Use base SHA for patches and diffs

This commit changes the revisions used for diffs. The current behaviour is
to show all changes between current tip of master and tip of the MR, rather
than matching the output of the web frontend (which just shows the changes
in the MR). Switching from start_sha to base_sha fixes this.

lib/gitlab/workhorse.rb

@@ -60,7 +60,7 @@ module Gitlab
       def send_git_diff(repository, diff_refs)
         params = {
           'RepoPath'  => repository.path_to_repo,
-          'ShaFrom'   => diff_refs.start_sha,
+          'ShaFrom'   => diff_refs.base_sha,
           'ShaTo'     => diff_refs.head_sha
         }
@@ -73,7 +73,7 @@ module Gitlab
       def send_git_patch(repository, diff_refs)
         params = {
           'RepoPath'  => repository.path_to_repo,
-          'ShaFrom'   => diff_refs.start_sha,
+          'ShaFrom'   => diff_refs.base_sha,
           'ShaTo'     => diff_refs.head_sha
         }
@@ -107,15 +107,15 @@ module Gitlab
           bytes
         end
       end
-      
+
       def write_secret
         bytes = SecureRandom.random_bytes(SECRET_LENGTH)
-        File.open(secret_path, 'w:BINARY', 0600) do |f| 
+        File.open(secret_path, 'w:BINARY', 0600) do |f|
           f.chmod(0600)
           f.write(Base64.strict_encode64(bytes))
         end
       end
-      
+
       def verify_api_request!(request_headers)
         JWT.decode(
           request_headers[INTERNAL_API_REQUEST_HEADER],
@@ -128,7 +128,7 @@ module Gitlab
       def secret_path
         Rails.root.join('.gitlab_workhorse_secret')
       end
-      
+
       protected
       def encode(hash)

spec/lib/gitlab/workhorse_spec.rb

 require 'spec_helper'
 describe Gitlab::Workhorse, lib: true do
-  let(:project) { create(:project) }
-  let(:subject) { Gitlab::Workhorse }
+  let(:project)    { create(:project) }
+  let(:repository) { project.repository }
+
+  def decode_workhorse_header(array)
+    key, value = array
+    command, encoded_params = value.split(":")
+    params = JSON.parse(Base64.urlsafe_decode64(encoded_params))
+
+    [key, command, params]
+  end
   describe ".send_git_archive" do
     context "when the repository doesn't have an archive file path" do
@@ -11,11 +19,37 @@ describe Gitlab::Workhorse, lib: true do
       end
       it "raises an error" do
-        expect { subject.send_git_archive(project.repository, ref: "master", format: "zip") }.to raise_error(RuntimeError)
+        expect { described_class.send_git_archive(project.repository, ref: "master", format: "zip") }.to raise_error(RuntimeError)
       end
     end
   end
+  describe '.send_git_patch' do
+    let(:diff_refs) { double(base_sha: "base", head_sha: "head") }
+    subject { described_class.send_git_patch(repository, diff_refs) }
+
+    it 'sets the header correctly' do
+      key, command, params = decode_workhorse_header(subject)
+
+      expect(key).to eq("Gitlab-Workhorse-Send-Data")
+      expect(command).to eq("git-format-patch")
+      expect(params).to eq("RepoPath" => repository.path_to_repo, "ShaFrom" => "base", "ShaTo" => "head")
+    end
+  end
+
+  describe '.send_git_diff' do
+    let(:diff_refs) { double(base_sha: "base", head_sha: "head") }
+    subject { described_class.send_git_patch(repository, diff_refs) }
+
+    it 'sets the header correctly' do
+      key, command, params = decode_workhorse_header(subject)
+
+      expect(key).to eq("Gitlab-Workhorse-Send-Data")
+      expect(command).to eq("git-format-patch")
+      expect(params).to eq("RepoPath" => repository.path_to_repo, "ShaFrom" => "base", "ShaTo" => "head")
+    end
+  end
+
   describe ".secret" do
     subject { described_class.secret }