Bits and pieces

FCKeditor v2.4.3 Firefox "script stack space quota is exhausted" fixed !

2009-07-17T03:59:00.000-07:00

Hi all,

I was uploading a document of about 10 MB doc in FCKeditor v 2.4.3 from server. In IE it works fine but for the Firefox v>2.0 , I was getting this strange bug "script stack space quota is exhausted" . Thought it was inherent firefox problem, But why did FCKeditor caused it ?

After reading the code and having some inline tests , I found that the following code in fckeditorcode_ie.js FCKeditor start function caused this problem,


   /* Buggy regex match for body contents*/
   /* Results in "script stack space quota is exhausted" for large documents*/

           var G=A.match(FCKRegexLib.BeforeBody);
   var H=A.match(FCKRegexLib.AfterBody);
   if (G&&H){
       var I=A.substr(G[1].length,A.length-G[1].length-H[1].length);
       A=G[1]+' '+H[1];
       if (FCKBrowserInfo.IsGecko&&(I.length==0||FCKRegexLib.EmptyParagraph.test(I)))
            I='
';
       this._BodyHTML=I;
   }else
       this._BodyHTML=A;
   };

Here the regex match for stripping the before body and after body elements is the main problem which makes the firefox browser to run out of the memory for large documents.

I replaced the regex match with indexOf to find out start and end of the body tags and stripped it , it solved this problem.

Here is the fixed code.


          /*fixed the memory problem using indexOf in mozilla browsers*/
   if (FCKBrowserInfo.IsIE)
        A=A.replace(/(]*?)\s*\/?>(?!\s*<\/base>)/gi,'$1>');
   else if (!B){
   var G=A.indexOf("");
   var H=A.indexOf("");
   if (G!=-1&&H!=-1){
       var I=A.substr(G,H);
       //A=G[1]+' '+H[1];
       if (FCKBrowserInfo.IsGecko&&(I.length==0||FCKRegexLib.EmptyParagraph.test(I)))
            I='
';
       this._BodyHTML=I;
   }else
       this._BodyHTML=A;
   };

I don't see a fix for this in the future versions also , Is this fixed in CKEditor3.0 ? If not please FCKeditor guys save the developer man days ..............

Good to be back.

2009-07-07T05:39:00.000-07:00

Reasons for my inactivity for past few months,

Reason 1: Have been involved in lots of projects.
Reason 2: Have been involved in hours of learning.
Reason 3: Have been involved in self-building and introspecting myself.
Reason 4: Found how a small dream can grow so much in span of months of hard-work and persistence.

What's the good news ?

Not being posting for a long time ?? :). Just joking . Good News is that there are lots of small things in store to share with you all.

Now I feel good to be back. So Keep checking.

HTML Search Text and Highlight

2008-09-12T06:29:00.000-07:00

Jumping straight to the solution:

//modified search function
1.function searchtext(inputText, searchString){
2.
3.
4. //building RegExp object for the search text g-global match,i-ignore case
5. var myregexp = new RegExp(searchString, "gi");
6.
7. //custom replace function just to highlight the match word in the html source
8. var myNewString = inputText.replace(myregexp,
9. function(matchTxt,key,txt){
10. return "'" + matchTxt + "";
11. } );
12.
13. //return the new highlighted text
14. return myNewString;
15.
16.}

I think going through the code will be just self explanatory as the solution is straight-forward.But did you see some weird implementation ? Bingo! you found it :) It's the custom replace function.

Let's get dirty with some syntax explanation and we will be soon back with the explanation of its implementation here.

7. //custom replace function just to highlight the match word in the html source
8. var myNewString = inputText.replace(myregexp,
9. function(matchTxt,key,txt){
10. return "'" + matchTxt + "";
11. } );

Here we have written a custom replace function to replace the matching text.We will see how it works.

First it will match the regular expression and it passes the matched text to the first argument of the replace custom function , the second argument is the runtime unique key , the third is whole text to which the search has been made.

So here is the steps that will be followed while executing the code,

1. Match the mySearchField with myregexp and find the match
2. Pass the match to matchTxt field of the custom function.
3. Wrap the matchTxt with some background color and return the modified text.
4. Replace the match with the modified text .
5. Repeat the steps 1-4 till no match is found.

Thus the explanation of the solution.

Alternatives:

1.We can just write the implementation as mySearchField.replace(myregexp,"" + textse + "");

Here,
textse - is the user entered search string

But the problem is the alphabets lower case and upper case of the original content will not be preserved, so our implementation will be a neat solution for this problem.

2. We can use indexOf and lastIndexOf of the search strings and replace the content to highlight search.
As shown in this page indexOf implementation

But when compared for efficiency ours O(n) algorithm and indexOf would be O(n*m)

Here,
n - is the number of search string match in the given content
m - is the number of tag matches

So our solution holds good for this case.

Hope this helps and will meet you soon with another cool post fo custom replace method implementation :) .

An alternate efficient implementation posted by h3 for this code is

function highlight(i, s) {
return i.replace((new RegExp('('+s+')', 'gi')), '$1');
}

This bit straight forward and more efficient . Thanks h3 for your comment. :)

Bits and pieces: Detecting browser event closing in Javascript

2008-01-07T21:57:00.000-08:00

Bits and pieces: Detecting browser event closing in Javascript

Detecting browser event closing in Javascript

2007-10-02T04:23:00.000-07:00

I've been working on a feature where the user must be prompted to take up certain action when he leaves a page by closing the browser window or by clicking an external URL,though I searched for the best possible solution but unfortunately couldn't find one.

The first thing that got my attention is the browser's "onbeforeunload" event and here is the implementation of it,

window.onbeforeunload=confirmExit;

function confirmExit(){

return "Do u want to close this page?"

}

So here the user will be prompted when he clicks the close button of the browser and when the user clicks "cancel" in prompt, it stays the same page.So far works fine.

When testing is on the way , suddenly problems getting piled up and I need to reconsider the solution above, since the requirement is to "prompt the user only when he leaves the current domain (website)" and here for the above code, the user is prompted whenever he clicks any of the links that points to other pages in the same website.

So the above code is to prompt the user, whenever he leaves the current page by refreshing it or by clicking the close button.But this was not what I wanted to implement.

So the user should not be prompted whenever,

1.An link to the same website is clicked

2.Refreshes the current page

3.Clicks mailto anchors

4.clicks the navigators containing "#" for the same page

Now to avoid these conditions, we need the anchors to be tested for the pages of the current website and external links. So the following code solves all of these problems and prompts the user only when ,

1.He clicks an external link

2.Closes the current window.

window.onbeforeunload = confirmExit;

var aClick=false;

function confirmExit(e)

{

if(document.all)e = event;

if(!e)e=window.event;

if (e)

{

if(aClick==false && (e.target==document || e.clientX<0 || e.clientY<0)){

return "You have attempted to leave this page. Are you sure you want to exit this page?";

}

}

}

The following code should be strictly placed below all the contents of the current page .

function setAClick(){

aClick=true;

}

function cancelAClick(){

aClick=false;

}

var aList=document.getElementsByTagName("a");

if(aList && aList.length>0){

for(i=0;i < alist.length;i++){

var a=aList[i];

if(checkForLocal(a.href)){

a.onclick=setAClick;

}else{

a.onclick=cancelAClick;

}

}

}

function checkForLocal(src){

return (src.indexOf("localhost")!=-1 ||
src.indexOf("urdomain")!=-1 || src.indexOf("javascript")!=-1 ||src.indexOf("mailto") !=-1 || src.indexOf("#")==0);

}

This eliminates all the above problems and confirms with the user only when navigating to the external URL's or closing the browser. :)

And may be this is an really odd solution for this problem and your comments are always expected. :)

Java - Interesting Stuffs

2007-06-26T03:24:00.000-07:00

I am just still an admirer and constant learner of JAVA, So here are some interesting stuffs .I will try to constantly update once I come across some interesting things (atleast to me:) ),

To resurrect an object(to make the object alive again) instead of reassigning in the object in finalize method "create a clone"
Java Object are created in heap while in C++ ,they are created in Stack
Object persistence can be done using object serialization and DATA ACCESS OBJECTS(DAO)
Making an object alive in finalize method is useful when we use JNI for a c++ class and do it with a "termination condition"(when there is a code to check whether all the object references in the program has been made null) during garbage collection.
System.gc() may or may not run finalize() of for the orphans (object that holds no reference) but Runtime.runFinalizersonExit(true) and System.runFinalizersonExit(true) will surely make the objects ready for the garbage collected.
Java supports only pass by value, either for an object or a primitive type.
Suprising,regertfull!!!
Let's discuss,

Actually when we call a method swap(p1,p2) and the method definition goes like this

public void swap(Point p,Point q){
Point temp=p;
p=q;
q=temp;
}

Simple swap isn't but here there are lot more to analyse if p1.i=10,p2.i=11 what
will happen if we call
swap(p1,p2);
p1.i is 11 and p2.i is 10 ??? NO..

when we call swap(p1,p2) the reference value is passed not the object itself
(note it passes only reference value) so in method swap
p-->p1 and q-->p2 (Note: --> synonymous to 'refers')

so for this snippet,
Point temp=p; // temp-->p-->p1
p=q; // p-->q
q=temp; // q-->temp-->p-->q ( as by above step)

So both p and q refers to p2 now ... so we will get the output p1.i is 10 and p2.i is 10.
Since the Java uses objects to be created in heap.It's not fast to access as in C++ ( it uses stack ).
The memory model goes like this,

1.Processor Registers - faster access since they live in processor itself and they are limited
2.Stack - They live in RAM but has direct support from processor using "stack pointers".
It is needed to know the size of the storage element ,since we are in need to move the pointers.So object references are stored in stack not the object.
Object references are 4 bytes for 32 bit computers and 8 bytes for 64 bit computers.
3.Heap - It is a memory pool that living in RAM area.It's flexible since the compiler need not to know
the amount and life of storage.but it is slower when it compared to stack storage allocations.
4.Static storage - "fixed location" in java the static members of the object are stored in these
locations but not the object itself.They also live in RAM.
5.Constant Storage - The constant values are placed directly in the program code, which is safe sice they can never change
but optionally they are stored in ROM(in embedded systems).
6.Non-RAM Storage - external file where persistent object mechanisms are used to store the object in the secondary memory
files and in streaming where object are sent to another machine.

Since the heap holds the objects, the garbage collection can be expensive and the compiler must be built with effective algorithm to solve this. This can be achieved in the following ways,
- Like a conveyor belt the object can be allocated with the help of "heap pointer" so it will function like a stack
(but there is still overhead for book-keeping(maintaining heap pointer) operations but effective
than searching for a memory ) but this might lead to paging it can be avoided like compacting the memory once a while
the garbage collectior steps in.

- There is simple method called 'reference counting' each object has a constant with no. of reference made in it.
If one reference goes null then the object's referece count is decreased by 1.Likewise , when the reference countof an object goes 0 it is garbage collected.
One drawback in this is if there is a circular reference like a->b b->a we can find the fault in
it by putting a->b->a so this is equal to just a,so the reference count of a is 1 , but this just implies it has no
meaning full reference and it has to be garbage collected.
So these type of checks needs special algorithm to do it and this method is seldom used.

- Actually the JVM uses an adaptive method for garbage collection,

It is the combination of STOP AND COPY , MARK AND SWEEP

"STOP AND COPY" involves stop the current execution and copy the live objects
(found out by tracing the path of references in stack and static storage) to another heap while leaving the
dead objects(those have no references in the stack or static storage) in the old heap for garbage collection.

Two issues are in this method:
1.Copy-collectors : since we need to allocate two heaps of same size to copy the live objects.
2.Copying : sometimes the program gets stabilized and no or only few objects needs to be garbage collected
at that time the its really in-efficient to copy the whole heap to another heap of same size.

So this method can be used when there is large amount of objects need to be garbage collected.

"MARK AND SWEEP":
Finds the live objects as in STOP AND COPY but the garbage collection is different.
It marks each live object by setting a flag.
Here only the marking process is finished the sweep(releasing dead objects) occur.
It is generally slow but if it is used with small no. of garbage then its pretty fast.

So the JVM can switch to any one of these methods depending upon the no. of garbage.
Thats why it is called adaptive method.It can switch to any method in middle of the garbage collection.

A better alternative available for garbage collection is JIT(Just in time).
which converts the byte code(.class files) partially or fully to native codes.
but it has 2 drawbacks:
1.the conversions slows the execution.
2.It increases the exectuble memory size resulting fragments(paging) to occur which will still reduce the execution speed.

So it uses "lazy evaluation" technique where it is not compiled to native code until it is asked for.
The recent JDK's uses similar approaches to optimize the code like more code it executes faster it gets.
un-initialized member variable are assigned to proper startup value according to the types and if they are local variables they are assigned with garbage values instead compiler error is thrown.
If we have same method with same signature in a abstract class and an interface extended and implemented respectively in a class , it doesn't cause any error but if they have return types different then they give a compile time error this is one of the problems we may face and the possible is to create a inner class with implements or extends depending upon its enclosing class's usage.
equals and hascode method of object should always comply to the following contracts,

-Reflexive,Symmetric,Transitive,Consistent,Systematic treatment of null values.
If two objects are equal then their hashcode should always be equal and its not necessary that if objects have same
hascode can't be equal.
-when implementing ur own equals method give Object as its argument not ur own class 'coz if u use ur own class
then it will just overload the equal method but not override,so it always safe to have equals method with object
argument in order avoid weird beahviours

Here are some useful guidelines for implementing the hashCode method correctly.

1. Store an arbitrary non-zero constant integer value (say 7) in an int variable, called hash.
2. Involve significant variables of your object in the calculation of the hash code, all the variables that are part of equals comparison should be considered for this. Compute an individual hash code int var_code for each variable var as follows -
1. If the variable(var) is byte, char, short or int, then var_code = (int)var;
2. If the variable(var) is long, then var_code = (int)(var ^ (var >>> 32));
3. If the variable(var) is float, then var_code = Float.floatToIntBits(var);
4. If the variable(var) is double, then -
long bits = Double.doubleToLongBits(var);
var_code = (int)(bits ^ (bits >>> 32));
5. If the variable(var) is boolean, then var_code = var ? 1 : 0;
6. If the variable(var) is an object reference, then check if it is null, if yes then var_code = 0; otherwise invoke the hashCode method recursively on this object reference to get the hash code. This can be simplified and given as -
var_code = (null == var ? 0 : var.hashCode());
3. Combine this individual variable hash code var_code in the original hash code hash as follows -
hash = 31 * hash + var_code;
4. Follow these steps for all the significant variables and in the end return the resulting integer hash.
5. Lastly, review your hashCode method and check if it is returning equal hash codes for equal objects. Also, verify that the hash codes returned for the object are consistently the same for multiple invocations during the same execution.

The guidelines provided here for implementing equals and hashCode methods are merely useful as guidelines, these are not absolute laws or rules. Nevertheless, following them while implementing these two methods will certainly give you correct and consistent results.

TIPS,
* Equal objects must produce the same hash code as long as they are equal, however unequal objects need not produce distinct hash codes.
* The equals method provides "deep comparison" by checking if two objects are logically equal as opposed to the "shallow comparison" provided by the equality operator ==.
* However, the equals method in java.lang.Object class only provides "shallow comparison", same as provided by the equality operator ==.
* The equals method only takes Java objects as an argument, and not primitives; passing primitives will result in a compile time error.
* Passing objects of different types to the equals method will never result in a compile time error or runtime error.
* For standard Java wrapper classes and for java.lang.String, if the equals argument type (class) is different from the type of the object on which the equals method is invoked, it will return false.
* The class java.lang.StringBuffer does not override the equals method, and hence it inherits the implementation from java.lang.Object class.
* The equals method must not provide equality comparison with any built in Java class, as it would result in the violation of the symmetry requirement stated in the general contract of the equals method.
* If null is passed as an argument to the equals method, it will return false.
* Equal hash codes do not imply that the objects are equal.
* return 1; is a legal implementation of the hashCode method, however it is a very bad implementation. It is legal because it ensures that equal objects will have equal hash codes, it also ensures that the hash code returned will be consistent for multiple invocations during the same execution. Thus, it does not violate the general contract of the hashCode method. It is a bad implementation because it returns same hash code for all the objects. This explanation applies to all implementations of the hashCode method which return same constant integer value for all the objects.
* In standard JDK 1.4, the wrapper classes java.lang.Short, java.lang.Byte, java.lang.Character and java.lang.Integer simply return the value they represent as the hash code by typecasting it to an int.
* Since JDK version 1.3, the class java.lang.String caches its hash code, i.e. it calculates the hash code only once and stores it in an instance variable and returns this value whenever the hashCode method is called. It is legal because java.lang.String represents an immutable string.
* It is incorrect to involve a random number directly while computing the hash code of the class object, as it would not consistently return the same hash code for multiple invocations during the same execution.

ref:http://www.geocities.com/technofundo/tech/java/equalhash_cartoon.html

Fckeditor - removing tool bar items

2007-01-26T00:01:00.000-08:00

I was working around for a couple of days to enable a feature were we can remove the tool bar items depending upon some permissions like hiding Style and Bold for a particular user group.
I don't find any feature in-built in the FCKeditor to do this , so thought of trying some hack on it.
The possible workaround I tried was this,

In the FCKeditor the editor/fckeditor.html page loads up all the configurations while start-up , so we can possibly remove the tool bar items for a specific Toolbarset before creating it.Here is how I did it.

In LoadToolbar() function in the fckeditor.html page I added the following lines,

function LoadToolbar()
{
var oToolbarSet = FCK.ToolbarSet = FCKToolbarSet_Create() ;
var removeToolBarSet=FCKURLParams['RemoveToolBarSet'] || '';
if ( oToolbarSet.IsLoaded )
StartEditor() ;
else
{
oToolbarSet.OnLoad = StartEditor ;

//get the current tool bar from the URL and look up in the FCKConfig.js

hyCurrentToolBar=FCKURLParams['Toolbar'] || 'Default' ;
var toolBarArray=FCKConfig.ToolbarSets[hyCurrentToolBar];

if(removeToolBarSet.indexOf('upload')!=-1){ //disable the upload Tab
FCKConfig.ImageUpload = false ;
}

//Remove the tool bar items specified in the list
var strippedToolBar=RemoveToolBarItems(toolBarArray,removeToolBarSet);
if(strippedToolBar){
FCKConfig.ToolbarSets[hyCurrentToolBar]=strippedToolBar;
}
oToolbarSet.Load( FCKURLParams['Toolbar'] || 'Default' ) ;
}
}

function RemoveToolBarItems(toolBarArray,removeToolBarSet){

if(removeToolBarSet && removeToolBarSet.length>0){

for(i=0;i<toolBarArray.length;i++){

var rowStrip=toolBarArray[i];

for(j=0;j<rowStrip.length;j++){

if(removeToolBarSet.indexOf(rowStrip[j])!=-1){

toolBarArray[i].splice(j,1);//dynamically removes the array item and re-arranges it

j--;
}
}
}

}
return toolBarArray;
}

In JAVA , in the FCKeditorTag.java add the following lines,

private String removeToolBarSet=null;
//add its getters and setters

in doStartTag() add,
if(removeToolBarSet!=null){
fcked.setRemoveRoolBarSet(removeToolBarSet);
}

then perform the same definitions in the FCKEditor.java and append the appropriate query string in the createIFrameHTML().

And all over just don't forget to give the attribute setting in tld specifications and also in the custom tag in JSP page!!! :)

It's as simple is it 8-) ..

Please feel free to comment me if any doubts and also If i am wrong..

The HaCkERdOm-A ViEw

2006-11-06T20:51:00.000-08:00

"Hacker Emblem".

It's an article which changed my perception about technology Vs Life !!! .I am bit got attached to the world of hackers and their culture.(P.S Hacker is one who build systems and the Cracker is one who breaks it) It's all about the world of fascinating technology!!..

The Words I found in this link http://catb.org/~esr/faqs/hacker-howto.html by Eric Steven Raymond
captured most of my interests .I thank Eric for this wonderful page. He has explained about who is an hacker and what he should do to be labelled as hacker(this label is not stick by him but by others reputation on his work!!).

Now as a first step I have decided to learn all and everything about linux,python(the most simple and wonderful language I have ever seen 'coz I have some previous exp. in this language but not fully) and JAVA(the most respected language by me, once I thought this is my life and still it is) now have to move forward with it by learning v1.5 .. and also I am learning Struts along with these , 'coz I have started learning before itself and can't leave it all together now and moreover I love this framework too :)

So for linux I don't find any good books here especially in coimby but had to go chennai or b'lore to get a nice one and I will get it soon.. But for now I have decided to learn it from the web.

Though I know some basics about linux , I decided to start it from scratch.To begin with , http://www.linux.org/lessons/beginner/index.html is a good link,
Another interesting and a very good project for linux documentation!!! can be found in this link
http://kernelbook.sourceforge.net/.Then for all about linux kernel architecture, see here http://plg.uwaterloo.ca/~itbowman/CS746G/a2/. and also don't forget about http://mehmoodbluffs.blogspot.com/ I will be more interested about sharing your thoughts regarding these subjects and also regarding anything that catches your interest.

ok Now I can see clearly thru my dreams uppps.. and will make it true one day.huh.. but how much I have to learn!!! hmmm.. thats the way .. I love it..... :)

TeChNiQuEs-DiStRiBuTeD

2006-11-02T00:40:00.000-08:00

Hey folks,

I like to share what I learn and Where I went wrong . I like to be more out of box in programming and I am very much interested in mile stone technologies and softwares.I like to share more about Fckeditor,eclipse PDE,Mozilla extensions,Python cool stuffs and much more..

K see you then within a short while .. have fun..