roswasm

ROS C++ client library for emscripten WASM

Intro

Under the hood, roswasm uses both native ROS binary serialization and json serialization to provide an interface that looks like native roscpp when communcating through rosbridge_websocket (see details below).

roswasm supports the following primitives, mirroring the ones in roscpp. For complete example nodes, see roswasm_tutorials.

NodeHandle

You can create several NodeHandles. They can not be configured with a namespace. To achieve this, namespace the rosbridge_websocket instance instead.

#include <roswasm/roswasm.h>
...
roswasm::NodeHandle* nh = new roswasm::NodeHandle();

Subscriber

Subscribers receive data through the new cbor-raw compression protocol. In practice, this means rosbridge_websocket transmits the binary serialized ROS messages, making overhead minimal.

void string_callback(const std_msgs::String& msg) {}
...
roswasm::Subscriber* sub = nh->subscribe<std_msgs::String>("test", callback);

To throttle the rate of messages to at most 1 message every 100 ms (10Hz), change the call to

roswasm::Subscriber* sub = nh->subscribe<std_msgs::String>("test", callback, 100);

Publisher

Publishers use the json compression protocol, since it is expected that the bandwidth of publishers will be low.

roswasm::Publisher* pub = nh->advertise<std_msgs::String>("test");
std_msgs::String msg;
msg.data = "TEST";
pub->publish(msg);

ServiceClient

Similarly, ServiceClients also send and receive data using json serialization.

roswasm::ServiceClient* service = nh->serviceClient<rosapi::TopicType>("/rosapi/topic_type", service_callback);
rosapi::TopicType::Request req;
req.topic = "/connected_clients";
service->call<rosapi::TopicType>(req);

Timer

Timers adhere to the roscpp timer callback interface. However, the TimerEvent will not contain any meaningful data.

void callback(const ros::TimerEvent& ev) {}
...
roswasm::Timer* timer = nh->createTimer(5., callback);

Building

Any nodes that are to use roswasm and compile using Emscripten just need to depend on roswasm in the catkin build configuration. This will automatically pull in the build configuration by importing a CFG_EXTRAS Cmake file. Note that some configurations still are necessary and that the produced Webassembly and JavaScript files need to be imported by an html file in order to run in the web browser. See the tutorials package for examples on the necessary configurations.

Running

Before starting any of the roswasm nodes, you need to have one instance of rosbridge_websocket running:

roslaunch rosbridge_server rosbridge_websocket.launch

After building your node, you can run it similar to the following command:

rosrun roswasm run.py _pkg:=roswasm_tutorials _node:=listener.html _display_port:=8080

This will start a webserver and allow you to view the page at localhost:8080. If you want to see the output from the node, open the browser debug console.