p_rosbridge_server_cpp

The node is a C++ implementation of the Rosbridge protocol. It is close to a drop-in replacement of the Python rosbridge_server. Only websocket connections are supported.

We use the Qt library for the Websocket implementation, included in the libqt5websockets5-dev ubuntu package.

The following compressions are supported :

• JSON
• CBOR
• CBOR-RAW

Features of the RobotWebTools' rosbridge that are not implemented

• PNG compression
• fragmented packets
• authentification (rosauth)
• service server
• TCP and UDP transport (only Websocket)
• BSON mode
• Regex used to authorize only some specific topics or services

Changes compared to the RobotWebTools' rosbridge

In addition the previous listed unimplemented features, we have some design changes :

• When using the call_service request, the type parameter is mandatory. RobotWebTools' rosbridge uses the rosmaster API to find the correct type.
• A watchdog is activated by default, see more details below
• CBOR requests are supported (service call, subscribe, advertise...). The response will be in CBOR only if "compression":"cbor" is present.

Node watchdog

The watchdog is used to protect this node from freezes. If the main thead blocks, the process will terminate with a SIGABRT. If the respawn="true" attribute has been set in the .launch file, roslaunch will automatically the process.

Qt version

Qt 5.14+ fixes some bugs in QWebsocketServer : 5s freeze on client disconnection during frame reception and connection header size too big. Ubuntu 18.04 and 20.04 is missing these fixes.

If you want to apply these fixes you need to install the newer Qt in another directory (for example /opt/Qt5.15) and set the CMake variables ROSBRIDGE_FORCE_CUSTOM_QT and ROSBRIDGE_FORCE_CUSTOM_QT_DIR.

Implementation details

Binary data in JSON objects

int8[] and uint8[] arrays are encoding in base64. This is done in the same way as RobotWebTools' rosbridge.

For example, the following sensors_msgs/CompressedImage message

m.header...
m.format = "jpeg"
m.data = [0,1,2,3,4,5,6,7,8,9]

Will be encoded as :

{
    "header": {"seq":123,"stamp":{"secs":123,"nsecs":456},"frame_id":"frame_id"},"format":"jpeg",
    "data":"AAECAwQFBgcICQ=="
}

Dependancies

• libqt5websockets5-dev
• roscpp
• ros_babel_fish
• rosbridge_cpp_msgs
• std_msgs

Optionnal ROS parameters

• port (int) : Websocket TCP port. 0 will let the OS attribute a random port (default value: 9090)
• service_timeout (double) : Timeout, in seconds, for service requests (default value: 5.0)
• pong_timeout_s (double) : Timeout, in seconds, of the websocket connection for each client (default value: 30.0)
• watchdog_enabled (bool) : Enable the watchdog (default value: true)
• watchdog_timeout (double) : Watchdog timeout in seonds (default value: 5.0)

Parameters set by the node

The parameter actual_port will be set on startup. This is useful if port configured to 0.

Published topics

• client_count (std_msgs/Int32) : Number of clients connected to the server.
• connected_clients (rosbridge_msgs/ConnectedClients**) : Information on all the connected clients.

How to install in ROS noetic

sudo apt install python3-catkin-tools # optionnal
sudo apt install qtbase5-dev libqt5websockets5-dev ros-noetic-diagnostic-updater

source /opt/ros/noetic/setup.bash
mkdir -p ws/src
cd ws/src
git clone https://github.com/ixblue/rosbridge_server_cpp.git
git clone https://github.com/StefanFabian/ros_babel_fish
catkin build

Tests

rosunit 1.15.8 is needed to make the unit tests work. When using ROS melodic the rosunit package must be updated manually.