Help with header(location)

bobbygreen

Hi Guys,

After many hours research I still can't get my head around redirecting with header(location) and so am hoping someone out there would be kind enough to help me out?

Basically i am posting form results to a url and waiting for a response. If the response is yes then i would like to redirect the user to a url that was sent back with the response, otherwise the results are posted to a 2nd url and if the response from that is yes i would like to redirect the user to a url that was sent back with that response etc... etc...

<body>
<?php
if(isset($_POST['submit'])){

$email = $_POST['email'];
$title = $_POST['title'];
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];

$ip = $_SERVER['REMOTE_ADDR'];

$id = $_SESSION['id'];
$date = date("Y-m-d");
$time = date("H:i:s");

//DO CURL STUFF

if ($response == "true"){
            $xml = new SimpleXMLElement($leadResult);
            $url = $xml->Redirect;
	header("Location: $url"); // if i get a positive response i want to redirect
}	
else {	

//DO MORE CURL STUFF

if ($response == "true") {
            $xml = new SimpleXMLElement($leadResult);
            $url = $xml->Redirect;
	header("Location: $url"); // if i get a positive response i want to redirect
}
else {
	($response == "false");
}
}
// WRITE RESULTS TO DATABASE
}
?>
</body>

I realise that this won't work, i'm just not sure why it won't work and, more importantly, how to make it work.

Thanks in advance.

johanafm

All headers must be set before sending any output, since they have to come first.

<body>
<?php

Thus, what you see above have allready disabled your ability to send any headers. This however, would work

<?php
header('stuff');
?>
<html>

bobbygreen

so i need to put the header before html tag?
would that not redirect the page before i have posted my stuff and thus before i have a url to redirect to?

johanafm

I'll start with the most compelling "argument" to why you should not send output before you set a location header (or any other header for that matter): it's impossible => you can't do it.

What do you mean by "posted your stuff"?

The header has to be set, not just before the body tag, it has to appear before ANY output. That is really any kind of output, no matter what it is. This will not work

  <?php
header('location...');

since there is a whitespace before the php tag. Whitespace is output.

A HTTP request or response always contains http message header. The header is possibly followed by a blank line and the http message body (a HTTP HEAD request for example will only get a response containing http header).
Do note that what is called http message body has nothing to do with an html body element. When you send an html document, first comes the http header, and then the http body, and the body contains the entire html document: including html, head and body elements.

So as soon as you tell the webserver it's time to send any kind of output the web server will immediately send http headers, which might look like this

response headers from a get request to example.com wrote:
HTTP/1.1 200 OK
Server: Apache/2.2.3 (CentOS)
Last-Modified: Wed, 09 Feb 2011 17:13:15 GMT
Content-Type: text/html; charset=UTF-8
Accept-Ranges: bytes
Connection: Keep-Alive
Date: Wed, 22 Jun 2011 09:40:10 GMT
Age: 1
Content-Length: 2945

This means that if you wish to redirect the browser somewhere else using a location header, you have to do this instead of displaying any output. You do not do both.

And looking at your code...

<body>
<?php
	if ($response == "true"){
                $xml = new SimpleXMLElement($leadResult);
                $url = $xml->Redirect;
		header("Location: $url"); // if i get a positive response i want to redirect
	}

What is the reason to display a body element before you (try to) set location header? The logic performed to decide that you should redirect doesn't check if a body element has been sent to the browser since this has nothing to do with why you redirect. Also, the body element isn't visible to the user, so they won't know it's there. In short, your code doesn't need to send the body element to make its decision, and the user will not notice anything at all, which means there is no reason to send anything before you want to do your redirect.

bobbygreen

Thanks for your detailed reply, i am beginning to (slowly) understand.

By posting 'stuff' i meant running the curl and also writing to database. There is no reason why i display a body element before i set location header, indeed i realise now i don't have to.

Also there is no reason why i don't write to my database before running the curl.

So my understanding is that this will now work?

<?php
if(isset($_POST['submit'])){

$email = $_POST['email'];
$title = $_POST['title'];
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];

$ip = $_SERVER['REMOTE_ADDR'];

$id = $_SESSION['id'];
$date = date("Y-m-d");
$time = date("H:i:s");

// WRITE RESULTS TO DATABASE

//DO CURL STUFF

if ($response == "true"){
            $xml = new SimpleXMLElement($leadResult);
            $url = $xml->Redirect;
	header("Location: $url"); // if i get a positive response i want to redirect
}	
else {	

//DO MORE CURL STUFF

if ($response == "true") {
            $xml = new SimpleXMLElement($leadResult);
            $url = $xml->Redirect;
	header("Location: $url"); // if i get a positive response i want to redirect
}
else {
	($response == "false");
}
}
}
?>
<body>
</body>

I will test it but if you could give me a yay or nay for peace of mind?

johanafm

It will work as far as the user is concerned (i.e. the location redirect), but what happens at the server side may or may not be what you intend.

# some code...

header('location: http://example.com');
# at this point, the browser goes to the indicated address

# but the server doesn't care... and continues its work. if you wish the server to end
# execution at the same point,
exit;

sneakyimp

johana has a very good point. if the point is to redirect to some other page and make sure your script does not continue to run then you should call die() or exit.

Also, generally speaking, you should try to keep your PHP and HTML as separate as possible. Maintaining code where it's all mixed up together gets to be a nightmare. Minimally, I try to put all my PHP first and then HTML later (with some mixing if looping is required for output). When I have time to do it properly, I'll use a template system or something.

As to your question "will my code work" that would depend. It looks good that you have your HTML tags after your PHP logic has done its work, but I'm not sure what sort of value you are getting out of your XML. You might want to verify that it's a valid URL.