How to improve function to detect the mime type using an agnostic method?

Question

This function is used to get the mime type of any given file. The intended purpose was to have it working within any of our servers that vary from the latest PHP version down to PHP 4.

/**
 * Get the mime type for any given file.
 *
 * @param str $filename Path to the file including the filename
 *
 * @return mixed bol|arr Either false or the array provided by the PHP function
 */
function getMimeType($filename) {
  $mimetype = false;

  if (function_exists('finfo_fopen')) {
    $mimetype = finfo_fopen($filename);
  } elseif (function_exists('getimagesize')) {
    $mimetype = getimagesize($filename);
  } elseif (function_exists('exif_imagetype')) {
    $mimetype = exif_imagetype($filename);
  } elseif (function_exists('mime_content_type')) {
    $mimetype = mime_content_type($filename);
  }

  return $mimetype;
}

While the function is already tested on different PHP versions, I'm trying to ascertain if the methodology implemented can be improved, thus leading to code reduction and preventing any redundant verifications.

My question is:

Can this function receive any type of improvement?

Answer 1

General Issues

If you are going to call something getMimeType then it should return exactly that. This is probably best defined by Multipurpose Internet Mail Extensions RFC 2046. Read the wikipedia page for more general information and related RFCs.

As Corbin commented on this implementation is broken due to the number of assumptions that are required to consume the information provided by this function. You really should return just a string with the mime type or an array with the primary type and subtype. Whatever you return should be consistent with your documentation.

You could consider some of the following instead of returning false:

• Throw an exception.
• Trigger an error and default the MIME type.
• Create a second function hasMimeType to avoid exception/errors.

Specific Issues

finfo_fopen

I think finfo_fopen should probably be finfo_open.

Its usage is something like:

$finfo = finfo_open(FILEINFO_MIME_TYPE);
return finfo_file($finfo, $filename);

However there are some catches. FILEINFO_MIME_TYPE has only been defined since PHP 5.3.0. You can use version_compare to determine which version of php you are using (If the version_compare function doesn't exist you are using PHP < 4.1.0).

if (version_compare(PHP_VERSION, '5.3.0') >= 0) { /* Do Stuff */ }

getimagesize

Only the mime index from the returned array should be used.

exif_imagetype

The string returned from this does not conform to the MIME type format. You will have to massage this data to return something appropriate.