rqt_bag ROSBagFormatException problem

[KitKat7]

If Publish or View is selected in the newest rqt_bag (0.4.3), an exception will occur when Playing (under Ubuntu 14.04, ROS indigo 1.11.20, tried in two computers with the same environments).
Following are the typical exception messages (the data in the rosbag consists of imu and PointCloud2):

Exception in thread Thread-11:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 83, in run
    msg_data = self._get_message(bag, playhead_position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 96, in _get_message
    msg_data = self.timeline.read_message(bag, position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/bag_timeline.py", line 480, in read_message
    return bag._read_message(position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 980, in _read_message
    return self._reader.seek_and_read_message_data_record(position, raw)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 2453, in seek_and_read_message_data_record
    header = _read_header(f)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 1682, in _read_header
    raise ROSBagFormatException('Error reading header field: expected %d bytes, read %d' % (size, len(header)))
ROSBagFormatException: Error reading header field: expected 38 bytes, read 34

Exception in thread Thread-10:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 83, in run
    msg_data = self._get_message(bag, playhead_position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 96, in _get_message
    msg_data = self.timeline.read_message(bag, position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_bag/bag_timeline.py", line 480, in read_message
    return bag._read_message(position)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 980, in _read_message
    return self._reader.seek_and_read_message_data_record(position, raw)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 2453, in seek_and_read_message_data_record
    header = _read_header(f)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rosbag/bag.py", line 1669, in _read_header
    raise ROSBagFormatException('Error reading header: %s' % str(ex))
ROSBagFormatException: Error reading header: error unpacking uint32: unpack requires a string argument of length 4

When the exception appears, none of the the messages will be published.
It shouldn't be the problems in bag files, since the messages can be published by rosbag in console and rqt_bag in another computer with an older version of rqt_bag. rosbag reindex and rosbag fix were tried, yet with no help.
But, when all the files (*.py, *.pyc, etc.) in rqt_bag are replaced by the ones in an old version (modified on Mar 9, 2016, might be version 0.3.13), the problem is gone!
Perhaps, it was caused by some bugs in the newest version (guessing).

[dirk-thomas]

I would be helpful if you could share the bag file in question in order to reproduce the problem.

[KitKat7]

Hi @dirk-thomas, thanks for your reply!
Here is the clipped bag file which could cause the same problem: IMU_PC.bag.

[KitKat7]

Also tested in Kinetic 1.12.6, it had the same problem with that bag file. However, replacing parts of the files in rqt_bag with old version's could still be useful.

[dirk-thomas]

I think this problem has been fixed by #412. Can you please try the patch from that PR and confirm that it works for you too.

[KitKat7]

I've tried the patch and it could solve this problem. Thank you and @jspricke!