Don't catch the SerialException we just raised
In Python3 we get double tracebacks for this error:
Traceback (most recent call last):
File "/home/chn/repo/pyserial/serial/serialposix.py", line 557, in read
raise SerialException(
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "test/test_exceptions.py", line 26, in <module>
test_unexpected_eof()
File "/usr/lib/python3.8/unittest/mock.py", line 1348, in patched
return func(*newargs, **newkeywargs)
File "test/test_exceptions.py", line 21, in test_unexpected_eof
s.read()
File "/home/chn/repo/pyserial/serial/serialposix.py", line 566, in read
raise SerialException('read failed: {}'.format(e))
serial.serialutil.SerialException: read failed: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
The patch moves the checking for EOF to after the IO block, resulting
in a much nicer traceback. This is the test script (Python3-specific):
from unittest import mock
import serial
import select
import os
@mock.patch('select.select')
@mock.patch('os.read')
def test_unexpected_eof(mock_read, mock_select):
s = serial.Serial()
s.is_open = True
s.fd = 99
s.pipe_abort_read_r = 98
mock_select.return_value = ([99],[],[])
mock_read.return_value = b''
try:
s.read()
except serial.SerialException as e:
if e.__context__: raise
if __name__ == '__main__':
test_unexpected_eof()
diff --git a/serial/serialposix.py b/serial/serialposix.py
index 334ba9f..d5d6397 100644
--- a/serial/serialposix.py
+++ b/serial/serialposix.py
@@ -548,16 +548,6 @@
if not ready:
break # timeout
buf = os.read(self.fd, size - len(read))
- # read should always return some data as select reported it was
- # ready to read when we get to this point.
- if not buf:
- # Disconnected devices, at least on Linux, show the
- # behavior that they are always ready to read immediately
- # but reading returns nothing.
- raise SerialException(
- 'device reports readiness to read but returned no data '
- '(device disconnected or multiple access on port?)')
- read.extend(buf)
except OSError as e:
# this is for Python 3.x where select.error is a subclass of
# OSError ignore BlockingIOErrors and EINTR. other errors are shown
@@ -570,6 +560,18 @@
# see also http://www.python.org/dev/peps/pep-3151/#select
if e[0] not in (errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK, errno.EINPROGRESS, errno.EINTR):
raise SerialException('read failed: {}'.format(e))
+ else:
+ # read should always return some data as select reported it was
+ # ready to read when we get to this point.
+ if not buf:
+ # Disconnected devices, at least on Linux, show the
+ # behavior that they are always ready to read immediately
+ # but reading returns nothing.
+ raise SerialException(
+ 'device reports readiness to read but returned no data '
+ '(device disconnected or multiple access on port?)')
+ read.extend(buf)
+
if timeout.expired():
break
return bytes(read)