is_writeable function bug problem

[Title] PHP's is_writeable() function has a bug and cannot accurately determine whether a directory/file is writable. Please write a function to determine whether the directory/file is absolutely writable.
【Level】Level 6
[Solution] The following is the solution to the is_really_writable function in CodeIgniter. Please see the function comments for details
The bug exists in two aspects,
1. In windows, when the file only has a read-only attribute, the is_writeable() function returns false. When it returns true, the file is not necessarily writable.
If it is a directory, create a new file in the directory and judge by opening the file;
If it is a file, you can test whether the file is writable by opening the file (fopen).
2. In Unix, when safe_mode is turned on in the php configuration file (safe_mode=on), is_writeable() is also unavailable.
Read the configuration file to see if safe_mode is turned on.

<code><span>/**
 * Tests for file writability
 *
 * is_writable() returns TRUE on Windows servers when you really can't write to
 * the file, based on the read-only attribute.  is_writable() is also unreliable
 * on Unix servers if safe_mode is on.
 *
 *<span> @access</span>  private
 *<span> @return</span>  void
 */</span><span>if</span> ( ! function_exists(<span>'is_really_writable'</span>))
{
    <span><span>function</span><span>is_really_writable</span><span>(<span>$file</span>)</span>
    {</span><span>// If we're on a Unix server with safe_mode off we call is_writable</span><span>if</span> (DIRECTORY_SEPARATOR == <span>'/'</span><span>AND</span> @ini_get(<span>"safe_mode"</span>) == <span>FALSE</span>)
        {
            <span>return</span> is_writable(<span>$file</span>);
        }

        <span>// For windows servers and safe_mode "on" installations we'll actually</span><span>// write a file then read it.  Bah...</span><span>if</span> (is_dir(<span>$file</span>))
        {
            <span>$file</span> = rtrim(<span>$file</span>, <span>'/'</span>).<span>'/'</span>.md5(mt_rand(<span>1</span>,<span>100</span>).mt_rand(<span>1</span>,<span>100</span>));

            <span>if</span> ((<span>$fp</span> = @fopen(<span>$file</span>, FOPEN_WRITE_CREATE)) === <span>FALSE</span>)
            {
                <span>return</span><span>FALSE</span>;
            }

            fclose(<span>$fp</span>);
            @chmod(<span>$file</span>, DIR_WRITE_MODE);
            @unlink(<span>$file</span>);
            <span>return</span><span>TRUE</span>;
        }
        <span>elseif</span> ( ! is_file(<span>$file</span>) <span>OR</span> (<span>$fp</span> = @fopen(<span>$file</span>, FOPEN_WRITE_CREATE)) === <span>FALSE</span>)
        {
            <span>return</span><span>FALSE</span>;
        }

        fclose(<span>$fp</span>);
        <span>return</span><span>TRUE</span>;
    }
}</code>

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The above introduces the is_writeable function bug problem, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.