firefox reports uncaught exception NS_ERROR_FAILURE with nsIXMLHttpRequest.send

[Plater]

I am using the XMLHttpRequest to send a request every 5ish seconds or so.
Everything works fine until I take the server down that the object is trying to retrieve data from.
Then the firefox console keeps racking up these:

uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIXMLHttpRequest.send]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" 
 

If I turn the server back on, it continues to update it's data just fine. I know a simple solution is to just trap the exception, but I don't think I should have to. There should be something I can do to keep it from generating one in the first place.

Relevant code:

function createRequestObject() 
{//creates an httprequest object
    var ro;
 
    var browser = navigator.appName;
    if(browser == "Microsoft Internet Explorer"){
        ro = new ActiveXObject("Microsoft.XMLHTTP");
    }else{
        ro = new XMLHttpRequest();
    }
    return ro;
}
 
var http = createRequestObject();
var ourinterval=setInterval("SendUpdate()",5000);
 
function SendUpdate()
{
  http.open('get', '/refresh.cgi?time='+ new Date().getTime());
  http.onreadystatechange = handleSendUpdateReponse;
  http.send(null);
}
function handleSendUpdateReponse()
{
    if(http.readyState == 4)
    {
        var update = new Array();
        if (http.status=="200")
        {
            var response = http.responseText;    
            if (response!="")
            {
              if(response.indexOf('|' != -1)) 
              {
                    update=response.split('|');
                    if (update.length>0)
                  {
                    if (update[1].indexOf("SUCCESS")>-1)
                    {
                        var line=update[1];
 
                        var things=new Array();
                        things=line.split('&');
                        var i;
                        for (i=0;i<things.length;i++)
                        {
                            var nameval=things[i].split('=');
                            if (i>0)
                            {
                                returnObjById(nameval[0]).innerHTML=nameval[1];
                            }
                        }
                    }//end of found "SUCCESS"
                    }//end of update split("|") to have multiple sections
              }//end of response.indexof("|")
            }//end of response!=""
        }//end of status==200
    }//end of readystate=4
}//end of function
 

[Plater]

Well, turns out that its something firefox just hasn't gotten around to fixing yet:
http://www.fleegix.org/articles/2006..._failure-error

The activeX equiv of XMLHttpRequest does not have this problem, providing a much more usefull notification as "12029" in the http.status
Those error codes can be found here:
http://support.microsoft.com/kb/193625

A lot of people use the XMLHTTPRequest object, why am I the only one doing checking for if the talkbalk host is no longer there?

Here are the changes I made to keep both browsers quiet and happy:

function SendUpdate()
{
    var action="DATETIME&TEMPERATURE&HUMIDITY&SAMPLESTATE";
    action+="&CHAN1&CHAN2&CHAN3&CHAN4&CHAN5&CHAN6&CHAN7&CHAN8&CHAN9&CHAN10";
    try
    {
        http.open('get', '/refresh.cgi?'+action+'&time='+ new Date().getTime());
      http.onreadystatechange = handleSendUpdateReponse;
      http.send(null);
    }
    catch(error)
    {
        //alert(error);
        returnObjById("SAMPLESTATE").innerHTML="Problem Communicating";
    }
 
}
 
function handleSendUpdateReponse()
{
    if(http.readyState == 4)
    {
        var update = new Array();
        if (http.status=="200")
        {
            var response = http.responseText;    
            if (response!="")
            {
              if(response.indexOf('|' != -1)) 
              {
                    update=response.split('|');
                    if (update.length>0)
                  {
                    if (update[1].indexOf("SUCCESS")>-1)
                    {
                        var line=update[1];
 
                        var things=new Array();
                        things=line.split('&');
                        var i;
                        for (i=0;i<things.length;i++)
                        {
                            var nameval=things[i].split('=');
                            if (i>0)
                            {
                                returnObjById(nameval[0]).innerHTML=nameval[1];
                            }
                        }
                    }//end of found "SUCCESS"
                    }//end of update split("|") to have multiple sections
              }//end of response.indexof("|")
            }//end of response!=""
        }//end of status==200
        else if(http.status==12029)
        {
            returnObjById("SAMPLESTATE").innerHTML="Problem Communicating";
        }            
    }//end of readystate=4
}//end of function
 

[cleaner]

Hi.

I also had a though time figure out a way to make this happen in firefox.

////////////////////////////////////////////////////////////////////////////////////////////// 
// firefox reports uncaught exception NS_ERROR_FAILURE with nsIXMLHttpRequest.send
// http://bytes.com/forum/thread681905.html
// http://radio.javaranch.com/pascarello/2006/02/07/1139345471027.html
// http://dev.rubyonrails.org/ticket/4267      
// 
// I needed a way to track server downtime even if the callback does not work when 
// server closes down. Since firefox does not support failover on server downtime I made this object
// where I track errors even if there is no callbacks to track.
// 
//    To use the object from your main app: 
//        failover = new clientFailover();   , create object in seperate "thread" (unsing setInterval)
//        failover.start("fail.php");            , the url where the request is made against as parameter
// object that handles failover between client and server. It pings the server in smal intervals
// and reporttext is generated every 10 seconds. Let me know if anyone comes up with a better solution
 
//////////////////////////////////////////////////////////////////////////////////////////////
function clientFailover(){
       var start,url,frequest;
       var uinterval = 10000;   // set update interval
       var pinterval = 1000;    // set ping interval
       var intervalID = 0;
       var fstatus = false; // true on error, false on normal operation
       var active = false;  // flag on when thread is aktiv
       var errorflag = 0;
 
     // Set error value code, 0 = connection and callback ok, 1 = connection ok but status error
     // 2 = connection ok but page error, 4 = Connection and callback lost
       var setError = function(value){
            errorflag = value;
      };
 
      var getError = function(){
        return errorflag;
      };
 
       // cObject is the XMLHTTPRequest instance
       var cObject = function(){
              var conn = false;
              if (window.XMLHttpRequest){
                  conn = new XMLHttpRequest();
              }else if (window.ActiveXObject){
                  try{
                      conn = new ActiveXObject("Msxml2.XMLHTTP");
                      }catch (e){
                          try{
                          conn = new ActiveXObject("Microsoft.XMLHTTP");
                      }catch (e){
                          conn = false;
                          }
                      }    
                  }
                 return conn;
      }
        // start method, this method is called from the main application
        // Parameter is the URL, This is where the "ping" is making request against
 
        this.start = function(value){
 
            url = value;
            frequest = cObject();
            if (!frequest || !url){
                return false;
            }else{
 
             ping();
             // set interval for the update info (every 10 second), this should be higher than the ping interval
             setInterval(function(){
                          pushInfo();}
                          ,uinterval);
 
                   return true;
            }
        };
      var pushInfo = function(){
              if (getError() == 4){
                  alert("Server and callback down " + getError());
              }else{
                  alert("Server and callback works " + getError());
              }
      };  
 
      // request (ping) the url page on server. The ping interval is set to one second
     var ping = function(){
 
           intervalID = setInterval(function(){
                setError(4);
                frequest.onreadystatechange = check;
                frequest.open("GET", url, true);
            try{
                frequest.send(null);
 
            }catch (e){
                // catch NS_ERROR_NOT_INITZIALIZED
            }
        }, pinterval);
 
      }
     // Check if the request return anything, if so, set status to true meaning that server is down
     var check = function(){
 
        try{
            if (frequest.readyState >= 1){
 
                if (frequest.status !=200){
 
                    fstatus = true;
                    setError(2);
                }else{
                    fstatus = false;
                    setError(0);
                }
            }
        }catch (e){
            setError(4);
            // firefox reports uncaught exception NS_ERROR_FAILURE with nsIXMLHttpRequest.send
            // this failure is catched here
        }    
 
      };
 
 }