Serve RSS feeds through app with host rewrites

repub/web.py

@@ -31,6 +31,7 @@ from repub.model import (
     delete_job_source,
     delete_source,
     initialize_database,
+    load_feed_url,
     load_job_enabled,
     load_settings_form,
     load_source_form,
@@ -151,15 +152,19 @@ def create_app(*, dev_mode: bool = False) -> Quart:
 
     @app.get("/feeds/<path:feed_path>")
     async def published_feed(feed_path: str) -> Response:
+        if Path(feed_path).suffix == ".rss":
+            return _rss_feed_response(
+                _read_feed_text(
+                    feeds_dir=Path(app.config["REPUB_FEEDS_DIR"]),
+                    feed_path=feed_path,
+                )
+            )
         if not bool(app.config["REPUB_DEV_MODE"]):
             return Response(status=404)
-        response = await send_from_directory(
+        return await send_from_directory(
             str(Path(app.config["REPUB_FEEDS_DIR"])),
             feed_path,
         )
-        if Path(feed_path).suffix == ".rss":
-            response.mimetype = "application/rss+xml"
-        return response
 
     @app.get("/static/<string:asset_name>-<string:asset_hash>.<string:extension>")
     async def versioned_static_asset(
@@ -582,6 +587,42 @@ def _load_sidebar_counts(app: Quart) -> dict[str, int]:
     }
 
 
+def _rss_feed_response(feed_text: str | None) -> Response:
+    if feed_text is None:
+        return Response(status=404)
+    return Response(feed_text, mimetype="application/rss+xml")
+
+
+def _read_feed_text(*, feeds_dir: Path, feed_path: str) -> str | None:
+    resolved_path = _resolve_feed_path(feeds_dir=feeds_dir, feed_path=feed_path)
+    if resolved_path is None:
+        return None
+    return _rewrite_feed_text(
+        resolved_path.read_text(encoding="utf-8"),
+        configured_feed_url=load_feed_url(),
+        request_host=request.host,
+    )
+
+
+def _resolve_feed_path(*, feeds_dir: Path, feed_path: str) -> Path | None:
+    base_dir = feeds_dir.resolve()
+    candidate_path = (base_dir / feed_path).resolve()
+    try:
+        candidate_path.relative_to(base_dir)
+    except ValueError:
+        return None
+    return candidate_path if candidate_path.is_file() else None
+
+
+def _rewrite_feed_text(
+    feed_text: str, *, configured_feed_url: str, request_host: str
+) -> str:
+    configured_origin = configured_feed_url.rstrip("/")
+    if configured_origin == "":
+        return feed_text
+    return feed_text.replace(configured_origin, f"https://{request_host}")
+
+
 async def _clean_tab_state_periodically(app: Quart) -> None:
     while True:
         await asyncio.sleep(TAB_STATE_CLEAN_INTERVAL.total_seconds())