image_transport: 'Republish' as a nodelet

[furushchev]

Ported republish node as a nodelet, and changed to call the nodelet from republish executable.

This PR requires and is an application of #72

[skohlbr]

+1, Just searched if this is available somewhere and was close to implementing myself.

[Sefrin]

This might yield a warning from the ReconfigureServer of the CompressedSubscriber. Since a new subscriber is created before the old one is destroyed, the new Server wants to advertise an existing service. My solution would be, to manually destroy the sub_ object in unsubscribe().

[furushchev]

@Sefrin Thanks for the review! I could reproduced the bug,

# Terminal 1
roscore &
rosrun uvc_camera uvc_camera_node &
rosrun image_transport republish in:=image_raw compressed out:=foo

# Terminal 2
rostopic hz /foo/compressed
^C
rostopic hz /foo/compressed

And I could see the error message on the terminal 1:

furushchev@dango:~/ros/kinetic_test/src/image_common/image_transport/src [republish-nodelet]$ rosrun image_transport republish in:=image_raw compressed out:=foo
[ INFO] [1533828252.220730375] [/image_republisher_1533828252119766128:ros.nodelet]: Initializing nodelet with 8 worker threads.
[ WARN] [1533828257.226403951] [/image_republisher_1533828252119766128:ros.image_transport./image_republisher_1533828252119766128]: This node/nodelet subscribes topics only when subscribed.
[ERROR] [1533828263.122396843] [/image_republisher_1533828252119766128:ros.roscpp]: Tried to advertise a service that is already advertised in this node [/image_republisher_1533828252119766128/compressed/set_parameters]

[Sefrin]

There's a small bug that might produce warnings from the dynamic reconfigure server. I did not test this solution but I encountered this bug, when I rewrote the republish node for myself so that it stops subscribing when no one is listening.

[furushchev]

@skohlbr I updated this PR to ensure the shutdown method destructs the subscriber impl object which holds dynamic_reconfigure server object.
I tested on the same commands as the reproduced and confirmed that the error message now disappears.
Could you double check if you don't mind?

[Sefrin]

Thanks for the fast reply! This change might yield errors if we call methods (getTopic etc) on the subscriber after calling shutdown. I'm not sure if that causes trouble somewhere. I think it might be an option to just create a boost::shared_ptr<Subscriber> sub_; for the subscriber object in the RepublishNodelet and call sub_->shutdown() and sub_.reset() in unsubscribe.. But maybe there is a better solution..

If we want to fix this completely, we might need to change the CompressedSubscriber plugin (http://docs.ros.org/lunar/api/compressed_image_transport/html/compressed__subscriber_8cpp_source.html). Maybe we can override shutdown there and let it destroy the reconfigure_server_ object...

[Sefrin]

Confirmed! Fixed in this PR: ros-perception/image_transport_plugins#25
With that, you can reverse the changes made to this PR..

[furushchev]

@Sefrin Thanks too! That is indeed a far better solution. I reverted the change now.

[knorth55]

What is the status of this PR?

[ahcorde]

This PR is targeting hydro which is EOL Feel free to reopen this PR if the problem persists