From eeb58a09eee49c12eb6f524d10ab9ef7c3904cf4 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Mon, 7 Mar 2022 08:01:03 -0800
Subject: [PATCH] Redirect old % URLs to new - encoded URLs, closes #1650

Refs #1439
---
 datasette/app.py   | 7 +++++++
 tests/test_html.py | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/datasette/app.py b/datasette/app.py
index 8c5480cf56..2907d90eaa 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -1211,6 +1211,13 @@ async def route_path(self, scope, receive, send, path):
         return await self.handle_404(request, send)
 
     async def handle_404(self, request, send, exception=None):
+        # If path contains % encoding, redirect to dash encoding
+        if "%" in request.path:
+            # Try the same path but with "%" replaced by "-"
+            # and "-" replaced with "-2D"
+            new_path = request.path.replace("-", "-2D").replace("%", "-")
+            await asgi_send_redirect(send, new_path)
+            return
         # If URL has a trailing slash, redirect to URL without it
         path = request.scope.get(
             "raw_path", request.scope["path"].encode("utf8")
diff --git a/tests/test_html.py b/tests/test_html.py
index b4a12b8a61..3e24009eae 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -952,3 +952,9 @@ def test_no_alternate_url_json(app_client, path):
     assert (
         '<link rel="alternate" type="application/json+datasette"' not in response.text
     )
+
+
+def test_redirect_percent_encoding_to_dash_encoding(app_client):
+    response = app_client.get("/fivethirtyeight/twitter-ratio%2Fsenators")
+    assert response.status == 302
+    assert response.headers["location"] == "/fivethirtyeight/twitter-2Dratio-2Fsenators"