cmd/gitaly-lfs-smudge: Introduce driver types

Until now, gitaly-lfs-smudge only supports converting a single LFS
pointer into its object. This is inefficient though, and Git has an
alternative protocol that allows us to convert multiple LFS pointers in
a single session via the long-running filter protocol.

Introduce a new driver type so that we can easily discern which type of
filter Git is expecting: either the old one-shot "filter", or the newer
"process" type.

For now, this functionality is neither implemented nor used.

4 files changed, 38 insertions, 9 deletions

diff --git a/cmd/gitaly-lfs-smudge/main.go b/cmd/gitaly-lfs-smudge/main.go
index 7e4ba6fc2..c5ce5e4cb 100644
--- a/cmd/gitaly-lfs-smudge/main.go
+++ b/cmd/gitaly-lfs-smudge/main.go
@@ -72,9 +72,16 @@ func run(environment []string, out io.Writer, in io.Reader) error {
 		return fmt.Errorf("loading configuration: %w", err)
 	}
 
-	if err := filter(ctx, cfg, out, in); err != nil {
-		return fmt.Errorf("running smudge filter: %w", err)
-	}
+	switch cfg.DriverType {
+	case smudge.DriverTypeFilter:
+		if err := filter(ctx, cfg, out, in); err != nil {
+			return fmt.Errorf("running smudge filter: %w", err)
+		}
 
-	return nil
+		return nil
+	case smudge.DriverTypeProcess:
+		return fmt.Errorf("process driver type not yet supported")
+	default:
+		return fmt.Errorf("unknown driver type: %v", cfg.DriverType)
+	}
 }
diff --git a/internal/git/smudge/config.go b/internal/git/smudge/config.go
index aa3d10a5b..d7f5a48d0 100644
--- a/internal/git/smudge/config.go
+++ b/internal/git/smudge/config.go
@@ -15,6 +15,18 @@ import (
 // value of this environment variable should be the JSON-encoded `Config` struct.
 const ConfigEnvironmentKey = "GITALY_LFS_SMUDGE_CONFIG"
 
+// DriverType determines the type of the smudge filter.
+type DriverType int
+
+const (
+	// DriverTypeFilter indicates that the smudge filter is to be run once per object. This is
+	// the current default but will be phased out eventually in favor of DriverTypeProcess.
+	DriverTypeFilter = DriverType(0)
+	// DriverTypeProcess is a long-running smudge filter that can process multiple objects in
+	// one session. See gitattributes(5), "Long Running Filter Process".
+	DriverTypeProcess = DriverType(1)
+)
+
 // Config is the configuration used to run gitaly-lfs-smudge. It must be injected via environment
 // variables.
 type Config struct {
@@ -26,6 +38,8 @@ type Config struct {
 	Gitlab config.Gitlab `json:"gitlab"`
 	// TLS contains configuration for setting up a TLS-encrypted connection to Rails.
 	TLS config.TLS `json:"tls"`
+	// DriverType is the type of the smudge driver that should be used.
+	DriverType DriverType `json:"driver_type"`
 }
 
 // ConfigFromEnvironment loads the Config structure from the set of given environment variables.
@@ -82,8 +96,15 @@ func (c Config) Environment() (string, error) {
 
 // GitConfiguration returns the Git configuration required to run the smudge filter.
 func (c Config) GitConfiguration(cfg config.Cfg) (git.ConfigPair, error) {
-	return git.ConfigPair{
-		Key:   "filter.lfs.smudge",
-		Value: filepath.Join(cfg.BinDir, "gitaly-lfs-smudge"),
-	}, nil
+	switch c.DriverType {
+	case DriverTypeFilter:
+		return git.ConfigPair{
+			Key:   "filter.lfs.smudge",
+			Value: filepath.Join(cfg.BinDir, "gitaly-lfs-smudge"),
+		}, nil
+	case DriverTypeProcess:
+		return git.ConfigPair{}, fmt.Errorf("processor driver type not yet supported")
+	default:
+		return git.ConfigPair{}, fmt.Errorf("unknown driver type: %v", c.DriverType)
+	}
 }
diff --git a/internal/git/smudge/config_test.go b/internal/git/smudge/config_test.go
index d988bf16c..e2299b763 100644
--- a/internal/git/smudge/config_test.go
+++ b/internal/git/smudge/config_test.go
@@ -169,5 +169,5 @@ func TestConfig_Environment(t *testing.T) {
 
 	env, err := cfg.Environment()
 	require.NoError(t, err)
-	require.Equal(t, `GITALY_LFS_SMUDGE_CONFIG={"gl_repository":"repo","gitlab":{"url":"https://example.com","relative_url_root":"gitlab","http_settings":{"read_timeout":1,"user":"user","password":"correcthorsebatterystaple","ca_file":"/ca/file","ca_path":"/ca/path","self_signed_cert":true},"secret_file":"/secret/path"},"tls":{"cert_path":"/cert/path","key_path":"/key/path"}}`, env)
+	require.Equal(t, `GITALY_LFS_SMUDGE_CONFIG={"gl_repository":"repo","gitlab":{"url":"https://example.com","relative_url_root":"gitlab","http_settings":{"read_timeout":1,"user":"user","password":"correcthorsebatterystaple","ca_file":"/ca/file","ca_path":"/ca/path","self_signed_cert":true},"secret_file":"/secret/path"},"tls":{"cert_path":"/cert/path","key_path":"/key/path"},"driver_type":0}`, env)
 }
diff --git a/internal/gitaly/service/repository/archive.go b/internal/gitaly/service/repository/archive.go
index 040fa4aba..8cb7947df 100644
--- a/internal/gitaly/service/repository/archive.go
+++ b/internal/gitaly/service/repository/archive.go
@@ -200,6 +200,7 @@ func (s *server) handleArchive(p archiveParams) error {
 			GlRepository: p.in.GetRepository().GetGlRepository(),
 			Gitlab:       s.cfg.Gitlab,
 			TLS:          s.cfg.TLS,
+			DriverType:   smudge.DriverTypeFilter,
 		}
 
 		smudgeEnv, err := smudgeCfg.Environment()