How to Determine the Content-Type of Email Attachments in PHP?

Determining File Content-Type for Email Attachments in PHP

In PHP, sending an email with file attachments requires specifying the content-type of the file. This information enables the email client to correctly interpret and display the attachment. This article addresses how to set the $the_content_type variable properly for this purpose.

Solution:

One approach involves using the getFileMimeType() function, which employs a series of fallbacks to handle different PHP versions and unreliable mime type functions:

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

    // Check for unreliable results
    if (!$type || in_array($type, array('application/octet-stream', 'text/plain'))) {
        // Try file command (only available on *NIX systems)
        $secondOpinion = exec('file -b --mime-type ' . escapeshellarg($file), $foo, $returnCode);
        if ($returnCode === 0 && $secondOpinion) {
            $type = $secondOpinion;
        }
    }

    // Try exif_imagetype for images
    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;
}

This function sequentially tries the native finfo_file, mime_content_type, file command, and exif_imagetype functions to determine the content-type. If one of these methods returns a reliable result, it's used. Otherwise, the function returns a fallback content-type.

Once the content-type has been determined, you can set the $the_content_type variable as follows:

$the_content_type = getFileMimeType($filepath);

This approach provides a robust solution for determining the content-type of various file types in PHP, ensuring that your email attachments are displayed correctly by email clients.

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