Merge branch '22229-use-base-sha-when-downloading-merge-requests' into 'master'

Use base SHA for patches and diffs

## What does this MR do?

Switch from using 'start SHA' to 'base SHA' for patches and diffs

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

Makes the downloaded patches and diffs on the merge request page match the frontend-rendered "changes" in these scenarios:

* Unpatched gitlab-workhorse, downloading patchsets of open MRs (https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/68)
* Unpatched gitlab-workhorse, downloading diffs of open and merged MRs
* Patched gitlab-workhorse, downloading patchsets of merged merge requests

## What are the relevant issue numbers?

Closes #22229

See merge request !6435

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 }