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Stop RebufferedBytesIO from hanging at EOF (fixes #988) #1140

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Stop RebufferedBytesIO from hanging at EOF (fixes #988) #1140

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20 changes: 16 additions & 4 deletions construct/lib/bitstream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -91,9 +91,13 @@ def read(self, count=None):
newdata = self.substream.read(128*1024)
except BlockingIOError:
newdata = None
if not newdata:
if newdata is None:
# non-blocking stream has no data ready yet, keep polling
sleep(0)
continue
if not newdata:
# empty bytes signal end of file, stop reading
break
self.rwbuffer += newdata
data = self.rwbuffer[startsat-self.moved:endsat-self.moved]
self.offset += count
Expand All @@ -109,10 +113,18 @@ def write(self, data):
startsat = self.offset
endsat = startsat + len(data)
while self.moved + len(self.rwbuffer) < startsat:
newdata = self.substream.read(128*1024)
self.rwbuffer += newdata
if not newdata:
try:
newdata = self.substream.read(128*1024)
except BlockingIOError:
newdata = None
if newdata is None:
# non-blocking stream has no data ready yet, keep polling
sleep(0)
continue
if not newdata:
# empty bytes signal end of file, stop reading
break
self.rwbuffer += newdata
self.rwbuffer = self.rwbuffer[:startsat-self.moved] + data + self.rwbuffer[endsat-self.moved:]
self.offset = endsat
if self.tailcutoff is not None and self.moved < self.offset - self.tailcutoff:
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9 changes: 9 additions & 0 deletions tests/lib/test_bitstream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,3 +53,12 @@ def test_rebuffered():
assert bstream.read(50) == data[at:at+50]
jumpback = random.randrange(1, 19)
assert bstream.seek(-jumpback, 1)

def test_rebuffered_reading_past_eof():
# reading past end of stream must raise, not hang forever (issue #988)
bstream = RebufferedBytesIO(io.BytesIO(b"abc"))
assert bstream.read(3) == b"abc"
assert raises(bstream.read, 1) == IOError

bstream = RebufferedBytesIO(io.BytesIO(b"abc"))
assert raises(bstream.read, 5) == IOError