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:
[code=javascript]
function createRequestOb ject()
{//creates an httprequest object
var ro;

var browser = navigator.appNa me;
if(browser == "Microsoft Internet Explorer"){
ro = new ActiveXObject(" Microsoft.XMLHT TP");
}else{
ro = new XMLHttpRequest( );
}
return ro;
}

var http = createRequestOb ject();
var ourinterval=set Interval("SendU pdate()",5000);

function SendUpdate()
{
http.open('get' , '/refresh.cgi?tim e='+ new Date().getTime( ));
http.onreadysta techange = handleSendUpdat eReponse;
http.send(null) ;
}
function handleSendUpdat eReponse()
{
if(http.readySt ate == 4)
{
var update = new Array();
if (http.status==" 200")
{
var response = http.responseTe xt;
if (response!="")
{
if(response.ind exOf('|' != -1))
{
update=response .split('|');
if (update.length> 0)
{
if (update[1].indexOf("SUCCE SS")>-1)
{
var line=update[1];

var things=new Array();
things=line.spl it('&');
var i;
for (i=0;i<things.l ength;i++)
{
var nameval=things[i].split('=');
if (i>0)
{
returnObjById(n ameval[0]).innerHTML=nam eval[1];
}
}
}//end of found "SUCCESS"
}//end of update split("|") to have multiple sections
}//end of response.indexo f("|")
}//end of response!=""
}//end of status==200
}//end of readystate=4
}//end of function
[/code]

[Plater]

Well, turns out that its something firefox just hasn't gotten around to fixing yet:

http://www.fleegix.org/articles/2006/10/21/xmlhttprequest-and-0x80004005-ns_error_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:
[code=javascript]
function SendUpdate()
{
var action="DATETIM E&TEMPERATURE&H UMIDITY&SAMPLES TATE";
action+="&CHAN1 &CHAN2&CHAN3&CH AN4&CHAN5&CHAN6 &CHAN7&CHAN8&CH AN9&CHAN10";
try
{
http.open('get' , '/refresh.cgi?'+a ction+'&amp;tim e='+ new Date().getTime( ));
http.onreadysta techange = handleSendUpdat eReponse;
http.send(null) ;
}
catch(error)
{
//alert(error);
returnObjById(" SAMPLESTATE").i nnerHTML="Probl em Communicating";
}

}

function handleSendUpdat eReponse()
{
if(http.readySt ate == 4)
{
var update = new Array();
if (http.status==" 200")
{
var response = http.responseTe xt;
if (response!="")
{
if(response.ind exOf('|' != -1))
{
update=response .split('|');
if (update.length> 0)
{
if (update[1].indexOf("SUCCE SS")>-1)
{
var line=update[1];

var things=new Array();
things=line.spl it('&');
var i;
for (i=0;i<things.l ength;i++)
{
var nameval=things[i].split('=');
if (i>0)
{
returnObjById(n ameval[0]).innerHTML=nam eval[1];
}
}
}//end of found "SUCCESS"
}//end of update split("|") to have multiple sections
}//end of response.indexo f("|")
}//end of response!=""
}//end of status==200
else if(http.status= =12029)
{
returnObjById(" SAMPLESTATE").i nnerHTML="Probl em Communicating";
}
}//end of readystate=4
}//end of function
[/code]

[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
		}	
			
      };
      
 }