Feb 17, 2024 · Feb 17, 2024
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
        return written

    def tell(self):
        return _BufferedIOMixin.tell(self) - len(self._read_buf) + self._read_pos
        # GH-95782: Keep return value non-negative
        return max(_BufferedIOMixin.tell(self) - len(self._read_buf) + self._read_pos, 0)

    def seek(self, pos, whence=0):
        if whence not in valid_seek_flags:
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
    UnsupportedOperation = pyio.UnsupportedOperation


 class MockCharPseudoDevFileIO(MockFileIO):
    # GH-95782
    # ftruncate() does not work on these special files (and CPython then raises
    # appropriate exceptions), so truncate() does not have to be accounted for
    # here.
    def __init__(self, data):
        super().__init__(data)

    def seek(self, *args):
        return 0

    def tell(self, *args):
        return 0

 class CMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, io.BytesIO):
    pass

 class PyMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, pyio.BytesIO):
    pass


 class MockNonBlockWriterIO:

    def __init__(self):
        self.assertRaises(self.UnsupportedOperation, bufio.truncate)
        self.assertRaises(self.UnsupportedOperation, bufio.truncate, 0)

    def test_tell_character_device_file(self):
        # GH-95782
        # For the (former) bug in BufferedIO to manifest, the wrapped IO obj
        # must be able to produce at least 2 bytes.
        raw = self.MockCharPseudoDevFileIO(b"12")
        buf = self.tp(raw)
        self.assertEqual(buf.tell(), 0)
        self.assertEqual(buf.read(1), b"1")
        self.assertEqual(buf.tell(), 0)

    def test_seek_character_device_file(self):
        raw = self.MockCharPseudoDevFileIO(b"12")
        buf = self.tp(raw)
        self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
        self.assertEqual(buf.seek(1, io.SEEK_SET), 0)
        self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
        self.assertEqual(buf.read(1), b"1")

        # In the C implementation, tell() sets the BufferedIO's abs_pos to 0,
        # which means that the next seek() could return a negative offset if it
        # does not sanity-check:
        self.assertEqual(buf.tell(), 0)
        self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)


 class CBufferedReaderTest(BufferedReaderTest, SizeofTest):
    tp = io.BufferedReader
    # classes in the __dict__ of each test.
    mocks = (MockRawIO, MisbehavedRawIO, MockFileIO, CloseFailureIO,
             MockNonBlockWriterIO, MockUnseekableIO, MockRawIOWithoutRead,
             SlowFlushRawIO)
             SlowFlushRawIO, MockCharPseudoDevFileIO)
    all_members = io.__all__
    c_io_ns = {name : getattr(io, name) for name in all_members}
    py_io_ns = {name : getattr(pyio, name) for name in all_members}
diff --git a/Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst b/Misc/NEWS.d/next/Library/2022-11-22-23-17-43.gh-issue-95782.an_and.rst
 Fix :func:`io.BufferedReader.tell`, :func:`io.BufferedReader.seek`,
 :func:`_pyio.BufferedReader.tell`, :func:`io.BufferedRandom.tell`,
 :func:`io.BufferedRandom.seek` and :func:`_pyio.BufferedRandom.tell`
 being able to return negative offsets.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
    if (pos == -1)
        return NULL;
    pos -= RAW_OFFSET(self);
    /* TODO: sanity check (pos >= 0) */

    // GH-95782
    if (pos < 0)
        pos = 0;

    return PyLong_FromOff_t(pos);
 }

                offset = target;
            if (offset >= -self->pos && offset <= avail) {
                self->pos += offset;

                // GH-95782
                if (current - avail + offset < 0)
                    return PyLong_FromOff_t(0);

                return PyLong_FromOff_t(current - avail + offset);
            }
        }
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1209,7 +1209,8 @@ def _readinto(self, buf, read1):
		return written

		def tell(self):
		return _BufferedIOMixin.tell(self) - len(self._read_buf) + self._read_pos
		# GH-95782: Keep return value non-negative
		return max(_BufferedIOMixin.tell(self) - len(self._read_buf) + self._read_pos, 0)

		def seek(self, pos, whence=0):
		if whence not in valid_seek_flags:
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -263,6 +263,27 @@ class PyMockUnseekableIO(MockUnseekableIO, pyio.BytesIO):
		UnsupportedOperation = pyio.UnsupportedOperation


		class MockCharPseudoDevFileIO(MockFileIO):
		# GH-95782
		# ftruncate() does not work on these special files (and CPython then raises
		# appropriate exceptions), so truncate() does not have to be accounted for
		# here.
		def __init__(self, data):
		super().__init__(data)

		def seek(self, *args):
		return 0

		def tell(self, *args):
		return 0

		class CMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, io.BytesIO):
		pass

		class PyMockCharPseudoDevFileIO(MockCharPseudoDevFileIO, pyio.BytesIO):
		pass


		class MockNonBlockWriterIO:

		def __init__(self):
Expand DownExpand Up		@@ -1659,6 +1680,30 @@ def test_truncate_on_read_only(self):
		self.assertRaises(self.UnsupportedOperation, bufio.truncate)
		self.assertRaises(self.UnsupportedOperation, bufio.truncate, 0)

		def test_tell_character_device_file(self):
		# GH-95782
		# For the (former) bug in BufferedIO to manifest, the wrapped IO obj
		# must be able to produce at least 2 bytes.
		raw = self.MockCharPseudoDevFileIO(b"12")
		buf = self.tp(raw)
		self.assertEqual(buf.tell(), 0)
		self.assertEqual(buf.read(1), b"1")
		self.assertEqual(buf.tell(), 0)

		def test_seek_character_device_file(self):
		raw = self.MockCharPseudoDevFileIO(b"12")
		buf = self.tp(raw)
		self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
		self.assertEqual(buf.seek(1, io.SEEK_SET), 0)
		self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)
		self.assertEqual(buf.read(1), b"1")

		# In the C implementation, tell() sets the BufferedIO's abs_pos to 0,
		# which means that the next seek() could return a negative offset if it
		# does not sanity-check:
		self.assertEqual(buf.tell(), 0)
		self.assertEqual(buf.seek(0, io.SEEK_CUR), 0)


		class CBufferedReaderTest(BufferedReaderTest, SizeofTest):
		tp = io.BufferedReader
Expand DownExpand Up		@@ -4888,7 +4933,7 @@ def load_tests(loader, tests, pattern):
		# classes in the __dict__ of each test.
		mocks = (MockRawIO, MisbehavedRawIO, MockFileIO, CloseFailureIO,
		MockNonBlockWriterIO, MockUnseekableIO, MockRawIOWithoutRead,
		SlowFlushRawIO)
		SlowFlushRawIO, MockCharPseudoDevFileIO)
		all_members = io.__all__
		c_io_ns = {name : getattr(io, name) for name in all_members}
		py_io_ns = {name : getattr(pyio, name) for name in all_members}
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,4 @@
		Fix :func:`io.BufferedReader.tell`, :func:`io.BufferedReader.seek`,
		:func:`_pyio.BufferedReader.tell`, :func:`io.BufferedRandom.tell`,
		:func:`io.BufferedRandom.seek` and :func:`_pyio.BufferedRandom.tell`
		being able to return negative offsets.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1286,7 +1286,11 @@ _io__Buffered_tell_impl(buffered *self)
		if (pos == -1)
		return NULL;
		pos -= RAW_OFFSET(self);
		/* TODO: sanity check (pos >= 0) */

		// GH-95782
		if (pos < 0)
		pos = 0;

		return PyLong_FromOff_t(pos);
		}

Expand DownExpand Up		@@ -1355,6 +1359,11 @@ _io__Buffered_seek_impl(buffered self, PyObject targetobj, int whence)
		offset = target;
		if (offset >= -self->pos && offset <= avail) {
		self->pos += offset;

		// GH-95782
		if (current - avail + offset < 0)
		return PyLong_FromOff_t(0);

		return PyLong_FromOff_t(current - avail + offset);
		}
		}
Expand Down