How to use $_SERVER['HTTP_REFERER'] correc

问题:

Lets say i have two pages page1.php and page2.php and i want page2.php to be displayed only if it is redirected form page1.php and i inserted this code to page2.php

if($_SERVER['HTTP_REFERER'] == "page1.php")
{
    //keep displaying page2.php
}else{
    //if it is not redirected from page1.php
    header('Location:page1.php')
    //redirect the user back to page1.php 
}

this code worked fine until i have a form and a submit button on page2.php when the submit button is clicked the page refreshes which means the HTTP_REFERER will change to page2.php so my if statement fails and it takes me back to page1.php i don't want that to happen. Is there any way to prevent this from happening?

Thanks in advance.

回答1:

I wouldn't recommend using HTTP_REFERER:

1. It's fairly simple to manipulable in browser.

2. Some users might have security settings in their browser to not send this header at all.

3. It's not accessible over HTTPS.

4. Some proxies strip this header from the request

5. Added - See answer to this quesion

---

As Charlotte Dunois stated in the comment, better set session value before sending the form and then check it on page2.

page1.php:

$_SESSION[ 'display_page2' ] = TRUE;
//rest of the content

page2.php:

if ( (isset( $_SESSION[ 'display_page2' ] ) && $_SESSION[ 'display_page2' ] === TRUE ) || isset( $_POST[ 'some_form_input' ] ) ) {
  //keep displaying page2.php
} else {
  header('Location:page1.php');
  exit;
}

With isset( $_POST[ 'some_form_input' ] ), you can check whether the form has been sent (via POST method).

When needed, you can unset the session with unset( $_SESSION[ 'display_page2' ] ); or by setting it to different value.

回答2:

<?php
if(($_SERVER['HTTP_REFERER'] == "page1.php") || (isset($_POST['submit']) && $_SERVER['HTTP_REFERER']=="page2.php"))
{
    //keep displaying page2.php
}else{
    //if it is not redirected from page1.php
    header('Location:page1.php');
    //redirect the user back to page1.php 
}

?>

if the referrer is not page 1 you could check the condition if referrer = page2 and post is submitted. or check if the referrer is page1 or post is submitted. this is a possibility to avoid your problem.

回答3:

I advise against using $_SERVER['HTTP_REFERER'] as it can be easily spoofed.

Instead , you could set a cookie when they load page 1 using setcookie("page1", 1); before any markup is output. Then check for it on page 2 using

if(isset($_COOKIE['page1']))
{
    //keep displaying page2.php
}else{
    //if it is not redirected from page1.php
    header('Location:page1.php')
    //redirect the user back to page1.php 
}

By not specifying the expiry date the cookie will expire when the browser is closed. In this situation, using cookies also makes for much more readable code to others.

回答4:

<?php

/* 
    this page allows links from the following pages

    public.php?id=links
    private.php?id=links

don't allow if visitors come from anywhere else

this example would only work if I used the entire URL in the 'if' statement 
*/

$referringpage = $_SERVER['HTTP_REFERER'];

if ( $referringpage == "http://www.example.com/public.php?id=links" ) {
$pass = "yes";
} elseif ( $referringpage == "http://www.example.com/private.php?id=links" ) {
$pass = "yes";
} else {
$pass = "no";
}


if ( $pass == "yes" ) {
// do the function this page was made to do
} 

header( "Location: http://www.example.com/public.php?id=links" );

?>