Merge 2fbf6f31fd into 460f8d2cc8

fastapi/routing.py

@@ -425,6 +425,14 @@ def get_request_handler(
                         else:
                             body = body_bytes
         except json.JSONDecodeError as e:
+            start_pos = max(0, e.pos - 40)
+            end_pos = min(len(e.doc), e.pos + 40)
+            error_snippet = e.doc[start_pos:end_pos]
+            if start_pos > 0:
+                error_snippet = "..." + error_snippet
+            if end_pos < len(e.doc):
+                error_snippet = error_snippet + "..."
+
             validation_error = RequestValidationError(
                 [
                     {
@@ -432,7 +440,13 @@ def get_request_handler(
                         "loc": ("body", e.pos),
                         "msg": "JSON decode error",
                         "input": {},
-                        "ctx": {"error": e.msg},
+                        "ctx": {
+                            "error": e.msg,
+                            "position": e.pos,
+                            "line": e.lineno - 1,
+                            "column": e.colno - 1,
+                            "snippet": error_snippet,
+                        },
                     }
                 ],
                 body=e.doc,

tests/test_json_body_decode_error.py

@@ -0,0 +1,157 @@
+import pytest
+from dirty_equals import IsDict
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+INVALID_JSON = """
+{
+  "name": "Test",
+  "price": 'invalid'
+}"""
+
+
+class Item(BaseModel):
+    name: str
+    price: float
+    description: str = None
+
+
+@app.post("/items/")
+async def create_item(item: Item):
+    return item  # pragma: no cover
+
+
+client = TestClient(app)
+
+
+def test_json_decode_error_single_line():
+    response = client.post(
+        "/items/",
+        content='{"name": "Test", "price": None}',
+        headers={"Content-Type": "application/json"},
+    )
+
+    assert response.status_code == 422
+    error = response.json()["detail"][0]
+
+    assert error["loc"] == ["body", 26]
+    assert error["msg"] == "JSON decode error"
+    assert error["input"] == {}
+    assert error["ctx"]["error"] == "Expecting value"
+    assert error["ctx"]["position"] == 26
+    assert error["ctx"]["line"] == 0
+    assert error["ctx"]["column"] == 26
+    assert "None" in error["ctx"]["snippet"]
+
+
+def test_json_decode_error_multiline():
+    response = client.post(
+        "/items/", content=INVALID_JSON, headers={"Content-Type": "application/json"}
+    )
+
+    assert response.status_code == 422
+    error = response.json()["detail"][0]
+
+    assert error["loc"][0] == "body"
+    assert isinstance(error["loc"][1], int)
+    assert error["msg"] == "JSON decode error"
+    assert error["input"] == {}
+    assert error["ctx"]["line"] == 3
+    assert error["ctx"]["column"] == 11
+    assert "invalid" in error["ctx"]["snippet"]
+
+
+def test_json_decode_error_empty_body():
+    response = client.post(
+        "/items/", content="", headers={"Content-Type": "application/json"}
+    )
+
+    assert response.status_code == 422
+    # Handle both Pydantic v1 and v2 - empty body is handled differently
+    assert response.json() == IsDict(
+        {
+            "detail": [
+                {
+                    "loc": ["body"],
+                    "msg": "Field required",
+                    "type": "missing",
+                    "input": None,
+                }
+            ]
+        }
+    ) | IsDict(
+        # Pydantic v1
+        {
+            "detail": [
+                {
+                    "loc": ["body"],
+                    "msg": "field required",
+                    "type": "value_error.missing",
+                }
+            ]
+        }
+    )
+
+
+def test_json_decode_error_unclosed_brace():
+    response = client.post(
+        "/items/",
+        content='{"name": "Test"',
+        headers={"Content-Type": "application/json"},
+    )
+
+    assert response.status_code == 422
+    error = response.json()["detail"][0]
+
+    assert error["msg"] == "JSON decode error"
+    assert error["type"] == "json_invalid"
+    assert error["input"] == {}
+    assert "position" in error["ctx"]
+    assert "line" in error["ctx"]
+    assert "column" in error["ctx"]
+    assert "snippet" in error["ctx"]
+
+
+@pytest.mark.parametrize(
+    "json_content,expected_starts_with_ellipsis,expected_ends_with_ellipsis",
+    [
+        (
+            '{"field": invalid, "padding_field": "this needs to be long enough that we have more than forty characters after the error position"}',
+            False,
+            True,
+        ),
+        (
+            '{"very_long_field_name_here": "some value that is long enough to push us past the forty character mark", "another_field": invalid}',
+            True,
+            False,
+        ),
+        (
+            '{"very_long_field_name_here": "some value", "field": invalid, "padding_field": "this needs to be long enough that we have more than forty characters after the error position"}',
+            True,
+            True,
+        ),
+        ('{"field": invalid}', False, False),
+    ],
+)
+def test_json_decode_error_snippet_ellipsis(
+    json_content, expected_starts_with_ellipsis, expected_ends_with_ellipsis
+):
+    response = client.post(
+        "/items/", content=json_content, headers={"Content-Type": "application/json"}
+    )
+
+    assert response.status_code == 422
+    error = response.json()["detail"][0]
+
+    assert error["msg"] == "JSON decode error"
+    assert error["input"] == {}
+    assert "invalid" in error["ctx"]["snippet"]
+    assert error["type"] == "json_invalid"
+
+    snippet = error["ctx"]["snippet"]
+    assert snippet.startswith("...") == expected_starts_with_ellipsis
+    assert snippet.endswith("...") == expected_ends_with_ellipsis

tests/test_tutorial/test_body/test_tutorial001.py

@@ -150,7 +150,13 @@ def test_post_broken_body(client: TestClient):
                 "loc": ["body", 1],
                 "msg": "JSON decode error",
                 "input": {},
-                "ctx": {"error": "Expecting property name enclosed in double quotes"},
+                "ctx": {
+                    "error": "Expecting property name enclosed in double quotes",
+                    "position": 1,
+                    "line": 0,
+                    "column": 1,
+                    "snippet": "{some broken json}",
+                },
             }
         ]
     }