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gh-59598: Ignore leading whitespace in JSONDecoder.raw_decode #117397

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3 changes: 3 additions & 0 deletions Doc/library/json.rst
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Expand Up @@ -402,6 +402,9 @@ Encoders and Decoders
This can be used to decode a JSON document from a string that may have
extraneous data at the end.

.. versionchanged:: 3.14
Now ignores any leading whitespace instead of returning an error
Comment on lines +405 to +406
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@eendebakpt eendebakpt Jun 19, 2025 •
edited by picnixz
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Suggested change
.. versionchanged:: 3.14
Now ignores any leading whitespace instead of returning an error
.. versionchanged:: next
Leading whitespaces are now ignored instead of raising an exception.



.. class:: JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)

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10 changes: 7 additions & 3 deletions Lib/json/decoder.py
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Expand Up @@ -341,23 +341,27 @@ def decode(self, s, _w=WHITESPACE.match):
containing a JSON document).

"""
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
obj, end = self.raw_decode(s)
end = _w(s, end).end()
if end != len(s):
raise JSONDecodeError("Extra data", s, end)
return obj

def raw_decode(self, s, idx=0):
def raw_decode(self, s, idx=0, _w=WHITESPACE.match):
"""Decode a JSON document from ``s`` (a ``str`` beginning with
a JSON document) and return a 2-tuple of the Python
representation and the index in ``s`` where the document ended.
Whitespace at the beginning of the document will be ignored.

Optionally, ``idx`` can be used to specify an offset in ``s``
where the document begins.

This can be used to decode a JSON document from a string that may
have extraneous data at the end.

"""
try:
obj, end = self.scan_once(s, idx)
obj, end = self.scan_once(s, idx=_w(s, idx).end())
except StopIteration as err:
raise JSONDecodeError("Expecting value", s, err.value) from None
return obj, end
14 changes: 14 additions & 0 deletions Lib/test/test_json/test_decode.py
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Expand Up @@ -124,6 +124,20 @@ def test_limit_int(self):
with self.assertRaises(ValueError):
self.loads('1' * (maxdigits + 1))

class TestRawDecode:
def test_whitespace(self):
decoder = self.json.JSONDecoder()
self.assertEqual(decoder.raw_decode(' {}'), ({}, 3))
self.assertEqual(decoder.raw_decode(' []'), ([], 4))
self.assertEqual(decoder.raw_decode(' ""'), ('', 5))
s = ' { "key" : "value" , "k":"v" } \n' \
' { "key": "value", "k" :"v"} '
val1, n1 = decoder.raw_decode(s)
val2, n2 = decoder.raw_decode(s[n1:])
self.assertEqual(val1, {"key":"value", "k":"v"})
self.assertEqual(val2, {"key":"value", "k":"v"})
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Suggested change
class TestRawDecode:
def test_whitespace(self):
decoder = self.json.JSONDecoder()
self.assertEqual(decoder.raw_decode(' {}'), ({}, 3))
self.assertEqual(decoder.raw_decode(' []'), ([], 4))
self.assertEqual(decoder.raw_decode(' ""'), ('', 5))
s = ' { "key" : "value" , "k":"v" } \n' \
' { "key": "value", "k" :"v"} '
val1, n1 = decoder.raw_decode(s)
val2, n2 = decoder.raw_decode(s[n1:])
self.assertEqual(val1, {"key":"value", "k":"v"})
self.assertEqual(val2, {"key":"value", "k":"v"})
class TestRawDecode:
def test_whitespace(self):
decoder = self.json.JSONDecoder()
self.assertEqual(decoder.raw_decode(' {}'), ({}, 3))
self.assertEqual(decoder.raw_decode(' []'), ([], 4))
self.assertEqual(decoder.raw_decode(' ""'), ('', 5))
s = ' { "key" : "value" , "k":"v" } \n' \
' { "key": "value", "k" :"v"} '
val1, n1 = decoder.raw_decode(s)
val2, n2 = decoder.raw_decode(s[n1:])
self.assertEqual(val1, {"key":"value", "k":"v"})
self.assertEqual(val2, {"key":"value", "k":"v"})

In addition, let's test n1 and n2. And test when there are whitespaces inside the values or keys.


class TestPyDecode(TestDecode, PyTest): pass
class TestCDecode(TestDecode, CTest): pass
class TestPyRawDecode(TestRawDecode, PyTest): pass
class TestCRawDecode(TestRawDecode, CTest): pass
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2024-04-22-07-05-05.gh-issue-59598.LyEKW3.rst
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@@ -0,0 +1 @@
Ignore leading whitespace in :func:`JSONDecoder.raw_decode`
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