一个强大的文件类型检测函数，它可以判断你上传的文件是什么类型，利用这个函数使用文件的类型没有办法伪装过去,代码如下:

1. * @access public
2. * @param string filename 文件名
3. * @param string limit_ext_types 允许的文件类型，用|包围的类型如：|gif|txt|
4. * @return string
5. */<span ></span>
6. function check_file_type($filename, $limit_ext_types = ''){
7. $extname = strtolower(substr($filename, strrpos($filename, '.') + 1));
8. if ($limit_ext_types &&
9. stristr($limit_ext_types, '|' . $extname . '|') === false){
10. return '';
11. }
12. $str = $format = '';
13. $file = @fopen($filename, 'rb');
14. if ($file){
15. $str = @fread($file, 0x400); // 读取前 1024 个字节
16. @fclose($file);
17. }
18. else{
19. $format=$extname;
20. }
21. if ($format == '' && strlen($str) >= 2 ){
22. if (substr($str, 0, 4) == 'MThd' && $extname != 'txt'){
23. $format = 'mid';
24. }
25. elseif (substr($str, 0, 4) == 'RIFF' && $extname == 'wav'){
26. $format = 'wav';
27. }
28. elseif (substr($str ,0, 3) == "xFFxD8xFF"){
29. $format = 'jpg';
30. }
31. elseif (substr($str ,0, 4) == 'GIF8' && $extname != 'txt'){
32. $format = 'gif';
33. }
34. elseif (substr($str ,0, 8) == "x89x50x4Ex47x0Dx0Ax1Ax0A"){
35. $format = 'png';
36. }
37. elseif (substr($str ,0, 2) == 'BM' && $extname != 'txt'){
38. $format = 'bmp';
39. }
40. elseif ((substr($str ,0, 3) == 'CWS' || substr($str ,0, 3) == 'FWS')
41. && $extname != 'txt'){
42. $format = 'swf';
43. }
44. elseif (substr($str ,0, 4) == "xD0xCFx11xE0"){ // D0CF11E == DOCFILE == Microsoft Office Document
45. if (substr($str,0x200,4) == "xECxA5xC1x00"
46. || $extname == 'doc'){
47. $format = 'doc';
48. }
49. elseif (substr($str,0x200,2) == "x09x08" || $extname == 'xls'){
50. $format = 'xls';
51. }
52. elseif (substr($str,0x200,4) == "xFDxFFxFFxFF"
53. || $extname == 'ppt'){
54. $format = 'ppt';
55. }
56. }
57. elseif (substr($str ,0, 4) == "PKx03x04"){
58. $format = 'zip';
59. }
60. elseif (substr($str ,0, 4) == 'Rar!' && $extname != 'txt'){
61. $format = 'rar';
62. }
63. elseif (substr($str ,0, 4) == "x25PDF"){
64. $format = 'pdf';
65. }
66. elseif (substr($str ,0, 3) == "x30x82x0A"){
67. $format = 'cert';
68. }
69. elseif (substr($str ,0, 4) == 'ITSF' && $extname != 'txt'){
70. $format = 'chm';
71. }
72. elseif (substr($str ,0, 4) == "x2ERMF"){
73. $format = 'rm';
74. }
75. elseif ($extname == 'sql'){
76. $format = 'sql';
77. }
78. elseif ($extname == 'txt'){
79. $format = 'txt';
80. }
81. }
82. if ($limit_ext_types &&
83. stristr($limit_ext_types, '|' . $format . '|') === false){
84. $format = '';
85. }
86. return $format;
87. }