为什么会出现此PHP session_start（）错误？ [英] Why am I getting this PHP session_start() error?
问题描述
我不知道为什么会出现此会话错误...
I can not figure out why I am getting this session error...
警告：session_start（）
[ function.session-start]：无法发送
会话缓存限制器-标头
已发送（输出从
开始C：\webserver\htdocs\project2\labs\form- commits\index.php：2）
在
中C：\webserver\htdocs\project2\labs\form-submits\index.php
第2行/ p>
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\webserver\htdocs\project2\labs\form-submits\index.php:2) in C:\webserver\htdocs\project2\labs\form-submits\index.php on line 2
据我所知，只有在调用session_start（）函数之前浏览器有某种输出时，这种情况才会发生在这种情况下，通话前屏幕上没有打印任何内容，甚至没有空格。为什么我仍然会收到错误的任何想法？
As far as I knew this happens only when there is some sort of output to the browser before the session_start() function is called, in this case there is nothing printed to screen before the call, not even any white space. Any ideas why I would still get the errors?
我发布了此演示的完整源代码，因此您可以确切地看到我用来创建错误的内容。
I posted the full source code of this demo so you can see exactly what I used to create the error.
<?php
session_start();
require('formkey.class.php');
$formKey = new formKey();
$error = 'No error';
//Is request?
if($_SERVER['REQUEST_METHOD'] == 'post')
{
//Validate the form key
if(!isset($_POST['form_key']) || !$formKey->validate())
{
//Form key is invalid, show an error
$error = 'Form key error!';
}
else
{
//Do the rest of your validation here
$error = 'No form key error!';
}
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="content-type" content="text/html;charset=UTF-8" />
<title>Securing forms with form keys</title>
</head>
<body>
<div><?php if($error) { echo($error); } ?>
<form action="" method="post">
<dl>
<?php $formKey->outputKey(); ?>
<dt><label for="username">Username:</label></dt>
<dd><input type="text" name="username" id="username" /></dd>
<dt><label for="username">Password:</label></dt>
<dd><input type="password" name="password" id="password" /></dd>
<dt></dt>
<dd><input type="submit" value="Submit" /></dd>
<dl>
</form>
</body>
</html>
课程文件
<?php
class formKey
{
//Here we store the generated form key
private $formKey;
//Here we store the old form key
private $old_formKey;
//The constructor stores the form key (if one excists) in our class variable
function __construct()
{
//We need the previous key so we store it
if(isset($_SESSION['form_key']))
{
$this->old_formKey = $_SESSION['form_key'];
}
}
//Function to generate the form key
private function generateKey()
{
$ip = $_SERVER['REMOTE_ADDR'];
$uniqid = uniqid(mt_rand(), true);
return md5($ip . $uniqid);
}
//Function to output the form key
public function outputKey()
{
//Generate the key and store it inside the class
$this->formKey = $this->generateKey();
//Store the form key in the session
$_SESSION['form_key'] = $this->formKey;
//Output the form key
echo "<input type='hidden' name='form_key' id='form_key' value='".$this->formKey."' />";
}
//Function that validated the form key POST data
public function validate()
{
//We use the old formKey and not the new generated version
if($_POST['form_key'] == $this->old_formKey)
{
//The key is valid, return true.
return true;
}
else
{
//The key is invalid, return false.
return false;
}
}
}
?>
推荐答案
我一次遇到此错误文件开头有一个BOM（字节顺序标记）。显然，这也导致发送标头。但是，这可能是自修复以来的php错误。值得一看。.
编辑：在这一点上，我认为session_start（）在获取cookie之前会抛出错误。已发送。较早的错误将被发送到浏览器，并阻止cookie的发送。但是，在这种情况下，您应该在屏幕上看到之前的错误。我知道这可能不是问题所在，但我想不出是什么原因引起的。
At this point, I am thinking that session_start() is throwing an error before it can get the cookie sent. An early error would get sent to the browser and prevent the cookie from being sent. However, in this case, you should see the earlier error on your screen. I know this is probably not the issue, but I can't think of what else could be causing the problem.
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