Improve multipart middleware

* don't try to close `nil` objects
* include `Dir.tmpdir` in the `Handler#allowed_paths`

This allows us to simplify multipart spec.
Make it more readable by using clear contexts and minimize the reading
noise using shared context and examples

lib/gitlab/middleware/multipart.rb

@@ -57,7 +57,8 @@ module Gitlab
 
           yield
         ensure
-          @open_files.each(&:close)
+          @open_files.compact
+                     .each(&:close)
         end
 
         # This function calls itself recursively
@@ -122,6 +123,7 @@ module Gitlab
 
         def allowed_paths
           [
+            Dir.tmpdir,
             ::FileUploader.root,
             ::Gitlab.config.uploads.storage_path,
             ::JobArtifactUploader.workhorse_upload_path,

lib/uploaded_file.rb

@@ -52,8 +52,7 @@ class UploadedFile
     elsif path.present?
       file_path = File.realpath(path)
 
-      paths = Array(upload_paths) << Dir.tmpdir
-      unless self.allowed_path?(file_path, paths.compact)
+      unless self.allowed_path?(file_path, Array(upload_paths).compact)
         raise InvalidPathError, "insecure path used '#{file_path}'"
       end
     end

spec/lib/gitlab/middleware/multipart/handler_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Middleware::Multipart::Handler do
+  using RSpec::Parameterized::TableSyntax
+
+  let_it_be(:env) { Rack::MockRequest.env_for('/', method: 'post', params: {}) }
+  let_it_be(:message) { { 'rewritten_fields' => {} } }
+
+  describe '#allowed_paths' do
+    let_it_be(:expected_allowed_paths) do
+      [
+        Dir.tmpdir,
+        ::FileUploader.root,
+        ::Gitlab.config.uploads.storage_path,
+        ::JobArtifactUploader.workhorse_upload_path,
+        ::LfsObjectUploader.workhorse_upload_path,
+        File.join(Rails.root, 'public/uploads/tmp')
+      ]
+    end
+
+    let_it_be(:expected_with_packages_path) { expected_allowed_paths + [::Packages::PackageFileUploader.workhorse_upload_path] }
+
+    subject { described_class.new(env, message).send(:allowed_paths) }
+
+    where(:package_features_enabled, :object_storage_enabled, :direct_upload_enabled, :expected_paths) do
+      false | false | true  | :expected_allowed_paths
+      false | false | false | :expected_allowed_paths
+      false | true  | true  | :expected_allowed_paths
+      false | true  | false | :expected_allowed_paths
+      true  | false | true  | :expected_with_packages_path
+      true  | false | false | :expected_with_packages_path
+      true  | true  | true  | :expected_allowed_paths
+      true  | true  | false | :expected_with_packages_path
+    end
+
+    with_them do
+      before do
+        stub_config(packages: {
+          enabled: package_features_enabled,
+          object_store: {
+            enabled: object_storage_enabled,
+            direct_upload: direct_upload_enabled
+          },
+          storage_path: '/any/dir'
+        })
+      end
+
+      it { is_expected.to eq(send(expected_paths)) }
+    end
+  end
+end

spec/lib/gitlab/middleware/multipart_spec.rb

@@ -2,311 +2,138 @@
 
 require 'spec_helper'
 
-require 'tempfile'
-
 RSpec.describe Gitlab::Middleware::Multipart do
-  include_context 'multipart middleware context'
-
-  RSpec.shared_examples_for 'multipart upload files' do
-    it 'opens top-level files' do
-      Tempfile.open('top-level') do |tempfile|
-        rewritten = { 'file' => tempfile.path }
-        in_params = { 'file.name' => original_filename, 'file.path' => file_path, 'file.remote_id' => remote_id, 'file.size' => file_size }
-        env = post_env(rewritten, in_params, Gitlab::Workhorse.secret, 'gitlab-workhorse')
-
-        expect_uploaded_file(tempfile, %w(file))
+  include MultipartHelpers
 
-        middleware.call(env)
-      end
+  describe '#call' do
+    let(:app) { double(:app) }
+    let(:middleware) { described_class.new(app) }
+    let(:secret) { Gitlab::Workhorse.secret }
+    let(:issuer) { 'gitlab-workhorse' }
+
+    subject do
+      env = post_env(
+        rewritten_fields: rewritten_fields,
+        params: params,
+        secret: secret,
+        issuer: issuer
+      )
+      middleware.call(env)
     end
 
-    it 'opens files one level deep' do
-      Tempfile.open('one-level') do |tempfile|
-        rewritten = { 'user[avatar]' => tempfile.path }
-        in_params = { 'user' => { 'avatar' => { '.name' => original_filename, '.path' => file_path, '.remote_id' => remote_id, '.size' => file_size } } }
-        env = post_env(rewritten, in_params, Gitlab::Workhorse.secret, 'gitlab-workhorse')
+    context 'with remote file mode params' do
+      let(:mode) { :remote }
 
-        expect_uploaded_file(tempfile, %w(user avatar))
+      it_behaves_like 'handling all upload parameters conditions'
 
-        middleware.call(env)
-      end
-    end
+      context 'and a path set' do
+        include_context 'with one temporary file for multipart'
 
-    it 'opens files two levels deep' do
-      Tempfile.open('two-levels') do |tempfile|
-        in_params = { 'project' => { 'milestone' => { 'themesong' => { '.name' => original_filename, '.path' => file_path, '.remote_id' => remote_id, '.size' => file_size } } } }
-        rewritten = { 'project[milestone][themesong]' => tempfile.path }
-        env = post_env(rewritten, in_params, Gitlab::Workhorse.secret, 'gitlab-workhorse')
+        let(:rewritten_fields) { rewritten_fields_hash('file' => uploaded_filepath) }
+        let(:params) { upload_parameters_for(key: 'file', filename: filename, remote_id: remote_id).merge('file.path' => '/should/not/be/read') }
 
-        expect_uploaded_file(tempfile, %w(project milestone themesong))
-
-        middleware.call(env)
-      end
-    end
+        it 'builds an UploadedFile' do
+          expect_uploaded_files(original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(file))
 
-    def expect_uploaded_file(tempfile, path)
-      expect(app).to receive(:call) do |env|
-        file = get_params(env).dig(*path)
-        expect(file).to be_a(::UploadedFile)
-        expect(file.original_filename).to eq(original_filename)
-
-        if remote_id
-          expect(file.remote_id).to eq(remote_id)
-          expect(file.path).to be_nil
-        else
-          expect(file.path).to eq(File.realpath(tempfile.path))
-          expect(file.remote_id).to be_nil
+          subject
         end
       end
     end
-  end
 
-  RSpec.shared_examples_for 'handling CI artifact upload' do
-    it 'uploads both file and metadata' do
-      Tempfile.open('file') do |file|
-        Tempfile.open('metadata') do |metadata|
-          rewritten = { 'file' => file.path, 'metadata' => metadata.path }
-          in_params = { 'file.name' => 'file.txt', 'file.path' => file_path, 'file.remote_id' => file_remote_id, 'file.size' => file_size, 'metadata.name' => 'metadata.gz' }
-          env = post_env(rewritten, in_params, Gitlab::Workhorse.secret, 'gitlab-workhorse')
-
-          with_expected_uploaded_artifact_files(file, metadata) do |uploaded_file, uploaded_metadata|
-            expect(uploaded_file).to be_a(::UploadedFile)
-            expect(uploaded_file.original_filename).to eq('file.txt')
-
-            if file_remote_id
-              expect(uploaded_file.remote_id).to eq(file_remote_id)
-              expect(uploaded_file.size).to eq(file_size)
-              expect(uploaded_file.path).to be_nil
-            else
-              expect(uploaded_file.path).to eq(File.realpath(file.path))
-              expect(uploaded_file.remote_id).to be_nil
-            end
-
-            expect(uploaded_metadata).to be_a(::UploadedFile)
-            expect(uploaded_metadata.original_filename).to eq('metadata.gz')
-            expect(uploaded_metadata.path).to eq(File.realpath(metadata.path))
-            expect(uploaded_metadata.remote_id).to be_nil
-          end
-
-          middleware.call(env)
-        end
-      end
-    end
+    context 'local file mode' do
+      let(:mode) { :local }
 
-    def with_expected_uploaded_artifact_files(file, metadata)
-      expect(app).to receive(:call) do |env|
-        file = get_params(env).dig('file')
-        metadata = get_params(env).dig('metadata')
+      it_behaves_like 'handling all upload parameters conditions'
 
-        yield file, metadata
-      end
-    end
-  end
+      context 'when file is' do
+        include_context 'with one temporary file for multipart'
 
-  it 'rejects headers signed with the wrong secret' do
-    env = post_env({ 'file' => '/var/empty/nonesuch' }, {}, 'x' * 32, 'gitlab-workhorse')
+        let(:allowed_paths) { [Dir.tmpdir] }
 
-    expect { middleware.call(env) }.to raise_error(JWT::VerificationError)
-  end
-
-  it 'rejects headers signed with the wrong issuer' do
-    env = post_env({ 'file' => '/var/empty/nonesuch' }, {}, Gitlab::Workhorse.secret, 'acme-inc')
-
-    expect { middleware.call(env) }.to raise_error(JWT::InvalidIssuerError)
-  end
-
-  context 'with invalid rewritten field' do
-    invalid_field_names = [
-      '[file]',
-      ';file',
-      'file]',
-      ';file]',
-      'file]]',
-      'file;;'
-    ]
-
-    invalid_field_names.each do |invalid_field_name|
-      it "rejects invalid rewritten field name #{invalid_field_name}" do
-        env = post_env({ invalid_field_name => nil }, {}, Gitlab::Workhorse.secret, 'gitlab-workhorse')
-
-        expect { middleware.call(env) }.to raise_error(RuntimeError, "invalid field: \"#{invalid_field_name}\"")
-      end
-    end
-  end
-
-  context 'with remote file' do
-    let(:remote_id) { 'someid' }
-    let(:file_size) { 300 }
-    let(:file_path) { '' }
-
-    it_behaves_like 'multipart upload files'
-  end
-
-  context 'with remote file and a file path set' do
-    let(:remote_id) { 'someid' }
-    let(:file_size) { 300 }
-    let(:file_path) { 'not_a_valid_file_path' } # file path will come from the rewritten_fields
-
-    it_behaves_like 'multipart upload files'
-  end
+        before do
+          expect_next_instance_of(::Gitlab::Middleware::Multipart::Handler) do |handler|
+            expect(handler).to receive(:allowed_paths).and_return(allowed_paths)
+          end
+        end
 
-  context 'with local file' do
-    let(:remote_id) { nil }
-    let(:file_size) { nil }
-    let(:file_path) { 'not_a_valid_file_path' } # file path will come from the rewritten_fields
+        context 'in allowed paths' do
+          let(:rewritten_fields) { rewritten_fields_hash('file' => uploaded_filepath) }
+          let(:params) { upload_parameters_for(filepath: uploaded_filepath, key: 'file', filename: filename, remote_id: remote_id) }
 
-    it_behaves_like 'multipart upload files'
-  end
+          it 'builds an UploadedFile' do
+            expect_uploaded_files(filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(file))
 
-  context 'with remote CI artifact upload' do
-    let(:file_remote_id) { 'someid' }
-    let(:file_size) { 300 }
-    let(:file_path) { 'not_a_valid_file_path' } # file path will come from the rewritten_fields
+            subject
+          end
+        end
 
-    it_behaves_like 'handling CI artifact upload'
-  end
+        context 'not in allowed paths' do
+          let(:allowed_paths) { [] }
 
-  context 'with local CI artifact upload' do
-    let(:file_remote_id) { nil }
-    let(:file_size) { nil }
-    let(:file_path) { 'not_a_valid_file_path' } # file path will come from the rewritten_fields
+          let(:rewritten_fields) { rewritten_fields_hash('file' => uploaded_filepath) }
+          let(:params) { upload_parameters_for(filepath: uploaded_filepath, key: 'file') }
 
-    it_behaves_like 'handling CI artifact upload'
-  end
+          it 'returns an error' do
+            result = subject
 
-  it 'allows files in uploads/tmp directory' do
-    with_tmp_dir('public/uploads/tmp') do |dir, env|
-      expect(app).to receive(:call) do |env|
-        expect(get_params(env)['file']).to be_a(::UploadedFile)
+            expect(result[0]).to eq(400)
+            expect(result[2]).to include('insecure path used')
+          end
+        end
       end
-
-      middleware.call(env)
     end
-  end
 
-  it 'allows files in the job artifact upload path' do
-    with_tmp_dir('artifacts') do |dir, env|
-      expect(JobArtifactUploader).to receive(:workhorse_upload_path).and_return(File.join(dir, 'artifacts'))
-      expect(app).to receive(:call) do |env|
-        expect(get_params(env)['file']).to be_a(::UploadedFile)
-      end
+    context 'with dummy params in remote mode' do
+      let(:rewritten_fields) { { 'file' => 'should/not/be/read' } }
+      let(:params) { upload_parameters_for(key: 'file') }
+      let(:mode) { :remote }
 
-      middleware.call(env)
-    end
-  end
+      context 'with an invalid secret' do
+        let(:secret) { 'INVALID_SECRET' }
 
-  it 'allows files in the lfs upload path' do
-    with_tmp_dir('lfs-objects') do |dir, env|
-      expect(LfsObjectUploader).to receive(:workhorse_upload_path).and_return(File.join(dir, 'lfs-objects'))
-      expect(app).to receive(:call) do |env|
-        expect(get_params(env)['file']).to be_a(::UploadedFile)
+        it { expect { subject }.to raise_error(JWT::VerificationError) }
       end
 
-      middleware.call(env)
-    end
-  end
+      context 'with an invalid issuer' do
+        let(:issuer) { 'INVALID_ISSUER' }
 
-  it 'allows symlinks for uploads dir' do
-    Tempfile.open('two-levels') do |tempfile|
-      symlinked_dir = '/some/dir/uploads'
-      symlinked_path = File.join(symlinked_dir, File.basename(tempfile.path))
-      env = post_env({ 'file' => symlinked_path }, { 'file.name' => original_filename, 'file.path' => symlinked_path }, Gitlab::Workhorse.secret, 'gitlab-workhorse')
-
-      allow(FileUploader).to receive(:root).and_return(symlinked_dir)
-      allow(UploadedFile).to receive(:allowed_paths).and_return([symlinked_dir, Gitlab.config.uploads.storage_path])
-      allow(File).to receive(:realpath).and_call_original
-      allow(File).to receive(:realpath).with(symlinked_dir).and_return(Dir.tmpdir)
-      allow(File).to receive(:realpath).with(symlinked_path).and_return(tempfile.path)
-      allow(File).to receive(:exist?).and_call_original
-      allow(File).to receive(:exist?).with(symlinked_dir).and_return(true)
-
-      # override Dir.tmpdir because this dir is in the list of allowed paths
-      # and it would match FileUploader.root path (which in this test is linked
-      # to /tmp too)
-      allow(Dir).to receive(:tmpdir).and_return(File.join(Dir.tmpdir, 'tmpsubdir'))
-
-      expect(app).to receive(:call) do |env|
-        expect(get_params(env)['file']).to be_a(::UploadedFile)
+        it { expect { subject }.to raise_error(JWT::InvalidIssuerError) }
       end
 
-      middleware.call(env)
-    end
-  end
-
-  describe '#call' do
-    context 'with packages storage' do
-      using RSpec::Parameterized::TableSyntax
-
-      let(:storage_path) { 'shared/packages' }
-
-      RSpec.shared_examples 'allowing the multipart upload' do
-        it 'allows files to be uploaded' do
-          with_tmp_dir('tmp/uploads', storage_path) do |dir, env|
-            allow(Packages::PackageFileUploader).to receive(:root).and_return(File.join(dir, storage_path))
+      context 'with invalid rewritten field key' do
+        invalid_keys = [
+          '[file]',
+          ';file',
+          'file]',
+          ';file]',
+          'file]]',
+          'file;;'
+        ]
 
-            expect(app).to receive(:call) do |env|
-              expect(get_params(env)['file']).to be_a(::UploadedFile)
-            end
+        invalid_keys.each do |invalid_key|
+          context invalid_key do
+            let(:rewritten_fields) { { invalid_key => 'should/not/be/read' } }
 
-            middleware.call(env)
+            it { expect { subject }.to raise_error(RuntimeError, "invalid field: \"#{invalid_key}\"") }
           end
         end
       end
 
-      RSpec.shared_examples 'not allowing the multipart upload when package upload path is used' do
-        it 'does not allow files to be uploaded' do
-          with_tmp_dir('tmp/uploads', storage_path) do |dir, env|
-            # with_tmp_dir sets the same workhorse_upload_path for all Uploaders,
-            # so we have to prevent JobArtifactUploader and LfsObjectUploader to
-            # allow the tested path
-            allow(JobArtifactUploader).to receive(:workhorse_upload_path).and_return(Dir.tmpdir)
-            allow(LfsObjectUploader).to receive(:workhorse_upload_path).and_return(Dir.tmpdir)
+      context 'with invalid key in parameters' do
+        include_context 'with one temporary file for multipart'
 
-            status, headers, body = middleware.call(env)
+        let(:rewritten_fields) { rewritten_fields_hash('file' => uploaded_filepath) }
+        let(:params) { upload_parameters_for(filepath: uploaded_filepath, key: 'wrong_key', filename: filename, remote_id: remote_id) }
 
-            expect(status).to eq(400)
-            expect(headers).to eq({ 'Content-Type' => 'text/plain' })
-            expect(body).to start_with('insecure path used')
+        it 'builds no UploadedFile' do
+          expect(app).to receive(:call) do |env|
+            received_params = get_params(env)
+            expect(received_params['file']).to be_nil
+            expect(received_params['wrong_key']).to be_nil
           end
-        end
-      end
 
-      RSpec.shared_examples 'adding package storage to multipart allowed paths' do
-        before do
-          expect(::Packages::PackageFileUploader).to receive(:workhorse_upload_path).and_call_original
+          subject
         end
-
-        it_behaves_like 'allowing the multipart upload'
-      end
-
-      RSpec.shared_examples 'not adding package storage to multipart allowed paths' do
-        before do
-          expect(::Packages::PackageFileUploader).not_to receive(:workhorse_upload_path)
-        end
-
-        it_behaves_like 'not allowing the multipart upload when package upload path is used'
-      end
-
-      where(:object_storage_enabled, :direct_upload_enabled, :example_name) do
-        false | true  | 'adding package storage to multipart allowed paths'
-        false | false | 'adding package storage to multipart allowed paths'
-        true  | true  | 'not adding package storage to multipart allowed paths'
-        true  | false | 'adding package storage to multipart allowed paths'
-      end
-
-      with_them do
-        before do
-          stub_config(packages: {
-            enabled: true,
-            object_store: {
-              enabled: object_storage_enabled,
-              direct_upload: direct_upload_enabled
-            },
-            storage_path: storage_path
-          })
-        end
-
-        it_behaves_like params[:example_name]
       end
     end
   end

spec/lib/uploaded_file_spec.rb

@@ -23,7 +23,7 @@ RSpec.describe UploadedFile do
     end
 
     subject do
-      described_class.from_params(params, :file, upload_path, file_path_override)
+      described_class.from_params(params, :file, [upload_path, Dir.tmpdir], file_path_override)
     end
 
     context 'when valid file is specified' do

spec/support/helpers/multipart_helpers.rb

+# frozen_string_literal: true
+
+module MultipartHelpers
+  def post_env(rewritten_fields:, params:, secret:, issuer:)
+    token = JWT.encode({ 'iss' => issuer, 'rewritten_fields' => rewritten_fields }, secret, 'HS256')
+    Rack::MockRequest.env_for(
+      '/',
+      method: 'post',
+      params: params,
+      described_class::RACK_ENV_KEY => token
+    )
+  end
+
+  # This function assumes a `mode` variable to be set
+  def upload_parameters_for(filepath: nil, key: nil, filename: 'filename', remote_id: 'remote_id')
+    result = {
+      "#{key}.name" => filename,
+      "#{key}.type" => "application/octet-stream",
+      "#{key}.sha256" => "1234567890"
+    }
+
+    case mode
+    when :local
+      result["#{key}.path"] = filepath
+    when :remote
+      result["#{key}.remote_id"] = remote_id
+      result["#{key}.size"] = 3.megabytes
+    else
+      raise ArgumentError, "can't handle #{mode} mode"
+    end
+
+    result
+  end
+
+  # This function assumes a `mode` variable to be set
+  def rewritten_fields_hash(hash)
+    if mode == :remote
+      # For remote uploads, workhorse still submits rewritten_fields,
+      # but all the values are empty strings.
+      hash.keys.each { |k| hash[k] = '' }
+    end
+
+    hash
+  end
+
+  def expect_uploaded_files(uploaded_file_expectations)
+    expect(app).to receive(:call) do |env|
+      Array.wrap(uploaded_file_expectations).each do |expectation|
+        file = get_params(env).dig(*expectation[:params_path])
+        expect_uploaded_file(file, expectation)
+      end
+    end
+  end
+
+  # This function assumes a `mode` variable to be set
+  def expect_uploaded_file(file, expectation)
+    expect(file).to be_a(::UploadedFile)
+    expect(file.original_filename).to eq(expectation[:original_filename])
+    expect(file.sha256).to eq('1234567890')
+
+    case mode
+    when :local
+      expect(file.path).to eq(File.realpath(expectation[:filepath]))
+      expect(file.remote_id).to be_nil
+      expect(file.size).to eq(expectation[:size])
+    when :remote
+      expect(file.remote_id).to eq(expectation[:remote_id])
+      expect(file.path).to be_nil
+      expect(file.size).to eq(3.megabytes)
+    else
+      raise ArgumentError, "can't handle #{mode} mode"
+    end
+  end
+
+  # Rails doesn't combine the GET/POST parameters in
+  # ActionDispatch::HTTP::Parameters if action_dispatch.request.parameters is set:
+  # https://github.com/rails/rails/blob/aea6423f013ca48f7704c70deadf2cd6ac7d70a1/actionpack/lib/action_dispatch/http/parameters.rb#L41
+  def get_params(env)
+    req = ActionDispatch::Request.new(env)
+    req.GET.merge(req.POST)
+  end
+end

spec/support/shared_contexts/lib/gitlab/middleware/multipart_shared_contexts.rb

 # frozen_string_literal: true
 
-RSpec.shared_context 'multipart middleware context' do
-  let(:app) { double(:app) }
-  let(:middleware) { described_class.new(app) }
-  let(:original_filename) { 'filename' }
-
-  # Rails 5 doesn't combine the GET/POST parameters in
-  # ActionDispatch::HTTP::Parameters if action_dispatch.request.parameters is set:
-  # https://github.com/rails/rails/blob/aea6423f013ca48f7704c70deadf2cd6ac7d70a1/actionpack/lib/action_dispatch/http/parameters.rb#L41
-  def get_params(env)
-    req = ActionDispatch::Request.new(env)
-    req.GET.merge(req.POST)
+# This context provides one temporary file for the multipart spec
+#
+# Here are the available variables:
+# - uploaded_file
+# - uploaded_filepath
+# - filename
+# - remote_id
+RSpec.shared_context 'with one temporary file for multipart' do |within_tmp_sub_dir: false|
+  let(:uploaded_filepath) { uploaded_file.path }
+
+  around do |example|
+    Tempfile.open('uploaded_file2') do |tempfile|
+      @uploaded_file = tempfile
+      @filename = 'test_file.png'
+      @remote_id = 'remote_id'
+
+      example.run
+    end
   end
 
-  def post_env(rewritten_fields, params, secret, issuer)
-    token = JWT.encode({ 'iss' => issuer, 'rewritten_fields' => rewritten_fields }, secret, 'HS256')
-    Rack::MockRequest.env_for(
-      '/',
-      method: 'post',
-      params: params,
-      described_class::RACK_ENV_KEY => token
-    )
+  attr_reader :uploaded_file, :filename, :remote_id
+end
+
+# This context provides two temporary files for the multipart spec
+#
+# Here are the available variables:
+# - uploaded_file
+# - uploaded_filepath
+# - filename
+# - remote_id
+# - tmp_sub_dir (only when using within_tmp_sub_dir: true)
+# - uploaded_file2
+# - uploaded_filepath2
+# - filename2
+# - remote_id2
+RSpec.shared_context 'with two temporary files for multipart' do
+  include_context 'with one temporary file for multipart'
+
+  let(:uploaded_filepath2) { uploaded_file2.path }
+
+  around do |example|
+    Tempfile.open('uploaded_file2') do |tempfile|
+      @uploaded_file2 = tempfile
+      @filename2 = 'test_file2.png'
+      @remote_id2 = 'remote_id2'
+
+      example.run
+    end
   end
 
-  def with_tmp_dir(uploads_sub_dir, storage_path = '')
-    Dir.mktmpdir do |dir|
-      upload_dir = File.join(dir, storage_path, uploads_sub_dir)
-      FileUtils.mkdir_p(upload_dir)
+  attr_reader :uploaded_file2, :filename2, :remote_id2
+end
+
+# This context provides three temporary files for the multipart spec
+#
+# Here are the available variables:
+# - uploaded_file
+# - uploaded_filepath
+# - filename
+# - remote_id
+# - tmp_sub_dir (only when using within_tmp_sub_dir: true)
+# - uploaded_file2
+# - uploaded_filepath2
+# - filename2
+# - remote_id2
+# - uploaded_file3
+# - uploaded_filepath3
+# - filename3
+# - remote_id3
+RSpec.shared_context 'with three temporary files for multipart' do
+  include_context 'with two temporary files for multipart'
 
-      allow(Rails).to receive(:root).and_return(dir)
-      allow(Dir).to receive(:tmpdir).and_return(File.join(Dir.tmpdir, 'tmpsubdir'))
-      allow(GitlabUploader).to receive(:root).and_return(File.join(dir, storage_path))
+  let(:uploaded_filepath3) { uploaded_file3.path }
 
-      Tempfile.open('top-level', upload_dir) do |tempfile|
-        env = post_env({ 'file' => tempfile.path }, { 'file.name' => original_filename, 'file.path' => tempfile.path }, Gitlab::Workhorse.secret, 'gitlab-workhorse')
+  around do |example|
+    Tempfile.open('uploaded_file3') do |tempfile|
+      @uploaded_file3 = tempfile
+      @filename3 = 'test_file3.png'
+      @remote_id3 = 'remote_id3'
 
-        yield dir, env
-      end
+      example.run
     end
   end
+
+  attr_reader :uploaded_file3, :filename3, :remote_id3
 end

spec/support/shared_examples/lib/gitlab/middleware/multipart_shared_examples.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples 'handling all upload parameters conditions' do
+  context 'one root parameter' do
+    include_context 'with one temporary file for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('file' => uploaded_filepath) }
+    let(:params) { upload_parameters_for(filepath: uploaded_filepath, key: 'file', filename: filename, remote_id: remote_id) }
+
+    it 'builds an UploadedFile' do
+      expect_uploaded_files(filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(file))
+
+      subject
+    end
+  end
+
+  context 'two root parameters' do
+    include_context 'with two temporary files for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('file1' => uploaded_filepath, 'file2' => uploaded_filepath2) }
+    let(:params) do
+      upload_parameters_for(filepath: uploaded_filepath, key: 'file1', filename: filename, remote_id: remote_id).merge(
+        upload_parameters_for(filepath: uploaded_filepath2, key: 'file2', filename: filename2, remote_id: remote_id2)
+      )
+    end
+
+    it 'builds UploadedFiles' do
+      expect_uploaded_files([
+        { filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(file1) },
+        { filepath: uploaded_filepath2, original_filename: filename2, remote_id: remote_id2, size: uploaded_file2.size, params_path: %w(file2) }
+      ])
+
+      subject
+    end
+  end
+
+  context 'one nested parameter' do
+    include_context 'with one temporary file for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('user[avatar]' => uploaded_filepath) }
+    let(:params) { { 'user' => { 'avatar' => upload_parameters_for(filepath: uploaded_filepath, filename: filename, remote_id: remote_id) } } }
+
+    it 'builds an UploadedFile' do
+      expect_uploaded_files(filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(user avatar))
+
+      subject
+    end
+  end
+
+  context 'two nested parameters' do
+    include_context 'with two temporary files for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('user[avatar]' => uploaded_filepath, 'user[screenshot]' => uploaded_filepath2) }
+    let(:params) do
+      {
+        'user' => {
+          'avatar' => upload_parameters_for(filepath: uploaded_filepath, filename: filename, remote_id: remote_id),
+          'screenshot' => upload_parameters_for(filepath: uploaded_filepath2, filename: filename2, remote_id: remote_id2)
+        }
+      }
+    end
+
+    it 'builds UploadedFiles' do
+      expect_uploaded_files([
+        { filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(user avatar) },
+        { filepath: uploaded_filepath2, original_filename: filename2, remote_id: remote_id2, size: uploaded_file2.size, params_path: %w(user screenshot) }
+      ])
+
+      subject
+    end
+  end
+
+  context 'one deeply nested parameter' do
+    include_context 'with one temporary file for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('user[avatar][bananas]' => uploaded_filepath) }
+    let(:params) { { 'user' => { 'avatar' => { 'bananas' => upload_parameters_for(filepath: uploaded_filepath, filename: filename, remote_id: remote_id) } } } }
+
+    it 'builds an UploadedFile' do
+      expect_uploaded_files(filepath: uploaded_file, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(user avatar bananas))
+
+      subject
+    end
+  end
+
+  context 'two deeply nested parameters' do
+    include_context 'with two temporary files for multipart'
+
+    let(:rewritten_fields) { rewritten_fields_hash('user[avatar][bananas]' => uploaded_filepath, 'user[friend][ananas]' => uploaded_filepath2) }
+    let(:params) do
+      {
+        'user' => {
+          'avatar' => {
+            'bananas' => upload_parameters_for(filepath: uploaded_filepath, filename: filename, remote_id: remote_id)
+          },
+          'friend' => {
+            'ananas' => upload_parameters_for(filepath: uploaded_filepath2, filename: filename2, remote_id: remote_id2)
+          }
+        }
+      }
+    end
+
+    it 'builds UploadedFiles' do
+      expect_uploaded_files([
+        { filepath: uploaded_file, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(user avatar bananas) },
+        { filepath: uploaded_file2, original_filename: filename2, remote_id: remote_id2, size: uploaded_file2.size, params_path: %w(user friend ananas) }
+      ])
+
+      subject
+    end
+  end
+
+  context 'three parameters nested at different levels' do
+    include_context 'with three temporary files for multipart'
+
+    let(:rewritten_fields) do
+      rewritten_fields_hash(
+        'file' => uploaded_filepath,
+        'user[avatar]' => uploaded_filepath2,
+        'user[friend][avatar]' => uploaded_filepath3
+      )
+    end
+
+    let(:params) do
+      upload_parameters_for(filepath: uploaded_filepath, filename: filename, key: 'file', remote_id: remote_id).merge(
+        'user' => {
+          'avatar' => upload_parameters_for(filepath: uploaded_filepath2, filename: filename2, remote_id: remote_id2),
+          'friend' => {
+            'avatar' => upload_parameters_for(filepath: uploaded_filepath3, filename: filename3, remote_id: remote_id3)
+          }
+        }
+      )
+    end
+
+    it 'builds UploadedFiles' do
+      expect_uploaded_files([
+        { filepath: uploaded_filepath, original_filename: filename, remote_id: remote_id, size: uploaded_file.size, params_path: %w(file) },
+        { filepath: uploaded_filepath2, original_filename: filename2, remote_id: remote_id2, size: uploaded_file2.size, params_path: %w(user avatar) },
+        { filepath: uploaded_filepath3, original_filename: filename3, remote_id: remote_id3, size: uploaded_file3.size, params_path: %w(user friend avatar) }
+      ])
+
+      subject
+    end
+  end
+end