.rar, .zip files MIME Type

Question

The answers from freedompeace, Kiyarash and Sam Vloeberghs:

.rar    application/x-rar-compressed, application/octet-stream
.zip    application/zip, application/octet-stream, application/x-zip-compressed, multipart/x-zip

I would do a check on the file name too. Here is how you could check if the file is a RAR or ZIP file. I tested it by creating a quick command line application.

<?php

if (isRarOrZip($argv[1])) {
    echo 'It is probably a RAR or ZIP file.';
} else {
    echo 'It is probably not a RAR or ZIP file.';
}

function isRarOrZip($file) {
    // get the first 7 bytes
    $bytes = file_get_contents($file, FALSE, NULL, 0, 7);
    $ext = strtolower(substr($file, - 4));

    // RAR magic number: Rar!\x1A\x07\x00
    // http://en.wikipedia.org/wiki/RAR
    if ($ext == '.rar' and bin2hex($bytes) == '526172211a0700') {
        return TRUE;
    }

    // ZIP magic number: none, though PK\003\004, PK\005\006 (empty archive), 
    // or PK\007\008 (spanned archive) are common.
    // http://en.wikipedia.org/wiki/ZIP_(file_format)
    if ($ext == '.zip' and substr($bytes, 0, 2) == 'PK') {
        return TRUE;
    }

    return FALSE;
}

Notice that it still won't be 100% certain, but it is probably good enough.

$ rar.exe l somefile.zip
somefile.zip is not RAR archive

But even WinRAR detects non RAR files as SFX archives:

$ rar.exe l somefile.srr
SFX Volume somefile.srr

For upload:

An official list of mime types can be found at The Internet Assigned Numbers Authority (IANA) . According to their list Content-Type header for zip is application/zip.

The media type for rar files is not officially registered at IANA but the unofficial commonly used mime-type value is application/x-rar-compressed.

application/octet-stream means as much as: "I send you a file stream and the content of this stream is not specified" (so it is true that it can be a zip or rar file as well). The server is supposed to detect what the actual content of the stream is.

Note: For upload it is not safe to rely on the mime type set in the Content-Type header. The header is set on the client and can be set to any random value. Instead you can use the php file info functions to detect the file mime-type on the server.

---

For download:

If you want to download a zip file and nothing else you should only set one single Accept header value. Any additional values set will be used as a fallback in case the server cannot satisfy your in the Accept header requested mime-type.

According to the WC3 specifications this:

application/zip, application/octet-stream 

will be intrepreted as: "I prefer a application/zip mime-type, but if you cannot deliver this an application/octet-stream (a file stream) is also fine".

So only a single:

application/zip

Will guarantee you a zip file (or a 406 - Not Acceptable response in case the server is unable to satisfy your request).

You should not trust $_FILES['upfile']['mime'], check MIME type by yourself. For that purpose, you may use fileinfo extension, enabled by default as of PHP 5.3.0.

  $fileInfo = new finfo(FILEINFO_MIME_TYPE);
  $fileMime = $fileInfo->file($_FILES['upfile']['tmp_name']);
  $validMimes = array( 
    'zip' => 'application/zip',
    'rar' => 'application/x-rar',
  );

  $fileExt = array_search($fileMime, $validMimes, true);
  if($fileExt != 'zip' && $fileExt != 'rar')
    throw new RuntimeException('Invalid file format.');

NOTE: Don't forget to enable the extension in your php.ini and restart your server:

extension=php_fileinfo.dll

I see many answer reporting for zip and rar the Media Types application/zip and application/x-rar-compressed, respectively.

While the former matching is correct, for the latter IANA reports here https://www.iana.org/assignments/media-types/application/vnd.rar that for rar application/x-rar-compressed is a deprecated alias name and instead application/vnd.rar is the official one. So, right Media Types from IANA in 2020 are:

1. zip: application/zip
2. rar: application/vnd.rar