URGENT: How to debug headers already sent php/server error

techguy

Hi There,

I need to solve this problem tonight, if anybody could help me i'd really appreciate it.

Basically i've wrtten a CodeIgniter app for outputting PDF files using dompdf. It works fine on my local server but won't work on my webserver.

I'm getting the error "session headers already sent". Now, I know how this error is caused but i'm having trouble finding the source of the error.

Is there a way that I can debug the application to see what text is being echoed before the header() functions are called in dompdf?

ocallagh

I would say it's 99% a problem with the format you are saving your files in. Some editors add what is called a BOM to the file which is ignored by most but PHP interprets it as output. It is also invisible so difficult to remove.

What editor are you using? Do a google on "remove BOM"

http://tomasz.sterna.tv/2009/06/php-cannot-modify-header-information-and-the-dreaded-bom/

techguy

i'm using notepad++..

I'll check BOM now..

techguy

Actually i'm using VS.PHP plugin in Visual studio at the moment..

Kenno90

I had that problem last year.The solution for me was there was extra spaces after the <?php and ?> tags.

Wouldn't hurt to try

techguy

Ok, I just tried that.. no go!!

So, i've tried everything and i'm not even sure i'm doing it right.

There's loads of files and I can't go trying them all. I've spent over an hour on this now.

What am I to do now??

ocallagh

Can you link me to the file? What is the exact error you get? Does it give a line number?

Aside from the file format and rogue whitespace outside of <?php ?> as Kenno90 said I can't see an easy way around this...

The fact it is ok on your dev server and not live led me to believe it was an issue with file format.

One last quick fix might be your error handling. Perhaps your live server has a different error setting and it is outputting an error prior to the headers being sent? Try to supress errors to at least see if that is the problem.

Insert at top of page (before any includes)

ini_set("display_errors", 0);

techguy

Ok, i just tried that ocallagh and it doesn't seem to change anything.

I have found the line that produces the error in the DOMPDF code. It is basically

if  ( headers_sent())
      die("Unable to stream pdf: headers already sent");

I don't think DOMPDF is the problem here. I just went and made a simple PHP script to implement that on it's own (away from my CodeIgniter App) and it worked.

This leads me to believe that my CodeIgniter app has an error in it somewhere. But I don't know how to find/fix it.

ocallagh

You could use (top of script before any includes etc)

ob_start();

and then place (just before that code you quoted above)

$output = ob_get_clean();

. This will stop anything from getting sent to the browser.. and you could even inspect the contents of $output to see what is getting sent. That's just a hack and if you are using a framework like CI I don't know if it will cause issues. Also I don't know if this will stop that BOM problem


perhaps stick a die(); function just before that code you quoted and see what the output is at that stage. I would guess it's a white space character or nothing..

techguy

OK,

This hasn't been fixed.

...

techguy

Hey ocallagh, that hack worked.. Thanks A LOT!!!!

Now to find out what caused it.. I'll try the die() command now. Thanks.

techguy

Look at this badboy..

*Thats selected whitespace.. 1 space to be precise. Now how in gods name do I find that.

Some kind of program that would print out the filename and line number before each piece of text that is sent to the browser would be nice...

I wonder if something like that exists.

ocallagh

satan.gif, has me in stitches glad you have a hack working!

It's a matter of inspecting each included file. I guarantee it's a white space character before the <?php at the top or bottom of some random file.. or else that BOM issue.

techguy

ocallagh wrote: »

satan.gif, has me in stitches glad you have a hack working!

It's a matter of inspecting each included file. I guarantee it's a white space character before the <?php at the top or bottom of some random file.. or else that BOM issue.

Yea you see the problem is that i'm using a framework so it's all about including files and including more files..

CI doesn't use closing tags and i'm pretty sure i've checked all the opening tags for spaces..

Must BOM. I must get/make a program to find these bad guys..

Thanks for all your help.