Create Gitlab::Utils::MimeType that wraps calls

to mimemagic gem.

A different gem will replace this soon.

app/controllers/projects/jobs_controller.rb

@@ -226,10 +226,12 @@ class Projects::JobsController < Projects::ApplicationController
   end
 
   def raw_trace_content_disposition(raw_data)
-    mime_type = MimeMagic.by_magic(raw_data)
+    return 'inline' if raw_data.nil?
+
+    mime_type = Gitlab::Utils::MimeType.from_string(raw_data)
 
     # if mime_type is nil can also represent 'text/plain'
-    return 'inline' if mime_type.nil? || mime_type.type == 'text/plain'
+    return 'inline' if mime_type.nil? || mime_type == 'text/plain'
 
     'attachment'
   end

app/uploaders/content_type_whitelist.rb

@@ -43,7 +43,7 @@ module ContentTypeWhitelist
     def mime_magic_content_type(path)
       if path
         File.open(path) do |file|
-          MimeMagic.by_magic(file).try(:type) || 'invalid/invalid'
+          Gitlab::Utils::MimeType.from_io(file) || 'invalid/invalid'
         end
       end
     rescue Errno::ENOENT

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

+---
+title: Refactor MimeMagic calls to new MimeType class
+merge_request: 57421
+author:
+type: other

lib/gitlab/utils/mime_type.rb

+# frozen_string_literal: true
+
+# This wraps calls to a gem which support mime type detection.
+# Currently uses `mimemagic`, but that will be replaced shortly.
+module Gitlab
+  module Utils
+    class MimeType
+      Error = Class.new(StandardError)
+
+      class << self
+        def from_io(io)
+          raise Error, "input isn't an IO object" unless io.is_a?(IO) || io.is_a?(StringIO)
+
+          MimeMagic.by_magic(io).try(:type)
+        end
+
+        def from_string(string)
+          raise Error, "input isn't a string" unless string.is_a?(String)
+
+          MimeMagic.by_magic(string)
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/utils/mime_type_spec.rb

+# frozen_string_literal: true
+
+require "fast_spec_helper"
+require "rspec/parameterized"
+
+RSpec.describe Gitlab::Utils::MimeType do
+  describe ".from_io" do
+    subject { described_class.from_io(io) }
+
+    context "input isn't an IO" do
+      let(:io) { "test" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(Gitlab::Utils::MimeType::Error)
+      end
+    end
+
+    context "input is a file" do
+      using RSpec::Parameterized::TableSyntax
+
+      where(:fixture, :mime_type) do
+        "banana_sample.gif"          | "image/gif"
+        "rails_sample.jpg"           | "image/jpeg"
+        "rails_sample.png"           | "image/png"
+        "rails_sample.bmp"           | "image/bmp"
+        "rails_sample.tif"           | "image/tiff"
+        "blockquote_fence_before.md" | nil
+        "csv_empty.csv"              | nil
+      end
+
+      with_them do
+        let(:io) { File.open(File.join(__dir__, "../../../fixtures", fixture)) }
+
+        it { is_expected.to eq(mime_type) }
+      end
+    end
+  end
+
+  describe ".from_string" do
+    subject { described_class.from_string(str) }
+
+    context "input isn't a string" do
+      let(:str) { nil }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(Gitlab::Utils::MimeType::Error)
+      end
+    end
+
+    context "input is a string" do
+      let(:str) { "plain text" }
+
+      it { is_expected.to eq(nil) }
+    end
+  end
+end

spec/support/shared_contexts/upload_type_check_shared_context.rb

@@ -13,7 +13,6 @@ end
 # @param mime_type [String] mime type to forcibly detect.
 RSpec.shared_context 'force content type detection to mime_type' do
   before do
-    magic_mime_obj = MimeMagic.new(mime_type)
-    allow(MimeMagic).to receive(:by_magic).with(anything).and_return(magic_mime_obj)
+    allow(Gitlab::Utils::MimeType).to receive(:from_io).and_return(mime_type)
   end
 end