Why does calling finfo_close directly without calling finfo_open first cause an error?

gitbox 2025-06-12

In PHP, the finfo function family is used for detecting various types of file information, especially for determining the MIME type of files. When using this set of functions, the typical flow is to first call finfo_open() to create a resource handle for file information, perform the necessary operations, and then call finfo_close() to release the resources.

However, if you attempt to call finfo_close() without first calling finfo_open(), an error will occur. This happens because PHP expects a valid file information resource to be passed to finfo_close(), and when you skip the finfo_open() step, PHP does not have a valid resource to close.

finfo_open and finfo_close flow

finfo_open(): This function is used to create a file information resource, which can then be used by functions like finfo_file() and finfo_buffer() to retrieve MIME type information.
finfo_close(): This function is used to close the file information resource created by finfo_open().

Calling finfo_open() properly ensures that you have a valid resource, which can then be passed to finfo_close() to avoid PHP errors.

Common Issues and Error Messages

If you attempt to call finfo_close() without having successfully called finfo_open(), you may encounter the following warning message:

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// Warning: finfo_close expects parameter 1 to be resource, null given in...</span></span><span>
</span><span><span class="hljs-variable">$finfo</span></span><span> = </span><span><span class="hljs-title function_ invoke__">finfo_open</span></span><span>(FILEINFO_MIME_TYPE); </span><span><span class="hljs-comment">// Attempting to open file info resource</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$finfo</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
    </span><span><span class="hljs-keyword">die</span></span><span>(</span><span><span class="hljs-string">"Error opening file info resource"</span></span><span>);
}
<p></span>$file = 'example.jpg';<br>
$mimeType = finfo_file($finfo, $file);<br>
echo "File MIME type is: $mimeType\n";</p>
<p>finfo_close($finfo); // Closing the resource<br>
?><br>
</span>

This code demonstrates the correct flow when using finfo_open() and finfo_close(), ensuring that the resource is opened and closed properly.

Potential Causes of Errors

Errors can arise when you fail to open a valid resource using finfo_open() before calling finfo_close(). In such cases, PHP will not be able to process the file information resource, and you may see errors indicating a missing or invalid resource.

Conclusion

Properly managing file resources with finfo is essential for accurate MIME type detection. Always ensure that you call finfo_open() to open a valid resource before calling finfo_close() to avoid errors in PHP.

getmxrr