Experimental path_from_header feature, refs #712

datasette/app.py

@@ -136,6 +136,7 @@ CONFIG_OPTIONS = (
         "Allow display of template debug information with ?_context=1",
     ),
     ConfigOption("base_url", "/", "Datasette URLs should use this base"),
+    ConfigOption("path_from_header", "", "HTTP header to override incoming path"),
 )
 
 DEFAULT_CONFIG = {option.name: option.default for option in CONFIG_OPTIONS}
@@ -739,6 +740,16 @@ class DatasetteRouter(AsgiRouter):
         self.ds = datasette
         super().__init__(routes)
 
+    async def __call__(self, scope, receive, send):
+        path_from_header = self.ds.config("path_from_header")
+        path = scope["path"]
+        raw_path = scope.get("raw_path")
+        if path_from_header:
+            raw_path = dict(scope["headers"])[path_from_header.encode("utf8")]
+        if raw_path:
+            path = raw_path.decode("ascii")
+        return await self.route_path(scope, receive, send, path)
+
     async def route_path(self, scope, receive, send, path):
         # Strip off base_url if present before routing
         base_url = self.ds.config("base_url")

docs/config.rst

@@ -241,3 +241,10 @@ For example, if you are sending traffic from ``https://www.example.com/tools/dat
 You can do that like so::
 
     datasette mydatabase.db --config base_url:/tools/datasette/
+
+.. _path_from_header:
+
+path_from_header
+----------------
+
+See `issue #712 <https://github.com/simonw/datasette/issues/712>`__.

tests/test_api.py

@@ -1308,6 +1308,7 @@ def test_config_json(app_client):
         "hash_urls": False,
         "template_debug": False,
         "base_url": "/",
+        "path_from_header": "",
     } == response.json