):
+        await router({"type": "http", "path": "/", "root_path": "/root"}, None, None)
 
     # Invalid matches
     with pytest.raises(ValueError):
@@ -261,6 +278,29 @@ async def test_path_remaining():
         == 2
     )
 
+    assert (
+        await outermost_router(
+            {"type": "http", "path": "/root/prefix/stuff/", "root_path": "/root"},
+            None,
+            None,
+        )
+        == 2
+    )
+
+    with pytest.raises(ValueError):
+        await outermost_router(
+            {"type": "http", "path": "/root/root/prefix/stuff/", "root_path": "/root"},
+            None,
+            None,
+        )
+
+    with pytest.raises(ValueError):
+        await outermost_router(
+            {"type": "http", "path": "/root/prefix/root/stuff/", "root_path": "/root"},
+            None,
+            None,
+        )
+
 
 def test_invalid_routes():
     """