如何在 XPath 求值之前处理字符串中的双引号？

Question

在下面的函数中，当 $keyword 中的字符串包含双引号时，它会创建一个 “Warning: DOMXPath::evaluate(): Invalid expression”:

$keyword = 'This is "causing" an error';
$xPath->evaluate('boolean(//img[contains(@alt, "'.$keyword.'")])');

我应该做什么来准备

$keyword

来评估 xpath 表达式？

完整功能代码：

$keyword = trim(strtolower(rseo_getKeyword($post)));

function sx_function($heading, $post){
    $content = $post->post_content;
    if($content=="" || !class_exists('DOMDocument')) return false;
    $keyword = trim(strtolower(rseo_getKeyword($post)));
    @$dom = new DOMDocument;
    @$dom->loadHTML(strtolower($post->post_content));
    $xPath = new DOMXPath(@$dom);
    switch ($heading)
        {
        case "img-alt": return $xPath->evaluate('boolean(//img[contains(@alt, "'.$keyword.'")])');
        default: return $xPath->evaluate('boolean(/html/body//'.$heading.'[contains(.,"'.$keyword.'")])');
        }
}   

Answer 1

PHP 有 Xpath 1.0，如果您有一个带有双引号和单引号的字符串，解决方法是使用 Xpath

concat()

函数。辅助函数可以决定何时使用什么。示例/用法：

xpath_string('I lowe "double" quotes.');
// xpath:    'I lowe "double" quotes.'

xpath_string('It\'s my life.');
// xpath:    "It's my life."

xpath_string('Say: "Hello\'sen".');
// xpath:    concat('Say: "Hello', "'", "'sen".')

辅助功能：

/**
 * xpath string handling xpath 1.0 "quoting"
 *
 * @param string $input
 * @return string
 */
function xpath_string($input) {

    if (false === strpos($input, "'")) {
        return "'$input'";
    }

    if (false === strpos($input, '"')) {
        return "\"$input\"";
    }

    return "concat('" . strtr($input, array("'" => '\', "\'", \'')) . "')";
}

Answer 2

要转义 XPath 2.0 字符串文字中的字符串分隔符，您需要将每个分隔符替换为两个，因此

"

需要替换为

""

:

[74]      StringLiteral      ::=      ('"' (EscapeQuot | [^"])* '"') | ("'" (EscapeApos | [^'])* "'") /* ws: explicit */
[75]      EscapeQuot     ::=      '""'
[76]      EscapeApos     ::=      "''"

我不确定是否已经有一个函数可以做到这一点，但你可以使用这个函数：

function xpath_quote($str, $quotation='"') {
    if ($quotation != '"' && $quotation != "'") return false;
    return str_replace($quotation, $quotation.$quotation, $str);
}

用法：

'boolean(/html/body//'.$heading.'[contains(.,"'.xpath_quote($keyword).'")])'

Answer 3

即将推出的 PHP8.4.0 将具有 DOMXPath::quote() （我编写的 https://github.com/php/php-src/pull/13456 ），因此从 PHP8.4.0 开始：

        case "img-alt": return $xPath->evaluate('boolean(//img[contains(@alt, '.$xPath->quote($keyword).')])');
        default: return $xPath->evaluate('boolean(/html/body//'.$heading.'[contains(.,'.$xPath->quote($keyword).')])');

PHP8.4.0之前，可以使用

function UserlandDOMXPathQuote(string $string): string {
{
    if (false === \strpos($string, '\'')) {
        return '\'' . $string . '\'';
    }
    if (false === \strpos($string, '"')) {
        return '"' . $string . '"';
    }
    // if the string contains both single and double quotes, construct an
    // expression that concatenates all non-double-quote substrings with
    // the quotes, e.g.:
    //  'foo'"bar => concat("'foo'", '"bar")
    $sb = [];
    while ($string !== '') {
        $bytesUntilSingleQuote = \strcspn($string, '\'');
        $bytesUntilDoubleQuote = \strcspn($string, '"');
        $quoteMethod = ($bytesUntilSingleQuote > $bytesUntilDoubleQuote) ? "'" : '"';
        $bytesUntilQuote = \max($bytesUntilSingleQuote, $bytesUntilDoubleQuote);
        $sb[] = $quoteMethod . \substr($string, 0, $bytesUntilQuote) . $quoteMethod;
        $string = \substr($string, $bytesUntilQuote);
    }
    $sb = \implode(',', $sb);
    return 'concat(' . $sb . ')';
}