"Headers already sent", not the usual case!

Bijan

I'm trying to send some headers to stop the page from being cached, but I get this usual error: "Headers are already sent"!

Hey, I'm not sending my headers in the middle of the page, there is NO space before these commands, and I'm putting them exactly above my document, only after the php starting tag! Here it's my code:

<?php
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");    // Date in the past
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); 
                                                    // always modified
header("Cache-Control: no-store, no-cache, must-revalidate");  // HTTP/1.1
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");                          // HTTP/1.0
?>

Don't bother yourself, it's nothing wrong with the code! I copied that exactly from the php manuals, the only thing that might be the cause of my problem (I think!) is that I'm trying to use it in the "index.php" file, the file that is loaded automatically by the server when the address is entered. I say it because I wrote the same thing for other pages and I didn't have any problem.

If I'm missing anything in here, I really appriciate it if you point it out!

bijan

PS: There is no extra space in my file!

Weedpacket

It says the error is on line 2 of index.php?

stolzyboy

you could always try putting

<?
ob_start();
//header stuff
//header stuff
?>

at the beginning

alanzhao

are there any whitespaces before <?php ?

Bijan

Weedpacket: yes, it does! It starts from line 2 and goes till line 5 (exactly the length of my headers!).

stolzyboy: I didn't know about this directive, I have to check it out and see what happens, thanks.

alanzhoa: No, there are not!

Weedpacket

It sounds like the server is including something that generates output before this script is run (or this script is included in something else); something to do with the server's URL resolution rules (does it happen when you specify "index.php" explicitly in the URL?). Try serving up an empty HTML file called empty.php ("<html><body></body></html>") and see what arrives at the browser by viewing the source (note that IE's "View Source" doesn't display the source that actually gets sent, but its own interpretation of what it reckons should have been sent.)

Sxooter

I've also had some gui editors insert non-viewable characters ahead of my <?php before. Take a look at it in something like vi or a hex editor and make sure you don't have some non-printable at the front.

Bijan

note that IE's "View Source" doesn't display the source that actually gets sent, but its own interpretation of what it reckons should have been sent.

Then how would I know what is inside the file?! Should I use Mozilla or something?

I've also had some gui editors insert non-viewable characters ahead of my <?php before. Take a look at it in something like vi or a hex editor and make sure you don't have some non-printable at the front.

I don't think so, because I wrote several other pages with my current editor (Edit Plus) and they didn't have any problem.

stolzyboy

did you try

<?
ob_start();
?>

and did it work, it should as long as you put it as the first line

jnuneznyc

To remove the web server out of the range of possible problems. Rename the file and try it... If it works then the server is pre-pending stuff to the index.php file.

jimson

you put this file on your own server or you upload it into the hosting site?

jnuneznyc

Umm... the server

Sxooter

When I said I'd had some editors do that, what I meant was that I'd typed something like CTRL-J while in the editor, and it had silently inserted the CTRL-J into the file without telling me, and you couldn't see it with normal editing and whatnot, only with a hex viewer (or vi or some other editor primitive enough to tell me there were CTRL characters in my file.)

Bijan

Originally posted by Weedpacket
It sounds like the server is including something that generates output before this script is run (or this script is included in something else); something to do with the server's URL resolution rules (does it happen when you specify "index.php" explicitly in the URL?). Try serving up an empty HTML file called empty.php ("<html><body></body></html>") and see what arrives at the browser by viewing the source (note that IE's "View Source" doesn't display the source that actually gets sent, but its own interpretation of what it reckons should have been sent.)

Well, I did it and it doesn't return anything bad:

<html>
<body>
</body>
</html>

Bijan

Originally posted by stolzyboy
did you try

<?
ob_start();
?>

and did it work, it should as long as you put it as the first line

I did try it, but it gives me the same error. Nothing changed! Also I looked up the PHP manuals, it says ob_start can buffer everything but the headers. So, if we have a hidden header (?!!) in here, it'll be still sent, am I right?

Bijan

Originally posted by jnuneznyc
To remove the web server out of the range of possible problems. Rename the file and try it... If it works then the server is pre-pending stuff to the index.php file.

It doesn't work!

Bijan

Hey! I found out something!

I made this file:

<?php
ob_start();
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");    // Date in the past
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); // always modified
header("Cache-Control: no-store, no-cache, must-revalidate");  // HTTP/1.1
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");                          // HTTP/1.0
?>

<html>
<body>
Hello!
</body>
</html>

And uploaded it, when I tried to see it, I saw the same errors. It seems whatever is copied in the main directory of the server (host), generates the same errors, so, it's something wrong with them, huh?

Edit: No, I was wrong! I made a new directory and copied that file inside of it, and it still gives me the same warnings! I still can not understand why it doesn't gimme any error for the "admin" directory that I have. That directory contains all the admin files and I use the headers in all the files without any error. Using them in any other directory/file will generate those damn warnings! Just confused!

stolzyboy

well like i have been saying, the ob_start() is used to allow you to use headers after output, probably no the best way, the best way is to ensure you don't have any output, text, whitespace, hidden characters, etc...., and you apparently have looked at the php manual wrong if it says that it doesn't work with headers, cuz

This function will turn output buffering on. While output buffering is active no output is sent from the script (other than headers), instead the output is stored in an internal buffer.

not sure why it isn't working for you just make a simple page like this:

<?
ob_start();
header("Location: http://www.yahoo.com");
?>

and save it as whatever.php and test that, if that doesn't work, then your host may be limiting you somehow, not sure how, but...

Sxooter

If you're on a linux box, use 'wget -s http://yourserver/yourfile.html'

to grab the file WITH HEADERS that you can then read in a text editor.

If you're on Windows, find a friend with a Linux box. :-)