Fix rosbag API for Python 3

[nstiurca]

Closes #1047.

It would be great to get this backported to Kinetic as well.

[dirk-thomas]

Please provide a reproducible example which failed before / works with the patch.

[nstiurca]

#!/usr/bin/env python3
import rosbag

with rosbag.Bag('any-bagfile.bag', 'r') as bag:
    for topic, msg, t in bag.read_messages():
        pass

crashes with

Traceback (most recent call last):
  File "./foo.py", line 5, in <module>
    for topic, msg, t in bag.read_messages():
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosbag/bag.py", line 2331, in read_messages
    yield self.seek_and_read_message_data_record((entry.chunk_pos, entry.offset), raw)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosbag/bag.py", line 2440, in seek_and_read_message_data_record
    raise ROSBagException('unsupported compression type: %s' % chunk_header.compression)
rosbag.bag.ROSBagException: unsupported compression type: b'none'

---

Or just run the test suite with Python 3.

[dirk-thomas]

Currently some of the test are failing. I will try to rerun them (in case they are flaky). @ros-pull-request-builder retest this please

If that doesn't resolve them please look into why they started to fail.

[nstiurca]

Hmm, they didn't fail locally, but I only tested against Kinetic admittedly. I'm not sure how easy it is for me to test against anything else.

…

-- Nicu Știurcă (sent from my phone)

On May 8, 2017 1:50 PM, "Dirk Thomas" ***@***.***> wrote: Currently some of the test are failing. I will try to rerun them (in case they are flaky). @ros-pull-request-builder <https://github.com/ros-pull-request-builder> retest this please If that doesn't resolve them please look into why they started to fail. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#1048 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABhfE58A0G8iTqD_muiBps3pFvl5nQH5ks5r32P0gaJpZM4NUHYZ> .

[nstiurca]

This patch only addresses reading bag files. The test code first creates a bag file, and I found today that there might be some Python 3 related issues there as well. I will update on this as I can.

Although I presume the failed tests above were run using Python 2, so I'm still not sure about that.

[dirk-thomas]

Although I presume the failed tests above were run using Python 2

Yes, the CI builds only use Python 2.

[dirk-thomas]

The function name doesn't make much sense in the case of Python 3. Since you invoke decode on v it can't be a str but must be bytes?

[nstiurca]

So it looks like the build is still failing, but if I'm reading the logs right it's an issue with rosdep having timed out during the build rather than anything to do with this patch. Is there a way to re-run the build?

[dirk-thomas]

I accidentally assumed that #1150 would address the remaining comment on this PR but relied on other parts of the patch. Now I see that the new PR is "complete" on its own. Therefore I have merged #1150 and will close this as a duplicate. Anyway thanks for working on this.