How would you check if a file is an image? I'm thinking you could use an method like so:
def image?(file)
file.to_s.include?(".gif") or file.to_s.include?(".png") or file.to_s.include?(".jpg")
end
But that might be a little inefficient and not correct. Any ideas?
(I'm using the paperclip plugin, btw, but I don't see any methods to determine whether a file is an image in paperclip)
Please check it once
MIME::Types.type_for('tmp/img1.jpg').first.try(:media_type)
=> "image"
MIME::Types.type_for('tmp/img1.jpeg').first.try(:media_type)
=> "image"
MIME::Types.type_for('tmp/img1.gif').first.try(:media_type)
=> "image"
MIME::Types.type_for('tmp/ima1.png').first.try(:media_type)
=> "image"
I would use the ruby-filemagic gem which is a Ruby binding for libmagic.
One approach is to use the "magic number" convention to read the first bits of a file.
http://www.astro.keele.ac.uk/oldusers/rno/Computing/File_magic.html
Examples:
"BM" is a Bitmap image "GIF8" is a GIF image "\xff\xd8\xff\xe0" is a JPEG image
Example in Ruby:
def bitmap?(data)
return data[0,2]=="MB"
end
def gif?(data)
return data[0,4]=="GIF8"
end
def jpeg?(data)
return data[0,4]=="\xff\xd8\xff\xe0"
end
def file_is_image?(filename)
f = File.open(filename,'rb') # rb means to read using binary
data = f.read(9) # magic numbers are up to 9 bytes
f.close
return bitmap?(data) or gif?(data) or jpeg?(data)
end
Why use this instead of the file name extension or the filemagic module?
To detect the data type before writing any data to disk. For example, we can read upload data stream before we write any data to disk. If the magic number doesn't match the web form content type, then we can immediately report an error.
We implement our real-world code slightly differently. We create a hash: each key is a magic number string, each value is a symbol like :bitmap, :gif, :jpeg, etc. If anyone would like to see our real-world code, feel free to contact me here.
Since you're using Paperclip, you can use the built in "validates_attachment_content_type" method in the model where "has_attached_file" is used, and specify which file types you want to allow.
Here's an example from an application where users upload an avatar for their profile:
has_attached_file :avatar,
:styles => { :thumb => "48x48#" },
:default_url => "/images/avatars/missing_avatar.png",
:default_style => :thumb
validates_attachment_content_type :avatar, :content_type => ["image/jpeg", "image/pjpeg", "image/png", "image/x-png", "image/gif"]
The documentation is here http://dev.thoughtbot.com/paperclip/classes/Paperclip/ClassMethods.html
i honestly think this is way easier, use mimemagic gem:
first install it
gem 'mimemagic'
open stream(bytes of target image)
url="https://i.ebayimg.com/images/g/rbIAAOSwojpgyQz1/s-l500.jpg"
result = URI.parse(url).open
then check data-stream's file type
for example:
MimeMagic.by_magic(result).type == "image/jpeg"
even though this might be more elegant
%w(JPEG GIF TIFF PNG).include?(MimeMagic.by_magic(result).type)
imagemagick has a command called identity that handles this - check w/ the paperclip documentation - there's probably a way to handle this from within your RoR app.
As an addition to Joel's answer, in Rails 5 I had to transform the comparison string to a bytecode. Eg:
def jpeg?(data)
return data[0,4]=="\xff\xd8\xff\xe0".b
end
