GWT Query fails second time -only.

Question

HI,

I have a visualization function in GWT which calls for two instances of the same panels - two queries. Now, suppose one url is A and the other url is B. Here, I am facing an issue in that if A is called first, then both A and B works. If B is called first, then only B works, A - times out. If I call both times A, only the first time A works, second time it times out. If I call B twice, it works both times without a hitch.

Even though the error comes at timed out, it actually is not timing out - in FF status bar, it shows till - transferring data from A, and then it gets stuck. This doesnt even show up in the first time query.

The only difference between A and B is that B returns very fast, while A returns comparitively slow.

The sample code is given below:

public Panel(){
    Runnable onLoadCallback = new Runnable() {
       public void run() {
          Query query = Query.create(dataUrl);
          query.setTimeout(60);
          query.send(new Callback() {
          public void onResponse(QueryResponse response) {
                  if (response.isError()){
                       Window.alert(response.getMessage());
                  }
              }
           }
      }
      VisualizationUtils.loadVisualizationApi(onLoadCallback, PieChart.PACKAGE);
 }

What could be the reason for this? I cannot think of any reason why this should happen? Why is this happening only for A and not for B?

EDIT: More research.

The query which works all the time (i.e. B is the example URL given in GWT visualization site: see comment [1]). So, I tried in my app engine to reproduce it - the following way

    s = "google.visualization.Query.setResponse({version:'0.6',status:'ok',sig:'106459472',table:{cols:[{id:'A',label:'Source',type:'string',pattern:''},{id:'B',label:'Percent',type:'number',pattern:'#0.01%'}],rows:[{c:[{v:'Oil'},{v:0.37,f:'37.00%'}]},{c:[{v:'Coal'},{v:0.25,f:'25.00%'}]},{c:[{v:'Natural Gas'},{v:0.23,f:'23.00%'}]},{c:[{v:'Nuclear'},{v:0.06,f:'6.00%'}]},{c:[{v:'Biomass'},{v:0.04,f:'4.00%'}]},{c:[{v:'Hydro'},{v:0.03,f:'3.00%'}]},{c:[{v:'Solar Heat'},{v:0.005,f:'0.50%'}]},{c:[{v:'Wind'},{v:0.003,f:'0.30%'}]},{c:[{v:'Geothermal'},{v:0.002,f:'0.20%'}]},{c:[{v:'Biofuels'},{v:0.002,f:'0.20%'}]},{c:[{v:'Solar photovoltaic'},{v:4.0E-4,f:'0.04%'}]}]}});";
    response =  HttpResponse(s, content_type="text/plain; charset=utf-8")
    response['Expires'] = time.strftime('%a, %d %b %Y %H:%M:%S GMT', time.gmtime())
    return response

Where s is the data when we run the query for B. I tried to add Expires etc too, since that seems to be the only header which has the difference, but now, the query fails all the time.

For more info - I am now sending the difference between my server response vs the working server response. They seems to be pretty similar.

HTTP/1.0 200 OK
Content-Type: text/plain
Date: Wed, 16 Jun 2010 11:07:12 GMT
Server: Google Frontend
Cache-Control: private, x-gzip-ok=""

google.visualization.Query.setResponse({version:'0.6',status:'ok',sig:'106459472',table:{cols:[{id:'A',label:'Source',type:'string',pattern:''},{id:'B',label:'Percent',type:'number',pattern:'#0.01%'}],rows:[{c:[{v:'Oil'},{v:0.37,f:'37.00%'}]},{c:[{v:'Coal'},{v:0.25,f:'25.00%'}]},{c:[{v:'Natural Gas'},{v:0.23,f:'23.00%'}]},{c:[{v:'Nuclear'},{v:0.06,f:'6.00%'}]},{c:[{v:'Biomass'},{v:0.04,f:'4.00%'}]},{c:[{v:'Hydro'},{v:0.03,f:'3.00%'}]},{c:[{v:'Solar Heat'},{v:0.005,f:'0.50%'}]},{c:[{v:'Wind'},{v:0.003,f:'0.30%'}]},{c:[{v:'Geothermal'},{v:0.002,f:'0.20%'}]},{c:[{v:'Biofuels'},{v:0.002,f:'0.20%'}]},{c:[{v:'Solar photovoltaic'},{v:4.0E-4,f:'0.04%'}]}]}});Connection closed by foreign host.


Mac$ telnet spreadsheets.google.com 80
Trying 209.85.231.100...
Connected to spreadsheets.l.google.com.
Escape character is '^]'.
GET http://spreadsheets.google.com/tq?key=pWiorx-0l9mwIuwX5CbEALA&range=A1:B12&gid=0&headers=-1
HTTP/1.0 200 OK
Content-Type: text/plain; charset=UTF-8
Date: Wed, 16 Jun 2010 11:07:58 GMT
Expires: Wed, 16 Jun 2010 11:07:58 GMT
Cache-Control: private, max-age=0
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Server: GSE

google.visualization.Query.setResponse({version:'0.6',status:'ok',sig:'106459472',table:{cols:[{id:'A',label:'Source',type:'string',pattern:''},{id:'B',label:'Percent',type:'number',pattern:'#0.01%'}],rows:[{c:[{v:'Oil'},{v:0.37,f:'37.00%'}]},{c:[{v:'Coal'},{v:0.25,f:'25.00%'}]},{c:[{v:'Natural Gas'},{v:0.23,f:'23.00%'}]},{c:[{v:'Nuclear'},{v:0.06,f:'6.00%'}]},{c:[{v:'Biomass'},{v:0.04,f:'4.00%'}]},{c:[{v:'Hydro'},{v:0.03,f:'3.00%'}]},{c:[{v:'Solar Heat'},{v:0.005,f:'0.50%'}]},{c:[{v:'Wind'},{v:0.003,f:'0.30%'}]},{c:[{v:'Geothermal'},{v:0.002,f:'0.20%'}]},{c:[{v:'Biofuels'},{v:0.002,f:'0.20%'}]},{c:[{v:'Solar photovoltaic'},{v:4.0E-4,f:'0.04%'}]}]}});Connection closed by foreign host.

Also, please note that App engine did not allow the Expires header to go through - can that be the reason? But if that is the reason, then it should not fail if B is sent first and then A.

Comment [1] : http://spreadsheets.google.com/tq?key=pWiorx-0l9mwIuwX5CbEALA&range=A1:B12&gid=0&headers=-1

Answer 1

This issue is solved. The reason for this error was that google QueryResponse function expects the response reqId to be incremented for each query in the same session - which I did not see documented anywhere. Once the reqId was incremented, it started working perfectly.