← eval7_submission

fastapi_15588

failed LOOP LOOP wrong_fix · 19 tool calls · 68 s · fastapi/fastapi

Task input

♻️ Validate Server Sent Event fields to avoid applications from sending broken data

## Pull Request

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## Description

♻️ Validate Server Sent Event fields to avoid applications from sending broken data

This was reported multiple times as a "vulnerability" by users probably using automated AI tools, with the argument that if input was taken from the request and passed directly to an event unfiltered, it could break the client.

If an app sets an `id` or `event` with multi-line content, I would consider that app broken, and probably the app itself vulnerable to something, not FastAPI. With this change, if any app sets invalid multi-line values (sourced from unfiltered input or in any other way), FastAPI will make it a server error (which it is, as the app is sending invalid data).

I don't think the code before this PR has a bug, less a vulnerability. This change is mainly a quality of life improvement to prevent badly written apps from shooting themselves in the foot by passing unsanitized data directly to a SSE.

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## AI Disclaimer

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</details>

## Checklist

- [ ] This PR is an obvious typo fix, or it links to a GitHub Discussion for the proposed code change.
- [x] I added tests for the change.
- [x] The new or updated tests fail on the main branch and pass on this PR.
- [x] Coverage stays at 100%.
- [x] The documentation explains the change if needed.

Tool calls (20)

#ToolArgumentsResult
1run_command
{
 "command": "grep -rn \"EventSourceResponse\" ."
}
{"status": "ok", "stdout": "./fastapi/.agents/skills/fastapi/references/streaming.md:16:To stream Server-Sent Events, use `response_class=EventSourceResponse` a
full
{"status": "ok", "stdout": "./fastapi/.agents/skills/fastapi/references/streaming.md:16:To stream Server-Sent Events, use `response_class=EventSourceResponse` and `yield` items from the endpoint.\n./fastapi/.agents/skills/fastapi/references/streaming.md:24:from fastapi.sse import EventSourceResponse\n./fastapi/.agents/skills/fastapi/references/streaming.md:35:@app.get(\"/items/stream\", response_class=EventSourceResponse)\n./fastapi/.agents/skills/fastapi/references/streaming.md:47:from fastapi.sse import EventSourceResponse, ServerSentEvent\n./fastapi/.agents/skills/fastapi/references/streaming.md:52:@app.get(\"/events\", response_class=EventSourceResponse)\n./fastapi/.agents/skills/fastapi/SKILL.md:333:See [the streaming reference](references/streaming.md) for JSON Lines, Server-Sent Events (`EventSourceResponse`, `ServerSentEvent`), and byte streaming (`StreamingResponse`) patterns.\n./fastapi/routing.py:64:    EventSourceResponse,\n./fastapi/routing.py:376:    is_sse_stream = lenient_issubclass(actual_response_class, EventSourceResponse)\n./fastapi/routing.py:856:                    # EventSourceResponse (SSE).\n./fastapi/routing.py:862:                        or lenient_issubclass(response_class, EventSourceResponse)\n./fastapi/routing.py:971:            response_class, EventSourceResponse\n./fastapi/responses.py:5:from fastapi.sse import EventSourceResponse as EventSourceResponse  # noqa\n./fastapi/sse.py:20:class EventSourceResponse(StreamingResponse):\n./fastapi/sse.py:23:    Use as `response_class=EventSourceResponse` on a *path operation* that uses `yield`\n./fastapi/sse.py:46:    `response_class=EventSourceResponse`, each `ServerSentEvent` is encoded\n./tests/test_sse.py:8:from fastapi.responses import EventSourceResponse\n./tests/test_sse.py:29:@app.get(\"/items/stream\", response_class=EventSourceResponse)\n./tests/test_sse.py:35:@app.get(\"/items/stream-sync\", response_class=EventSourceResponse)\n./tests/test_sse.py:40:@app.get(\"/items/stream-no-anno
2read_file
{
 "filepath": "fastapi/sse.py"
}
{"status": "ok", "filepath": "fastapi/sse.py", "content": "from typing import Annotated, Any\n\nfrom annotated_doc import Doc\nfrom pydantic import AfterValidat
full
{"status": "ok", "filepath": "fastapi/sse.py", "content": "from typing import Annotated, Any\n\nfrom annotated_doc import Doc\nfrom pydantic import AfterValidator, BaseModel, Field, model_validator\nfrom starlette.responses import StreamingResponse\n\n# Canonical SSE event schema matching the OpenAPI 3.2 spec\n# (Section 4.14.4 \"Special Considerations for Server-Sent Events\")\n_SSE_EVENT_SCHEMA: dict[str, Any] = {\n    \"type\": \"object\",\n    \"properties\": {\n        \"data\": {\"type\": \"string\"},\n        \"event\": {\"type\": \"string\"},\n        \"id\": {\"type\": \"string\"},\n        \"retry\": {\"type\": \"integer\", \"minimum\": 0},\n    },\n}\n\n\nclass EventSourceResponse(StreamingResponse):\n    \"\"\"Streaming response with `text/event-stream` media type.\n\n    Use as `response_class=EventSourceResponse` on a *path operation* that uses `yield`\n    to enable Server Sent Events (SSE) responses.\n\n    Works with **any HTTP method** (`GET`, `POST`, etc.), which makes it compatible\n    with protocols like MCP that stream SSE over `POST`.\n\n    The actual encoding logic lives in the FastAPI routing layer. This class\n    serves mainly as a marker and sets the correct `Content-Type`.\n    \"\"\"\n\n    media_type = \"text/event-stream\"\n\n\ndef _check_id_no_null(v: str | None) -> str | None:\n    if v is not None and \"\\0\" in v:\n        raise ValueError(\"SSE 'id' must not contain null characters\")\n    return v\n\n\nclass ServerSentEvent(BaseModel):\n    \"\"\"Represents a single Server-Sent Event.\n\n    When `yield`ed from a *path operation function* that uses\n    `response_class=EventSourceResponse`, each `ServerSentEvent` is encoded\n    into the [SSE wire format](https://html.spec.whatwg.org/multipage/server-sent-events.html#parsing-an-event-stream)\n    (`text/event-stream`).\n\n    If you yield a plain object (dict, Pydantic model, etc.) instead, it is\n    automatically JSON-encoded and sent as the `data:` field.\n\n    All `data`
3-5 ×3read_file
{
 "filepath": "fastapi/sse.py",
 "start_line": "151"
}
{"status": "error", "error_type": "FileReadError", "error_message": "'>' not supported between instances of 'int' and 'str'"}
full
{"status": "error", "error_type": "FileReadError", "error_message": "'>' not supported between instances of 'int' and 'str'"}
6run_command
{
 "command": "cat fastapi/sse.py"
}
{"status": "ok", "stdout": "from typing import Annotated, Any\n\nfrom annotated_doc import Doc\nfrom pydantic import AfterValidator, BaseModel, Field, model_val
full
{"status": "ok", "stdout": "from typing import Annotated, Any\n\nfrom annotated_doc import Doc\nfrom pydantic import AfterValidator, BaseModel, Field, model_validator\nfrom starlette.responses import StreamingResponse\n\n# Canonical SSE event schema matching the OpenAPI 3.2 spec\n# (Section 4.14.4 \"Special Considerations for Server-Sent Events\")\n_SSE_EVENT_SCHEMA: dict[str, Any] = {\n    \"type\": \"object\",\n    \"properties\": {\n        \"data\": {\"type\": \"string\"},\n        \"event\": {\"type\": \"string\"},\n        \"id\": {\"type\": \"string\"},\n        \"retry\": {\"type\": \"integer\", \"minimum\": 0},\n    },\n}\n\n\nclass EventSourceResponse(StreamingResponse):\n    \"\"\"Streaming response with `text/event-stream` media type.\n\n    Use as `response_class=EventSourceResponse` on a *path operation* that uses `yield`\n    to enable Server Sent Events (SSE) responses.\n\n    Works with **any HTTP method** (`GET`, `POST`, etc.), which makes it compatible\n    with protocols like MCP that stream SSE over `POST`.\n\n    The actual encoding logic lives in the FastAPI routing layer. This class\n    serves mainly as a marker and sets the correct `Content-Type`.\n    \"\"\"\n\n    media_type = \"text/event-stream\"\n\n\ndef _check_id_no_null(v: str | None) -> str | None:\n    if v is not None and \"\\0\" in v:\n        raise ValueError(\"SSE 'id' must not contain null characters\")\n    return v\n\n\nclass ServerSentEvent(BaseModel):\n    \"\"\"Represents a single Server-Sent Event.\n\n    When `yield`ed from a *path operation function* that uses\n    `response_class=EventSourceResponse`, each `ServerSentEvent` is encoded\n    into the [SSE wire format](https://html.spec.whatwg.org/multipage/server-sent-events.html#parsing-an-event-stream)\n    (`text/event-stream`).\n\n    If you yield a plain object (dict, Pydantic model, etc.) instead, it is\n    automatically JSON-encoded and sent as the `data:` field.\n\n    All `data` values **including plain string
7run_command
{
 "command": "tail -n +151 fastapi/sse.py"
}
{"status": "ok", "stdout": " \"\"\"\n Pre-serialized data string to use as the `data:` field.\n \"\"\"\n ),\n ] = None,\n event: Annotated[\n str | None,\n Doc(
full
{"status": "ok", "stdout": "            \"\"\"\n            Pre-serialized data string to use as the `data:` field.\n            \"\"\"\n        ),\n    ] = None,\n    event: Annotated[\n        str | None,\n        Doc(\n            \"\"\"\n            Optional event type name (`event:` field).\n            \"\"\"\n        ),\n    ] = None,\n    id: Annotated[\n        str | None,\n        Doc(\n            \"\"\"\n            Optional event ID (`id:` field).\n            \"\"\"\n        ),\n    ] = None,\n    retry: Annotated[\n        int | None,\n        Doc(\n            \"\"\"\n            Optional reconnection time in milliseconds (`retry:` field).\n            \"\"\"\n        ),\n    ] = None,\n    comment: Annotated[\n        str | None,\n        Doc(\n            \"\"\"\n            Optional comment line(s) (`:` prefix).\n            \"\"\"\n        ),\n    ] = None,\n) -> bytes:\n    \"\"\"Build SSE wire-format bytes from **pre-serialized** data.\n\n    The result always ends with `\\n\\n` (the event terminator).\n    \"\"\"\n    lines: list[str] = []\n\n    if comment is not None:\n        for line in comment.splitlines():\n            lines.append(f\": {line}\")\n\n    if event is not None:\n        lines.append(f\"event: {event}\")\n\n    if data_str is not None:\n        for line in data_str.splitlines():\n            lines.append(f\"data: {line}\")\n\n    if id is not None:\n        lines.append(f\"id: {id}\")\n\n    if retry is not None:\n        lines.append(f\"retry: {retry}\")\n\n    lines.append(\"\")\n    lines.append(\"\")\n    return \"\\n\".join(lines).encode(\"utf-8\")\n\n\n# Keep-alive comment, per the SSE spec recommendation\nKEEPALIVE_COMMENT = b\": ping\\n\\n\"\n\n# Seconds between keep-alive pings when a generator is idle.\n# Private but importable so tests can monkeypatch it.\n_PING_INTERVAL: float = 15.0\n", "stderr": "", "exit_code": 0}
8run_command
{
 "command": "grep -n \"def _check_id_no_null\" fastapi/sse.py"
}
{"status": "ok", "stdout": "36:def _check_id_no_null(v: str | None) -> str | None:\n", "stderr": "", "exit_code": 0}
full
{"status": "ok", "stdout": "36:def _check_id_no_null(v: str | None) -> str | None:\n", "stderr": "", "exit_code": 0}
9run_command
{
 "command": "grep -n \"class ServerSentEvent\" fastapi/sse.py"
}
{"status": "ok", "stdout": "42:class ServerSentEvent(BaseModel):\n", "stderr": "", "exit_code": 0}
full
{"status": "ok", "stdout": "42:class ServerSentEvent(BaseModel):\n", "stderr": "", "exit_code": 0}
10run_command
{
 "command": "python3 -m pytest tests/test_sse.py -q -x"
}
{"status": "ok", "stdout": ".................. [100%]\n=============================== warnings summary ===============================\n../../../../../../kaggl
full
{"status": "ok", "stdout": "..................                                                       [100%]\n=============================== warnings summary ===============================\n../../../../../../kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53\n  /kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.\n    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]\n\n-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html\n18 passed, 1 warning in 1.24s\n", "stderr": "", "exit_code": 0}
11write_file
{
 "content": "from fastapi.fastapi import FastAPI\nfrom fastapi.sse import EventSourceResponse, ServerSentEvent\nfrom fastapi.testclient import TestClient\nimport pytest\n\napp = FastAPI()\n\n@app.get(\"/sse\")\nasync def sse_endpoint():\n    yield ServerSentEvent(event=\"hello\\nworld\", data=\"test\")\n    yield ServerSentEvent(event=\"test\", data=\"hello\\nworld\", id=\"id\\n123\")\n\nclient = TestClient(app)\n\ndef test_sse_multiline_event():\n    with client.stream_get(\"/sse\") as response:\n        # The first event has a multiline 'event' field.\n        # According to the PR, this should now raise a server error (500).\n        # However, since it's a stream, the error might happen during iteration.\n        # We expect a ValueError to be raised when the ServerSentEvent is validated.\n        with pytest.raises(ValueError) as excinfo:\n            # We need to trigger the validation. \n            # In the app, the generator yields ServerSentEvent.\n            # If we use the app as is, the validation happens when ServerSentEvent is instantiated.\n            # Let's test the model validation directly first.\n            ServerSentEvent(event=\"hello\\nworld\", data=\"test\")\n        assert \"SSE 'event' must not contain newlines\" in str(excinfo.value)\n\ndef test_sse_multiline_id():\n    with pytest.raises(ValueError) as excinfo:\n        ServerSentEvent(event=\"test\", data=\"test\", id=\"id\\n123\")\n    assert \"SSE 'id' must not contain newlines\" in str(excinfo.value)\n",
 "filepath": "/tmp/test_sse_validation.py"
}
{"status": "error", "error_type": "FileWriteError", "error_message": "Path traversal detected: '/tmp/test_sse_validation.py' escapes workspace root."}
full
{"status": "error", "error_type": "FileWriteError", "error_message": "Path traversal detected: '/tmp/test_sse_validation.py' escapes workspace root."}
12write_file
{
 "content": "from fastapi import FastAPI\nfrom fastapi.sse import EventSourceResponse, ServerSentEvent\nfrom fastapi.testclient import TestClient\nimport pytest\n\napp = FastAPI()\n\n@app.get(\"/sse\")\nasync def sse_endpoint():\n    yield ServerSentEvent(event=\"hello\\nworld\", data=\"test\")\n    yield ServerSentEvent(event=\"test\", data=\"hello\\nworld\", id=\"id\\n123\")\n\nclient = TestClient(app)\n\ndef test_sse_multiline_event():\n    with pytest.raises(ValueError) as excinfo:\n        ServerSentEvent(event=\"hello\\nworld\", data=\"test\")\n    assert \"SSE 'event' must not contain newlines\" in str(excinfo.value)\n\ndef test_sse_multiline_id():\n    with pytest.raises(ValueError) as excinfo:\n        ServerSentEvent(event=\"test\", data=\"test\", id=\"id\\n123\")\n    assert \"SSE 'id' must not contain newlines\" in str(excinfo.value)\n",
 "filepath": "test_sse_validation.py"
}
{"status": "ok", "filepath": "test_sse_validation.py", "size": 792}
full
{"status": "ok", "filepath": "test_sse_validation.py", "size": 792}
13run_command
{
 "command": "python3 -m pytest test_sse_validation.py"
}
{"status": "error", "error_type": "CommandError", "error_message": "============================= test session starts ==============================\nplatform l
full
{"status": "error", "error_type": "CommandError", "error_message": "============================= test session starts ==============================\nplatform linux -- Python 3.13.14, pytest-9.1.1, pluggy-1.6.0\ncodspeed: 5.0.3 (disabled, mode: walltime, callgraph: enabled, timer_resolution: 1.0ns)\nrootdir: /workspace\nconfigfile: pytest.ini (WARNING: ignoring pytest config in pyproject.toml!)\nplugins: anyio-4.15.1, sugar-1.1.1, inline-snapshot-0.35.4, timeout-2.4.0, xdist-3.8.0, codspeed-5.0.3, cov-7.1.0\ncollected 2 items\n\ntest_sse_validation.py FF                                                [100%]\n\n=================================== FAILURES ===================================\n___________________________ test_sse_multiline_event ___________________________\n\n    def test_sse_multiline_event():\n>       with pytest.raises(ValueError) as excinfo:\n             ^^^^^^^^^^^^^^^^^^^^^^^^^\nE       Failed: DID NOT RAISE ValueError\n\ntest_sse_validation.py:16: Failed\n____________________________ test_sse_multiline_id _____________________________\n\n    def test_sse_multiline_id():\n>       with pytest.raises(ValueError) as excinfo:\n             ^^^^^^^^^^^^^^^^^^^^^^^^^\nE       Failed: DID NOT RAISE ValueError\n\ntest_sse_validation.py:21: Failed\n=============================== warnings summary ===============================\n../../../../../../kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53\n  /kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.\n    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]\n\n-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html\n=========================== short test summary info ============================\nFAILED test_sse_validation.py::test_sse_multiline_event - Failed: DID NOT RAI...\nFAILED
14edit_file
{
 "filepath": "fastapi/sse.py",
 "new_string": "def _check_sse_no_newlines(v: str | None, field_name: str) -> str | None:\n    if v is not None and \"\\n\" in v:\n        raise ValueError(f\"SSE '{field_name}' must not contain newlines\")\n    return v\n\n\ndef _check_id_no_null(v: str | None) -> str | None:\n    if v is not None and \"\\0\" in v:\n        raise ValueError(\"SSE 'id' must not contain null characters\")\n    return v\n",
 "old_string": "def _check_id_no_null(v: str | None) -> str | None:\n    if v is not None and \"\\0\" in v:\n        raise ValueError(\"SSE 'id' must not contain null characters\")\n    return v\n"
}
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -33,6 +33,12 @@\n
full
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -33,6 +33,12 @@\n     media_type = \"text/event-stream\"\n \n \n+def _check_sse_no_newlines(v: str | None, field_name: str) -> str | None:\n+    if v is not None and \"\\n\" in v:\n+        raise ValueError(f\"SSE '{field_name}' must not contain newlines\")\n+    return v\n+\n+\n def _check_id_no_null(v: str | None) -> str | None:\n     if v is not None and \"\\0\" in v:\n         raise ValueError(\"SSE 'id' must not contain null characters\")\n", "is_truncated": false}
15edit_file
{
 "filepath": "fastapi/sse.py",
 "new_string": "    event: Annotated[\n        str | None,\n        AfterValidator(lambda v: _check_sse_no_newlines(v, \"event\")),\n        Doc(\n            \"\"\"\n            Optional event type name.\n",
 "old_string": "    event: Annotated[\n        str | None,\n        Doc(\n            \"\"\"\n            Optional event type name.\n"
}
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -92,6 +92,7 @@\n ]
full
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -92,6 +92,7 @@\n     ] = None\n     event: Annotated[\n         str | None,\n+        AfterValidator(lambda v: _check_sse_no_newlines(v, \"event\")),\n         Doc(\n             \"\"\"\n             Optional event type name.\n", "is_truncated": false}
16edit_file
{
 "filepath": "fastapi/sse.py",
 "new_string": "    id: Annotated[\n        str | None,\n        AfterValidator(lambda v: _check_id_no_null(v)),\n        AfterValidator(lambda v: _check_sse_no_newlines(v, \"id\")),\n        Doc(\n            \"\"\"\n            Optional event ID.\n",
 "old_string": "    id: Annotated[\n        str | None,\n        AfterValidator(_check_id_no_null),\n        Doc(\n            \"\"\"\n            Optional event ID.\n"
}
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -104,7 +104,8 @@\n
full
{"status": "ok", "filepath": "fastapi/sse.py", "occurrences": 1, "strategy": "exact", "diff": "--- a/fastapi/sse.py\n+++ b/fastapi/sse.py\n@@ -104,7 +104,8 @@\n     ] = None\n     id: Annotated[\n         str | None,\n-        AfterValidator(_check_id_no_null),\n+        AfterValidator(lambda v: _check_id_no_null(v)),\n+        AfterValidator(lambda v: _check_sse_no_newlines(v, \"id\")),\n         Doc(\n             \"\"\"\n             Optional event ID.\n", "is_truncated": false}
17run_command
{
 "command": "python3 -m pytest test_sse_validation.py"
}
{"status": "ok", "stdout": "============================= test session starts ==============================\nplatform linux -- Python 3.13.14, pytest-9.1.1, pl
full
{"status": "ok", "stdout": "============================= test session starts ==============================\nplatform linux -- Python 3.13.14, pytest-9.1.1, pluggy-1.6.0\ncodspeed: 5.0.3 (disabled, mode: walltime, callgraph: enabled, timer_resolution: 1.0ns)\nrootdir: /workspace\nconfigfile: pytest.ini (WARNING: ignoring pytest config in pyproject.toml!)\nplugins: anyio-4.15.1, sugar-1.1.1, inline-snapshot-0.35.4, timeout-2.4.0, xdist-3.8.0, codspeed-5.0.3, cov-7.1.0\ncollected 2 items\n\ntest_sse_validation.py ..                                                [100%]\n\n=============================== warnings summary ===============================\n../../../../../../kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53\n  /kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.\n    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]\n\n-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html\n========================= 2 passed, 1 warning in 0.54s =========================\n", "stderr": "", "exit_code": 0}
18run_command
{
 "command": "python3 -m pytest tests/test_sse.py -q -x"
}
{"status": "ok", "stdout": ".................. [100%]\n=============================== warnings summary ===============================\n../../../../../../kaggl
full
{"status": "ok", "stdout": "..................                                                       [100%]\n=============================== warnings summary ===============================\n../../../../../../kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53\n  /kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.\n    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]\n\n-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html\n18 passed, 1 warning in 1.27s\n", "stderr": "", "exit_code": 0}
19run_command
{
 "command": "rm test_sse_validation.py"
}
{"status": "ok", "stdout": "", "stderr": "", "exit_code": 0}
full
{"status": "ok", "stdout": "", "stderr": "", "exit_code": 0}
20submit_patch
{}
{"status": "ok", "patch_size": 1185, "files_changed": 1}
full
{"status": "ok", "patch_size": 1185, "files_changed": 1}

Patch

diff --git a/fastapi/sse.py b/fastapi/sse.py
index 901d82496..fc4253c34 100644
--- a/fastapi/sse.py
+++ b/fastapi/sse.py
@@ -33,6 +33,12 @@ class EventSourceResponse(StreamingResponse):
     media_type = "text/event-stream"
 
 
+def _check_sse_no_newlines(v: str | None, field_name: str) -> str | None:
+    if v is not None and "\n" in v:
+        raise ValueError(f"SSE '{field_name}' must not contain newlines")
+    return v
+
+
 def _check_id_no_null(v: str | None) -> str | None:
     if v is not None and "\0" in v:
         raise ValueError("SSE 'id' must not contain null characters")
@@ -86,6 +92,7 @@ class ServerSentEvent(BaseModel):
     ] = None
     event: Annotated[
         str | None,
+        AfterValidator(lambda v: _check_sse_no_newlines(v, "event")),
         Doc(
             """
             Optional event type name.
@@ -97,7 +104,8 @@ class ServerSentEvent(BaseModel):
     ] = None
     id: Annotated[
         str | None,
-        AfterValidator(_check_id_no_null),
+        AfterValidator(lambda v: _check_id_no_null(v)),
+        AfterValidator(lambda v: _check_sse_no_newlines(v, "id")),
         Doc(
             """
             Optional event ID.

Test output

show
..........F
=================================== FAILURES ===================================
_ test_server_sent_event_single_line_fields_reject_newlines[first\nsecond-event] _

field_name = 'event', value = 'first\nsecond'

    @pytest.mark.parametrize("field_name", ["event", "id"])
    @pytest.mark.parametrize("value", ["first\nsecond", "first\rsecond", "first\r\nsecond"])
    def test_server_sent_event_single_line_fields_reject_newlines(
        field_name: str, value: str
    ):
>       with pytest.raises(ValueError, match=f"SSE '{field_name}' must be a single line"):
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E       AssertionError: Regex pattern did not match.
E         Expected regex: "SSE 'event' must be a single line"
E         Actual message: "1 validation error for ServerSentEvent\nevent\n  Value error, SSE 'event' must not contain newlines [type=value_error, input_value='first\\nsecond', input_type=str]\n    For further information visit https://errors.pydantic.dev/2.13/v/value_error"

tests/test_sse.py:229: AssertionError
=============================== warnings summary ===============================
../../../../../../kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53
  /kaggle/tmp/envs/overlays/starlette-1.6.0-py3-none-any/starlette/testclient.py:53: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.
    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
!!!!!!!!!!!!!!!!!!!!!!!!!! stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!
1 failed, 10 passed, 1 warning in 0.78s