How to Determine the Content Type of a File in PHP?

How to Determine File Content Type in PHP

When sending emails with attachments, it's crucial to set the correct Content-Type header for the attachment to ensure successful delivery and proper display. In PHP, you can use the file_get_contents() function to retrieve the attachment's contents, but determining the content type requires an additional step.

The getFileMimeType() Function

To simplify this task, consider using the following getFileMimeType() function:

function getFileMimeType($file) {
    if (function_exists('finfo_file')) {
        $finfo = finfo_open(FILEINFO_MIME_TYPE);
        $type = finfo_file($finfo, $file);
        finfo_close($finfo);
    } else {
        require_once 'upgradephp/ext/mime.php';
        $type = mime_content_type($file);
    }

    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        $secondOpinion = exec('file -b --mime-type ' . escapeshellarg($file), $foo, $returnCode);
        if ($returnCode === 0 && $secondOpinion) {
            $type = $secondOpinion;
        }
    }

    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        require_once 'upgradephp/ext/mime.php';
        $exifImageType = exif_imagetype($file);
        if ($exifImageType !== false) {
            $type = image_type_to_mime_type($exifImageType);
        }
    }

    return $type;
}

How it Works

This function tries several methods to determine the content type:

1. finfo_file(): If available, it uses the PHP finfo functions.
2. mime_content_type(): It falls back to the mime_content_type() alternative if finfo is not available.
3. file command: If the above methods fail, it attempts to execute the OS's file command for mime type identification.
4. exif_imagetype(): As a last resort, it uses exif_imagetype() to determine the mime type for images.

By using a combination of these methods, the function provides a robust way to retrieve the content type of various file types.

The above is the detailed content of How to Determine the Content Type of a File in PHP?. For more information, please follow other related articles on the PHP Chinese website!