2 files changed, 162 insertions, 0 deletions
diff --git a/go/internal/executable/executable.go b/go/internal/executable/executable.go
new file mode 100644
index 0000000..63f4c90
--- /dev/null
+++ b/go/internal/executable/executable.go
@@ -0,0 +1,58 @@
+package executable
+
+import (
+	"os"
+	"path/filepath"
+)
+
+const (
+	GitlabShell               = "gitlab-shell"
+	AuthorizedKeysCheck       = "gitlab-shell-authorized-keys-check"
+	AuthorizedPrincipalsCheck = "gitlab-shell-authorized-principals-check"
+)
+
+type Executable struct {
+	Name    string
+	RootDir string
+}
+
+var (
+	// osExecutable is overridden in tests
+	osExecutable = os.Executable
+)
+
+func New() (*Executable, error) {
+	path, err := osExecutable()
+	if err != nil {
+		return nil, err
+	}
+
+	rootDir, err := findRootDir(path)
+	if err != nil {
+		return nil, err
+	}
+
+	executable := &Executable{
+		Name:    filepath.Base(path),
+		RootDir: rootDir,
+	}
+
+	return executable, nil
+}
+
+func findRootDir(path string) (string, error) {
+	// Start: /opt/.../gitlab-shell/bin/gitlab-shell
+	// Ends:  /opt/.../gitlab-shell
+	rootDir := filepath.Dir(filepath.Dir(path))
+	pathFromEnv := os.Getenv("GITLAB_SHELL_DIR")
+
+	if pathFromEnv != "" {
+		if _, err := os.Stat(pathFromEnv); os.IsNotExist(err) {
+			return "", err
+		}
+
+		rootDir = pathFromEnv
+	}
+
+	return rootDir, nil
+}
diff --git a/go/internal/executable/executable_test.go b/go/internal/executable/executable_test.go
new file mode 100644
index 0000000..4d2174b
--- /dev/null
+++ b/go/internal/executable/executable_test.go
@@ -0,0 +1,104 @@
+package executable
+
+import (
+	"errors"
+	"testing"
+
+	"gitlab.com/gitlab-org/gitlab-shell/go/internal/testhelper"
+
+	"github.com/stretchr/testify/require"
+)
+
+type fakeOs struct {
+	OldExecutable func() (string, error)
+	Path          string
+	Error         error
+}
+
+func (f *fakeOs) Executable() (string, error) {
+	return f.Path, f.Error
+}
+
+func (f *fakeOs) Setup() {
+	f.OldExecutable = osExecutable
+	osExecutable = f.Executable
+}
+
+func (f *fakeOs) Cleanup() {
+	osExecutable = f.OldExecutable
+}
+
+func TestNewSuccess(t *testing.T) {
+	testCases := []struct {
+		desc            string
+		fakeOs          *fakeOs
+		environment     map[string]string
+		expectedRootDir string
+	}{
+		{
+			desc:            "GITLAB_SHELL_DIR env var is not defined",
+			fakeOs:          &fakeOs{Path: "/tmp/bin/gitlab-shell"},
+			expectedRootDir: "/tmp",
+		},
+		{
+			desc:   "GITLAB_SHELL_DIR env var is defined",
+			fakeOs: &fakeOs{Path: "/opt/bin/gitlab-shell"},
+			environment: map[string]string{
+				"GITLAB_SHELL_DIR": "/tmp",
+			},
+			expectedRootDir: "/tmp",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			restoreEnv := testhelper.TempEnv(tc.environment)
+			defer restoreEnv()
+
+			fake := tc.fakeOs
+			fake.Setup()
+			defer fake.Cleanup()
+
+			result, err := New()
+
+			require.NoError(t, err)
+			require.Equal(t, result.Name, "gitlab-shell")
+			require.Equal(t, result.RootDir, tc.expectedRootDir)
+		})
+	}
+}
+
+func TestNewFailure(t *testing.T) {
+	testCases := []struct {
+		desc        string
+		fakeOs      *fakeOs
+		environment map[string]string
+	}{
+		{
+			desc:   "failed to determine executable",
+			fakeOs: &fakeOs{Path: "", Error: errors.New("error")},
+		},
+		{
+			desc:   "GITLAB_SHELL_DIR doesn't exist",
+			fakeOs: &fakeOs{Path: "/tmp/bin/gitlab-shell"},
+			environment: map[string]string{
+				"GITLAB_SHELL_DIR": "/tmp/non/existing/directory",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			restoreEnv := testhelper.TempEnv(tc.environment)
+			defer restoreEnv()
+
+			fake := tc.fakeOs
+			fake.Setup()
+			defer fake.Cleanup()
+
+			_, err := New()
+
+			require.Error(t, err)
+		})
+	}
+}