Adds ability to check mime-type of a file using the libmagic (magic(4)). It uses native extensions and it's quite performant.

On Linux, you need to install libmagic. The version we recommend is at least 5.36. But if you have an older version of libmagic, it will compile and work flawlessly but with a few caveats:

• Many constants (modes and params) will be not defined
• LibmagicRb::MAGIC_VERSION constant will be set to 0.
• Few methods will not work. some methods that can return a String or Integer will return nil (like setparam and getparam).

[ Do note that the minimum tested version is 5.11, older than that may fail to compile the gem ]

You also need Ruby > 1.9.0 in order to run this gem.

With that info in mind, let's continue to the installation part for your Linux distributions...

# pacman -S ruby file gcc make --needed

# apt install ruby libmagic-dev ruby-dev gcc make

# yum install ruby file-devel ruby-devel gcc make

# zypper in ruby ruby-devel file-devel gcc make

There are already make, and magic.h available for Gentoo. You just need Ruby:

# emerge --ask dev-lang/ruby

Versions upto 0.1.2 is tested on DragonflyBSD (Version 6.0-SYNTH).

# pkg install ruby devel/ruby-gems gcc gmake

You can install libmagic with homebrew:

$ brew install libmagic

# if the link is already created is going to fail, don't worry about that
$ brew link libmagic

[ Source: eparreno/gist:1845561 ]

Windows is currently not tested, hence the support is unknown.

Add this line to your application's Gemfile:

gem 'libmagic_rb'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install libmagic_rb

We recommend getting the gem only from Rubygems.org. Do not download this repo as zip, compile to install the gem. A rubygem version is released after various tests. Any branch here including Master branch can be unstable can even segfault your app. You've been warned!

The target of this gem is to add mime-type checking easily.

Using the LibmagicRb class we can check the mime type, EXIF data and other information of a file.

To check a file, you need to pass a hash argument to the FilemagicRb.new():

1. db: Path to the Database (String)
2. file: A file to check (String)
3. mode: Modes of the file (Integer) (Optional, defaults to LibmagicRb::MAGIC_MIME | LibmagicRb::MAGIC_CHECK | LibmagicRb::MAGIC_SYMLINK)

require 'libmagic_rb'

cookie = LibmagicRb.new(
    file: '/usr/share/backgrounds/myimage.webp',
    mode: LibmagicRb::MAGIC_MIME | LibmagicRb::MAGIC_CHECK | LibmagicRb::MAGIC_SYMLINK
)

p cookie # =>    #<LibmagicRb:0x000055cf96d8f868 @db="/home/sourav/.gem/ruby/3.0.0/gems/libmagic_rb-0.1.0/data/magic.mgc", @file="/usr/share/backgrounds/myimage.webp", @mode=1106, @closed=false>

# In case The file path needs to be changed
cookie.file = '/usr/share/backgrounds/vienna-5164602.jpg'

p cookie.file    # => "/usr/share/backgrounds/vienna-5164602.jpg"
p cookie.db    # => nil

cookie.check()    # => image/jpeg; charset=binary
cookie.close()    # => #<LibmagicRb:0x000055fa77699818 @closed=true, @db="/home/sourav/.gem/ruby/3.0.0/gems/libmagic_rb-0.1.0/data/magic.mgc", @file="/usr/share/backgrounds/vienna-5164602.jpg", @mode=1106>
cookie.closed?() # => true

When the db: key is nil, it will use NULL as the database file - which gets the database automatically from the system. You can omit db: nil as well for a nil value.

require 'libmagic_rb'

cookie = LibmagicRb.new(
    db: '/usr/share/file/magic.mgc',
    file: '/usr/share/backgrounds/vienna-5164602.jpg',
    mode: LibmagicRb::NONE
)

cookie.check()    # => "JPEG image data, JFIF standard 1.01, resolution (DPI), density 300x300, segment length 16, Exif Standard: [TIFF image data, big-endian, direntries=4, manufacturer=NIKON CORPORATION, model=NIKON D5300], baseline, precision 8, 5959x3973, components 3""
cookie.close()    # => #<LibmagicRb:0x000055fa77699818 @closed=true, @db="/home/sourav/.gem/ruby/3.0.0/gems/libmagic_rb-0.1.0/data/magic.mgc", @file="/usr/share/backgrounds/vienna-5164602.jpg", @mode=1106>
cookie.closed?() # => true

Surely, you can automatically get db path if you pass nil to it. But If you happen to remove the database file or you are unsure, db: nil will not work (so will linux's file command). Specifying the path gives you the privilege to pass a locally stored database.

Do note that there should be version match for the magic files, otherwise it will raise LibmagicRb::InvalidDBError.

LibmagicRb also provides a handy singleton method :check. You just need to pass the filename and modes:

require 'libmagic_rb'

LibmagicRb.check(file: '/dev/zero', mode: LibmagicRb::MAGIC_NONE)    #=> "character special (1/5)"
LibmagicRb.check(file: '/', mode: LibmagicRb::MAGIC_NONE)    # => "directory"
LibmagicRb.check(file: '/')    # => "inode/directory; charset=binary"

Optional:

• You can use the db: keyword for a custom path. By default it's set to nil. And as mentioned above, nil = automatically find the db from the system.
• The mode: key is optional, by default it's set to LibmagicRb::MAGIC_MIME | LibmagicRb::MAGIC_CHECK | LibmagicRb::MAGIC_SYMLINK.

Notes:

• It's really mandatory to close the cookie (cookie.close()) when you are done with the cookie. Otherwise, you rely on the GC and that can cause various problems. You can't also use the file after it's closed.
• You can change the file and db on the fly. But you can't change the mode. The mode can be assigned only with LibmagicRb.new(db: ..., file: ..., mode: ...)
• To list all the modes, please refer to the man page.

Files can be opened in various modes. You can use this short hand to see the supported modes:

LibmagicRb.lsmodes    # => {:MAGIC_NONE=>0, :MAGIC_DEBUG=>1, :MAGIC_SYMLINK=>2, :MAGIC_COMPRESS=>4, :MAGIC_DEVICES=>8, :MAGIC_MIME_TYPE=>16, :MAGIC_MIME_ENCODING=>1024, :MAGIC_MIME=>1040, :MAGIC_CONTINUE=>32, :MAGIC_CHECK=>64, :MAGIC_PRESERVE_ATIME=>128, :MAGIC_RAW=>256, :MAGIC_ERROR=>512, :MAGIC_APPLE=>2048, :MAGIC_EXTENSION=>16777216, :MAGIC_COMPRESS_TRANSP=>33554432, :MAGIC_NO_CHECK_APPTYPE=>32768, :MAGIC_NO_CHECK_CDF=>262144, :MAGIC_NO_CHECK_COMPRESS=>4096, :MAGIC_NO_CHECK_ELF=>65536, :MAGIC_NO_CHECK_ENCODING=>2097152, :MAGIC_NO_CHECK_SOFT=>16384, :MAGIC_NO_CHECK_TAR=>8192, :MAGIC_NO_CHECK_TEXT=>131072, :MAGIC_NO_CHECK_TOKENS=>1048576, :MAGIC_NO_CHECK_CSV=>524288, :MAGIC_NO_CHECK_JSON=>4194304}

Note:

• Some keys can be missing or can have modified values, depending on your libmagic version.

LibmagicRb.lsparams    # => {:MAGIC_PARAM_INDIR_MAX=>0, :MAGIC_PARAM_NAME_MAX=>1, :MAGIC_PARAM_ELF_NOTES_MAX=>4, :MAGIC_PARAM_ELF_PHNUM_MAX=>2, :MAGIC_PARAM_ELF_SHNUM_MAX=>3, :MAGIC_PARAM_REGEX_MAX=>5, :MAGIC_PARAM_BYTES_MAX=>6}

Note:

• Some keys can be missing or can have modified values, depending on your libmagic version.

cookie.getparam(LibmagicRb::MAGIC_PARAM_REGEX_MAX) # => 8192; but can differ. Returns nil on error.

cookie.setparam(LibmagicRb::MAGIC_PARAM_REGEX_MAX, 2 ** 14) # => 16384; but can differ. Returns nil on error.

• To get the parameters, you can run LibmagicRb.lsparams() for description, please refer to the man page.
• cookie.setparam() returns the value after getting the param as well. So you don't need to confirm by calling getparam() again.
• The maximum size depends on the parameter. But the value that can be passed should not be more than 2 ** 32.
• On older versions of libmagic, where the function isn't available, both getparam() and setparam() will perform no operations, and return nil!

The following errors are implemented and raised on appropriate situation:

1. LibmagicRb::FileNotFound: When the file is not found.
2. LibmagicRb::FileUnreadable: When the file is unreadable.
3. LibmagicRb::InvalidDBError: When the database given is invalid.
4. LibmagicRb::IsDirError: When the database path is a directory.
5. LibmagicRb::FileClosedError: When the file is already closed (closed?()) but you are trying to access the cookie.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version.

Bug reports and pull requests are welcome on GitHub at https://github.com/cybergizer-hq/LibmagicRb This project is intended to be a safe, welcoming space for collaboration.

The gem is available as open-source under the terms of the MIT License.