Refactor JSON error handling in routing and tests for improvements.

fastapi/routing.py

@@ -266,10 +266,6 @@ def get_request_handler(
                             else:
                                 body = body_bytes
             except json.JSONDecodeError as e:
-                lines_before = e.doc[: e.pos].split("\n")
-                line_number = len(lines_before)
-                column_number = len(lines_before[-1]) + 1 if lines_before else 1
-
                 start_pos = max(0, e.pos - 40)
                 end_pos = min(len(e.doc), e.pos + 40)
                 error_snippet = e.doc[start_pos:end_pos]
@@ -282,14 +278,15 @@ def get_request_handler(
                     [
                         {
                             "type": "json_invalid",
-                            "loc": ("body", line_number, column_number),
-                            "msg": f"JSON decode error - {e.msg} at line {line_number}, column {column_number}",
-                            "input": error_snippet,
+                            "loc": ("body", e.pos),
+                            "msg": "JSON decode error",
+                            "input": {},
                             "ctx": {
                                 "error": e.msg,
                                 "position": e.pos,
-                                "line": line_number,
-                                "column": column_number,
+                                "line": e.lineno - 1,
+                                "column": e.colno - 1,
+                                "snippet": error_snippet,
                             },
                         }
                     ],

tests/test_json_error_improvements.py

@@ -30,12 +30,14 @@ def test_json_decode_error_single_line():
     assert response.status_code == 422
     error = response.json()["detail"][0]
 
-    assert error["loc"] == ["body", 1, 27]
-    assert "line 1" in error["msg"]
-    assert "column 27" in error["msg"]
-    assert error["ctx"]["line"] == 1
-    assert error["ctx"]["column"] == 27
-    assert "None" in error["input"]
+    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():
@@ -52,12 +54,13 @@ def test_json_decode_error_multiline():
     assert response.status_code == 422
     error = response.json()["detail"][0]
 
-    assert error["loc"] == ["body", 4, 12]
-    assert "line 4" in error["msg"]
-    assert "column 12" in error["msg"]
-    assert error["ctx"]["line"] == 4
-    assert error["ctx"]["column"] == 12
-    assert "invalid" in error["input"]
+    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_shows_snippet():
@@ -70,9 +73,10 @@ def test_json_decode_error_shows_snippet():
     assert response.status_code == 422
     error = response.json()["detail"][0]
 
-    assert "..." in error["input"]
-    assert "invalid" in error["input"]
-    assert len(error["input"]) <= 83
+    assert error["msg"] == "JSON decode error"
+    assert error["input"] == {}
+    assert "invalid" in error["ctx"]["snippet"]
+    assert len(error["ctx"]["snippet"]) <= 83
 
 
 def test_json_decode_error_empty_body():
@@ -117,10 +121,13 @@ def test_json_decode_error_unclosed_brace():
     assert response.status_code == 422
     error = response.json()["detail"][0]
 
-    assert "line" in error["msg"].lower()
-    assert "column" in error["msg"].lower()
+    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"]
 
 
 def test_json_decode_error_in_middle_of_long_document():
@@ -135,9 +142,10 @@ def test_json_decode_error_in_middle_of_long_document():
     assert response.status_code == 422
     error = response.json()["detail"][0]
 
-    # The error snippet should have "..." at the end since error is early in doc
-    assert error["input"].endswith("...")
-    assert "invalid" in error["input"]
+    assert error["msg"] == "JSON decode error"
+    assert error["input"] == {}
+    assert error["ctx"]["snippet"].endswith("...")
+    assert "invalid" in error["ctx"]["snippet"]
     assert error["type"] == "json_invalid"
 
 

tests/test_tutorial/test_body/test_tutorial001.py

@@ -206,14 +206,15 @@ def test_post_broken_body(client: TestClient):
             "detail": [
                 {
                     "type": "json_invalid",
-                    "loc": ["body", 1, 2],
-                    "msg": "JSON decode error - Expecting property name enclosed in double quotes at line 1, column 2",
-                    "input": "{some broken json}",
+                    "loc": ["body", 1],
+                    "msg": "JSON decode error",
+                    "input": {},
                     "ctx": {
                         "error": "Expecting property name enclosed in double quotes",
                         "position": 1,
-                        "line": 1,
-                        "column": 2,
+                        "line": 0,
+                        "column": 1,
+                        "snippet": "{some broken json}",
                     },
                 }
             ]