Use ruby-magic gem instead of mimemagic gem

due to licensing issues

Gemfile

@@ -274,7 +274,7 @@ gem 'licensee', '~> 9.14.1'
 gem 'charlock_holmes', '~> 0.7.7'
 
 # Detect mime content type from content
-gem 'mimemagic', '~> 0.3.2'
+gem 'ruby-magic'
 
 # Faster blank
 gem 'fast_blank'

Gemfile.lock

@@ -1109,6 +1109,7 @@ GEM
       i18n
     ruby-fogbugz (0.2.1)
       crack (~> 0.4)
+    ruby-magic (0.2.0)
     ruby-prof (1.3.1)
     ruby-progressbar (1.11.0)
     ruby-saml (1.7.2)
@@ -1481,7 +1482,6 @@ DEPENDENCIES
   marginalia (~> 1.10.0)
   memory_profiler (~> 0.9)
   method_source (~> 1.0)
-  mimemagic (~> 0.3.2)
   mini_magick (~> 4.10.1)
   minitest (~> 5.11.0)
   multi_json (~> 1.14.1)
@@ -1555,6 +1555,7 @@ DEPENDENCIES
   rspec_junit_formatter
   rspec_profiling (~> 0.0.6)
   ruby-fogbugz (~> 0.2.1)
+  ruby-magic
   ruby-prof (~> 1.3.0)
   ruby-progressbar (~> 1.10)
   ruby_parser (~> 3.15)

changelogs/unreleased/remove-direct-mimemagic-dependency.yml

+---
+title: Remove direct mimemagic dependency
+merge_request: 57387
+author:
+type: other

lib/gitlab/utils/mime_type.rb

 # frozen_string_literal: true
+require 'magic'
 
 # This wraps calls to a gem which support mime type detection.
-# Currently uses `mimemagic`, but that will be replaced shortly.
+# We use the `ruby-magic` gem instead of `mimemagic` due to licensing issues
 module Gitlab
   module Utils
     class MimeType
@@ -9,13 +10,14 @@ module Gitlab
         def from_io(io)
           return unless io.is_a?(IO) || io.is_a?(StringIO)
 
-          MimeMagic.by_magic(io).try(:type)
+          mime_type = File.magic(io, Magic::MIME_TYPE)
+          mime_type == 'inode/x-empty' ? nil : mime_type
         end
 
         def from_string(string)
           return unless string.is_a?(String)
 
-          MimeMagic.by_magic(string)
+          string.type
         end
       end
     end

spec/lib/gitlab/utils/mime_type_spec.rb

@@ -24,7 +24,7 @@ RSpec.describe Gitlab::Utils::MimeType do
         "rails_sample.png"           | "image/png"
         "rails_sample.bmp"           | "image/bmp"
         "rails_sample.tif"           | "image/tiff"
-        "blockquote_fence_before.md" | nil
+        "blockquote_fence_before.md" | "text/plain"
         "csv_empty.csv"              | nil
       end
 
@@ -50,7 +50,7 @@ RSpec.describe Gitlab::Utils::MimeType do
     context "input is a string" do
       let(:str) { "plain text" }
 
-      it { is_expected.to eq(nil) }
+      it { is_expected.to eq('text/plain') }
     end
   end
 end