如何防止xss和sql注入攻击

php防sql注入和xss攻击通用过滤如下：

function string_remove_xss($html) {
preg_match_all("/\<([^\<]+)\>/is", $html, $ms);
$searchs[] = '<';
$replaces[] = '<';
$searchs[] = '>';
$replaces[] = '>';
if ($ms[1]) {
$allowtags = 'img|a|font|div|table|tbody|caption|tr|td|th|br|p|b|strong|i|u|em|span|ol|ul|li|blockquote';
$ms[1] = array_unique($ms[1]);
foreach ($ms[1] as $value) {
$searchs[] = "<".$value.">";
$value = str_replace('&', '_uch_tmp_str_', $value);
$value = string_htmlspecialchars($value);
$value = str_replace('_uch_tmp_str_', '&', $value);
$value = str_replace(array('\\', '/*'), array('.', '/.'), $value);
$skipkeys = array('onabort','onactivate','onafterprint','onafterupdate','onbeforeactivate','onbeforecopy','onbeforecut','onbeforedeactivate',
'onbeforeeditfocus','onbeforepaste','onbeforeprint','onbeforeunload','onbeforeupdate','onblur','onbounce','oncellchange','onchange',
'onclick','oncontextmenu','oncontrolselect','oncopy','oncut','ondataavailable','ondatasetchanged','ondatasetcomplete','ondblclick',
'ondeactivate','ondrag','ondragend','ondragenter','ondragleave','ondragover','ondragstart','ondrop','onerror','onerrorupdate',
'onfilterchange','onfinish','onfocus','onfocusin','onfocusout','onhelp','onkeydown','onkeypress','onkeyup','onlayoutcomplete',
'onload','onlosecapture','onmousedown','onmouseenter','onmouseleave','onmousemove','onmouseout','onmouseover','onmouseup','onmousewheel',
'onmove','onmoveend','onmovestart','onpaste','onpropertychange','onreadystatechange','onreset','onresize','onresizeend','onresizestart',
'onrowenter','onrowexit','onrowsdelete','onrowsinserted','onscroll','onselect','onselectionchange','onselectstart','onstart','onstop',
'onsubmit','onunload','javascript','script','eval','behaviour','expression','style','class');
$skipstr = implode('|', $skipkeys);
$value = preg_replace(array("/($skipstr)/i"), '.', $value);
if (!preg_match("/^[\/|\s]?($allowtags)(\s+|$)/is", $value)) {
$value = '';
}
$replaces[] = empty($value) ? '' : "<" . str_replace('"', '"', $value) . ">";
}
}
$html = str_replace($searchs, $replaces, $html);
return $html;
}
//php防sql注入和xss攻击通用过滤 
function string_htmlspecialchars($string, $flags = null) {
if (is_array($string)) {
foreach ($string as $key => $val) {
$string[$key] = string_htmlspecialchars($val, $flags);
}
} else {
if ($flags === null) {
$string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);
if (strpos($string, '&#') !== false) {
$string = preg_replace('/&((#(\d{3,5}|x[a-fA-F0-9]{4}));)/', '&\\1', $string);
}
} else {
if (PHP_VERSION < '5.4.0') {
$string = htmlspecialchars($string, $flags);
} else {
if (!defined('CHARSET') || (strtolower(CHARSET) == 'utf-8')) {
$charset = 'UTF-8';
} else {
$charset = 'ISO-8859-1';
}
$string = htmlspecialchars($string, $flags, $charset);
}
}
}
return $string;
}