How do I get the MIME type of a file basing on its content and not its extension?

Question

I want to get the exact MIME type basing on the file content, not its extension. I have used PHP methods and the API exposed by a module, but they return the MIME type basing on the file extension.

How do I get the MIME type from the file content?

Answer 1

Suppose you have the file binary source sent in a post request JSON encoded or any encoding method you could get the MIME type like in the following piece of code

$data = base64_decode(trim($_REQUEST['file']));
$finfo = finfo_open();
$mime_type = finfo_buffer($finfo, $data, FILEINFO_MIME_TYPE);
finfo_close($finfo);
// get file type png. jpg
$ext = $mime_type ? str_replace('image/', '', $mime_type) : 'png';

Hint:Its better to send the file mime type in the request as encoding and decoding may cause not get the MIME type.

Using file_get_contents

$buffer = file_get_contents($url);
$finfo = new finfo(FILEINFO_MIME_TYPE);
$ext = $finfo->buffer($buffer);

More information found here

Save the file using file_save_data to be a managed file and you could then use it as a field in any entity

Answer 2

You can easily get the MIME type of a file using mime_content_type() function.

$mime_type = mime_content_type($path_to_the_file);

I've just tested it on my local machine; placed a test.pdf file in my home folder and renamed it giving it no and an incorrect extension. In both cases I got the right MIME type:

$ ls
test.pdf

$ drush eval 'var_dump(mime_content_type("/home/elin/test.pdf"))'
string(15) "application/pdf"

$ mv test.pdf test
$ drush eval 'var_dump(mime_content_type("/home/elin/test"))'
string(15) "application/pdf"

$ mv test test.jpg
$ drush eval 'var_dump(mime_content_type("/home/elin/test.jpg"))'
string(15) "application/pdf"

$ mv test.jpg test.png
$ drush eval 'var_dump(mime_content_type("/home/elin/test.png"))'
string(15) "application/pdf"