Issue #9550: a BufferedReader could issue an additional read when the

original read request had been satisfied, which can block indefinitely
when the underlying raw IO channel is e.g. a socket.  Report and original
patch by Jason V. Miller.
This commit is contained in:
Antoine Pitrou 2010-08-11 13:31:33 +00:00
parent 5ea3d93708
commit 32cfedeb1c
4 changed files with 34 additions and 1 deletions

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@ -52,12 +52,14 @@ class MockRawIO:
self._read_stack = list(read_stack)
self._write_stack = []
self._reads = 0
self._extraneous_reads = 0
def read(self, n=None):
self._reads += 1
try:
return self._read_stack.pop(0)
except:
self._extraneous_reads += 1
return b""
def write(self, b):
@ -88,6 +90,7 @@ class MockRawIO:
try:
data = self._read_stack[0]
except IndexError:
self._extraneous_reads += 1
return 0
if data is None:
del self._read_stack[0]
@ -824,6 +827,27 @@ class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
self.assertRaises(IOError, bufio.seek, 0)
self.assertRaises(IOError, bufio.tell)
def test_no_extraneous_read(self):
# Issue #9550; when the raw IO object has satisfied the read request,
# we should not issue any additional reads, otherwise it may block
# (e.g. socket).
bufsize = 16
for n in (2, bufsize - 1, bufsize, bufsize + 1, bufsize * 2):
rawio = self.MockRawIO([b"x" * n])
bufio = self.tp(rawio, bufsize)
self.assertEqual(bufio.read(n), b"x" * n)
# Simple case: one raw read is enough to satisfy the request.
self.assertEqual(rawio._extraneous_reads, 0,
"failed for {}: {} != 0".format(n, rawio._extraneous_reads))
# A more complex case where two raw reads are needed to satisfy
# the request.
rawio = self.MockRawIO([b"x" * (n - 1), b"x"])
bufio = self.tp(rawio, bufsize)
self.assertEqual(bufio.read(n), b"x" * n)
self.assertEqual(rawio._extraneous_reads, 0,
"failed for {}: {} != 0".format(n, rawio._extraneous_reads))
class CBufferedReaderTest(BufferedReaderTest):
tp = io.BufferedReader

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@ -548,6 +548,7 @@ Trent Mick
Aristotelis Mikropoulos
Damien Miller
Chad Miller
Jason V. Miller
Jay T. Miller
Roman Milner
Andrii V. Mishkovskyi

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@ -70,6 +70,11 @@ Extensions
Library
-------
- Issue #9550: a BufferedReader could issue an additional read when the
original read request had been satisfied, which could block indefinitely
when the underlying raw IO channel was e.g. a socket. Report and original
patch by Jason V. Miller.
- Issue #3757: thread-local objects now support cyclic garbage collection.
Thread-local objects involved in reference cycles will be deallocated
timely by the cyclic GC, even if the underlying thread is still running.

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@ -1383,7 +1383,10 @@ _bufferedreader_read_generic(buffered *self, Py_ssize_t n)
self->pos = 0;
self->raw_pos = 0;
self->read_end = 0;
while (self->read_end < self->buffer_size) {
/* NOTE: when the read is satisfied, we avoid issuing any additional
reads, which could block indefinitely (e.g. on a socket).
See issue #9550. */
while (remaining > 0 && self->read_end < self->buffer_size) {
Py_ssize_t r = _bufferedreader_fill_buffer(self);
if (r == -1)
goto error;