尝试使用 Ruby on Rails 检测 mime 类型

Question

我使用的是 Rails 5.x，无法弄清楚如何自动检测 mime 类型。我在这里看到了这篇文章Detect MIME type of uploaded file in Ruby 但是，当我尝试使用require 'filemagic 时，我在控制台中收到以下错误：

# irb                                                                                                                                                                                                                        12:25PM/02.20
2.5.1 :001 > require 'filemagic'
Traceback (most recent call last):
       13: from /usr/local/rvm/rubies/ruby-2.5.1/bin/irb:11:in `<main>'
       12: from (irb):1
       11: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:39:in `require'
       10: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:135:in `rescue in require'
        9: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:135:in `require'
        8: from /usr/local/rvm/gems/ruby-2.5.1/gems/filemagic-0.4.0.0/lib/filemagic.rb:1:in `<top (required)>'
        7: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in `require'
        6: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in `require'
        5: from /usr/local/rvm/gems/ruby-2.5.1/gems/filemagic-0.4.0.0/lib/filemagic/engine.rb:1:in `<top (required)>'
        4: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in `require'
        3: from /usr/local/rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in `require'
        2: from /usr/local/rvm/gems/ruby-2.5.1/gems/refile-0.6.2/lib/refile/rails.rb:4:in `<top (required)>'
        1: from /usr/local/rvm/gems/ruby-2.5.1/gems/refile-0.6.2/lib/refile/rails.rb:6:in `<module:Refile>'
NameError (uninitialized constant Refile::Rails)
2.5.1 :002 >

当我尝试使用 gem install ruby-filemagic 手动安装 ruby​​-filemagic 时（以防出现问题），我收到以下错误：

# gem install ruby-filemagic                                                                                                                                                                                                 12:25PM/02.20
Building native extensions. This could take a while...
ERROR:  Error installing ruby-filemagic:
        ERROR: Failed to build gem native extension.

    current directory: /usr/local/rvm/gems/ruby-2.5.1/gems/ruby-filemagic-0.7.2/ext/filemagic
/usr/local/rvm/rubies/ruby-2.5.1/bin/ruby -r ./siteconf20200220-8004-1i08kxm.rb extconf.rb
checking for -lgnurx... no
checking for magic_open() in -lmagic... no
*** ERROR: missing required library to compile this module
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/usr/local/rvm/rubies/ruby-2.5.1/bin/$(RUBY_BASE_NAME)
        --with-magic-dir
        --without-magic-dir
        --with-magic-include
        --without-magic-include=${magic-dir}/include
        --with-magic-lib
        --without-magic-lib=${magic-dir}/lib
        --with-gnurx-dir
        --without-gnurx-dir
        --with-gnurx-include
        --without-gnurx-include=${gnurx-dir}/include
        --with-gnurx-lib
        --without-gnurx-lib=${gnurx-dir}/lib
        --with-gnurxlib
        --without-gnurxlib
        --with-magiclib
        --without-magiclib

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /usr/local/rvm/gems/ruby-2.5.1/extensions/x86_64-linux/2.5.0/ruby-filemagic-0.7.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-2.5.1/gems/ruby-filemagic-0.7.2 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.5.1/extensions/x86_64-linux/2.5.0/ruby-filemagic-0.7.2/gem_make.out

由于这并没有真正解决，我去了下一个建议的解决方案，建议使用 MIME::Types.type_for("filename.gif").first.content_type 用于 Ruby on Rails，但我无法使用它，因为我收到以下错误：

# rails c                                                                                                                                                                                                                    
Running via Spring preloader in process 8106
Loading development environment (Rails 5.2.4)
2.5.1 :001 > f = "/path/to/pdf"
 => "/path/to/pdf"
2.5.1 :002 > MIME::Types.type_for(f).first.content_type
Traceback (most recent call last):
        1: from (irb):2
NameError (uninitialized constant MIME)
2.5.1 :003 >

为了尝试修复这个错误，我看到了将require 'mime/types' 放在顶部的建议，但我也不能使用它：

2.5.1 :003 > require 'mime/types'
Traceback (most recent call last):
        1: from (irb):3
LoadError (cannot load such file -- mime/types)
2.5.1 :004 >

我想要做的只是检测 mimetype，以便我可以将它与 slack-ruby-client 一起使用，但似乎无法做到这一点。

Answer 1

最终能够使用mimemagic 而不是该文档中提出的其他解决方案。

require 'mimemagic'
MimeMagic.by_magic(File.open("/path/to/pdf")).type