Support falling back to ruby version of checkers

Rename the ruby scripts to have `-ruby` suffix and add a symlink
for both to `./gitlab-shell`. The executable name will be used to
determine how args will be parsed.

For now, we only parse the arguments for gitlab-shell commands. If
the executable is `gitlab-shell-authorized-keys-check` or
`gitlab-shell-authorized-principals-check`, it'll always fallback
to the ruby version.

Ruby specs test the ruby script, the fallback from go to ruby and
go implementation of both (still pending).

Makefile

@@ -16,8 +16,14 @@ test_ruby:
 	# bin/gitlab-shell must exist and needs to be the Ruby version for
 	# rspec to be able to test.
 	cp bin/gitlab-shell-ruby bin/gitlab-shell
+	# bin/gitlab-shell-authorized-keys-check and bin/gitlab-shell-authorized-principals-check
+	# should link to ruby scripts for rspec to be able to test.
+	ln -sf ./gitlab-shell-authorized-keys-check-ruby bin/gitlab-shell-authorized-keys-check
+	ln -sf ./gitlab-shell-authorized-principals-check-ruby bin/gitlab-shell-authorized-principals-check
 	bundle exec rspec --color --tag '~go' --format d spec
 	rm -f bin/gitlab-shell
+	ln -sf ./gitlab-shell bin/gitlab-shell-authorized-keys-check
+	ln -sf ./gitlab-shell bin/gitlab-shell-authorized-principals-check
 
 test_golang:
 	support/go-test

bin/gitlab-shell-authorized-keys-check

-#!/usr/bin/env ruby
-
-#
-# GitLab shell authorized_keys helper. Query GitLab API to get the authorized
-# command for a given ssh key fingerprint
-#
-# Ex.
-#   bin/gitlab-shell-authorized-keys-check <username> <public-key>
-#
-# Returns
-#   command="/bin/gitlab-shell key-#",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty ssh-rsa AAAA...
-#
-# Expects to be called by the SSH daemon, via configuration like:
-#     AuthorizedKeysCommandUser git
-#     AuthorizedKeysCommand /bin/gitlab-shell-authorized-keys-check git %u %k
-
-abort "# Wrong number of arguments. #{ARGV.size}. Usage:
-#     gitlab-shell-authorized-keys-check <expected-username> <actual-username> <key>" unless ARGV.size == 3
-
-expected_username = ARGV[0]
-abort '# No username provided' if expected_username.nil? || expected_username == ''
-
-actual_username = ARGV[1]
-abort '# No username provided' if actual_username.nil? || actual_username == ''
-
-# Only check access if the requested username matches the configured username.
-# Normally, these would both be 'git', but it can be configured by the user
-exit 0 unless expected_username == actual_username
-
-key = ARGV[2]
-abort "# No key provided" if key.nil? || key == ''
-
-require_relative '../lib/gitlab_init'
-require_relative '../lib/gitlab_net'
-require_relative '../lib/gitlab_keys'
-
-authorized_key = GitlabNet.new.authorized_key(key)
-if authorized_key.nil?
-  puts "# No key was found for #{key}"
-else
-  puts GitlabKeys.key_line("key-#{authorized_key['id']}", authorized_key['key'])
-end

bin/gitlab-shell-authorized-keys-check

+./gitlab-shell
\ No newline at end of file

bin/gitlab-shell-authorized-keys-check-ruby

+#!/usr/bin/env ruby
+
+#
+# GitLab shell authorized_keys helper. Query GitLab API to get the authorized
+# command for a given ssh key fingerprint
+#
+# Ex.
+#   bin/gitlab-shell-authorized-keys-check <username> <public-key>
+#
+# Returns
+#   command="/bin/gitlab-shell key-#",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty ssh-rsa AAAA...
+#
+# Expects to be called by the SSH daemon, via configuration like:
+#     AuthorizedKeysCommandUser git
+#     AuthorizedKeysCommand /bin/gitlab-shell-authorized-keys-check git %u %k
+
+abort "# Wrong number of arguments. #{ARGV.size}. Usage:
+#     gitlab-shell-authorized-keys-check <expected-username> <actual-username> <key>" unless ARGV.size == 3
+
+expected_username = ARGV[0]
+abort '# No username provided' if expected_username.nil? || expected_username == ''
+
+actual_username = ARGV[1]
+abort '# No username provided' if actual_username.nil? || actual_username == ''
+
+# Only check access if the requested username matches the configured username.
+# Normally, these would both be 'git', but it can be configured by the user
+exit 0 unless expected_username == actual_username
+
+key = ARGV[2]
+abort "# No key provided" if key.nil? || key == ''
+
+require_relative '../lib/gitlab_init'
+require_relative '../lib/gitlab_net'
+require_relative '../lib/gitlab_keys'
+
+authorized_key = GitlabNet.new.authorized_key(key)
+if authorized_key.nil?
+  puts "# No key was found for #{key}"
+else
+  puts GitlabKeys.key_line("key-#{authorized_key['id']}", authorized_key['key'])
+end

bin/gitlab-shell-authorized-principals-check

-#!/usr/bin/env ruby
-
-#
-# GitLab shell authorized principals helper. Emits the same sort of
-# command="..." line as gitlab-shell-authorized-principals-check, with
-# the right options.
-#
-# Ex.
-#   bin/gitlab-shell-authorized-keys-check <key-id> <principal1> [<principal2>...]
-#
-# Returns one line per principal passed in, e.g.:
-#   command="/bin/gitlab-shell username-{KEY_ID}",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty {PRINCIPAL}
-#   [command="/bin/gitlab-shell username-{KEY_ID}",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty {PRINCIPAL2}]
-#
-# Expects to be called by the SSH daemon, via configuration like:
-#     AuthorizedPrincipalsCommandUser root
-#     AuthorizedPrincipalsCommand /bin/gitlab-shell-authorized-principals-check git %i sshUsers
-
-abort "# Wrong number of arguments. #{ARGV.size}. Usage:
-#     gitlab-shell-authorized-principals-check <key-id> <principal1> [<principal2>...]" unless ARGV.size >= 2
-
-key_id = ARGV[0]
-abort '# No key_id provided' if key_id.nil? || key_id == ''
-
-principals = ARGV[1..-1]
-principals.each { |principal|
-  abort '# An invalid principal was provided' if principal.nil? || principal == ''  
-}
-
-require_relative '../lib/gitlab_init'
-require_relative '../lib/gitlab_net'
-require_relative '../lib/gitlab_keys'
-
-principals.each { |principal|
-  puts GitlabKeys.principal_line("username-#{key_id}", principal.dup)
-}

bin/gitlab-shell-authorized-principals-check

+./gitlab-shell
\ No newline at end of file

bin/gitlab-shell-authorized-principals-check-ruby

+#!/usr/bin/env ruby
+
+#
+# GitLab shell authorized principals helper. Emits the same sort of
+# command="..." line as gitlab-shell-authorized-principals-check, with
+# the right options.
+#
+# Ex.
+#   bin/gitlab-shell-authorized-keys-check <key-id> <principal1> [<principal2>...]
+#
+# Returns one line per principal passed in, e.g.:
+#   command="/bin/gitlab-shell username-{KEY_ID}",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty {PRINCIPAL}
+#   [command="/bin/gitlab-shell username-{KEY_ID}",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty {PRINCIPAL2}]
+#
+# Expects to be called by the SSH daemon, via configuration like:
+#     AuthorizedPrincipalsCommandUser root
+#     AuthorizedPrincipalsCommand /bin/gitlab-shell-authorized-principals-check git %i sshUsers
+
+abort "# Wrong number of arguments. #{ARGV.size}. Usage:
+#     gitlab-shell-authorized-principals-check <key-id> <principal1> [<principal2>...]" unless ARGV.size >= 2
+
+key_id = ARGV[0]
+abort '# No key_id provided' if key_id.nil? || key_id == ''
+
+principals = ARGV[1..-1]
+principals.each { |principal|
+  abort '# An invalid principal was provided' if principal.nil? || principal == ''
+}
+
+require_relative '../lib/gitlab_init'
+require_relative '../lib/gitlab_net'
+require_relative '../lib/gitlab_keys'
+
+principals.each { |principal|
+  puts GitlabKeys.principal_line("username-#{key_id}", principal.dup)
+}

go/cmd/gitlab-shell/main.go

@@ -6,7 +6,6 @@ import (
 	"path/filepath"
 
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command"
-	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/fallback"
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/readwriter"
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/config"
 )
@@ -28,17 +27,6 @@ func findRootDir() (string, error) {
 	return filepath.Dir(filepath.Dir(path)), nil
 }
 
-// rubyExec will never return. It either replaces the current process with a
-// Ruby interpreter, or outputs an error and kills the process.
-func execRuby(rootDir string, readWriter *readwriter.ReadWriter) {
-	cmd := &fallback.Command{RootDir: rootDir, Args: os.Args}
-
-	if err := cmd.Execute(); err != nil {
-		fmt.Fprintf(readWriter.ErrOut, "Failed to exec: %v\n", err)
-		os.Exit(1)
-	}
-}
-
 func main() {
 	readWriter := &readwriter.ReadWriter{
 		Out:    os.Stdout,
@@ -52,12 +40,10 @@ func main() {
 		os.Exit(1)
 	}
 
-	// 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(readWriter.ErrOut, "Failed to read config, falling back to gitlab-shell-ruby")
-		execRuby(rootDir, readWriter)
+		fmt.Fprintln(readWriter.ErrOut, "Failed to read config, exiting")
+		os.Exit(1)
 	}
 
 	cmd, err := command.New(os.Args, config, readWriter)

go/internal/command/command.go

@@ -19,7 +19,6 @@ type Command interface {
 
 func New(arguments []string, config *config.Config, readWriter *readwriter.ReadWriter) (Command, error) {
 	args, err := commandargs.Parse(arguments)
-
 	if err != nil {
 		return nil, err
 	}
@@ -30,7 +29,7 @@ func New(arguments []string, config *config.Config, readWriter *readwriter.ReadW
 		}
 	}
 
-	return &fallback.Command{RootDir: config.RootDir, Args: arguments}, nil
+	return &fallback.Command{RootDir: config.RootDir, Args: args}, nil
 }
 
 func buildCommand(args *commandargs.CommandArgs, config *config.Config, readWriter *readwriter.ReadWriter) Command {

go/internal/command/command_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/commandargs"
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/discover"
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/fallback"
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/lfsauthenticate"
@@ -21,6 +22,7 @@ func TestNew(t *testing.T) {
 		desc         string
 		config       *config.Config
 		environment  map[string]string
+		arguments    []string
 		expectedType interface{}
 	}{
 		{
@@ -33,6 +35,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &discover.Command{},
 		},
 		{
@@ -45,6 +48,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &fallback.Command{},
 		},
 		{
@@ -57,6 +61,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "2fa_recovery_codes",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &twofactorrecover.Command{},
 		},
 		{
@@ -69,6 +74,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-lfs-authenticate",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &lfsauthenticate.Command{},
 		},
 		{
@@ -81,6 +87,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-receive-pack",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &receivepack.Command{},
 		},
 		{
@@ -93,6 +100,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-upload-pack",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &uploadpack.Command{},
 		},
 		{
@@ -105,6 +113,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-upload-archive",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &uploadarchive.Command{},
 		},
 		{
@@ -117,6 +126,7 @@ func TestNew(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-unimplemented-feature",
 			},
+			arguments:    []string{string(commandargs.GitlabShell)},
 			expectedType: &fallback.Command{},
 		},
 	}
@@ -126,7 +136,7 @@ func TestNew(t *testing.T) {
 			restoreEnv := testhelper.TempEnv(tc.environment)
 			defer restoreEnv()
 
-			command, err := New([]string{}, tc.config, nil)
+			command, err := New(tc.arguments, tc.config, nil)
 
 			require.NoError(t, err)
 			require.IsType(t, tc.expectedType, command)
@@ -139,7 +149,7 @@ func TestFailingNew(t *testing.T) {
 		restoreEnv := testhelper.TempEnv(map[string]string{})
 		defer restoreEnv()
 
-		_, err := New([]string{}, &config.Config{}, nil)
+		_, err := New([]string{string(commandargs.GitlabShell)}, &config.Config{}, nil)
 
 		require.Error(t, err, "Only ssh allowed")
 	})

go/internal/command/commandargs/command_args.go

@@ -3,12 +3,14 @@ package commandargs
 import (
 	"errors"
 	"os"
+	"path/filepath"
 	"regexp"
 
 	"github.com/mattn/go-shellwords"
 )
 
 type CommandType string
+type Executable string
 
 const (
 	Discover         CommandType = "discover"
@@ -17,6 +19,7 @@ const (
 	ReceivePack      CommandType = "git-receive-pack"
 	UploadPack       CommandType = "git-upload-pack"
 	UploadArchive    CommandType = "git-upload-archive"
+	GitlabShell      Executable  = "gitlab-shell"
 )
 
 var (
@@ -25,6 +28,7 @@ var (
 )
 
 type CommandArgs struct {
+	arguments      []string
 	GitlabUsername string
 	GitlabKeyId    string
 	SshArgs        []string
@@ -32,12 +36,14 @@ type CommandArgs struct {
 }
 
 func Parse(arguments []string) (*CommandArgs, error) {
+	args := &CommandArgs{arguments: arguments}
+
+	if args.Executable() == GitlabShell {
 		if sshConnection := os.Getenv("SSH_CONNECTION"); sshConnection == "" {
 			return nil, errors.New("Only ssh allowed")
 		}
 
-	args := &CommandArgs{}
-	args.parseWho(arguments)
+		args.parseWho()
 
 		if err := args.parseCommand(os.Getenv("SSH_ORIGINAL_COMMAND")); err != nil {
 			return nil, errors.New("Invalid ssh command")
@@ -45,10 +51,21 @@ func Parse(arguments []string) (*CommandArgs, error) {
 		args.defineCommandType()
 
 		return args, nil
+	} else {
+		return args, nil
+	}
+}
+
+func (c *CommandArgs) Executable() Executable {
+	return Executable(filepath.Base(c.arguments[0]))
+}
+
+func (c *CommandArgs) Arguments() []string {
+	return c.arguments[1:]
 }
 
-func (c *CommandArgs) parseWho(arguments []string) {
-	for _, argument := range arguments {
+func (c *CommandArgs) parseWho() {
+	for _, argument := range c.arguments {
 		if keyId := tryParseKeyId(argument); keyId != "" {
 			c.GitlabKeyId = keyId
 			break

go/internal/command/commandargs/command_args_test.go

@@ -3,16 +3,16 @@ package commandargs
 import (
 	"testing"
 
-	"github.com/stretchr/testify/require"
-
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/testhelper"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestParseSuccess(t *testing.T) {
 	testCases := []struct {
 		desc         string
-		arguments    []string
 		environment  map[string]string
+		arguments    []string
 		expectedArgs *CommandArgs
 	}{
 		// Setting the used env variables for every case to ensure we're
@@ -23,7 +23,8 @@ func TestParseSuccess(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{}, CommandType: Discover},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{}, CommandType: Discover},
 		},
 		{
 			desc: "It finds the key id in any passed arguments",
@@ -31,72 +32,80 @@ func TestParseSuccess(t *testing.T) {
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "",
 			},
-			arguments:    []string{"hello", "key-123"},
-			expectedArgs: &CommandArgs{SshArgs: []string{}, CommandType: Discover, GitlabKeyId: "123"},
+			arguments:    []string{string(GitlabShell), "hello", "key-123"},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell), "hello", "key-123"}, SshArgs: []string{}, CommandType: Discover, GitlabKeyId: "123"},
 		}, {
 			desc: "It finds the username in any passed arguments",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "",
 			},
-			arguments:    []string{"hello", "username-jane-doe"},
-			expectedArgs: &CommandArgs{SshArgs: []string{}, CommandType: Discover, GitlabUsername: "jane-doe"},
+			arguments:    []string{string(GitlabShell), "hello", "username-jane-doe"},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell), "hello", "username-jane-doe"}, SshArgs: []string{}, CommandType: Discover, GitlabUsername: "jane-doe"},
 		}, {
 			desc: "It parses 2fa_recovery_codes command",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "2fa_recovery_codes",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"2fa_recovery_codes"}, CommandType: TwoFactorRecover},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"2fa_recovery_codes"}, CommandType: TwoFactorRecover},
 		}, {
 			desc: "It parses git-receive-pack command",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-receive-pack group/repo",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
 		}, {
 			desc: "It parses git-receive-pack command and a project with single quotes",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git receive-pack 'group/repo'",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
 		}, {
 			desc: `It parses "git receive-pack" command`,
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": `git receive-pack "group/repo"`,
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
 		}, {
 			desc: `It parses a command followed by control characters`,
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": `git-receive-pack group/repo; any command`,
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-receive-pack", "group/repo"}, CommandType: ReceivePack},
 		}, {
 			desc: "It parses git-upload-pack command",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": `git upload-pack "group/repo"`,
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-upload-pack", "group/repo"}, CommandType: UploadPack},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-upload-pack", "group/repo"}, CommandType: UploadPack},
 		}, {
 			desc: "It parses git-upload-archive command",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-upload-archive 'group/repo'",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-upload-archive", "group/repo"}, CommandType: UploadArchive},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-upload-archive", "group/repo"}, CommandType: UploadArchive},
 		}, {
 			desc: "It parses git-lfs-authenticate command",
 			environment: map[string]string{
 				"SSH_CONNECTION":       "1",
 				"SSH_ORIGINAL_COMMAND": "git-lfs-authenticate 'group/repo' download",
 			},
-			expectedArgs: &CommandArgs{SshArgs: []string{"git-lfs-authenticate", "group/repo", "download"}, CommandType: LfsAuthenticate},
+			arguments:    []string{string(GitlabShell)},
+			expectedArgs: &CommandArgs{arguments: []string{string(GitlabShell)}, SshArgs: []string{"git-lfs-authenticate", "group/repo", "download"}, CommandType: LfsAuthenticate},
 		},
 	}
 
@@ -115,7 +124,7 @@ func TestParseSuccess(t *testing.T) {
 
 func TestParseFailure(t *testing.T) {
 	t.Run("It fails if SSH connection is not set", func(t *testing.T) {
-		_, err := Parse([]string{})
+		_, err := Parse([]string{string(GitlabShell)})
 
 		require.Error(t, err, "Only ssh allowed")
 	})
@@ -128,7 +137,7 @@ func TestParseFailure(t *testing.T) {
 		restoreEnv := testhelper.TempEnv(environment)
 		defer restoreEnv()
 
-		_, err := Parse([]string{})
+		_, err := Parse([]string{string(GitlabShell)})
 
 		require.Error(t, err, "Invalid ssh command")
 	})

go/internal/command/fallback/fallback.go

 package fallback
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"syscall"
+
+	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/commandargs"
 )
 
+type CommandArgs interface {
+	Executable() commandargs.Executable
+	Arguments() []string
+}
+
 type Command struct {
 	RootDir string
-	Args    []string
+	Args    CommandArgs
 }
 
 var (
@@ -16,15 +24,15 @@ var (
 	execFunc = syscall.Exec
 )
 
-const (
-	RubyProgram = "gitlab-shell-ruby"
-)
-
 func (c *Command) Execute() error {
-	rubyCmd := filepath.Join(c.RootDir, "bin", RubyProgram)
+	rubyCmd := filepath.Join(c.RootDir, "bin", c.fallbackProgram())
 
 	// Ensure rubyArgs[0] is the full path to gitlab-shell-ruby
-	rubyArgs := append([]string{rubyCmd}, c.Args[1:]...)
+	rubyArgs := append([]string{rubyCmd}, c.Args.Arguments()...)
 
 	return execFunc(rubyCmd, rubyArgs, os.Environ())
 }
+
+func (c *Command) fallbackProgram() string {
+	return fmt.Sprintf("%s-ruby", c.Args.Executable())
+}

go/internal/command/fallback/fallback_test.go

@@ -6,6 +6,8 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+
+	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/commandargs"
 )
 
 type fakeExec struct {
@@ -18,8 +20,21 @@ type fakeExec struct {
 	Env      []string
 }
 
+type FakeCommandArgs struct {
+	executable commandargs.Executable
+	arguments  []string
+}
+
+func (f *FakeCommandArgs) Executable() commandargs.Executable {
+	return f.executable
+}
+
+func (f *FakeCommandArgs) Arguments() []string {
+	return f.arguments
+}
+
 var (
-	fakeArgs = []string{"./test", "foo", "bar"}
+	fakeArgs = &FakeCommandArgs{executable: commandargs.GitlabShell, arguments: []string{"foo", "bar"}}
 )
 
 func (f *fakeExec) Exec(filename string, args []string, env []string) error {

spec/gitlab_shell_authorized_keys_check_spec.rb

@@ -21,14 +21,9 @@ describe 'bin/gitlab-shell-authorized-keys-check' do
     end
   end
 
-  before(:all) do
-    write_config(
-      "gitlab_url" => "http+unix://#{CGI.escape(tmp_socket_path)}",
-    )
-  end
-
   let(:authorized_keys_check_path) { File.join(tmp_root_path, 'bin', 'gitlab-shell-authorized-keys-check') }
 
+  shared_examples 'authorized keys check' do
     it 'succeeds when a valid key is given' do
       output, status = run!
 
@@ -70,6 +65,41 @@ describe 'bin/gitlab-shell-authorized-keys-check' do
       expect(output).to eq('')
       expect(status).to be_success
     end
+  end
+
+  describe 'without go features' do
+    before(:all) do
+      write_config(
+        "gitlab_url" => "http+unix://#{CGI.escape(tmp_socket_path)}",
+      )
+    end
+
+    it_behaves_like 'authorized keys check'
+  end
+
+  describe 'without go features (via go)', :go do
+    before(:all) do
+      write_config(
+        "gitlab_url" => "http+unix://#{CGI.escape(tmp_socket_path)}",
+      )
+    end
+
+    it_behaves_like 'authorized keys check'
+  end
+
+  pending 'with the go authorized-keys-check feature', :go do
+    before(:all) do
+      write_config(
+        'gitlab_url' => "http+unix://#{CGI.escape(tmp_socket_path)}",
+        'migration' => {
+          'enabled' => true,
+          'features' => ['authorized-keys-check']
+        }
+      )
+    end
+
+    it_behaves_like 'authorized keys check'
+  end
 
   def run!(expected_user: 'git', actual_user: 'git', key: 'known-rsa-key')
     cmd = [

spec/gitlab_shell_authorized_principals_check_spec.rb

+require_relative 'spec_helper'
+
+describe 'bin/gitlab-shell-authorized-principals-check' do
+  include_context 'gitlab shell'
+
+  def mock_server(server)
+    # Do nothing as we're not connecting to a server in this check.
+  end
+
+  let(:authorized_principals_check_path) { File.join(tmp_root_path, 'bin', 'gitlab-shell-authorized-principals-check') }
+
+  shared_examples 'authorized principals check' do
+    it 'succeeds when a valid principal is given' do
+      output, status = run!
+
+      expect(output).to eq("command=\"#{gitlab_shell_path} username-key\",no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty principal\n")
+      expect(status).to be_success
+    end
+
+    it 'fails when not enough arguments are given' do
+      output, status = run!(key_id: nil, principals: [])
+
+      expect(output).to eq('')
+      expect(status).not_to be_success
+    end
+
+    it 'fails when key_id is blank' do
+      output, status = run!(key_id: '')
+
+      expect(output).to eq('')
+      expect(status).not_to be_success
+    end
+
+    it 'fails when principals include an empty item' do
+      output, status = run!(principals: ['principal', ''])
+
+      expect(output).to eq('')
+      expect(status).not_to be_success
+    end
+  end
+
+  describe 'without go features' do
+    before(:all) do
+      write_config({})
+    end
+
+    it_behaves_like 'authorized principals check'
+  end
+
+  describe 'without go features (via go)', :go do
+    before(:all) do
+      write_config({})
+    end
+
+    it_behaves_like 'authorized principals check'
+  end
+
+  pending 'with the go authorized-principals-check feature', :go do
+    before(:all) do
+      write_config(
+        'migration' => {
+          'enabled' => true,
+          'features' => ['authorized-principals-check']
+        }
+      )
+    end
+
+    it_behaves_like 'authorized principals check'
+  end
+
+  def run!(key_id: 'key', principals: ['principal'])
+    cmd = [
+      authorized_principals_check_path,
+      key_id,
+      principals,
+    ].flatten.compact
+
+    output = IO.popen(cmd, &:read)
+
+    [output, $?]
+  end
+end