rosbridge v2 msg format and subscriber callback in csharp

asked 2015-03-10 03:27:52 -0500

Morgane
41 ●3 ●4 ●8

With the help of the code provided here: RosBrigde client for windows in C# I managed to communicate with winros's tcp_server from my external program and subscribe to a topic. When I try to receive the topic data I face two problems:

I receive a string formatted as: "topic: ... msg: {data: ...} op: ..." How do I manage to retrieve the data value of the string? my message as I have created it consists of a class with three string variables, but that doesn't seem to work
I receive only one string and then the call back times out. I have put the code inside a loop but no results

Thank you for any help.

answered 2015-03-10 07:41:07 -0500

rtoris288
1173 ●21 ●30 ●40

rosbridge messages come in a JSON encoded string as defined in the rosbridge protocol spec ( https://github.com/RobotWebTools/rosb... ). You will need to utilize a JSON parser in C# to extract the data field which will contain your message data as a JSON object. This data comes in as a single JSON string.

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So when I receive this message ex: socket.receive(recdata); recdata is a string with the format I described. I made a class with op, msg and topic members, and if rd is an instance of that class I went on an called the deserializer rd = jsonconvert.deserializeobject(recdata); rd.msg doesn't work

Morgane ( 2015-03-11 02:57:42 -0500 )edit

I am unfamiliar with JSON parsing in C# but I suspect something needs to be done to parse the msg field which in itself is its own JSON object. Are the other fields set correctly? Can you post the recdata string that is coming in or verify it is valid JSON ( http://jsonlint.com/)?

rtoris288 ( 2015-03-11 07:03:06 -0500 )edit

yes the string is: {"topic": "/chatter", "msg":{"data": "hello world 1"}, "op": "publish"} The actual question is: what type of c# type is msg? (it must contain the string _data)

Morgane ( 2015-03-11 07:30:59 -0500 )edit

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