From b63721c45f2801c9ec4bb92a89b45e7e8c413fd6 Mon Sep 17 00:00:00 2001
From: Kcstring <jingkris452@gmail.com>
Date: Wed, 29 Apr 2026 17:11:03 +0800
Subject: [PATCH] fix(proxy): decode multipart user_config JSON

---
 .../proxy/common_utils/http_parsing_utils.py  | 15 ++++-
 .../test_multipart_json_form_fields.py        | 56 +++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)
 create mode 100644 tests/test_litellm/proxy/common_utils/test_multipart_json_form_fields.py

diff --git a/litellm/proxy/common_utils/http_parsing_utils.py b/litellm/proxy/common_utils/http_parsing_utils.py
index 71abdfa5e9e..826581ec375 100644
--- a/litellm/proxy/common_utils/http_parsing_utils.py
+++ b/litellm/proxy/common_utils/http_parsing_utils.py
@@ -13,6 +13,16 @@ from litellm.proxy.common_utils.callback_utils import (
 from litellm.types.router import Deployment
 
 
+def _parse_form_json_field(
+    parsed_body: Dict[str, Any], field_name: str, *, require_json: bool = False
+) -> None:
+    value = parsed_body.get(field_name)
+    if not isinstance(value, str):
+        return
+    if require_json or value.lstrip().startswith(("{", "[")):
+        parsed_body[field_name] = json.loads(value)
+
+
 async def _read_request_body(request: Optional[Request]) -> Dict:
     """
     Safely read the request body and parse it as JSON.
@@ -39,8 +49,9 @@ async def _read_request_body(request: Optional[Request]) -> Dict:
 
         if "form" in content_type:
             parsed_body = dict(await request.form())
-            if "metadata" in parsed_body and isinstance(parsed_body["metadata"], str):
-                parsed_body["metadata"] = json.loads(parsed_body["metadata"])
+            _parse_form_json_field(parsed_body, "metadata", require_json=True)
+            _parse_form_json_field(parsed_body, "user_config")
+            _parse_form_json_field(parsed_body, "tags")
         else:
             # Read the request body
             body = await request.body()
diff --git a/tests/test_litellm/proxy/common_utils/test_multipart_json_form_fields.py b/tests/test_litellm/proxy/common_utils/test_multipart_json_form_fields.py
new file mode 100644
index 00000000000..58ef62c5795
--- /dev/null
+++ b/tests/test_litellm/proxy/common_utils/test_multipart_json_form_fields.py
@@ -0,0 +1,56 @@
+import json
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from litellm.proxy.common_utils.http_parsing_utils import _read_request_body
+
+
+@pytest.mark.asyncio
+async def test_form_data_with_json_user_config_and_tags():
+    mock_request = MagicMock()
+    user_config = {
+        "model_list": [
+            {
+                "model_name": "openai/gpt-image-1",
+                "litellm_params": {
+                    "model": "openai/gpt-image-1",
+                    "api_key": "sk-fake",
+                },
+            }
+        ]
+    }
+    test_data = {
+        "model": "openai/gpt-image-1",
+        "prompt": "test",
+        "user_config": json.dumps(user_config),
+        "tags": json.dumps(["image-edit", "multipart"]),
+    }
+
+    mock_request.form = AsyncMock(return_value=test_data)
+    mock_request.headers = {"content-type": "multipart/form-data"}
+    mock_request.scope = {}
+    mock_request.state._cached_headers = None
+
+    result = await _read_request_body(mock_request)
+
+    assert result["user_config"] == user_config
+    assert result["tags"] == ["image-edit", "multipart"]
+    assert result["model"] == "openai/gpt-image-1"
+    assert result["prompt"] == "test"
+    mock_request.form.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_form_data_with_plain_string_tags_is_left_unchanged():
+    mock_request = MagicMock()
+    test_data = {"model": "whisper-1", "tags": "production"}
+
+    mock_request.form = AsyncMock(return_value=test_data)
+    mock_request.headers = {"content-type": "multipart/form-data"}
+    mock_request.scope = {}
+    mock_request.state._cached_headers = None
+
+    result = await _read_request_body(mock_request)
+
+    assert result["tags"] == "production"