hooks: Call reference-transaction hook from Ruby HooksService

When modifying Git references, we want to perform voting on the change
that's about to be made to enable strong consistency. While we're
currently emulating this behaviour mostly via the pre-receive hook,
eventually we'll want to fully migrate to the new reference-transaction
hook. This buys us more granularity, allows us to capture reference
updates across all commands and also allows us to abort any update.

To reach this goal, there's two steps we need to do: first we need to
always invoke Git with appropriate environment variables to make our
reference-transaction hook implementation aware of the ongoing
transaction. And second we'll need to adjust places where we manually
call out to Git hooks.

This commit addresses the second part for our Ruby sidecar, invoking the
reference-transaction hook in the hooks service. As the hook
implementation is currently hidden behind a feature flag, this commit
also sets up a separate feature flag for Ruby. If set, it knows to set
up the correct environment variables required by our hook implementation
to execute the actual logic.

5 files changed, 34 insertions, 3 deletions

diff --git a/changelogs/unreleased/pks-ruby-reftx-hook.yml b/changelogs/unreleased/pks-ruby-reftx-hook.yml
new file mode 100644
index 000000000..a39abc55e
--- /dev/null
+++ b/changelogs/unreleased/pks-ruby-reftx-hook.yml
@@ -0,0 +1,5 @@
+---
+title: 'hooks: Call reference-transaction hook from Ruby HooksService'
+merge_request: 2566
+author:
+type: added
diff --git a/internal/gitaly/service/operations/branches_test.go b/internal/gitaly/service/operations/branches_test.go
index db772db06..8a93f4abf 100644
--- a/internal/gitaly/service/operations/branches_test.go
+++ b/internal/gitaly/service/operations/branches_test.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"os/exec"
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -109,6 +110,15 @@ func TestSuccessfulGitHooksForUserCreateBranchRequest(t *testing.T) {
 }
 
 func TestUserCreateBranchWithTransaction(t *testing.T) {
+	t.Run("with reftx hook", func(t *testing.T) {
+		testUserCreateBranchWithTransaction(t, true)
+	})
+	t.Run("without reftx hook ", func(t *testing.T) {
+		testUserCreateBranchWithTransaction(t, false)
+	})
+}
+
+func testUserCreateBranchWithTransaction(t *testing.T, withRefTxHook bool) {
 	testRepo, testRepoPath, cleanup := testhelper.NewTestRepo(t)
 	defer cleanup()
 
@@ -177,6 +187,12 @@ func TestUserCreateBranchWithTransaction(t *testing.T) {
 			require.NoError(t, err)
 			ctx = helper.IncomingToOutgoing(ctx)
 
+			ctx = featureflag.OutgoingCtxWithFeatureFlagValue(
+				ctx,
+				featureflag.RubyReferenceTransactionHook,
+				strconv.FormatBool(withRefTxHook),
+			)
+
 			request := &gitalypb.UserCreateBranchRequest{
 				Repository: testRepo,
 				BranchName: []byte("new-branch"),
@@ -188,7 +204,12 @@ func TestUserCreateBranchWithTransaction(t *testing.T) {
 			response, err := client.UserCreateBranch(ctx, request)
 			require.NoError(t, err)
 			require.Empty(t, response.PreReceiveError)
-			require.Equal(t, 1, transactionServer.called)
+
+			if withRefTxHook {
+				require.Equal(t, 2, transactionServer.called)
+			} else {
+				require.Equal(t, 1, transactionServer.called)
+			}
 		})
 	}
 }
diff --git a/internal/metadata/featureflag/feature_flags.go b/internal/metadata/featureflag/feature_flags.go
index e4309db49..836db2201 100644
--- a/internal/metadata/featureflag/feature_flags.go
+++ b/internal/metadata/featureflag/feature_flags.go
@@ -29,6 +29,9 @@ var (
 	// ReferenceTransactionHook will enable the reference-transaction hook
 	// introduced with Git v2.28.0 for voting on transactions
 	ReferenceTransactionHook = FeatureFlag{Name: "reference_transaction_hook", OnByDefault: true}
+	// RubyReferenceTransactionHook will enable the reference-transaction hook
+	// introduced with Git v2.28.0 for voting on transactions in the Ruby sidecar.
+	RubyReferenceTransactionHook = FeatureFlag{Name: "ruby_reference_transaction_hook", OnByDefault: false}
 	// LogCommandStats will log additional rusage stats for commands
 	LogCommandStats = FeatureFlag{Name: "log_command_stats", OnByDefault: false}
 	// GoUserMergeBranch enables the Go implementation of UserMergeBranch
@@ -46,6 +49,7 @@ var All = []FeatureFlag{
 	ReferenceTransactionsSSHService,
 	ReferenceTransactionsPrimaryWins,
 	ReferenceTransactionHook,
+	RubyReferenceTransactionHook,
 	GoUserMergeBranch,
 }
 
diff --git a/ruby/lib/gitlab/git/hook.rb b/ruby/lib/gitlab/git/hook.rb
index 8a514da2c..4a6ee936f 100644
--- a/ruby/lib/gitlab/git/hook.rb
+++ b/ruby/lib/gitlab/git/hook.rb
@@ -133,7 +133,8 @@ module Gitlab
           'GIT_DIR' => repo_path,
           'GITALY_REPO' => repository.gitaly_repository.to_json,
           'GITALY_SOCKET' => Gitlab.config.gitaly.internal_socket,
-          'GITALY_GO_POSTRECEIVE' => repository.feature_enabled?('go-postreceive-hook').to_s
+          'GITALY_GO_POSTRECEIVE' => repository.feature_enabled?('go-postreceive-hook').to_s,
+          'GITALY_REFERENCE_TRANSACTION_HOOK' => repository.feature_enabled?('reference-transaction-hook').to_s
         }
       end
     end
diff --git a/ruby/lib/gitlab/git/hooks_service.rb b/ruby/lib/gitlab/git/hooks_service.rb
index 5ad8e43b7..67ac4c3fb 100644
--- a/ruby/lib/gitlab/git/hooks_service.rb
+++ b/ruby/lib/gitlab/git/hooks_service.rb
@@ -13,7 +13,7 @@ module Gitlab
         @push_options = push_options
         @transaction = transaction
 
-        %w[pre-receive update].each do |hook_name|
+        %w[pre-receive update reference-transaction].each do |hook_name|
           status, message = run_hook(hook_name)
 
           raise PreReceiveError, message unless status