From 14015b20fd8568a2eb4fd6ff70629e864faff90b Mon Sep 17 00:00:00 2001
From: bensynapse <118375461+bensynapse@users.noreply.github.com>
Date: Fri, 9 Oct 2026 04:38:08 +0300
Subject: [PATCH] [fix] Keep JSON slice offsets after leading whitespace

---
 src/partial_json_parser/core/complete.py |  3 +-
 tests/test_examples.py                   | 45 +++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/src/partial_json_parser/core/complete.py b/src/partial_json_parser/core/complete.py
index ed9b99e..4837e23 100644
--- a/src/partial_json_parser/core/complete.py
+++ b/src/partial_json_parser/core/complete.py
@@ -17,12 +17,13 @@ def fix(json_string: str, allow_partial: Union[Allow, int] = ALL):
 
 def _fix(json_string: str, allow: Allow, is_top_level=False):
     try:
+        start = len(json_string) - len(json_string.lstrip())
         result = complete_any(json_string.strip(), allow, is_top_level)
         if result is False:
             raise PartialJSON
 
         index, completion = result
-        return json_string[:index], ("" if completion is True else completion)
+        return json_string[: start + index], ("" if completion is True else completion)
 
     except (AssertionError, IndexError) as err:
         raise MalformedJSON(*err.args) from err
diff --git a/tests/test_examples.py b/tests/test_examples.py
index 7bf8727..868b7d0 100644
--- a/tests/test_examples.py
+++ b/tests/test_examples.py
@@ -1,10 +1,11 @@
 from itertools import accumulate
 from json import dumps
+from json import loads as standard_loads
 from math import isnan
 
 from hypothesis import given, settings
 from hypothesis.strategies import integers
-from pytest import raises
+from pytest import mark, raises
 from test_hypotheses import json
 
 from partial_json_parser import *
@@ -112,6 +113,48 @@ def test_fix_fast():
     assert fix_fast('["a" ,"b', ~STR) == ('["a" ', "]")
 
 
+@mark.parametrize("prefix", [" ", "\t", "\r\n", " \t\r\n "])
+@mark.parametrize("use_fast_fix", [True, False])
+@mark.parametrize("json_string", ["123", "-1.25e4", "true", "false", "null", '"tennis"', '"\\u0061"', "[1, true]", '{"score": 0}'])
+def test_complete_json_with_leading_whitespace(prefix, use_fast_fix, json_string):
+    original = prefix + json_string + " \r\n"
+    for allow in (ALL, 0):
+        assert parse_json(original, allow, use_fast_fix=use_fast_fix) == standard_loads(original)
+        assert ensure_json(original, allow, use_fast_fix=use_fast_fix).startswith(prefix)
+
+
+@mark.parametrize("prefix", [" ", "\t", "\r\n", " \t\r\n "])
+@mark.parametrize("complete", [fix, fix_fast])
+@mark.parametrize(
+    "json_string, head, tail, allow, expected",
+    [
+        ('"tennis', '"tennis', '"', STR, "tennis"),
+        ('"te\\u00', '"te', '"', STR, "te"),
+        ("12e+", "12", "", NUM, 12),
+        ("t", "", "true", BOOL, True),
+        ("f", "", "false", BOOL, False),
+        ("n", "", "null", NULL, None),
+        ('[1, "tennis', '[1, "tennis', '"]', ARR | STR, [1, "tennis"]),
+        ('{"score": t', '{"score": ', "true}", OBJ | BOOL, {"score": True}),
+    ],
+)
+def test_partial_json_with_leading_whitespace(prefix, complete, json_string, head, tail, allow, expected):
+    original = prefix + json_string
+    actual_head, actual_tail = complete(original, allow)
+    assert (actual_head, actual_tail) == (prefix + head, tail)
+    assert original.startswith(actual_head)
+    assert standard_loads(actual_head + actual_tail) == expected
+
+
+@mark.parametrize("prefix", [" ", "\t", "\r\n", " \t\r\n "])
+@mark.parametrize("complete", [fix, fix_fast])
+def test_leading_whitespace_keeps_partial_restrictions(prefix, complete):
+    with raises(PartialJSON):
+        complete(prefix + "t", ~BOOL)
+    with raises(MalformedJSON):
+        complete(prefix)
+
+
 def consistent(json_string, allow):
     try:
         res = fix(json_string, allow)