facebook, how to send tracking info for the user inside data?

i am using this example to send messages to my friends.

th开发者_JAVA技巧e problem i get into is how do i use the data property to add some tracking info.

I would like to pass a var $test and then be able to read it in a json format, or even an array.

In other words, I would like to pass a var when i send the message and when they accept it and it redirect them to the canvas, i would like to be able to grab it from somewhere: ex:

"data":[
  {
     "id":"167548189960088",
     "application":{
        "name":"Cat's Test Site",
        "id":"314268391344"
     },
     "to":{
        "name":"Cissy Lim",
        "id":"100001147247007"
     },


     "data":"'here is my var'",


     "message":"'INSERT_UT8_STRING_MSG'",
     "created_time":"2011-02-16T08:37:02+0000"
  },

Thanks

The "data" parameter currently only supports a string. Very annoying since Facebook seems to support json objects everywhere else. You could put a "json string" there and then eval that to a json object when you want to read it.