Providing schemaless transport over ROS pub/sub via JSON. This is useful when schema is enforced elsewhere, or the data is truly schemaless (i.e. parameters, diagnostics).
The provided serializers allow publishing and subscribing json_transport::json_t datatypes, which are nlohmann::json under the hood.
The nlohmann/json.hpp library is bundled in, but can be dropped for an apt dependency in artful, or if the package is bloomed into the rosdistro.
#include "json_transport/json_transport.hpp"
json_transport::json_t sent = {
{"this_is_json", true},
{"pi", 3.141},
{"list_of_plugins", {
"every_kind",
"of_plugin",
"you_can_imagine"
}},
};
ros::NodeHandle nh;
auto publisher = nh.advertise<json_transport::json_t>("json", 1, true);
publisher.publish(sent);
auto received = ros::topic::waitForMessage<json_transport::json_t>("json");
assert(*received == sent);
Nested json_msg/Json types can be packed/unpacked via helper methods:
MyCustomMessage message();
message.json_field = json_transport::pack(json_data)
assert(json_data == json_transport::unpack(message.json_field))
The provided json_transport.PackedJson data type allows publishing and subscribing anything that can be serialized/deserialized natively via the stdlib json module.
import json_transport
import rospy
rospy.init_node('json_talker')
pub = rospy.Publisher('json', json_transport.PackedJson, queue_size=1, latch=True)
pub.publish(1)
pub.publish([1, 2, 3])
pub.publish({'a': 1, 'b': 2, 'c': 3})
msg = rospy.wait_for_message('json', json_transport.PackedJson)
assert msg.data == {'a': 1, 'b': 2, 'c': 3}
Nested json_msg/Json types can be packed/unpacked via helper methods:
msg = MyCustomMessage(
json_field=json_transport.pack(serializable_data)
)
assert serializable_data == json_transport.unpack(msg.json_field)
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