backend/util: extract background handling code

internal/backend/rclone/backend.go

@@ -21,9 +21,9 @@ import (
 	"github.com/restic/restic/internal/backend/limiter"
 	"github.com/restic/restic/internal/backend/location"
 	"github.com/restic/restic/internal/backend/rest"
-	"github.com/restic/restic/internal/backend/util"
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
+	"github.com/restic/restic/internal/terminal"
 	"golang.org/x/net/http2"
 )
 
@@ -82,7 +82,7 @@ func run(command string, args ...string) (*StdioConn, *sync.WaitGroup, chan stru
 	cmd.Stdin = r
 	cmd.Stdout = w
 
-	bg, err := util.StartForeground(cmd)
+	bg, err := terminal.StartForeground(cmd)
 	// close rclone side of pipes
 	errR := r.Close()
 	errW := w.Close()

internal/backend/sftp/sftp.go

@@ -21,6 +21,7 @@ import (
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/feature"
+	"github.com/restic/restic/internal/terminal"
 
 	"github.com/cenkalti/backoff/v4"
 	"github.com/pkg/sftp"
@@ -84,7 +85,7 @@ func startClient(cfg Config) (*SFTP, error) {
 		return nil, errors.Wrap(err, "cmd.StdoutPipe")
 	}
 
-	bg, err := util.StartForeground(cmd)
+	bg, err := terminal.StartForeground(cmd)
 	if err != nil {
 		if errors.Is(err, exec.ErrDot) {
 			return nil, errors.Errorf("cannot implicitly run relative executable %v found in current directory, use -o sftp.command=./<command> to override", cmd.Path)

internal/backend/util/foreground.go

@@ -1,29 +0,0 @@
-package util
-
-import (
-	"os"
-	"os/exec"
-	"strings"
-)
-
-// StartForeground runs cmd in the foreground, by temporarily switching to the
-// new process group created for cmd. The returned function `bg` switches back
-// to the previous process group.
-//
-// The command's environment has all RESTIC_* variables removed.
-//
-// Return exec.ErrDot if it would implicitly run an executable from the current
-// directory.
-func StartForeground(cmd *exec.Cmd) (bg func() error, err error) {
-	env := os.Environ() // Returns a copy that we can modify.
-
-	cmd.Env = env[:0]
-	for _, kv := range env {
-		if strings.HasPrefix(kv, "RESTIC_") {
-			continue
-		}
-		cmd.Env = append(cmd.Env, kv)
-	}
-
-	return startForeground(cmd)
-}

internal/backend/util/foreground_test.go

@@ -1,41 +0,0 @@
-//go:build !windows
-// +build !windows
-
-package util_test
-
-import (
-	"bufio"
-	"os"
-	"os/exec"
-	"strings"
-	"testing"
-
-	"github.com/restic/restic/internal/backend/util"
-	rtest "github.com/restic/restic/internal/test"
-)
-
-func TestForeground(t *testing.T) {
-	err := os.Setenv("RESTIC_PASSWORD", "supersecret")
-	rtest.OK(t, err)
-
-	cmd := exec.Command("env")
-	stdout, err := cmd.StdoutPipe()
-	rtest.OK(t, err)
-
-	bg, err := util.StartForeground(cmd)
-	rtest.OK(t, err)
-	defer func() {
-		rtest.OK(t, cmd.Wait())
-	}()
-
-	err = bg()
-	rtest.OK(t, err)
-
-	sc := bufio.NewScanner(stdout)
-	for sc.Scan() {
-		if strings.HasPrefix(sc.Text(), "RESTIC_PASSWORD=") {
-			t.Error("subprocess got to see the password")
-		}
-	}
-	rtest.OK(t, err)
-}

internal/backend/util/foreground_unix.go

@@ -1,88 +0,0 @@
-//go:build unix
-
-package util
-
-import (
-	"os"
-	"os/exec"
-	"os/signal"
-
-	"github.com/restic/restic/internal/debug"
-	"github.com/restic/restic/internal/errors"
-	"github.com/restic/restic/internal/ui/termstatus"
-
-	"golang.org/x/sys/unix"
-)
-
-func startForeground(cmd *exec.Cmd) (bg func() error, err error) {
-	// run the command in its own process group
-	// this ensures that sending ctrl-c to restic will not immediately stop the backend process.
-	cmd.SysProcAttr = &unix.SysProcAttr{
-		Setpgid: true,
-	}
-
-	// open the TTY, we need the file descriptor
-	tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0)
-	if err != nil {
-		debug.Log("unable to open tty: %v", err)
-		return startFallback(cmd)
-	}
-
-	// only move child process to foreground if restic is in the foreground
-	prev, err := termstatus.Tcgetpgrp(int(tty.Fd()))
-	if err != nil {
-		_ = tty.Close()
-		return nil, err
-	}
-
-	self := termstatus.Getpgrp()
-	if prev != self {
-		debug.Log("restic is not controlling the tty; err = %v", err)
-		if err := tty.Close(); err != nil {
-			return nil, err
-		}
-		return startFallback(cmd)
-	}
-
-	// Prevent getting suspended when interacting with the tty
-	signal.Ignore(unix.SIGTTIN)
-	signal.Ignore(unix.SIGTTOU)
-
-	// start the process
-	err = cmd.Start()
-	if err != nil {
-		_ = tty.Close()
-		return nil, errors.Wrap(err, "cmd.Start")
-	}
-
-	// move the command's process group into the foreground
-	err = termstatus.Tcsetpgrp(int(tty.Fd()), cmd.Process.Pid)
-	if err != nil {
-		_ = tty.Close()
-		return nil, err
-	}
-
-	bg = func() error {
-		signal.Reset(unix.SIGTTIN)
-		signal.Reset(unix.SIGTTOU)
-
-		// reset the foreground process group
-		err = termstatus.Tcsetpgrp(int(tty.Fd()), prev)
-		if err != nil {
-			_ = tty.Close()
-			return err
-		}
-
-		return tty.Close()
-	}
-
-	return bg, nil
-}
-
-func startFallback(cmd *exec.Cmd) (bg func() error, err error) {
-	bg = func() error {
-		return nil
-	}
-
-	return bg, cmd.Start()
-}

internal/backend/util/foreground_windows.go

@@ -1,22 +0,0 @@
-package util
-
-import (
-	"os/exec"
-	"syscall"
-
-	"github.com/restic/restic/internal/errors"
-	"golang.org/x/sys/windows"
-)
-
-func startForeground(cmd *exec.Cmd) (bg func() error, err error) {
-	// just start the process and hope for the best
-	cmd.SysProcAttr = &syscall.SysProcAttr{}
-	cmd.SysProcAttr.CreationFlags = windows.CREATE_NEW_PROCESS_GROUP
-	err = cmd.Start()
-	if err != nil {
-		return nil, errors.Wrap(err, "cmd.Start")
-	}
-
-	bg = func() error { return nil }
-	return bg, nil
-}