[rosbag] Expose snapshot functionality

[gabrielSoudry]

Unlike #1414 I don't need more features, I just want the return of the deprecated command rosrecord -s like this topic in ros forum.
The functionnality seem to yet exist

ros_comm/tools/rosbag/src/recorder.cpp

Lines 182 to 188 in fad5134

	if (options_.snapshot)
	{
	record_thread = boost::thread(boost::bind(&Recorder::doRecordSnapshotter, this));
	// Subscribe to the snapshot trigger
	trigger_sub = nh.subscribe<std_msgs::Empty>("snapshot_trigger", 100, boost::bind(&Recorder::snapshotTrigger, this, _1));
	}

But not in any options

ros_comm/tools/rosbag/src/record.cpp

Lines 50 to 72 in d82f3f0

	desc.add_options()
	("help,h", "produce help message")
	("all,a", "record all topics")
	("regex,e", "match topics using regular expressions")
	("exclude,x", po::value<std::string>(), "exclude topics matching regular expressions")
	("quiet,q", "suppress console output")
	("publish,p", "Publish a msg when the record begin")
	("output-prefix,o", po::value<std::string>(), "prepend PREFIX to beginning of bag name")
	("output-name,O", po::value<std::string>(), "record bagnamed NAME.bag")
	("buffsize,b", po::value<int>()->default_value(256), "Use an internal buffer of SIZE MB (Default: 256)")
	("chunksize", po::value<int>()->default_value(768), "Set chunk size of message data, in KB (Default: 768. Advanced)")
	("limit,l", po::value<int>()->default_value(0), "Only record NUM messages on each topic")
	("min-space,L", po::value<std::string>()->default_value("1G"), "Minimum allowed space on recording device (use G,M,k multipliers)")
	("bz2,j", "use BZ2 compression")
	("lz4", "use LZ4 compression")
	("split", po::value<int>()->implicit_value(0), "Split the bag file and continue recording when maximum size or maximum duration reached.")
	("max-splits", po::value<int>(), "Keep a maximum of N bag files, when reaching the maximum erase the oldest one to keep a constant number of files.")
	("topic", po::value< std::vector<std::string> >(), "topic to record")
	("size", po::value<uint64_t>(), "The maximum size of the bag to record in MB.")
	("duration", po::value<std::string>(), "Record a bag of maximum duration in seconds, unless 'm', or 'h' is appended.")
	("node", po::value<std::string>(), "Record all topics subscribed to by a specific node.")
	("tcpnodelay", "Use the TCP_NODELAY transport hint when subscribing to topics.")
	("udp", "Use the UDP transport hint when subscribing to topics.");

Just add :
("snapshot,s","(EXPERIMENTAL) Enable snapshot recording (don't write to file unless triggered)")
("trigger,t","(EXPERIMENTAL) Trigger snapshot recording")
And
if (vm.count("snapshot")) { opts.snapshot = true; } if (vm.count("trigger")) { opts.trigger = true; }
And it's fixed.

Do you have any idea why it's not implemented ?

[dirk-thomas]

Do you have any idea why it's not implemented ?

There is no need for a trigger option. That is being done through the topic snapshot_trigger shown in the above snippet.

For a snapshot option please consider to provide a pull request for this. I assume it wasn't added when the feature was implemented because the author only used the API rather than the CLI.