Improve raw blobs downloading

This commit improves blobs downloading in two ways:

- When we send a blob via Workhorse, we don't need to download the
file first, so we can set the limit to zero and download the metadata
only

- When we serve a file via API, then we shouldn't load all unlimited
data, we'd better have a limit there

Changelog: performance

app/controllers/projects/raw_controller.rb

@@ -19,7 +19,7 @@ class Projects::RawController < Projects::ApplicationController
   feature_category :source_code_management
 
   def show
-    @blob = @repository.blob_at(@ref, @path)
+    @blob = @repository.blob_at(@ref, @path, limit: Gitlab::Git::Blob::LFS_POINTER_MAX_SIZE)
 
     send_blob(@repository, @blob, inline: (params[:inline] != 'false'), allow_caching: Guest.can?(:download_code, @project))
   end

app/models/repository.rb

@@ -502,8 +502,8 @@ class Repository
     end
   end
 
-  def blob_at(sha, path)
-    Blob.decorate(raw_repository.blob_at(sha, path), container)
+  def blob_at(sha, path, limit: Gitlab::Git::Blob::MAX_DATA_DISPLAY_SIZE)
+    Blob.decorate(raw_repository.blob_at(sha, path, limit: limit), container)
   rescue Gitlab::Git::Repository::NoRepository
     nil
   end

lib/api/repositories.rb

@@ -29,14 +29,13 @@ module API
           not_found!
         end
 
-        def assign_blob_vars!
+        def assign_blob_vars!(limit:)
           authorize! :download_code, user_project
 
           @repo = user_project.repository
 
           begin
-            @blob = Gitlab::Git::Blob.raw(@repo, params[:sha])
-            @blob.load_all_data!(@repo)
+            @blob = Gitlab::Git::Blob.raw(@repo, params[:sha], limit: limit)
           rescue StandardError
             not_found! 'Blob'
           end
@@ -71,7 +70,8 @@ module API
         requires :sha, type: String, desc: 'The commit hash'
       end
       get ':id/repository/blobs/:sha/raw' do
-        assign_blob_vars!
+        # Load metadata enough to ask Workhorse to load the whole blob
+        assign_blob_vars!(limit: 0)
 
         no_cache_headers
 
@@ -83,7 +83,7 @@ module API
         requires :sha, type: String, desc: 'The commit hash'
       end
       get ':id/repository/blobs/:sha' do
-        assign_blob_vars!
+        assign_blob_vars!(limit: -1)
 
         {
           size: @blob.size,

lib/gitlab/git/blob.rb

@@ -77,8 +77,8 @@ module Gitlab
           end
         end
 
-        def raw(repository, sha)
-          repository.gitaly_blob_client.get_blob(oid: sha, limit: MAX_DATA_DISPLAY_SIZE)
+        def raw(repository, sha, limit: MAX_DATA_DISPLAY_SIZE)
+          repository.gitaly_blob_client.get_blob(oid: sha, limit: limit)
         end
 
         # Returns an array of Blob instances, specified in blob_references as

lib/gitlab/git/repository.rb

@@ -827,8 +827,8 @@ module Gitlab
         end
       end
 
-      def blob_at(sha, path)
-        Gitlab::Git::Blob.find(self, sha, path) unless Gitlab::Git.blank_ref?(sha)
+      def blob_at(sha, path, limit: Gitlab::Git::Blob::MAX_DATA_DISPLAY_SIZE)
+        Gitlab::Git::Blob.find(self, sha, path, limit: limit) unless Gitlab::Git.blank_ref?(sha)
       end
 
       # Items should be of format [[commit_id, path], [commit_id1, path1]]

spec/controllers/projects/raw_controller_spec.rb

@@ -33,15 +33,25 @@ RSpec.describe Projects::RawController do
     end
 
     context 'regular filename' do
-      let(:filepath) { 'master/README.md' }
+      let(:filepath) { 'master/CONTRIBUTING.md' }
 
       it 'delivers ASCII file' do
+        allow(Gitlab::Workhorse).to receive(:send_git_blob).and_call_original
+
         subject
 
         expect(response).to have_gitlab_http_status(:ok)
         expect(response.header['Content-Type']).to eq('text/plain; charset=utf-8')
         expect(response.header[Gitlab::Workhorse::DETECT_HEADER]).to eq 'true'
         expect(response.header[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with('git-blob:')
+
+        expect(Gitlab::Workhorse).to have_received(:send_git_blob) do |repository, blob|
+          expected_blob = project.repository.blob_at('master', 'CONTRIBUTING.md')
+
+          expect(repository).to eq(project.repository)
+          expect(blob.id).to eq(expected_blob.id)
+          expect(blob).to be_truncated
+        end
       end
 
       it_behaves_like 'project cache control headers'

spec/requests/api/repositories_spec.rb

@@ -107,13 +107,18 @@ RSpec.describe API::Repositories do
 
     shared_examples_for 'repository blob' do
       it 'returns blob attributes as json' do
+        stub_const("Gitlab::Git::Blob::MAX_DATA_DISPLAY_SIZE", 5)
+
         get api(route, current_user)
 
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['size']).to eq(111)
         expect(json_response['encoding']).to eq("base64")
-        expect(Base64.decode64(json_response['content']).lines.first).to eq("class Commit\n")
         expect(json_response['sha']).to eq(sample_blob.oid)
+
+        content = Base64.decode64(json_response['content'])
+        expect(content.lines.first).to eq("class Commit\n")
+        expect(content).to eq(project.repository.gitaly_blob_client.get_blob(oid: sample_blob.oid, limit: -1).data)
       end
 
       context 'when sha does not exist' do
@@ -164,7 +169,10 @@ RSpec.describe API::Repositories do
 
     shared_examples_for 'repository raw blob' do
       it 'returns the repository raw blob' do
-        expect(Gitlab::Workhorse).to receive(:send_git_blob)
+        expect(Gitlab::Workhorse).to receive(:send_git_blob) do |_, blob|
+          expect(blob.id).to eq(sample_blob.oid)
+          expect(blob.loaded_size).to eq(0)
+        end
 
         get api(route, current_user)