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[web] PHP alternative to mysql_real_escape_string


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#1 noaktree   Members   -  Reputation: 734

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Posted 22 May 2007 - 04:49 AM

I need to create a PHP function that does the same thing as mysql_real_escape_string. The reason being that I need to use this function more than I actually need to connect to the database. According to the PHP Manual Page, mysql_real_escape_string escapes the following characters: \x00, \n, \r, \, ', " and \x1a. Is this an equivalent function? function my_real_escape_string($value) { $search = array("\x00", "\n", "\r", "\\", "'", "\"", "\x1a"); $replace = array("\\x00", "\\n", "\\r", "\\\\" ,"\'", "\\\"", "\\\x1a"); return str_replace($search, $replace, $value); } Or is there a reason this isn't safe, etc?

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#2 Sander   Members   -  Reputation: 1328

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Posted 22 May 2007 - 09:16 AM

Nope, looks good.

PS: You can save yourself a few headaches writing that by using single quoted strings. They don't need to be escaped by backslashes. I.e:


$search = array("\x00", "\n", "\r", '\', "'", '"', "\x1a");
$replace = array('\x00', '\n', '\r', '\\' ,"\'", '\"', '\x1a');


That's especially useful if you're dealing with multiple levels of backslash escaping (e.g. in some regular expessions) where you would otherwise end up with madness like "\\\\\\\\" for a simple backslash :-)

<hr />
Sander Marechal<small>[Lone Wolves][Hearts for GNOME][E-mail][Forum FAQ]</small>


#3 noaktree   Members   -  Reputation: 734

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Posted 22 May 2007 - 11:56 AM

Thanks Sander,

I'm having a little bit of trouble with the new code. In the top line you have '\' and it's causing an error as it thinks there is an open ended string. An elegant solution? Or must I replace '\\' with '\\\\'?

#4 Sander   Members   -  Reputation: 1328

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Posted 22 May 2007 - 12:09 PM

Oh, ofcourse. Silly me.

In a single quoted string, only the ' needs to be escaped. Not the rest like in double quoted strings. So the '\' should be '\\'. It's very easy to test. If you echo('\n') you will get \n as output, but when you echo("\n") you will get a newline.

See http://www.php.net/manual/en/language.types.string.php and compare single quoted strings to double quoted strings. To revise my example:


$search = array("\x00", "\n", "\r", '\\', "'", '"', "\x1a");
$replace = array('\x00', '\n', '\r', '\\\' ,"\'", '\"', '\x1a');


It does exactly the same as your code does, but IMHO it's a bit easier on the eyes. Whatever floats your boat I guess :-)

<hr />
Sander Marechal<small>[Lone Wolves][Hearts for GNOME][E-mail][Forum FAQ]</small>


#5 noaktree   Members   -  Reputation: 734

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Posted 22 May 2007 - 12:41 PM

Thanks again, and for the link. The echo() example really made things clear. I've always assumed that single and double quoted strings worked the same... now I know different. I didn't mean to sound picky about your code. I always appreciate smaller more readable code since that's what keeps my boat from sinking. [smile]

#6 konForce   Members   -  Reputation: 588

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Posted 23 May 2007 - 03:20 AM

That method won't work.

Let's say someone enters a NULL character. You want it to be stored in the string as \x00. However, your code will do this:

NULL => \x00
\x00 => \\x00

This is because calling str_replace with an array is no different from calling it multiple times. You need to use strtr.


return strtr($text, array(
"\x00" => '\x00',
"\n" => '\n',
"\r" => '\r',
'\\' => '\\\\',
"'" => "\'",
'"' => '\"',
"\x1a" => '\x1a'
));



strtr translates the biggest strings first and doesn't translates text that has already been translated. (You may want to double check that the above table is accurate.)

As an aside, I don't really recommend using this method at all. I much prefer using PDO and prepared statements.

#7 Sander   Members   -  Reputation: 1328

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Posted 23 May 2007 - 10:45 AM

Quote:
I much prefer using PDO and prepared statements.


The OP doesn't want to use this in combination with a database. That's why he needs to roll his own.

<hr />
Sander Marechal<small>[Lone Wolves][Hearts for GNOME][E-mail][Forum FAQ]</small>


#8 noaktree   Members   -  Reputation: 734

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Posted 24 May 2007 - 12:22 PM

Quote:
The OP doesn't want to use this in combination with a database. That's why he needs to roll his own.
Yes I do, sometimes, want to use this for database queries. Let me explain a little..

I have my database function wrapped in a class for caching purposes.

class->sql_query($query); // Simple example

The query may contain data that has been escaped with mysql_real_escape_string.

The class uses the query string to query the database and to create an ID for caching events.

A database connection is only made when data is not found in the cache. So it seems a waste to make a connection when it is only needed for mysql_real_escape_string.

I was hoping to make a replacement function for mysql_real_escape_string to avoid unnecessary connections to my mysql server.

So should I use the strstr to implement this function? What are the dangers?

#9 Sander   Members   -  Reputation: 1328

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Posted 24 May 2007 - 06:49 PM

Ah. In that case try lazy evaluation. If the data is in the cache then you do not need to query the database. If you do not query the batabase, you do not need to escape variables. Ergo: You only need mysql_real_escape_string() because *if* you escape something, you have a database connection.

This probably means that you need to modify your wrapper class to accept something like:

Quote:
$wrapper->sql_query('SELECT * FROM table WHERE col1=?, col2=?', $var1, $var2);


The sql_query() function checks the cache. If it's not there, make a database connection, escape $var1 and $var2, insert then in the query, run the query and cache the result.

<hr />
Sander Marechal<small>[Lone Wolves][Hearts for GNOME][E-mail][Forum FAQ]</small>





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