File upload UI obeys LFS filters

app/services/files/create_service.rb

 module Files
   class CreateService < Files::BaseService
     def create_commit!
+      handler = Lfs::FileModificationHandler.new(project, @branch_name)
+
+      handler.new_file(@file_path, @file_content) do |content_or_lfs_pointer|
+        create_transformed_commit(content_or_lfs_pointer)
+      end
+    end
+
+    private
+
+    def create_transformed_commit(content_or_lfs_pointer)
       repository.create_file(
         current_user,
         @file_path,
-        @file_content,
+        content_or_lfs_pointer,
         message: @commit_message,
         branch_name: @branch_name,
         author_email: @author_email,

app/services/lfs/file_modification_handler.rb

+module Lfs
+  class FileModificationHandler
+    attr_reader :project, :branch_name
+
+    delegate :repository, to: :project
+
+    def initialize(project, branch_name)
+      @project = project
+      @branch_name = branch_name
+    end
+
+    def new_file(file_path, file_content)
+      if project.lfs_enabled? && lfs_file?(file_path)
+        lfs_pointer_file = Gitlab::Git::LfsPointerFile.new(file_content)
+        lfs_object = create_lfs_object!(lfs_pointer_file, file_content)
+        content = lfs_pointer_file.pointer
+
+        success = yield(content)
+
+        link_lfs_object!(lfs_object) if success
+      else
+        yield(file_content)
+      end
+    end
+
+    private
+
+    def lfs_file?(file_path)
+      repository.attributes_at(branch_name, file_path)['filter'] == 'lfs'
+    end
+
+    def create_lfs_object!(lfs_pointer_file, file_content)
+      LfsObject.find_or_create_by(oid: lfs_pointer_file.sha256, size: lfs_pointer_file.size) do |lfs_object|
+        lfs_object.file = CarrierWaveStringFile.new(file_content)
+      end
+    end
+
+    def link_lfs_object!(lfs_object)
+      project.lfs_objects << lfs_object
+    end
+  end
+end

changelogs/unreleased/jej-upload-file-tracks-lfs.yml

+---
+title: File Upload UI can create LFS pointers based on .gitattributes
+merge_request: 16412
+author:
+type: fixed

lib/carrier_wave_string_file.rb

+class CarrierWaveStringFile < StringIO
+  def original_filename
+    ""
+  end
+end

lib/gitlab/git/lfs_pointer_file.rb

+module Gitlab
+  module Git
+    class LfsPointerFile
+      def initialize(data)
+        @data = data
+      end
+
+      def pointer
+        @pointer ||= <<~FILE
+          version https://git-lfs.github.com/spec/v1
+          oid sha256:#{sha256}
+          size #{size}
+        FILE
+      end
+
+      def size
+        @size ||= @data.bytesize
+      end
+
+      def sha256
+        @sha256 ||= Digest::SHA256.hexdigest(@data)
+      end
+    end
+  end
+end

spec/lib/gitlab/git/lfs_pointer_file_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Git::LfsPointerFile do
+  let(:data) { "1234\n" }
+
+  subject { described_class.new(data) }
+
+  describe '#size' do
+    it 'counts the bytes' do
+      expect(subject.size).to eq 5
+    end
+
+    it 'handles non ascii data' do
+      expect(described_class.new("ääää").size).to eq 8
+    end
+  end
+
+  describe '#sha256' do
+    it 'hashes the content correctly' do
+      expect(subject.sha256).to eq 'a883dafc480d466ee04e0d6da986bd78eb1fdd2178d04693723da3a8f95d42f4'
+    end
+  end
+
+  describe '#pointer' do
+    it 'starts with the LFS version' do
+      expect(subject.pointer).to start_with('version https://git-lfs.github.com/spec/v1')
+    end
+
+    it 'includes sha256' do
+      expect(subject.pointer).to match(/^oid sha256:[0-9a-fA-F]{64}/)
+    end
+
+    it 'ends with the size' do
+      expect(subject.pointer).to end_with("\nsize 5\n")
+    end
+  end
+end

spec/services/files/create_service_spec.rb

+require "spec_helper"
+
+describe Files::CreateService do
+  let(:project) { create(:project, :repository) }
+  let(:repository) { project.repository }
+  let(:user) { create(:user) }
+  let(:file_content) { 'Test file content' }
+  let(:branch_name) { project.default_branch }
+  let(:start_branch) { branch_name }
+
+  let(:commit_params) do
+    {
+      file_path: file_path,
+      commit_message: "Update File",
+      file_content: file_content,
+      file_content_encoding: "text",
+      start_project: project,
+      start_branch: start_branch,
+      branch_name: branch_name
+    }
+  end
+
+  subject { described_class.new(project, user, commit_params) }
+
+  before do
+    project.add_master(user)
+  end
+
+  describe "#execute" do
+    context 'when file matches LFS filter' do
+      let(:file_path) { 'test_file.lfs' }
+      let(:branch_name) { 'lfs' }
+
+      context 'with LFS disabled' do
+        it 'skips gitattributes check' do
+          expect(repository).not_to receive(:attributes_at)
+
+          subject.execute
+        end
+
+        it "doesn't create LFS pointers" do
+          subject.execute
+
+          blob = repository.blob_at('lfs', file_path)
+
+          expect(blob.data).not_to start_with('version https://git-lfs.github.com/spec/v1')
+          expect(blob.data).to eq(file_content)
+        end
+      end
+
+      context 'with LFS enabled' do
+        before do
+          allow(project).to receive(:lfs_enabled?).and_return(true)
+        end
+
+        it 'creates an LFS pointer' do
+          subject.execute
+
+          blob = repository.blob_at('lfs', file_path)
+
+          expect(blob.data).to start_with('version https://git-lfs.github.com/spec/v1')
+        end
+
+        it "creates an LfsObject with the file's content" do
+          subject.execute
+
+          expect(LfsObject.last.file.read).to eq file_content
+        end
+
+        it 'links the LfsObject to the project' do
+          expect do
+            subject.execute
+          end.to change { project.lfs_objects.count }.by(1)
+        end
+      end
+    end
+  end
+end