Correctly escape output of ?_trace, refs #1360

datasette/tracer.py

@@ -1,5 +1,6 @@
 import asyncio
 from contextlib import contextmanager
+from markupsafe import escape
 import time
 import json
 import traceback
@@ -123,7 +124,7 @@ async def wrapped_send(message):
                 except IndexError:
                     content_type = ""
                 if "text/html" in content_type and b"</body>" in accumulated_body:
-                    extra = json.dumps(trace_info, indent=2)
+                    extra = escape(json.dumps(trace_info, indent=2))
                     extra_html = f"<pre>{extra}</pre></body>".encode("utf8")
                     accumulated_body = accumulated_body.replace(b"</body>", extra_html)
                 elif "json" in content_type and accumulated_body.startswith(b"{"):

tests/test_html.py

@@ -1612,3 +1612,9 @@ def test_navigation_menu_links(
             assert (
                 details.find("a", {"href": link}) is None
             ), f"{link} found but should not have been in nav menu"
+
+
+def test_trace_correctly_escaped(app_client):
+    response = app_client.get("/fixtures?sql=select+'<h1>Hello'&_trace=1")
+    assert "select '<h1>Hello" not in response.text
+    assert "select &#39;&lt;h1&gt;Hello" in response.text