Trouble with webm mime types

[b...@dee.mx]

Hello, looking for some insight on this one

I first had troubles understanding why webm's files were not accepted, using with the following list of mime-types 

VIDEO_FORMATS = [ 'video/mp4','video/webm','application/mp4', 'video/mp4', 'video/quicktime', 'video/avi', 'video/mpeg', 'video/x-mpeg', 'video/x-msvideo', 'video/m4v', 'video/x-m4v', 'video/vnd.objectvideo'].freeze

using

Attacher.validate do

   validate_mime_type_inclusion [*IMAGE_FORMATS,*VIDEO_FORMATS,*AUDIO_FORMATS,*DOC_FORMATS]

end

I've added some tracing to debug, at different points :

plugin :determine_mime_type, analyzer: -> (io, analyzers) do

    mime_type = analyzers[:file].call(io)

    mime_type = analyzers[:mime_types].call(io) if mime_type == "text/plain"

    Rails.logger.info mime_type

    mime_type

end

and

add_metadata do |io, context|

  Rails.logger.info MIME::Types.type_for(io.path)

  ...

end

Turns out that :

- determine_mime_type that returns application/octet-stream

- MIME::Types.type_for returns and array [#<MIME::Type: audio/webm>, #<MIME::Type: video/webm>]

I expected shrine receiving video/webm only

You might be aware of, Shrine validates the first one, I add to include application/octet-stream in that accepted mime types

My problem is that, laking of enough knowledge in file types, it feels quite bad to declare an application/octet-stream to accept videos uploads on the app

Am i right to feel such setup unsafe ?

Thx for you help on that one

In case, I used this test video https://upload.wikimedia.org/wikipedia/commons/2/22/Volcano_Lava_Sample.webm

[Janko Marohnić]

I'm not able to reproduce this behaviour. For me the `file` utility correctly detects the web MIME type:

$ file --mime-type --brief Volcano_Lava_Sample.webm

video/webm

I also executed the following self-contained script:

require "shrine"

require "shrine/storage/file_system"

require "tmpdir"

require "fileutils"

Shrine.storages[:storage] = Shrine::Storage::FileSystem.new("#{Dir.tmpdir}/shrine")

at_exit { FileUtils.rm_rf Shrine.storages[:storage].directory }

class MyUploader < Shrine

  plugin :determine_mime_type, analyzer: -> (io, analyzers) do

    mime_type = analyzers[:file].call(io)

    mime_type = analyzers[:mime_types].call(io) if mime_type == "text/plain"

    mime_type

  end

end

file          = File.open("/Users/janko/Downloads/Volcano_Lava_Sample.webm")

uploaded_file = MyUploader.new(:storage).upload(file)

puts uploaded_file.mime_type

And it also correctly prints "video/webm". Can you execute this script on your machine and tell me what it prints out? It might be that you're having an older version of the "magic" database that the file utility uses.

Kind regards,

Janko

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[Ben Bonnet]

I'm on another machine, and all works fine. Sorry for disturbing , indeed it is due to my setup :/

Do have the same result with  your script, also within the app

I'll look into that, in case you have time, can you tell me what you call "magic" database ? meaning i should reinstall imagemagick with other specific extensions ?

In any case thx a lot for your time checking my first question;

best

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[Janko Marohnić]

I'll look into that, in case you have time, can you tell me what you call "magic" database ? meaning i should reinstall imagemagick with other specific extensions ?

The "magic" database isn't related to ImageMagick (even though it might sound like they are), it comes with the `file` comand package, and as far as I know it's only used by the `file` command.

As you might already know, the `file` command determines the MIME type from the content of the file. This is because most file types have something in their content that uniquely identifies their type (the most obvious exceptions are text-based files like CSV). The "magic" database is a file (or a group of files) that specify for which MIME type to look into which part of the file for which sequence of bytes.

The easiest way to understand it is to look at the MimeMagic gem, which has its own "magic" table written in Ruby. MimeMagic just iterates through the whole table, and looks for the "magic headers" at the specified byte range. If it finds the bytes "\211PNG" at the start of the file, it knows that it's an "image/png". If it find the bytes "WEBP" starting from the 9th byte, it knows that it's an "image/webp". And so on.

I think if you update the `file` command package, it will also update its "magic" database.

Kind regards,

Janko

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