Issue #12062: Fix a flushing bug when doing a certain type of I/O sequence
on a file opened in read+write mode (namely: reading, seeking a bit forward,
writing, then seeking before the previous write but still within buffered
data, and writing again).
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 5f62494..1ec6f93 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -1461,6 +1461,32 @@
self.assertEqual(s,
b"A" + b"B" * overwrite_size + b"A" * (9 - overwrite_size))
+ def test_write_rewind_write(self):
+ # Various combinations of reading / writing / seeking backwards / writing again
+ def mutate(bufio, pos1, pos2):
+ assert pos2 >= pos1
+ # Fill the buffer
+ bufio.seek(pos1)
+ bufio.read(pos2 - pos1)
+ bufio.write(b'\x02')
+ # This writes earlier than the previous write, but still inside
+ # the buffer.
+ bufio.seek(pos1)
+ bufio.write(b'\x01')
+
+ b = b"\x80\x81\x82\x83\x84"
+ for i in range(0, len(b)):
+ for j in range(i, len(b)):
+ raw = self.BytesIO(b)
+ bufio = self.tp(raw, 100)
+ mutate(bufio, i, j)
+ bufio.flush()
+ expected = bytearray(b)
+ expected[j] = 2
+ expected[i] = 1
+ self.assertEqual(raw.getvalue(), expected,
+ "failed result for i=%d, j=%d" % (i, j))
+
def test_truncate_after_read_or_write(self):
raw = self.BytesIO(b"A" * 10)
bufio = self.tp(raw, 100)
diff --git a/Misc/NEWS b/Misc/NEWS
index f065b5a..07e8a56 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -69,6 +69,11 @@
Library
-------
+- Issue #12062: Fix a flushing bug when doing a certain type of I/O sequence
+ on a file opened in read+write mode (namely: reading, seeking a bit forward,
+ writing, then seeking before the previous write but still within buffered
+ data, and writing again).
+
- Issue #1028: Tk returns invalid Unicode null in %A: UnicodeDecodeError.
With Tk < 8.5 _tkinter.c:PythonCmd() raised UnicodeDecodeError, caused
IDLE to exit. Converted to valid Unicode null in PythonCmd().
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 71c4052..25b91e3 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -1749,7 +1749,7 @@
avail = Py_SAFE_DOWNCAST(self->buffer_size - self->pos, Py_off_t, Py_ssize_t);
if (buf.len <= avail) {
memcpy(self->buffer + self->pos, buf.buf, buf.len);
- if (!VALID_WRITE_BUFFER(self)) {
+ if (!VALID_WRITE_BUFFER(self) || self->write_pos > self->pos) {
self->write_pos = self->pos;
}
ADJUST_POSITION(self, self->pos + buf.len);