3 files changed, 97 insertions, 12 deletions

diff --git a/go/cmd/gitlab-shell/main.go b/go/cmd/gitlab-shell/main.go
new file mode 100644
index 0000000..ae54151
--- /dev/null
+++ b/go/cmd/gitlab-shell/main.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"gitlab.com/gitlab-org/gitlab-shell/go/internal/config"
+)
+
+var (
+	binDir  string
+	rootDir string
+)
+
+func init() {
+	binDir = filepath.Dir(os.Args[0])
+	rootDir = filepath.Dir(binDir)
+}
+
+func migrate(*config.Config) (int, bool) {
+	// TODO: Dispatch appropriate requests to Go handlers and return
+	// <exitstatus, true> depending on how they fare
+	return 0, false
+}
+
+// rubyExec will never return. It either replaces the current process with a
+// Ruby interpreter, or outputs an error and kills the process.
+func execRuby() {
+	rubyCmd := filepath.Join(binDir, "gitlab-shell-ruby")
+
+	execErr := syscall.Exec(rubyCmd, os.Args, os.Environ())
+	if execErr != nil {
+		fmt.Fprintf(os.Stderr, "Failed to exec(%q): %v\n", rubyCmd, execErr)
+		os.Exit(1)
+	}
+}
+
+func main() {
+	// Fall back to Ruby in case of problems reading the config, but issue a
+	// warning as this isn't something we can sustain indefinitely
+	config, err := config.NewFromDir(rootDir)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "Failed to read config, falling back to gitlab-shell-ruby")
+		execRuby()
+	}
+
+	// Try to handle the command with the Go implementation
+	if exitCode, done := migrate(config); done {
+		os.Exit(exitCode)
+	}
+
+	// Since a migration has not handled the command, fall back to Ruby to do so
+	execRuby()
+}
diff --git a/go/internal/config/config.go b/go/internal/config/config.go
index 7d521f5..435cb29 100644
--- a/go/internal/config/config.go
+++ b/go/internal/config/config.go
@@ -13,31 +13,44 @@ const (
 	logFile    = "gitlab-shell.log"
 )
 
+type MigrationConfig struct {
+	Enabled  bool     `yaml:"enabled"`
+	Features []string `yaml:"features"`
+}
+
 type Config struct {
 	RootDir   string
-	LogFile   string `yaml:"log_file"`
-	LogFormat string `yaml:"log_format"`
+	LogFile   string          `yaml:"log_file"`
+	LogFormat string          `yaml:"log_format"`
+	Migration MigrationConfig `yaml:"migration"`
 }
 
 func New() (*Config, error) {
-	cfg := Config{}
-
 	dir, err := os.Getwd()
 	if err != nil {
 		return nil, err
 	}
-	cfg.RootDir = dir
 
-	configBytes, err := ioutil.ReadFile(path.Join(cfg.RootDir, configFile))
+	return NewFromDir(dir)
+}
+
+func NewFromDir(dir string) (*Config, error) {
+	return newFromFile(path.Join(dir, configFile))
+}
+
+func newFromFile(filename string) (*Config, error) {
+	cfg := &Config{RootDir: path.Dir(filename)}
+
+	configBytes, err := ioutil.ReadFile(filename)
 	if err != nil {
 		return nil, err
 	}
 
-	if err := parseConfig(configBytes, &cfg); err != nil {
+	if err := parseConfig(configBytes, cfg); err != nil {
 		return nil, err
 	}
 
-	return &cfg, nil
+	return cfg, nil
 }
 
 // parseConfig expects YAML data in configBytes and a Config instance with RootDir set.
diff --git a/go/internal/config/config_test.go b/go/internal/config/config_test.go
index 0a5c842..87a582f 100644
--- a/go/internal/config/config_test.go
+++ b/go/internal/config/config_test.go
@@ -2,20 +2,28 @@ package config
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 )
 
-func TestConfigLogFile(t *testing.T) {
+func TestParseConfig(t *testing.T) {
 	testRoot := "/foo/bar"
 	testCases := []struct {
-		yaml   string
-		path   string
-		format string
+		yaml      string
+		path      string
+		format    string
+		migration MigrationConfig
 	}{
 		{path: "/foo/bar/gitlab-shell.log", format: "text"},
 		{yaml: "log_file: my-log.log", path: "/foo/bar/my-log.log", format: "text"},
 		{yaml: "log_file: /qux/my-log.log", path: "/qux/my-log.log", format: "text"},
 		{yaml: "log_format: json", path: "/foo/bar/gitlab-shell.log", format: "json"},
+		{
+			yaml:      "migration:\n  enabled: true\n  features:\n    - foo\n    - bar",
+			path:      "/foo/bar/gitlab-shell.log",
+			format:    "text",
+			migration: MigrationConfig{Enabled: true, Features: []string{"foo", "bar"}},
+		},
 	}
 
 	for _, tc := range testCases {
@@ -25,6 +33,14 @@ func TestConfigLogFile(t *testing.T) {
 				t.Fatal(err)
 			}
 
+			if cfg.Migration.Enabled != tc.migration.Enabled {
+				t.Fatalf("migration.enabled: expected %v, got %v", tc.migration.Enabled, cfg.Migration.Enabled)
+			}
+
+			if strings.Join(cfg.Migration.Features, ":") != strings.Join(tc.migration.Features, ":") {
+				t.Fatalf("migration.features: expected %#v, got %#v", tc.migration.Features, cfg.Migration.Features)
+			}
+
 			if cfg.LogFile != tc.path {
 				t.Fatalf("expected %q, got %q", tc.path, cfg.LogFile)
 			}