Develop Reference

javascript php internal server error 500 random

Apologies if this question is a bit vague, but I have no idea how to make it more specific. I am a beginner when it comes to javascript. I have a web page which sends a number of ajax calls to the server to call php scripts which runs some sql against a mysql database. Everything was working fine then all of a sudden I started to get an internal server error 500 on one of my ajax calls. The ajax call is placed in a function, it works most of the time. Only when I pass the function one specific sql query does it give the error. I've tested the query in my database manually and it works so its not an issue with the query that I am passing. The strange thing is, since the error has started, every now and then it does work, however most of the time it is not working, the error seems to be somewhat random. I realise that with limited information it may be impossible to give an exact answer, but has anyone experienced anything like this before? OR does anyone have any clues as to how I can get to the bottom of this. I've tried everything. I will paste the function that is causing the error (not sure if that will help at all). The error comes on the "xmlhttp.send();" line.
function phpRequest2(prov, phpsc, funct, bolL) {
<!-- document.getElementById("demo").innerHTML = qry; -->
var xmlhttp;
if (window.XMLHttpRequest) { // code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
} else { // code for IE6, IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
document.getElementById("demo").innerHTML = prov;
xmlhttp.open("GET", phpsc + ".php?qry=" + prov, true);
xmlhttp.send();
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var arrLocs = JSON.parse(xmlhttp.responseText);
funct(arrLocs, bolL);
}
}
}

You best bet at finding out the reason when you get the Error 500 is to edit your php.ini file and change the following parameters
display_errors = Off
display_startup_errors = Off
to
display_errors = On
display_startup_errors = On
Hopefully that should give you exact details on what your error is and thereby help you solve it.

AJAX mysql command not immediately executed?

So I have some code, which checks for whether a one time use discount code exists, and if so, it applies it and then marks it as used in the database. The problem is, it ends up being useable more than once if you spam click it, and then some time maybe 15-20 seconds later it stops being useable.
The relevant javascript component:
if (window.XMLHttpRequest) {
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
} else { // code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState==4 && xmlhttp.status==200) {
discountAmount += parseFloat(xmlhttp.responseText);
modifyCartOrder();
}
}
xmlhttp.open("GET","forms/jsPromoCode.php?code="+code+"&type="+order_name,true);
xmlhttp.send();
This is processed over in the php file, and when a match is found we echo that amount and then delete the entry
$mysqli->query("DELETE FROM discounts_available WHERE `index`=$index");
The php file is indeed doing what its supposed to. When you click apply code, it is immediately deleted from the database. The problem is, even with the code no longer in the db, you can still apply the code over and over for some amount of time before the js file finally realises there is no entry in the db. Why is this?

You should first check if it exists in DB then only you should proceed with request, it should be very first statement.
If it does not exists you can send response saying code already applied.

You most likely need to lock the table ASAP so no other instances can modify the table concurrently.
http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html

I did not get your problem, exactly I am assuming lost of things, so..
//this is triggered on some click, right?
//TODO:- check if button is disabled? you can have some js variable or check button attribute disbled
//TODO:-if its not disaled->{so first disable the button when it is clicked } else do nothing
if (window.XMLHttpRequest) {
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
} else { // code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState==4 && xmlhttp.status==200) {
discountAmount += parseFloat(xmlhttp.responseText);
// if succefull keep button disabled
// else renable it, so that it can be clicked again.
modifyCartOrder();
}
}
xmlhttp.open("GET","forms/jsPromoCode.php?code="+code+"&type="+order_name,true);
xmlhttp.send();
thers's no syntax problem here in your code its logical,
ajax call is asynchronous call, it does not happen in sequence
1) You clicked
2) Request Sent
3) Request Processed
4) JS is informed : your modifyCartOrder function executed
what I am trying to say here is that, there is no 3 immediately after 2, 3 will take time to start, js has no control over it, whenever php is done it will reply there's no guarantee. so you can repeat 1 again and again, and 2 will keep repeating... and so 3 will...
I hope I understood your problem, and you understood what I am trying to say :)

Problem is : You are sending asynchronous ajax calls from following code :
xmlhttp.open("GET","forms/jsPromoCode.php?code="+code+"&type="+order_name,true);
Solution : as defined , for opening an ajax call , method is :
xmlhttp.open(method,url,async)
So, You have to modify above line as:
xmlhttp.open("GET","forms/jsPromoCode.php?code="+code+"&type="+order_name,false);

XMLHttpRequest state 2 waits for response from server

I'm trying to execute a block of code when my XMLHttpRequest reaches state 2. The reason why I want it to be in state 2 is that I don't want the user to wait for a response of the server( I would like to redirect the user at this point).
var xmlhttp;
if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
}
else {// code for IE6, IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 2) {
window.location.href = urlFromPreviousAjaxcall;
}
}
xmlhttp.open("POST", "url", true);
xmlhttp.send();
However the block of code inside the if(xmlhttp.readyState == 2) will only be called as soon as the server is done processing the call. This part has to be executed as soon as the call is made( without the waiting from the server).
In the documentation I found that state 2 is reached as soon as the call is send. However that is not the case.
Update:
the call I am trying to make involves calling a Api on the server( this takes time to complete). For the client it doesn't matter what happens to the call.The only thing I want is that the call is executed. So basicly I'm trying to gain speed here.
I know that as soon as I redirect the user, the code will stop running. However the call to the server should have been made(and send away).
What am I missing or doing wrong?

Thanks you all for your help.
I found the solution:
[HttpPost]
public void methode(String parameter,String parameter)
{
Task.Factory.StartNew<string>(() => RunTask(accessToken, parameter, parameter));
}
private string RunTask(String parameter, String parameter)
{
try
{
// Code to execute here
return "Done!";
}
catch (Exception e)
{
return "Error: " + e.Message;
}
}
At the server I started a Task. In this task I execute the long procces. It still takes a brief moment before the server returns the call to the user.
When debuggin ( in visual studio) you can see that the task is running without the presents of the user.
Note : all sessions are gone at the moment I redirected the user to an other page.

XMLHTTP readyState 3 Not Updating in Webkit

This question has been asked twice on these forums, but the answer provided is not working for me.
The issue is that I have JSP page which is returning and flushing small amounts of output.
I am using the following code to read the output:
var xmlhttp;
if (window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
} else {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 3) {
alert(xmlhttp.responseText);
}
}
xmlhttp.open("POST", "download.jsp", true);
xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlhttp.setRequestHeader('X-Requested-With', "XMLHttpRequest");
xmlhttp.send($('#submitDownloadForm').serialize());
On Firefox this works fine, and I am given 3 alerts during the duration of the process.
However, on Webkit based browsers such as Chrome and Safari, I am given the first alert, but not the other 2 until the process has completed.
Other answers have said that changing the Content-Type:text/plain or Content-Type:application/octet-stream, but if I do this, the readyState jumps straight to 4 as if the process has completed instantly.
I cannot find any solutions for this.
Any help greatly appreciated, thanks in advance everyone.

I added the following code to the JSP file just before where it produces the output, and this has resolved the issue on Webkit-based browsers:
response.setContentType("application/octet-stream");
I'm now getting the updates every time output is flushed.

Autorefresh a .gsp in Grails when a database table changes

What I have:
- A database table called 'orders' that is constantly populated by some java module on the back-end.
- A website running on Grails that displays those orders. More precisely - a list.gsp in the Orders view.
- the list.gsp will display new orders if the refresh button is pressed on the browser.
What I need:
- Some way for the .gsp page on a client to get refreshed automatically when a new order is placed on the database.
- The autorefresh needs only to autorefresh the .gsp page when the client is already in the .gsp page. i.e. if a client is on the show.gsp for a particular order, then no need for autorefresh.
Things I though might help:
option1: Having a grails service that will periodically (every 5sec.) query the database to see if there are any new orders. If there are, then somehow from the .gsp page call again and re-render the .gsp page ??!
- suboption1-1: create and destroy a new connection every 5 sec.
- suboption1-2: create and keep a connection alive ... forever
option2: Have the java module that places the orders call a refreshController thru the web and somehow re-render the .gsp page. i.e. Have the refreshController notify all clients currently in the .gsp page that a refresh is needed.
=================================================================================
Follow up:
How can I call a controller from java script?:
function checkDB()
{
t = setTimeout("com.mypackage.DBChecker.checkdbController.checkAction()", 5000)
}
==================================================================================
Follow up 2:
So I almost got what I wanted working except that I can't figure out how to AJAX back to my list.gsp page only part of itself. I dont want to refresh the whole page, but only a division with id="refresh table". i.e. .
I have the following code at the moment that is not working:
<script type="text/javascript">
function checkDB()
{
var xmlhttp;
var xmlDoc;
var x;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
xmlDoc=xmlhttp.responseText;
x=xmlDoc.getElementsByTagId("refreshTable");
for (i=0;i<x.length;i++)
{
txt = x[i].childNodes[0].nodeValue;
}
document.getElementById("refreshTable").innerHTML=txt;
}
else
{
}
}
xmlhttp.open("GET","http://localhost:8080/Orderlord/checkdb/checkdb",true);
xmlhttp.send();
}
window.load = checkDB();
</script>
=================================================================
Follow up 3:
I succeed in returning only a partial page through my ajax call by copy/paste the div that i wanted to a separate gsp. I dont know how It is working - it's a bit of a magic to me, but everything works, except for when I try to sort the columns of my table. Then, only that partial gsp is rendered on my browser, without the rest of the initial page resulting, in a simple tabulated text page. Also once I end up in that kind of html page - the autorefresh doesnt work anymore, but as long as I will stay in the checkDB list view, the page will refresh every 5 seconds.
...So , how do I fix my problem
Another thing i cant figure out is how to return True/False from a controller to a javascript function in the gsp and how exactly did you have in mind for me to use it?
And lastly, I am currently using 'window.load = timeDB' inside my tag to call the timer function. I tried using , but for some reason I cant get it to work no matter what. Is there something I should keep in mind when using ?
Very lastly: What can I do to simply refresh part of the gsp every 5 sec?

You could take the approach of setting a timer on the page via javascript. You would then invoke a lightweight ajax call from your gsp page back to your controller that would yield a true/false to indicate if you needed a full refresh. This is a fairly simple approach but you would want to be careful that the back end target of the ajax call is optimized as it will be called every 5 seconds for each user on that page. It also generates quite a bit of traffic.
I might explore the publish subscribe plugins from the earlier answer before falling back to this approach, however I have implemented the simple timer / ajax call (in the java struts world) on a medium size website with pretty good results.

What you're explaining is a typical publish - subscribe model.
There are a few plugins in grails that will help you do this. Look at Atmosphere and cometD for this. Both options provide this kind of pub/sub.
If they feel a little too heavy for what you want, you should checkout Pusher and the associated Grails plugin. It is a little nicer because you can just integrate a javascript library in your gsp page and do the push from the server side whenever an order is created. Feels slightly lighter than the 2 libraries above. It uses HTML5 web sockets.

So the following piece of code in my list.gsp did it for me. I decided that just refreshing the 'div id="myDiv"' under question every 5sec it's good enough, otherwise I would have hit the server every 5 seconds anyway since I am querying the database.
<script type="text/javascript">
function ajaxrefresh()
{
var xmlhttp;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
//alert("aaaaaaa")
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
else
{
//alert("state: "+xmlhttp.readyState)
//alert("status: "+xmlhttp.status)
}
}
xmlhttp.open("GET","http://${localHostAddress}:12080/Orderlord/refresh/refreshactiveorders",true);
xmlhttp.send();
var t=setTimeout(ajaxrefresh,5000);
}
window.load = ajaxrefresh();
</script>