MD5 checksum mismatch while using ROS melodic with mavros to subscribe topics

[soufi]

Hi,

First of all, thank you for this work really appreciate the effort put into this project !

I am trying to connect a node using this library with melodic ROS for ArduCopter (based on mavros - link for more info). I'm having a hard time getting the md5 checksum to match the master node ... Here's an example :

I am trying to create a struct to match mavros_msgs/State.msg. I followed your documentation and came up with this struct:

type State struct {
	msg.Package  `ros:"mavros_msgs"`
	Armed        bool
	Connected    bool
	Guided       bool
	Header       std_msgs.Header
	ManualInput  bool
	Mode         string
	SystemStatus uint8
}

When I use it with your subscriber-custom example, I keep getting this message :

[ERROR] [1620490036.273636365]: Client [/goroslib_sub] wants topic /mavros/state to have datatype/md5sum [mavros_msgs/State/608c752285437c30044799f13ed86d95], but our version has [mavros_msgs/State/65cd0a9fff993b062b91e354554ec7e9]. Dropping connection.

I tried the same using a standard struct message like sensor_msgs/BatteryState ... same thing ...

Furthermore, I tried with sensor_msgs.NavSatFix and it's working just fine....

Am I doing something wrong ?

Thank you :)

[soufi]

Hi,

I just found the definition of the BatteryState message here

There's a little difference with the one defined as standard in this library. In fact Temperature is not present in the definition above.
So I'm curious to understand why there's differences in standard messages for example ?

[soufi]

Ok, So I got the answer for the last part (State message). Obviously, the order of fields is very important ... and the structure should include the definition also. so here's how the structure should look like:

type State struct {
	msg.Package     `ros:"mavros_msgs"`
	msg.Definitions `ros:"string MODE_APM_PLANE_MANUAL=MANUAL,string MODE_APM_PLANE_CIRCLE=CIRCLE,string MODE_APM_PLANE_STABILIZE=STABILIZE,string MODE_APM_PLANE_TRAINING=TRAINING,string MODE_APM_PLANE_ACRO=ACRO,string MODE_APM_PLANE_FBWA=FBWA,string MODE_APM_PLANE_FBWB=FBWB,string MODE_APM_PLANE_CRUISE=CRUISE,string MODE_APM_PLANE_AUTOTUNE=AUTOTUNE,string MODE_APM_PLANE_AUTO=AUTO,string MODE_APM_PLANE_RTL=RTL,string MODE_APM_PLANE_LOITER=LOITER,string MODE_APM_PLANE_LAND=LAND,string MODE_APM_PLANE_GUIDED=GUIDED,string MODE_APM_PLANE_INITIALISING=INITIALISING,string MODE_APM_PLANE_QSTABILIZE=QSTABILIZE,string MODE_APM_PLANE_QHOVER=QHOVER,string MODE_APM_PLANE_QLOITER=QLOITER,string MODE_APM_PLANE_QLAND=QLAND,string MODE_APM_PLANE_QRTL=QRTL,string MODE_APM_COPTER_STABILIZE=STABILIZE,string MODE_APM_COPTER_ACRO=ACRO,string MODE_APM_COPTER_ALT_HOLD=ALT_HOLD,string MODE_APM_COPTER_AUTO=AUTO,string MODE_APM_COPTER_GUIDED=GUIDED,string MODE_APM_COPTER_LOITER=LOITER,string MODE_APM_COPTER_RTL=RTL,string MODE_APM_COPTER_CIRCLE=CIRCLE,string MODE_APM_COPTER_POSITION=POSITION,string MODE_APM_COPTER_LAND=LAND,string MODE_APM_COPTER_OF_LOITER=OF_LOITER,string MODE_APM_COPTER_DRIFT=DRIFT,string MODE_APM_COPTER_SPORT=SPORT,string MODE_APM_COPTER_FLIP=FLIP,string MODE_APM_COPTER_AUTOTUNE=AUTOTUNE,string MODE_APM_COPTER_POSHOLD=POSHOLD,string MODE_APM_COPTER_BRAKE=BRAKE,string MODE_APM_COPTER_THROW=THROW,string MODE_APM_COPTER_AVOID_ADSB=AVOID_ADSB,string MODE_APM_COPTER_GUIDED_NOGPS=GUIDED_NOGPS,string MODE_APM_ROVER_MANUAL=MANUAL,string MODE_APM_ROVER_LEARNING=LEARNING,string MODE_APM_ROVER_STEERING=STEERING,string MODE_APM_ROVER_HOLD=HOLD,string MODE_APM_ROVER_AUTO=AUTO,string MODE_APM_ROVER_RTL=RTL,string MODE_APM_ROVER_GUIDED=GUIDED,string MODE_APM_ROVER_INITIALISING=INITIALISING,string MODE_PX4_MANUAL=MANUAL,string MODE_PX4_ACRO=ACRO,string MODE_PX4_ALTITUDE=ALTCTL,string MODE_PX4_POSITION=POSCTL,string MODE_PX4_OFFBOARD=OFFBOARD,string MODE_PX4_STABILIZED=STABILIZED,string MODE_PX4_RATTITUDE=RATTITUDE,string MODE_PX4_MISSION=AUTO.MISSION,string MODE_PX4_LOITER=AUTO.LOITER,string MODE_PX4_RTL=AUTO.RTL,string MODE_PX4_LAND=AUTO.LAND,string MODE_PX4_RTGS=AUTO.RTGS,string MODE_PX4_READY=AUTO.READY,string MODE_PX4_TAKEOFF=AUTO.TAKEOFF"`
	Header          std_msgs.Header
	Connected       bool
	Armed           bool
	Guided          bool
	ManualInput     bool
	Mode            string
	SystemStatus    uint8
}

If any other noob comes across this :)

[aler9]

Hello,

• regarding BatteryState, its definition was updated by the ROS team between Melodic (released in 2018) and Noetic (relased in 2020). The library supports Noetic and uses this definition:
  http://docs.ros.org/en/noetic/api/sensor_msgs/html/msg/BatteryState.html
  Therefore you have to use noetic, or alternatively use a custom Go definition.

• regarding MAVROS, i've added MAVROS pre-generated messages to the library, so you can use them.

[soufi]

thank you @aler9