php准确获取文件MIME类型的方法

<?php
$mime = array (
    //applications
    'ai'  => 'application/postscript',
    'eps'  => 'application/postscript',
    'exe'  => 'application/octet-stream',
    'doc'  => 'application/vnd.ms-word',
    'xls'  => 'application/vnd.ms-excel',
    'ppt'  => 'application/vnd.ms-powerpoint',
    'pps'  => 'application/vnd.ms-powerpoint',
    'pdf'  => 'application/pdf',
    'xml'  => 'application/xml',
    'odt'  => 'application/vnd.oasis.opendocument.text',
    'swf'  => 'application/x-shockwave-flash',
    // archives
    'gz'  => 'application/x-gzip',
    'tgz'  => 'application/x-gzip',
    'bz'  => 'application/x-bzip2',
    'bz2'  => 'application/x-bzip2',
    'tbz'  => 'application/x-bzip2',
    'zip'  => 'application/zip',
    'rar'  => 'application/x-rar',
    'tar'  => 'application/x-tar',
    '7z'  => 'application/x-7z-compressed',
    // texts
    'txt'  => 'text/plain',
    'php'  => 'text/x-php',
    'html' => 'text/html',
    'htm'  => 'text/html',
    'js'  => 'text/javascript',
    'css'  => 'text/css',
    'rtf'  => 'text/rtf',
    'rtfd' => 'text/rtfd',
    'py'  => 'text/x-python',
    'java' => 'text/x-java-source',
    'rb'  => 'text/x-ruby',
    'sh'  => 'text/x-shellscript',
    'pl'  => 'text/x-perl',
    'sql'  => 'text/x-sql',
    // images
    'bmp'  => 'image/x-ms-bmp',
    'jpg'  => 'image/jpeg',
    'jpeg' => 'image/jpeg',
    'gif'  => 'image/gif',
    'png'  => 'image/png',
    'tif'  => 'image/tiff',
    'tiff' => 'image/tiff',
    'tga'  => 'image/x-targa',
    'psd'  => 'image/vnd.adobe.photoshop',
    //audio
    'mp3'  => 'audio/mpeg',
    'mid'  => 'audio/midi',
    'ogg'  => 'audio/ogg',
    'mp4a' => 'audio/mp4',
    'wav'  => 'audio/wav',
    'wma'  => 'audio/x-ms-wma',
    // video
    'avi'  => 'video/x-msvideo',
    'dv'  => 'video/x-dv',
    'mp4'  => 'video/mp4',
    'mpeg' => 'video/mpeg',
    'mpg'  => 'video/mpeg',
    'mov'  => 'video/quicktime',
    'wm'  => 'video/x-ms-wmv',
    'flv'  => 'video/x-flv',
    'mkv'  => 'video/x-matroska'
    );
function _getmimedetect() {
  if (class_exists('finfo')) {
    return 'finfo';
  } else if (function_exists('mime_content_type')) {
    return 'mime_content_type';
  } else if ( function_exists('exec')) {
    $result = exec('file -ib '.escapeshellarg(__file__));
    if ( 0 === strpos($result, 'text/x-php') or 0 === strpos($result, 'text/x-c++')) {
      return 'linux';
    }
    $result = exec('file -ib '.escapeshellarg(__file__));
    if ( 0 === strpos($result, 'text/x-php') or 0 === strpos($result, 'text/x-c++')) {
      return 'bsd';
    }
  }
  return 'internal';
}
function _getmimetype($path) {
  global $mime;
  $fmime = _getmimedetect();
  switch($fmime) {
    case 'finfo':
      $finfo = finfo_open(fileinfo_mime);
      if ($finfo) 
        $type = @finfo_file($finfo, $path);
      break;
    case 'mime_content_type':
      $type = mime_content_type($path);
      break;
    case 'linux':
      $type = exec('file -ib '.escapeshellarg($path));
      break;
    case 'bsd':
      $type = exec('file -ib '.escapeshellarg($path));
      break;
    default:
      $pinfo = pathinfo($path);
      $ext = isset($pinfo['extension']) ? strtolower($pinfo['extension']) : '';
      $type = isset($mime[$ext]) ? $mime[$ext] : 'unkown';
      break;
  }
  $type = explode(';', $type);
  //需要加上这段，因为如果使用mime_content_type函数来获取一个不存在的$path时会返回'application/octet-stream'
  if ($fmime != 'internal' and $type[0] == 'application/octet-stream') {
    $pinfo = pathinfo($path); 
    $ext = isset($pinfo['extension']) ? strtolower($pinfo['extension']) : '';
    if (!empty($ext) and !empty($mime[$ext])) {
      $type[0] = $mime[$ext];
    }
  }
  return $type[0];
}
$path = '1.txt'; //实际上当前路径并不存在1.txt
var_dump(_getmimetype($path));
/*end of php*/