feat: add backup recovery, setup wizard and user-view guards

backend/app/request_limits.py

@@ -0,0 +1,50 @@
+"""Bound security-sensitive request bodies before JSON/multipart parsing."""
+
+from starlette.exceptions import HTTPException
+from starlette.responses import JSONResponse
+from starlette.types import ASGIApp, Message, Receive, Scope, Send
+
+
+# Encrypted backup limit is 32 MiB. Allow a bounded margin for the multipart
+# envelope; count streamed chunks as well as checking the untrusted header.
+RESTORE_BODY_LIMIT = 34 * 1024 * 1024
+BOOTSTRAP_BODY_LIMIT = 16 * 1024
+
+
+class InstallationBodyLimitMiddleware:
+    def __init__(self, app: ASGIApp) -> None:
+        self.app = app
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        if scope["type"] != "http" or scope.get("method") != "POST":
+            await self.app(scope, receive, send)
+            return
+        path = scope.get("path", "").rstrip("/")
+        limit = {
+            "/admin/backups/restore": RESTORE_BODY_LIMIT,
+            "/admin/backups/export": BOOTSTRAP_BODY_LIMIT,
+            "/setup/bootstrap": BOOTSTRAP_BODY_LIMIT,
+        }.get(path)
+        if limit is None:
+            await self.app(scope, receive, send)
+            return
+        headers = dict(scope.get("headers", []))
+        try:
+            length = int(headers.get(b"content-length", b"0"))
+        except ValueError:
+            length = -1
+        if length < 0 or length > limit:
+            await JSONResponse({"detail": "Request body is too large or has an invalid length."}, status_code=413)(scope, receive, send)
+            return
+        received = 0
+
+        async def bounded_receive() -> Message:
+            nonlocal received
+            message = await receive()
+            if message["type"] == "http.request":
+                received += len(message.get("body", b""))
+                if received > limit:
+                    raise HTTPException(status_code=413, detail="Request body is too large.")
+            return message
+
+        await self.app(scope, bounded_receive, send)