refactor: centralize ndjson streaming transport

app/tests/test_http_streaming.py

@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+import io
+import json
+import unittest
+
+from backend.http.handler import HttpTransportMixin
+
+
+class StreamError(RuntimeError):
+    pass
+
+
+class TransportStub(HttpTransportMixin):
+    def __init__(self) -> None:
+        self.statuses: list[int] = []
+        self.response_headers: list[tuple[str, str]] = []
+        self.wfile = io.BytesIO()
+        self.close_connection = False
+
+    def send_response(self, status: int) -> None:
+        self.statuses.append(int(status))
+
+    def send_header(self, name: str, value: str) -> None:
+        self.response_headers.append((name, value))
+
+    def end_headers(self) -> None:
+        pass
+
+
+class HttpStreamingTests(unittest.TestCase):
+    def test_stream_transport_preserves_headers_events_and_completion(self) -> None:
+        handler = TransportStub()
+        handler.send_ndjson_stream(
+            ({"type": "delta", "content": value} for value in ("甲", "乙")),
+            (StreamError,),
+        )
+
+        self.assertEqual(handler.statuses, [200])
+        self.assertEqual(
+            dict(handler.response_headers),
+            {
+                "Content-Type": "application/x-ndjson; charset=utf-8",
+                "Cache-Control": "no-cache, no-transform",
+                "X-Accel-Buffering": "no",
+                "Connection": "close",
+            },
+        )
+        events = [
+            json.loads(line)
+            for line in handler.wfile.getvalue().decode("utf-8").splitlines()
+        ]
+        self.assertEqual(
+            events,
+            [
+                {"type": "delta", "content": "甲"},
+                {"type": "delta", "content": "乙"},
+                {"type": "done"},
+            ],
+        )
+        self.assertTrue(handler.close_connection)
+
+    def test_stream_transport_preserves_feature_error_event(self) -> None:
+        def events():
+            yield {"type": "delta", "content": "partial"}
+            raise StreamError("stream failed")
+
+        handler = TransportStub()
+        handler.send_ndjson_stream(events(), (StreamError,))
+        payloads = [
+            json.loads(line)
+            for line in handler.wfile.getvalue().decode("utf-8").splitlines()
+        ]
+        self.assertEqual(
+            payloads,
+            [
+                {"type": "delta", "content": "partial"},
+                {"type": "error", "error": "stream failed"},
+            ],
+        )
+        self.assertTrue(handler.close_connection)
+
+
+if __name__ == "__main__":
+    unittest.main()

app/tests/test_preservation_slice_accounts.py

@@ -40,6 +40,8 @@ class AccountSliceStructureTests(unittest.TestCase):
             "require_access",
             "serve_static",
             "send_json",
+            "_write_stream_event",
+            "send_ndjson_stream",
         ):
             self.assertNotIn(method, RequestHandler.__dict__)
             self.assertIn(method, HttpTransportMixin.__dict__)