如何从 yaler 获得 json 响应

Question

I create an account with yaler, to comunicate with my arduino yun. It works fine, and i'm able to switch on and off my leds. Then i created a web page, with a button that calls an ajax function with GET method to yaler (yaler web server accept REST style on the URL)

$.ajax({
   url: "http://RELAY_DOMAIN.try.yaler.net/arduino/digital/13/1",
   dataType: "json",
   success: function(msg){
      var jsonStr = msg;
    },
   error: function(err){
       alert(err.responseText);
   }

});

This code seem to work fine, infact the led switches off and on, but i expect a json response in success function (msg) like this:

{
"command":"digital",
"pin":13,
"value":1,
"action":"write"
}

But i get an error (error function). I also tried to alert the err.responseText, but it is undefined....

How could i solve the issue? Any suggestions??? Thanks in advance....

Answer 1

If the Web page containing the above Ajax request is served from a different origin, you'll have to work around the same origin policy of your Web browser.

There are two ways to do this (based on http://forum.arduino.cc/index.php?topic=304804 ):

• CORS , ie adding the header Access-Control-Allow-Origin: * to the Yun Web service
• JSONP , ie getting the Yun to serve an additional JS function if requested by the Ajax call with a query parameter ?callback=?

CORS can probably be configured in the OpenWRT part of the Yun, while JSONP could be added to the Brige.ino code (which you seem to be using).

Answer 2

I had the same problem. I used JSONP to solve it. JSONP is JSON with padding. Basically means you send the JSON data with a sort of wrapper. Instead of just the data you have to send a Java Script function and this is allowed by the internet.

So instead of your response being :

{"command":"digital","pin":13,"value":0,"action":"write"}

It should be:

showResult({command:"analog",pin:13,value:0,action:"write"});

I changed the yunYaler.ino to do this.

So for the html :

 var url = 'http://try.yaler.net/realy-domain/analog/13/210'; $.ajax({ type: 'GET', url: url, async: false, jsonpCallback: 'showResult', contentType: "application/json", dataType: 'jsonp', success: function(json) { console.dir(json.action); }, error: function(e) { console.log(e.message); } }); }; function showResult(show) { var str = "command = "+show.command;// you can do the others the same way. alert (str); }

My JSON is wrapped with a showResult() so its made JSONP and its the function I called in the callback.

Hope this helps. If CORS worked for you. Could you please put up how it worked here.