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<refentry xml:id="function.mysql-real-escape-string" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>mysql_real_escape_string</refname>
  <refpurpose>Escapes special characters in a string for use in a SQL statement</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>mysql_real_escape_string</methodname>
   <methodparam><type>string</type><parameter>unescaped_string</parameter></methodparam>
   <methodparam choice="opt"><type>resource</type><parameter>link_identifier</parameter></methodparam>
  </methodsynopsis>
  <para>
   Escapes special characters in the <parameter>unescaped_string</parameter>, 
   taking into account the current character set of the connection so that it 
   is safe to place it in a <function>mysql_query</function>. If binary data 
   is to be inserted, this function must be used.
  </para>
  <para>
   <function>mysql_real_escape_string</function> calls MySQL's library function
   mysql_real_escape_string, which prepends backslashes to the following characters:
   <literal>\x00</literal>, <literal>\n</literal>,
   <literal>\r</literal>, <literal>\</literal>, <literal>'</literal>,
   <literal>"</literal> and <literal>\x1a</literal>.
  </para>
  <para>
   This function must always (with few exceptions) be used to make data
   safe before sending a query to MySQL.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>unescaped_string</parameter></term>
     <listitem>
      <para>
       The string that is to be escaped.
      </para>
     </listitem>
    </varlistentry>
    &mysql.linkid.description;
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the escaped string, or &false; on error.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Simple <function>mysql_real_escape_string</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// Connect
$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')
    OR die(mysql_error());

// Query
$query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",
            mysql_real_escape_string($user),
            mysql_real_escape_string($password));
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>An example SQL Injection Attack</title>
    <programlisting role="php">
<![CDATA[
<?php
// Query database to check if there are any matching users
$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";
mysql_query($query);

// We didn't check $_POST['password'], it could be anything the user wanted! For example:
$_POST['username'] = 'aidan';
$_POST['password'] = "' OR ''='";

// This means the query sent to MySQL would be:
echo $query;
?>
]]>
    </programlisting>
     <para>
      The query sent to MySQL:
     </para>
    <screen>
<![CDATA[
SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''
]]>
    </screen>
    <para>
     This would allow anyone to log in without a valid password.
    </para>
   </example>
  </para>
  <para>
   <example>
    <title>A "Best Practice" query</title>
    <para>
     Using <function>mysql_real_escape_string</function> around each variable
     prevents SQL Injection. This example demonstrates the "best practice"
     method for querying a database, independent of the
     <link linkend="security.magicquotes">Magic Quotes</link> setting.
    </para>
    <programlisting role="php">
<![CDATA[
<?php

if (isset($_POST['product_name']) && isset($_POST['product_description']) && isset($_POST['user_id'])) {
    // Connect

    $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password');

    if(!is_resource($link)) {

        echo "Failed to connect to the server\n";
        // ... log the error properly

    } else {
        
        // Reverse magic_quotes_gpc/magic_quotes_sybase effects on those vars if ON.

        if(get_magic_quotes_gpc()) {
            $product_name        = stripslashes($_POST['product_name']);
            $product_description = stripslashes($_POST['product_description']);
        } else {
            $product_name        = $_POST['product_name'];
            $product_description = $_POST['product_description'];
        }

        // Make a safe query
        $query = sprintf("INSERT INTO products (`name`, `description`, `user_id`) VALUES ('%s', '%s', %d)",
                    mysql_real_escape_string($product_name, $link),
                    mysql_real_escape_string($product_description, $link),
                    $_POST['user_id']);

        mysql_query($query, $link);

        if (mysql_affected_rows($link) > 0) {
            echo "Product inserted\n";
        }
    }
} else {
    echo "Fill the form properly\n";
}
?>
]]>
    </programlisting>
    <para>
     The query will now execute correctly, and SQL Injection attacks will not work.
    </para>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    A MySQL connection is required before using 
    <function>mysql_real_escape_string</function> otherwise an error of
    level <literal>E_WARNING</literal> is generated, and &false; is 
    returned. If <parameter>link_identifier</parameter> isn't defined, the
    last MySQL connection is used.
   </para>
  </note>
  <note>
   <para>
    If <link linkend="ini.magic-quotes-gpc">magic_quotes_gpc</link> is enabled,
    first apply <function>stripslashes</function> to the data. Using this function
    on data which has already been escaped will escape the data twice.
   </para>
  </note>
  <note>
   <para>
    If this function is not used to escape data, the query is vulnerable to
    <link linkend="security.database.sql-injection">SQL Injection Attacks</link>.
   </para>
  </note>
  <note>
   <simpara>
    <function>mysql_real_escape_string</function> does not escape
    <literal>%</literal> and <literal>_</literal>. These are wildcards in
    MySQL if combined with <literal>LIKE</literal>, <literal>GRANT</literal>,
    or <literal>REVOKE</literal>.
   </simpara>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>mysql_client_encoding</function></member>
    <member><function>addslashes</function></member>
    <member><function>stripslashes</function></member>
    <member>The <link linkend="ini.magic-quotes-gpc">magic_quotes_gpc</link> directive</member>
    <member>The <link linkend="ini.magic-quotes-runtime">magic_quotes_runtime</link> directive</member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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