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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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 Posted: Thu Jul 20, 2006 6:49 pm Post subject:
$HTTP_REFERER crashes my system like clockwork
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I like to develop on my desktop, then when I get stuff working, I copy
to my web-site.
I set up a new version Xampp on my windows-2k desktop. And downloaded
the stuff from the website to edit. On the website, everything worked,
on my desktop, nothing works.
I am guessing this has to do with PHP versions. I know PHP breaks
everything whenever they come out with a new version.
On the website, I am using PHP 4.4.2. On my desktop, I'm using 5.1.4.
This is the routine that crashes everything.
#if either form field is empty return to the log-in page
if ( (!$username) or (!$password) )
{
header("Location:$HTTP_REFERER");
exit();
}
Again, it all works with PHP 4..4.2, crashes with PHP 5.1.4. Also if I
try to do anything else with $HTTP_REFERER, the system crashes.
By "crashes" I mean I either get a blank page, or an error message that
the headers are already loaded. |
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Benjamin Esham
*nix forums beginner
Joined: 13 Jul 2006
Posts: 7
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| Posted: Thu Jul 20, 2006 7:22 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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walterbyrd wrote:
| Quote: | This is the routine that crashes everything.
#if either form field is empty return to the log-in page
if ( (!$username) or (!$password) )
{
header("Location:$HTTP_REFERER");
exit();
}
Again, it all works with PHP 4..4.2, crashes with PHP 5.1.4. Also if I try
to do anything else with $HTTP_REFERER, the system crashes.
By "crashes" I mean I either get a blank page, or an error message that
the headers are already loaded.
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This may or may not help, but is there really no space between "Location:"
and "$HTTP_REFERER"? Because there should be.
Also, you might try using $_SERVER['HTTP_REFERER'] instead, assuming you're
running PHP >= 4.1.0.
HTH,
--
Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
"I think I'd most like to spend a day with Harry. I'd take him
out for a meal and apologise for everything I've put him through."
— J. K. Rowling |
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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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| Posted: Thu Jul 20, 2006 8:18 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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Benjamin Esham wrote:
| Quote: |
This may or may not help, but is there really no space between "Location:"
and "$HTTP_REFERER"? Because there should be.
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I found that I can set PHP to 4.4.2-pl1 with Xampp. That didn't help. I
tried putting in a space, that didn't help either.
| Quote: | Also, you might try using $_SERVER['HTTP_REFERER'] instead, assuming you're
running PHP >= 4.1.0.
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I am not sure exactly how to do this. I had:
header("Location: $HTTP_REFER");
Do I keep the quotes? Do I keep the "Location:" ? It doesn't seem to
work either way.
I tried it like this:
header($_SERVER['HTTP_REFERER']);
And got these errors:
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:2) in
C:\xampp\htdocs\WMS\authenticate.php on line 5
I also don't understand why this works perfectly on my web-site. Also,
I don't understand why I'm not getting my $username and $password
strings.
This is from by index.html file:
<form action="authenticate.php" method="post">
Username:<br>
<input type="text" name="username">
<br><br>
Password:<br>
<input type="password" name="password">
<br><br>
<input type="submit" name="Log In">
</form>
This is the authenticate.php file:
<?php
#if either form field is empty return to the log-in page
if ( (!$username) or (!$password) )
{
header($_SERVER['HTTP_REFERER']);
exit();
}
The $username and $password strings seem to be empty. I tested them.
| Quote: | HTH,
--
Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
"I think I'd most like to spend a day with Harry. I'd take him
out for a meal and apologise for everything I've put him through."
- J. K. Rowling |
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Benjamin Esham
*nix forums beginner
Joined: 13 Jul 2006
Posts: 7
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| Posted: Thu Jul 20, 2006 8:46 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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[quoted sections rearranged slightly]
walterbyrd wrote:
| Quote: | Benjamin Esham wrote:
Also, you might try using $_SERVER['HTTP_REFERER'] instead, assuming
you're running PHP >= 4.1.0.
I am not sure exactly how to do this.
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OK, try this function:
function authenticate()
{
if (!isset($_POST['username']) || !isset($_POST['password'])) {
header('Location: ' . $_SERVER['HTTP_REFERER']);
exit();
}
}
| Quote: | The $username and $password strings seem to be empty. I tested them.
|
The $username and $password were empty because you have register_globals
off; this means that you can only access your form variables through $_POST.
*This is the way it should be!* Turning register_globals on is potentially
a great security risk. Newer versions of PHP ship with register_globals
turned off by default, which is probably why you're experiencing
inconsistencies between the behavior of the two versions.
| Quote: | Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:2) in
C:\xampp\htdocs\WMS\authenticate.php on line 5
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This error is caused by sending output before headers. "Output" is usually
your outputted HTML code, but *any text at all*, including whitespace, that
comes before the opening <?php of your script will mess up your attempt to
send a header. Make sure that the <?php is the very first thing in your
file, and that you have no print or echo statements that are run before your
header() call.
By the way, I'm not sure whether using HTTP_REFERER is the best way to
return to the previous page. You're probably better off just doing a
header('Location: login_form.php');
as the HTTP_REFERER value is sometimes unreliable. Another alternative is
to display an error message instead of just sending the user back to the
input form. This is a bit more user-friendly; if a user clicks on "Submit"
and is sent back to the login page again, he or she might just try to submit
the form again and again until it works. With an error message, he or she
knows what the problem was.
Hope this helps! Feel free to post again if your script continues to give
you trouble.
--
Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
....and that's why I'm not wearing any pants. |
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Alvaro G. Vicario
*nix forums Guru Wannabe
Joined: 20 Feb 2005
Posts: 148
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| Posted: Thu Jul 20, 2006 9:57 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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*** walterbyrd escribió/wrote (20 Jul 2006 11:49:52 -0700):
| Quote: | #if either form field is empty return to the log-in page
if ( (!$username) or (!$password) )
{
header("Location:$HTTP_REFERER");
exit();
}
|
Do you check that $HTTP_REFERER actually has a value? Even if you have
register_globals set to on, you must be aware that browsers can send
HTTP_REFERER... or not.
If the variable is empty, it's not a good idea to send an empty location
header.
--
-+ http://alvaro.es - Álvaro G. Vicario - Burgos, Spain
++ Mi sitio sobre programación web: http://bits.demogracia.com
+- Mi web de humor con rayos UVA: http://www.demogracia.com
-- |
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chernyshevsky@hotmail.com
*nix forums Guru
Joined: 09 Mar 2005
Posts: 871
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| Posted: Thu Jul 20, 2006 10:32 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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Alvaro G. Vicario wrote:
| Quote: | *** walterbyrd escribió/wrote (20 Jul 2006 11:49:52 -0700):
#if either form field is empty return to the log-in page
if ( (!$username) or (!$password) )
{
header("Location:$HTTP_REFERER");
exit();
}
Do you check that $HTTP_REFERER actually has a value? Even if you have
register_globals set to on, you must be aware that browsers can send
HTTP_REFERER... or not.
If the variable is empty, it's not a good idea to send an empty location
header.
|
In that case I believe the browser would make a new request to the
current script, which of course, sends the redirect again. The
recursion would continue until the browser decides enough is enough and
kills the operation. That seems to match the symptoms described. |
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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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| Posted: Fri Jul 21, 2006 1:03 am Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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| Quote: | Benjamin Esham wrote:
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Okay, I think I may be making some progress. My authenticate.php now
starts like this:
<?php
#if either form field is empty return to the log-in page
if (!isset($_POST['username']) || !isset($_POST['password']))
{
header("Location: index.html");
exit();
}
And that seems to work.
| Quote: | The $username and $password were empty because you have register_globals
off; this means that you can only access your form variables through $_POST.
*This is the way it should be!* Turning register_globals on is potentially
a great security risk.
|
Okay, from now on I will have register_globals on. Er, how do I do
that?
| Quote: | This error is caused by sending output before headers. "Output" is usually
your outputted HTML code, but *any text at all*, including whitespace, that
comes before the opening <?php
|
I am certain that is not the case. I have absolutely nothing before the
<?php or after the ?>, not even white space.
| Quote: | By the way, I'm not sure whether using HTTP_REFERER is the best way to
return to the previous page. You're probably better off just doing a
header('Location: login_form.php');
|
Did that. It works. Thanks.
| Quote: | Hope this helps! Feel free to post again if your script continues to give
you trouble.
|
My script is still giving me trouble, only now in a different part.
This line:
setcookie("admin", $username, time()+18000);
Is giving me this error:
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:29) in
C:\xampp\htdocs\WMS\authenticate.php on line 30
I am certain that $username is set correctly. I checked.
And this line (directly after the setcookie line)
header("Location: table_list1.php");
is giving me this error:
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:29) in
C:\xampp\htdocs\WMS\authenticate.php on line 32
I am certain that the file table_list1.php is correct, it's there. And
it works fine when run on my remote web-site.
| Quote: | --
Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
...and that's why I'm not wearing any pants. |
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Benjamin Esham
*nix forums beginner
Joined: 13 Jul 2006
Posts: 7
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| Posted: Fri Jul 21, 2006 2:56 am Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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walterbyrd wrote:
| Quote: | Okay, I think I may be making some progress. My authenticate.php now
starts like this [...] And that seems to work.
|
Good to hear.
| Quote: | Benjamin Esham wrote:
The $username and $password were empty because you have register_globals
off; this means that you can only access your form variables through
$_POST. *This is the way it should be!* Turning register_globals on is
potentially a great security risk.
Okay, from now on I will have register_globals on. Er, how do I do that?
|
Perhaps you misunderstood: most people consider register_globals a potential
security risk and advise to leave it off, as it seems to be already for you.
Either way, reading this page will do a better job of explaining.
http://us3.php.net/register_globals
| Quote: | This error is caused by sending output before headers. "Output" is
usually your outputted HTML code, but *any text at all*, including
whitespace, that comes before the opening <?php
I am certain that is not the case. I have absolutely nothing before the
?php or after the ?>, not even white space.
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OK, but does this file contain any right-to-left (e.g. Hebrew or Arabic)
text? Another recent thread in this group involved some phantom bytes at
the beginning of a file due to the different text direction, and the same
problem occurred there. (The reason that I'm being really persistent about
the beginning of the file is because I can't really think of any other
possible cause to this problem.)
| Quote: | By the way, I'm not sure whether using HTTP_REFERER is the best way to
return to the previous page. You're probably better off just doing a
header('Location: login_form.php');
Did that. It works. Thanks.
|
OK, cool.
| Quote: | My script is still giving me trouble, only now in a different part.
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:29) in
C:\xampp\htdocs\WMS\authenticate.php on line 30
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This is the same problem you were having before: somehow, text is being
outputted before the headers or cookie information can be sent. Go back
through your code; take a look at *everything* that happens between the time
your script is called and your cookie commands. Make sure that nothing
generates any output (remember, error messages count as output). Hopefully
the error rests with something in there.
HTH,
--
Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
"Men never do evil so completely and cheerfully as when they
do it from religious conviction." — Blaise Pascal |
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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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| Posted: Fri Jul 21, 2006 2:09 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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Benjamin Esham wrote:
| Quote: | Make sure that nothing
generates any output (remember, error messages count as output). Hopefully
the error rests with something in there.
|
First, thank you again for all of your help.
I am very sure nothing is being output before, or after the <?php . .
?>. I am using 100% English, no right to left languages. The very first
and last lines of this file are below:
<?php
#if either form field is empty return to the log-in page
.. . . .
?>
Here is the section that is giving me all the trouble, complete with
error checking echo statements:
{
echo("1" . "\n\n");
setcookie("admin", $username, time()+18000);
echo("2" . "\n\n");
header("Location: table_list1.php");
echo("3" . "\n\n");
exit;
}
Here is the complete output:
1
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:22) in
C:\xampp\htdocs\WMS\authenticate.php on line 23
2
Warning: Cannot modify header information - headers already sent by
(output started at C:\xampp\htdocs\WMS\authenticate.php:22) in
C:\xampp\htdocs\WMS\authenticate.php on line 25
3
| Quote: | Benjamin D. Esham
bdesham@gmail.com | AIM: bdesham128 | Jabber: same as e-mail
"Men never do evil so completely and cheerfully as when they
do it from religious conviction." - Blaise Pascal |
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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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| Posted: Fri Jul 21, 2006 2:19 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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Another thing I forgot to mention. If I comment out the problem lines,
I do not get the error message about headers, i.e.:
{
echo("1" . "\n\n");
# setcookie("admin", $username, time()+18000);
echo("2" . "\n\n");
# header("Location: table_list1.php");
echo("3" . "\n\n");
exit;
}
Gives me this output:
1 2 3
Also, oddly enough, when this line is executed, it works fine. No error
messages:
header("Location: index.html");
And, again, this all works fine on my remote web-host, which runs about
the same version of php. My web-host runs Linux, and I am using
windows. |
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walterbyrd@iname.com
*nix forums beginner
Joined: 27 Mar 2006
Posts: 15
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| Posted: Fri Jul 21, 2006 2:30 pm Post subject:
Re: $HTTP_REFERER crashes my system like clockwork
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walterbyrd wrote:
Sorry to keep posting like this. It was the echo statements. This does
not really make sense to me. The echo are legal, and are placed between
the <?php . . ?>. Anyway, this works:
| Quote: |
{
#echo("1" . "\n\n");
setcookie("admin", $username, time()+18000);
# echo("2" . "\n\n");
header("Location: table_list1.php");
# echo("3" . "\n\n");
exit;
} |
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