UInt8[] message problem

[webe...@gmail.com]

Hi RWT community,

I have a problem with uint8 array messages over rosbridge websocket to roslibjs. Instead of the array I put in the message the browser outputs weird stuff.

I publish a uint8[] array from the console with

$ rostopic pub /array std_msgs/UInt8MultiArray "layout:
  dim:
  - label: ''
    size: 0
    stride: 0
  data_offset: 0
data: [1, 2]"

and print it in the browser with

var sub = new ROSLIB.Topic({

  ros : ros,

  name : '/array',

  messageType : 'std_msgs/UInt8MultiArray'

});

  

sub.subscribe(function(msg) {

  console.log(msg);
}

This results in this:

You see I get the string "AQI=". It isn't an array any more.

The array [0] results in "AA=="

With UInt16MultiArray it works as expected:

Tested with Chromium and Firefox on 14.04 and Indigo.

Is this a problem of the rosbridge or is this related to roslibjs? Any suggestions on how to solve this?

[Russell Toris]

I believe this is related to https://github.com/RobotWebTools/rosbridge_suite/pull/190/. uint8 are being encoded as BSON for faster transport to the browser. 

@dlu -- Do you have an example of how to read from uint8 in the browser/can we document this/should the BSON be enabled by a flag in rosbridge?

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Russell Toris
Graduate Student | WPI Department of Computer Science
rct...@wpi.edu | http://users.wpi.edu/~rctoris/

[webe...@gmail.com]

@dlu -- Any ideas about this?

[David Lu]

I apologize. Rookie mistake, I replied only to Russell. Below is my original reply. 

This is not BSON encoding, as that would result in a Blob binary object instead of the string. This is the standard Base64 encoding (https://en.wikipedia.org/wiki/Base64) that is used by default when binary encoding is not enabled. 

Both encodings are transmitted quicker than the straight forward json encoding of the data. 

There are a couple options for decoding the string in Javascript, although there is a larger question of whether it should be done automatically. 

[webe...@gmail.com]

Thanks very much.

A simple 

data = window.atob(msg.data)

did the trick.